Bothrigaster variolaris

Student guest post time! One of the assessments that I set for students in my ZOOL329 Evolutionary Parasitology class is for them to summarise and write about a paper that they have read in the manner of a blog post. The best blog posts from the class are selected for re-posting (with their permission) here on the Parasite of the Day blog. So from the class of 2023, here’s a post by Nikita Sheelah, about a bird of prey with too many flukes.

To dare to do what hasn’t been done before has been the driving force behind many advancements in society, such as the creation of vaccines, anime, or the ground-breaking Reese’s Peanut Butter Cups. Being the first in recorded history to do something different essentially immortalises people in the history books, which often carries incredible pride and achievement. This seems to be the case for a group of trematode flukes (Bothrigaster variolaris) which infected a snail kite (Rostrhamus sociabilis), and made their way into the bird’s air sacs, causing the snail kite’s fatal end. 

Left: Snail Kite, photo taken by Bernard DuPont, used under Creative Commons (CC BY-SA 2.0) license. 
Right: Bothrigaster variolaris fluke from Fig. 6 of the paper. Centre Insert: Bothrigaster variolaris fluke on the pericardium of the Snail kite's heart from Fig. 1 of the paper

“Big deal,” you say, “trematodes infect air sacs in birds all the time.” And you’re right! Death from trematodes infecting air sacs is fairly common,  but this has mostly been reported in Passeriformes; birds known to be more susceptible to these parasites. It has even been reported in snail kites themselves, but that was in Florida rather than South America. Every continent needs its own firsts, after all. 

So how did this even happen? Let me explain. Snail kites, as you might have ingenuously guessed from the name, eat snails! Apple snails (Pomacea spp.), to be precise. Trematodes in the Cyclocoelidae family use snails as their hosts for the larval stage, meaning when those snails are eaten, little baby trematodes get to grow up into a mature adult in the body of whatever ate the snail (usually birds). So, much like eating too many candy apples can rot your teeth with cavities, the snail kite indulged in too many infected apple snails and rotted their insides. With flukes. Not cavities. And the insides weren’t rotten, just parasitised. That wasn’t that great of an analogy, actually. 

A wildlife rehabilitation hospital brought this male adult snail kite into their care and did their best to help him, but he passed shortly after arrival. Immediately afterwards, a necropsy was performed to poke and prod at his insides, taking tissue samples and collecting the flukes. Not the most dignified funeral rites, but it’s all in the name of science, because over 200 flukes were counted in the bird! Thirty-five were collected for DNA analysis and were identified to be in a distinct clade within the Cyclocoelidae family. The physical characteristics of the flukes backed this up, especially the ventral sucker, which is characteristic to the genus Bothrigaster within that family.

Researchers concluded that the bird most likely died from suffocation due to the obstruction by the parasites, as well as lesions in the respiratory tissue. They also noted a mature trematode in one of the wing bones, which is a pretty uncommon spot for a parasitic flukes to be. What an adventurer!

So, these ambitious Cyclocoelidae made history by being the first reported trematodes to have caused death by air sac infection in snail kites in south America. Realistically, this may happen more than we think, and has probably been happening for quite some time, but being the first trematodes to be written about in this sense is a pretty big feat! Their mothers must be so proud. 

References: 

Díaz, E., Donoso, G., Mosquera, J. M., Ramírez-Villacís, D., González, G. T., Zapata, S. C., & Cisneros-Heredia, D. F. (2022). Death by massive air sac fluke (Trematoda: Bothriogaster variolaris) infection in a free-ranging snail kite (Rostrhamus sociabilis). International Journal for Parasitology. Parasites and Wildlife 19: 155–160.

This post was written by Nikita Sheelah

Parapulex chephrenis

Here's the second student guest posts from the third year Evolutionary Parasitology unit (ZOOL329) class of 2020. This post was written by Patra Petrohilos and it is about the social life of Egyptian Spiny Mouse and how that relates to their fleas. (you can also read a previous post about how a muscle-dwelling worm survives under a cover of snow here).

It doesn’t require a particularly vivid imagination to appreciate that being eaten by fleas is not exactly the most stress-free experience for an animal. Neither (to the surprise of introverts nowhere) is being bullied into submission by the resident bossy boots in your social group. Surely, then, it would logically follow that being bullied by your peers AND preyed upon by parasites at the same time would be the most stressful option of all? That’s certainly what some researchers thought – and were stunned to discover that the answer was not quite what they expected.

Photo of spiny mouse from here, photo of Parapulex flea from here

Before we get any further, you may be wondering how exactly one measures the stress levels of an animal. I’m so glad you asked. Turns out, when we get stressed our bodies produce this stuff called glucocorticoids – which is such a long clunky word that I’ll just refer to it from here on in as GC. In the short term (let’s say we see a predator across the street) this is a good thing – a short burst of GC takes the energy that we’d usually spend on boring things like digesting food and diverts it to more useful activities – like running away from predators. But in the long term (let’s say we are trapped in a cage with that predator for a year) it is a very bad thing. Too much GC can do all kinds of awful things, wreaking havoc on our immune system and our fertility. Scientists can measure how much GC an animal is producing (and therefore how stressed out it is) by analysing its poo. It’s all pretty glamorous.

These particular scientists were interested in how two different negative experiences (parasitism and social interaction) interact to affect an animal’s stress levels. They decided to investigate this by studying the Egyptian spiny mouse (Acomys cahirinus) – an incredibly social little fella that is found living in groups of one male and multiple females. Within this little society, one of those females usually stakes a claim to “Queen Bee” of the group. Bizarrely, they are also especially attractive to one particular species of flea (Parapulex chephrenis), who for some reason steer clear of all other mouse species in favour of this one.

Once they had gathered their mice, the scientists split the females into two groups. The first consisted of pairs of mice, two to a cage. As tends to happen in these situations, one of the pair invariably emerged as the bossier one. This two-mouse hierarchy was well and truly established after a week, by which time the submissive one knew her place well enough to not even attempt to rock the social boat. The second group was divided into single ladies. Each mouse in this group got an entire cage to herself (and peace from any potential bickering over petty things like food).

They then divided the groups further. Half of the paired mice and half of the single ladies were infected with P. chephrenis fleas, while the other half were left flea-free. For a brief period, a male was also added to each cage (just long enough to do the kinds of things that male mice like to do with female mice) and then mouse poo was collected at various points so the scientists could gauge each mouse’s stress levels.

To their amazement, the single mice were more stressed than their paired up counterparts – even the ones being dominated by the bossy boots cagemates. Apparently company is so important to such a social species that being alone is more traumatic than being at the bottom of the pecking order. But even more astoundingly, it was the mice who were not only solitary but also flea-free that were more stressed out than anyone!

It’s possible that flea infestation made these already-anxious solitary mice more likely to indulge in a bit of grooming (a behaviour that tends to soothe rodents), but regardless – it’s fascinating that the results were the exact opposite of expected. Rather than one stressful thing exacerbating the other (like adding Carolina Reaper chili peppers to an already hot sauce would) they almost seemed to cancel each other out (like adding yogurt to a vindaloo curry).

So what’s the moral of the story? If you’re an Egyptian spiny mouse, even having awful, flea infested friends that bully you is better than having no friends at all. And for those poor waifs who don’t have friends - any distraction is preferable to the loneliness of a solitary life. Even when that distraction is being eaten by fleas.

Reference: 

Warburton, E. M., Khokhlova, I. S., Palme, R., Surkova, E. N., van der Mescht, L., & Krasnov, B. R. (2020). Flea infestation, social contact, and stress in a gregarious rodent species: minimizing the potential parasitic costs of group-living. Parasitology 147: 78-86. 

This post was written by Patra Petrohilos

Trichinella britovi

It's time for some student guest posts! One of the assessments I set for students in my ZOOL329 Evolutionary Parasitology class is for them to summarise and write about a paper that they have read in the manner of a blog post. The best blog posts from the class are selected for re-posting (with their permission) here on the Parasite of the Day blog. For the class of 2020, two students' posts were selected. So to kick things off, here's a post written by Anna Clemann, and it's all about how a muscle-infecting nematode survives under cover through winter. 

Photo of Trichinella britovi from this paper

We’ve all heard the stories of people lost in the snow building ‘snow caves’ to survive the cold temperatures. Turns out the nematode Trichinella britovi, a small parasitic worm which have larvae that are found in the striated muscles of carnivorous animals, also survives better in ‘snow cave’ type conditions. 

Trichinella britovi can be found in a number of different hosts, with many scavenger species acting as carriers or reservoir hosts that themselves do not experience much ill effects from the parasite, but can be a source of infection for other host species. Trichinella britovi larvae are transmitted when the striated muscle (where the larval worm resides) of an infected host is consumed by another animal. This parasite has adapted to surviving in the decaying muscle of hosts via engaging in anaerobic metabolism, so they can survive in tissue that has little oxygen for long periods of time. 

A recent study has found that temperature and humidity also play a major role in the chances of survival for T. britovi. If a carcass infested with T. britovi is frozen, they can survive for up to several months in the muscles, which increase their chances of being ingested by another host. Researchers from Italy and Latvia decided to test whether the chance of survival for T. britovi was better if the infested carcass was buried under snow or above the snow. 

The researchers conducted their study on two carnivore scavengers, fox and raccoon dog. First, they placed the animal carcasses in a scavenger-proof netted mesh box that was surrounded by snow. They then divided the box into two sections and placed one set of the carcasses on each side. One side was filled almost to the top with snow while the other side was left exposed (see image below). 

A picture depicting the experimental set-up, taken from Fig. 1 of the paper.

Over the course of the study (112 days) the researchers collected muscle samples from all the carcasses and recorded the temperature and humidity for both environments over key periods of time. The muscle from all carcasses were fed to lab mice and researchers then looked at the prevalence of T britovi larvae surviving and reproducing within the mice. Through that, they found that T. britovi survived better if they were buried in the snow! 

Researchers found little difference in the reproduction capacity of T. britovi in the mice from the carcasses which are beneath and above the snow in the first two months of the experiment. However, during the last 42 days of the study, mice that were fed muscle from exposed carcasses above the snow (which were subjected to more temperature and humidity variation) showed a 100% reduction in T. britovi infection, meaning the worms they were fed with were not infecting them at all. While mice fed with muscles from carcasses that were buried also had a reduction in larvae reproduction, but at least some were successful in establishing infection in those final weeks up to the end of the experiment. 

The researchers found that the difference in temperature and humidity above snow and below snow were enough to provide a better environment for T. britovi over a longer period. They also noted that below the snow, the variation in temperature was 5.5 times lower than above the snow, producing a more stable and warmer environment. This was further confirmed when the researchers found that the extent of rotting in the muscle (which was more in the buried carcasses than the unburied) was not detrimental to T. britovi reproductive capacity. 

 So, life is better if you’re buried alive, at least if you’re a Trichinella britovi larvae. 

Reference: 

Rossi, L., Interisano, M., Deksne, G. & Pozio, E. (2019). The subnivium, a haven for Trichinella larvae in host carcasses. International Journal for Parasitology: Parasites and Wildlife 8: 229-233

This post was written by Anna Clemann

Passeromyia longicornis

This is the third and final post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2018. This particular post was written by Lachlan Thurtell and it is about a fly that parasitise the chicks of some birds in Tasmania (you can also read a previous post about how parasitoid larvae are affected by what their caterpillar host eats here, and a post about why cuckoo eggs have thicker shells here).

Top left: Pardalote hatchling with a single maggot
Passeromyia longicornis maggot (Top Right), pupa (Bottom left),
and adult (Bottom right). Photos from Fig. 1. of the paper.

Have you ever had a nightmare where you have some strange creature crawling under your skin? Only for that creature to burst from underneath your skin, wriggling around and you can’t do anything to prevent it, or even escape after it emerges? This nightmare is very real for some native Australian wildlife.

Surviving the extreme conditions of Tasmania, competing for territory with your own species and others, avoiding predation, and facing habitat loss caused by human activities are all part of a pardalote's  daily life. However along with these trials this endangered Australian bird also faces parasitism from Passeromyia longicornis, a native Australian parasite that feeds upon weak and defenseless pardalote young.

P. longicornis is a Dipteran (an order of insects comprised of flies and mosquitos) belonging to the same family as the houseflies - the Muscidae. Houseflies are often seen as vectors of disease, carrying pathogens and eggs of other parasites. Passeromyia longicornis itself is a parasite which targets avian hosts. As an adult these flies are not thought to be parasitic but rather free living flies that feast on the decaying flesh of fruit. The larvae, however, are subcutaneous parasites that burrow their way underneath the skin of newly hatched pardalote chicks, possibly hours after the chick’s birth. Location is not very important for the larvae as they bore through the skin in a variety of different places, including the head.

Once the larvae have burrowed into the body of its vulnerable host, they begin to feed on the blood of the helpless hatchlings, a form of parasitism known as hematophagous parasitism. These vampiric creatures are known to suck the blood from their hosts for up to a week! Whilst the larvae are only known to feed upon blood, the effects on their hosts can result in death. In this study the researcher found that a whopping 85% of forty-spotted pardalote (Pardalotus quadragintus) nestlings which are parasitised by the larvae end up dying. Striated pardalotes (Pardalotus striatus) seemed to be more resistant to parasitism with only 65% of nestlings experiencing mortality. The larvae begin to pupate 3-6 days after emerging from their bed ‘n’ breakfast hosts and form cocoons where they develop over the next 17 days, however the duration of the pupal stage is shorter in warmer weather. The adults emerge from the cocoon, transitioning from a parasitic to a free living lifestyle.

Parasitism by P. longicornis is quite prevalent in both species of pardalotes. The larvae of P.longicornis were found in 87% of forty-spotted pardalotes, and 88% of striated pardalotes. Other birds were found to be parasitised by P. longicornis, such as the New Holland honeyeater, house sparrow and European Goldfinch, but showed much lower levels of parasitism than pardalotes, indicating that pardalotes are important hosts for these little blood suckers.

The pardalotes themselves may be to blame for the prevalence of P. longicornis as, unlike other birds, they pack their nests full of bark strips and grass. The nesting material is used in the pupal stage of P. longicornis as it provides a toasty environment to transition from a vampire living beneath the skin into a beautiful (if that’s your thing) fly.

Reference:
Edworthy, A. B. (2016). Avian hosts, prevalence and larval life history of the ectoparasitic fly Passeromyia longicornis (Diptera: Muscidae) in south-eastern Tasmania. Australian journal of Zoology 64: 100-106.

This post was written by Lachlan Thurtell

Cuculus canorus

This is the second post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2018. This particular post was written by Simone Dutt and it was titled "Keeping eggs warm: brood parasites and their early-hatching thick-shelled eggs" about a rather different type of parasites to the ones usually featured on this blog - the cuckoo (you can also read a previous post about how parasitoid larvae are affected by what their caterpillar host eats here).

Some birds manage to evade the burdensome task of caring for their own young by laying their eggs in the nests of other birds for them to raise. Cowbirds, honeyguides and the more well-known cuckoos are families of birds in which some members have adopted this parasitic lifestyle. Known as brood parasites, they force unsuspecting host birds to care for the parasitic chicks, often at the expense of their own young.

Photo of newly-hatched Cuculus canorus chick by Per Harald Olsen

Previous studies have found that parasitic chicks tend to hatch earlier than the host’s chicks and that brood parasites also tend to lay eggs with shells that are structurally stronger and thicker than those of both their non-parasitic relatives and their hosts. Hatching early gives a parasitic chick a head-start to enacting their instinctual plans for total nest domination by out-competing their nestmates for food and space, and in some cases, evicting rival eggs from the nest altogether. It is obvious how such extreme sibling rivalry would suit a parasitic lifestyle, however the evolutionary advantages of producing thicker eggshells are not as clear.

Several suggestions have been made to explain this adaptation: to provide extra calcium for chicks that require stronger bodies with which to evict their nestmates; to provide protection from microorganisms; or to prevent damage incurred during laying, incubation or being punctured and evicted by a host. While these benefits certainly apply to some brood parasites, they don’t generally apply to all. For example, some parasitic chicks can play nicely and refrain from evicting their step-siblings, and many of the dangers faced by parasitic eggs also affect non-parasitic eggs, thus these explanations are not wholly adequate.

A recent study published in The Science of Nature offers evidence to support a more general explanation for the evolution of early-hatching eggs and thicker eggshells in brood parasites. Based on the well-established knowledge that elevated incubation temperatures improve the development rate of bird (and other egg-borne) embryos, the researchers hypothesised that the brood parasites’ thicker eggshells may have evolved as a kind of insulation to maintain high egg temperatures and improve resistance to temperature disturbances, increasing the embryo development rate and enabling the parasite chicks to hatch earlier and carry out their nest takeover plans unchallenged.

Comparing host and parasite eggs collected from the nests of Oriental reed warblers (Acrocephalus orientalis) parasitised by common cuckoos (Cuculus canorus), they found that the cuckoo eggshells were 17% thicker than the warbler eggshells and that, as expected, the cuckoo chicks all hatched before the warbler chicks. By incubating the eggs in a laboratory and measuring the temperature of the eggshells under different conditions, the researchers found that the cuckoo eggs were significantly warmer than the warbler eggs during normal incubation.

When the incubation temperature was disturbed by exposing the eggs to different-length bouts of cooling, they found that the temperature of the cuckoo eggs remained significantly more stable than the warbler eggs throughout the temperature disturbances. The researchers also found that the warbler eggs exposed to longer periods of cooling required a significantly longer total incubation time before they hatched, whereas the total incubation time for the cuckoo eggs was not significantly affected by the length of cooling bouts.

The researchers suggest that these findings provide a general explanation for the evolutionary drivers of the fast-hatching, thick-shelled eggs of brood parasites and noted that the parasitic eggs also tend to be more spherical than those of their hosts, potentially contributing to their heat-retaining qualities; a possible direction for future study. Evolutionarily speaking, being able to maintain an optimally high temperature and withstand longer periods of cooling is a useful trait for ensuring parasitic chicks maintain their ability to hatch early in the nests of a number of different host species, who may leave their eggs unattended for varying periods of time during incubation.

Reference:
Yang, C., Huang, Q., Wang, L., Du, W.-G., Liang, W., & Møller, A. P. (2018). Keeping eggs warm: thermal and developmental advantages for parasitic cuckoos of laying unusually thick-shelled eggs. The Science of Nature, 105:10

This post was written by Simone Dutt

Copidosoma floridanum

It's time for some student guest posts! One of the assessment I set for the students is for them to summarise a paper that they have read, and write it in the manner of a blog post. The best blog posts from the class are selected for re-posting (with their permission) here on the Parasite of the Day blog. I am pleased to be presenting these posts from the ZOOL329/529 class of 2018. To kick things off here's a tale of how what a caterpillar eats can affect the growing parasitoid brood within it, written by Deanna O’Leary.

Meet a cabbage looper caterpillar’s worst nightmare – Copidosoma floridanum. This parasitoid wasp cannot produce offspring without its caterpillar host, and the caterpillar, once parasitized is a terminal ticking time bomb. It kind of puts a new twist on the Harry Potter quote “neither can live while the other survives”, however the wasps have revamped the plot slightly. They do in fact need and allow the caterpillar to survive and grow in order for the wasps themselves to survive to adulthood. But once the caterpillar is ready to pupate – all bets are off for our herbivorous friend. This gruesome parasitoid life-cycle tale goes something like this…

Parasitized caterpillar filled with Copidosoma larvae.
Photo by Silvia Mecenaro from here

A female C. floridanum seeks out a moth egg from a Plusiinae moth. She then inserts her ovipositor (aka egg depositor) into the moth egg and lays 1-2 eggs of her own. Now here’s where things start to get insidious. These wasps are polyembryonic – meaning one egg can divide to produce more than one identical embryo. However, unlike the identical twins of humans, they produce an average of 1500 and up to 3000 clonal offspring! This larval legion need time and space to grow and the body cavity of the newly emerged caterpillar provides the perfect safe and nourishing abode.

You would think that having thousands of larvae living inside you – sucking off your energy supply - would mean you won't have long to live, but the wasps have another card up their tibia. They are gregarious koinobionts, meaning they regulate their host’s growth and immunity, allowing the caterpillar to continue to live, and most importantly eat, providing nutrients for all inside. This can result in caterpillars growing up to 50% larger than an unparasitized counterpart by their final stage. Once the caterpillar reaches this final stage - its fifth instar - it is completely eaten from the inside leaving a hollow casing known as a ‘mummy’. The wasps then emerge as adults from this tomb.

Caterpillars can have devastating  effects on plants and the cabbage looper, as its name suggests, is quite partial to a munch on cruciferous plants (think cabbage, broccoli, kale etc.). Cruciferous plants produce defensive chemicals called glucosinilates, designed to deter the feeding of a herbivorous insect generally by reducing the ‘well-being’ of that animal. Herbivores, in turn, have evolved mechanisms to aid in overcoming this obstacle, however as always, it is an evolutionary arms race between plant and insect. But what does this have to do with our parasitoid?

In general, parasitoids of pest herbivores are considered beneficial biological control agents, reducing the number of pests found on a plant population. However, there's been little research into how these parasitoids affect the insect host-plant interaction at a chemical level. Like the “dream within a dream” in Inception, is there an effect on the plants from the parasitoids through the caterpillar? The feature study of this post set out to answer this.

A group of researchers tested the expression of glucosinilates from four cabbage populations under three different conditions – (1) fed on by unparasitized caterpillars, (2) fed on by parasitized caterpillars, and (3) untouched (control) plants. They focused on two types of glucosinilates – indole and aliphatic. They not only wanted to measure the differences in plant chemical expression, but also the effect of these on both caterpillar and wasp growth, reproductive success, and survival. They found that plants fed on by parasitized caterpillars produced 1.5 times more indole glucosinilates than those fed on by unparasitized caterpillars, and 5 times more than the untouched plants! Because parasitized caterpillars needed to eat more to survive – the plants they fed on produced more defensive compounds in response.

An unexpected result of the study was that the effects of different glucosinilates have on the host and the parasitoids. Because of their close developmental ties, things that negatively affect the host can also affect the parasites inside them - but it depends on the specific compound. When feeding on plants producing higher levels of aliphatic glucosinilates, unparasitized caterpillars suffered reduced on growth and fertility, while parasitized caterpillars had decreased survival rates. In contrast high levels of indole glucosinilates resulted in negative brood size and developmental impacts on the parasitoid, with no effect on the caterpillars.

The researchers suggested that the reason for this could lie in the way the different compounds are broken down by the caterpillar during digestion. So, C. floridanum may have far reaching effects that not only impact their hosts, but also extend to other levels of the food web, and even possibly affecting the evolution of insect-plant interactions! Maybe these parasitoids are not such a hideous nightmare considering their beneficial traits – from a human perspective at least. But they’ll never be anything but a terror for the cabbage looper!

References
Ode, P. J., Harvey, J. A., Reichelt, M., Gershenzon, J., & Gols, R. (2016). Differential induction of plant chemical defenses by parasitized and unparasitized herbivores: consequences for reciprocal, multitrophic interactions. Oikos, 125(10), 1398-1407.

This post was written by Deanna O'Leary

Trypanosoma tungara

This is the fourth and final posts in a series of posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2016. This particular post was written by Sierra Weston and it is about how male Tungara frog end up receiving a parasitic present while trying to call out to female frogs.(see also the previous post about picky bat flies, monkey-infesting botflies, and the caring maternal side of a parasitoid wasp).

Like many species of frogs, during breeding season the males of the túngara frog produce a mating call to attract female frogs. But instead of just serenading his own species, the male frog may inadvertently be announcing his location to nearby frog-biting midges.

TFW you're trying to serenade the ladies and end up with a face full of 

blood-sucking midges. Photo from Fig. 1 of this paper

All adult frogs are at the mercy of a range of opportunistic and specialised insects, some of which are potential vectors for all kinds of blood parasite. There is a species of frog-biting midge (Corethrella spp.) which preys predominantly on the túngara frog (Engystomops pustulosus) - a species of small frog found in the region between the south of Mexico to northern South America. The female midge takes advantage of the male frog’s mating call during their breeding season as a host detection system. The midge follows the sound, finds the frog and voila, it gets a blood meal. A male can attract up to 511 midges in half an hour. Unfortunately, again for the poor frog, midges are the perfect vector for a wide variety of diseases and parasites including trypanosomes.

Trypanosomes are single-celled protozoan parasites that infects hosts from all vertebrate classes; birds, mammals, reptiles, fish and amphibians. Some of these protozoans can cause diseases, including sleeping sickness (Trypanosoma brucei gambiense), in humans, as well as making their hosts more susceptible to sickness. Although frog trypanosomes are a less studied group, there are some parasite-vector-host relationships that have been documented.

The study featured in this post investigated trypanosome infection in túngara frogs. The aim of the study was both to determine that trypanosomes affected the túngara frog and identify the species of parasite if present, and whether there is a difference in trypanosome prevalence between male and female frogs. Since it is the males that produce the mating call, it was predicted that any midge transmitted trypanosomes would only occur in male frogs.

The researchers confirmed the presence of trypanosomes in the blood of the frogs, but also observed that the parasites possessed a some unique characteristics that set them apart from previously described species. However, frog trypanosomes are also known to be able to significantly change their shape when infecting different hosts. This presents the possibility that the trypanosomes infecting the túngara frogs could be a previously identified species with a slightly altered form which make them more suited to life as a parasite in the túngara frog.

Through further analysis and DNA sequencing, researchers were able to confirmed the discovery of a new species of trypanosome: Trypanosoma tungara. In terms of prevalence in male and female hosts, results showed a much greater percentage of males infected with trypanosomes showing that the mating call results in the male frog being the ‘easiest’ and most predominant target for the frog-biting, trypanosome vectoring midges. There were also female frogs infected with trypanosomes, which was surprising because female frogs do not vocalise. A potential transmission path is presumed to be the close proximity of the frogs when they are in amplexus, (the mating ‘embrace’) which allows the midge to move directly from the male to the female frog.

Reference:
X.E. Bernal, C. M. Pinto (2015) Sexual differences in prevalence of a new species of trypanosome infecting túngara frogs. Internations Journal for Parasitology: Parasites and Wildlife 5: 40-47

This post was written by Sierra Weston.

That wraps it up for ZOOL329 class of 2016 - I would like to thank all the students for their posts! Next month, it's back to writing my usual posts about newly published parasite-related papers which you might not have noticed, and/or papers that were not as widely covered by the press - so stay tuned for more!

Sclerodermus harmandi

This is the third post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2016. This particular post was written by Jarrod Mesken the more maternal side of a parasitoid wasp (see also the previous post about picky bat flies and monkey-infesting botflies).

When most people think of parasite behaviour, horrific tales of behavioural and physiological manipulation are what come to mind. This is not without cause; many parasites are definitely scary to think about. However, many pursuers of the parasitic lifestyle also display behaviour that would be thought of as normal, perhaps even charming in an anthropomorphic kind of way. An example of this is seen in the parasitoid wasp Sclerodermus harmandi, in the form of maternal care.

Photo of multiple female Sclerodermus harmandi engaging in brood care from Figure 1 of this paper

This stories begins when the female wasp finds a suitable host for her eggs. She injects the host with paralysing venom, and cleans an area of the body to lay eggs on. Once laid, she routinely inspects the eggs with her antennae and mouthparts. If an egg is found to have detached from the host, she would gently reattach it. Maternal behaviour continues when the eggs hatch, when the larvae must be fed. To do so, the mother wasp bites a hole in the host, which is still alive at this point and injected with paralysing venom periodically to prevent it from moving. The hole fills with haemolymph, the insect equivalent of blood, which is consumed by the larvae.

During this stage the mother S. harmandi also moves the larvae around to prevent them from overlapping each other as they grow. If a larva dies, the mother moves the body far from the other larvae to prevent their habitat becoming unsanitary. Even during the cocoon stage the mother continues to rub the offspring, despite them being encased. Eventually, the males of the clutch hatch out as adults. These few males (there is considerable female bias in the ratio of this species) chew holes in the female wasps’ cocoons to assist them in emerging, after which they mate with them. While it has negative affects in many taxa, this kind of inbreeding is less likely to have negative effects in hymenopteran insects, where haploid males act as a purge of deleterious alleles.

So why does S. harmandi provide such comprehensive maternal care? Because it increases the likelihood of offspring surviving. Experiments in which the wasp mothers were removed at varying stages of offspring development showed that not only were offspring that received maternal care more likely to survive to adulthood, but that this was proportional to how much maternal care they received. Experiments also showed that when a mother was taken away and replaced with another female who has previously laid eggs, the ‘stepmother’ will exhibit the same behaviour as the mother would, with the same rise in offspring survival.

Why the stepmother expend her own energy to raise another wasp’s offspring is just as interesting; it is because of the high levels of inbreeding in the population. Since most of the reproduction in this species is done through inbreeding, there isn’t much genetic variation going around. This means that there is a good chance of two wasps being related, so the stepmother may increase the chance of her genes being passed on by raising another wasp’s offspring. Female S. harmandi that haven’t laid eggs yet do not exhibit this behaviour, preferring to leave the offspring alone; this would indicate that the maternal behaviour is initiated by laying eggs.

So for a parasitoid wasp, it turns out that the females of S. harmandi make for very responsible parents or stepparents. That is, if you consider letting your children live on the body of something you paralysed, feeding off its blood until they grow up, and then mate with each other to be “responsible”.

Reference;
Hu, Z., Zhao, X., Li, Y., Liu, X., & Zhang, Q. (2012). Maternal care in the parasitoid Sclerodermus harmandi (Hymenoptera: Bethylidae). PloS One 7: e51246.

This post was written by Jarrod Mesken

Alouattamyia baeri

This is the second post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2016. This particular post was written by Gabrielle Keaton and it is about a nasty botfly that lives in the neck of howler monkeys (you can read the previous post about picky bat flies that live on bats here).

Photo of botfly pores on howler monkey neck from Plate 1 of this paper

You know how itchy a mosquito bite can be - you scratch it then a lump forms. Imagine that lump forming but not going away. Instead, it grows and grows inside of you until finally a black grub plops out of a hole in your neck onto the ground. Well that’s what it’s like for the howler monkeys of Panama!

This nasty parasite in this case is the larvae of Alouattamyia baeri, a botfly that lives on free-ranging howler monkeys (Alouatta palliate). In a study conducted over seven years from 1987 to 1993, researcher Dr Katherine Milton investigated a variety of factors relating to this parasite's life cycle including its infection prevalence and intensity. She found that 60% of the howler monkeys on Barro Colorado Island (BCI) were infected by this botfly.

Alouattamyia baeri are large (18 to 20mm in length) black flies. The adult fly sounds and look like neotropical bees. When flies that were collected from the howler populations on BCI were reared in captivity, it was found that female flies produced an average 1400 eggs each, laid in discrete rows. These eggs required the appropriate stimuli (carbon dioxide and heat) to hatch into parasitic larvae that then invade their host through the nose and mouth where it migrates to the neck and opens a up larval pore. The larva reside in the howler’s neck for approximately 6 weeks, passing through 3 instars (developmental stages). After this, the larva drops out of the monkey's neck warble and burrows into the soil where it finishes the last developmental stage underground.  The study found that the entire life cycle takes approximately 13 weeks.

Dr Milton discovered that most of larval growth (86%) occurs during the 3rd instar when its food consumption increase by about 20%. This means the larva was trying to extract the most resources at the last possible moment of its stay, so if it ends up killing the host, it wouldn't matter to them because they are out of there.

Infestations were the highest during the wetter seasons and these periods also strongly correlated with peaks in the monkey’s mortality. Monkeys carrying the botfly larvae lack subcutaneous fat reserves. As if having a 2.4 centimetre long and 1.5 centimetre wide maggot in your neck wasn’t bad enough, even after the botfly has made its exit, the hole they made in their host remains open for several days. That’s pretty like much waving a neon ‘vacancy’ sign in front of the primary screw worm fly (Cochliomyia hominivorax) - an even nastier parasite that lays its eggs in open flesh wounds. When the screwfly larvae hatch, they feast on anything and everything surrounding that wound. Some monkey cadavers were even found with hands eaten down to the bone from these nasty little maggot and at least half of the C. hominivorax infestations found on howler monkeys were the result of prior A. baeri infections

Now, I’m sure you might have a bit of a panic next time you feel a little raised bump hanging around your neck, but remember - even if it is a botfly, at least you know it will be gone in 6 weeks' time.

References:
Milton, K. (1996), Effects of bot fly (Alouattamyia baeri) parasitism on a free-ranging howler monkey (Alouatta palliata) population in Panama. Journal of Zoology 239: 39–63.

This post was written by Gabrielle Keaton

Trichobius sp.

Those who have been reading this blog for a while will know that August is student guest post month! All this month this blog will be featuring posts written by students from my Evolutionary Parasitology  (ZOOL329/529) class. One of the assessment I set for the students is for them to summarise a paper that they have read, and write it in the manner of a blog post. The best blog posts from the class are selected for re-posting (with their permission) here on the Parasite of the Day blog. I am pleased to be presenting these posts from the ZOOL329/529 class of 2016. To kick things off, here's a post by Melissa Chenery about some picky bat flies.

Photo of Trichobius johnsonae from Figure 2 of this paper

The public often view bats as repulsive, disease-carrying animals and are subsequently disliked. “Argh! They’re repulsive!” is just one of the many lines I have heard from people walking by while I observed a local colony. But do you know what is even more horrifying than a bat? A bat fly! These ectoparasites belong to two families of flies know as Streblidae and Nycteribiidae. But these hematophagous (blood-feeding) parasites don’t always fly like the name suggests - most species actually have no wings at all, and some look more like spiders than flies.

Disgusting, right? But not to worry, these external parasites have evolved to feed exclusively on bats. The bat flies are quite specific towards their hosts and tend to stay on a particular bat host. They are even picky about where they live on the host, whether on the bat’s fur or hiding within folded wing membranes. Occasionally they can be found in the fur and these individuals possessed comb-like structures (called ctenidia) for attaching to fur. It is assumed that long-legged species move quickly to avoid being scratched by the bat during grooming, whereas the short-legged species hide within the membrane folds to avoid getting licked. Bats use grooming as a behavioural defence against bat flies and other external parasites, and bats with a high number of flies groom more often than those with only a few. For the parasites, action can result in their removal and often their death.

In a study which took place in Belize, Central America, a team of researchers demonstrated just how host-specific the bat flies can be. They examined over thirty two species of bat flies, and in the twenty species for which they were able to collect more than five individuals, they found that eighteen of those species showed strong site preferences. The majority of the bat flies were constrained to a single host-species, and amazingly, bat flies with functional wings (which would allow them to be more mobile) weren't any more or less picky than those without. The study also found that only two species (Trichobius yunkeri and Trichobius dugesioides) weren’t too fussy in respect to host-site preference.

For bat flies that were the dominant species of their respective hosts, six out of those seven species were fur-specific, suggesting that in most cases, bat flies are highly host site-specific. They also discovered an interesting correlation between leg length and host-site preference. Bat flies with longer legs are able to push up over the surface of the fur, and are more likely to be found dwelling in fur. Conversely, short-legged individuals moved much more slowly and were mostly membrane-dwelling.

The team also conducted a study where three bats were restrained and three left unrestrained, with six bat flies placed on each. All unrestrained bats had only one bat fly remaining after five days, whereas all bat flies remained on the restrained bats. This suggests that the elimination of the flies is due to grooming behaviour. This may also be the cause of host-site specificity in bat flies, although further studies are needed Despite their nightmarish appearance, bat flies can still be very fussy eaters, and they have adaptations which allows them to specialise on particular bat species and host-sites.

Reference:
Hofstede, H., Fenton, M., & Whitaker. J. (2004). Host and host-site specificity of bat flies (Diptera: Streblidae and Nycteribiidae) on neotropical bats (Chiroptera). Canadian Journal of Zoology 82: 616-626.

This post was written by Melissa Chenery

Pseudopulex jurassicus

This is the seventh and final posts in a series of posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2015. This particular post was written by Maxine Walter and it is about the fossils of some "giant fleas" dating from the Mesozoic period which might have fed on dinosaurs (Note: But see also this new paper which questions the interpretation of Pseudopulex as a "flea") (you can check out the previous post about how different parasitoid wasps induce different web-building behaviour in their zombified spider hosts here).

Reconstruction of Pseudopulex jurassicus 
by Wang Cheng via Oregon State University

Ever had an itch you just can’t scratch? Was it inappropriately placed while you were in pleasant company? Was it hard to reach? Or were your hands just otherwise occupied with day-to-day tasks? If you answered yes to any of the above, you must be familiar with the insanity-driving BURN that accompanies an un-neutralised itch. It’s no wonder that even the undisputed monster of Mesozoic beasts, the King of Dinosaurs and ruler of reptiles - Tyrannosaurus rex, was bugged by, er, bugs! Our beloved pooches scratch incessantly when infested by fleas. But spare a thought for the puny-armed Tyrant Reptile King himself!

But these were not your average bugs. Like the dinosaurs themselves, the parasites of the pre-mammalian reign were oversized with functional weaponry to match! A few years ago, a group of paleontologists uncovered evidence for up to three separate species of parasites categorized into the new genus Pseudopulex. This generic name has roots in Latin meaning “with visual similarity to flea(s)”. The three species P. jurassicus, P. magnus and P. tanlan appear to have plagued dinosaurs (and others) from the late Middle Jurassic (P. jurassicus) through to the early Cretaceous period (P. magnus and P. tanlan).

These giant ancient flea-like animals, possibly the first of their blood-sucking kind, featured many characteristics typical of an external (or ecto-) parasite including; a wingless, flattened body for wedging into the natural contours of the dinosaurs’ skin/feathers; reduced eyes (because how on Earth can you miss a giant walking buffet?); mouthparts for piercing thick hide; and scythe-like claws for added purchase and avoiding dislodgement.

Photo of Pseudopulex fossil from this paper

The striking piercing and blood-sucking apparatus that was the Pseudopulex's mouthparts, has been described by Entomology Curator Michael Engel as having saw-like projections, and zoologist George Poinar Jr. as “a large beak [that] looks like a syringe when you go to the doctor to get a shot… a flea shot if not a flu shot”. The unusually robust and sturdy nature of these siphon mouths is what led scientists such as Dr. Andre Nel from the Natural History Museum, France, to the idea that these parasites possibly attacked dinosaurs and their high flying pterosaurian counterparts. Although fleas were originally thought to have co-evolved alongside mammals, the large (and easily dislodged on small animals) size of these "fleas" indicates they likely feasted on thick skinned and/or feathered animals, such as Rex and other dinosaurs, rather than the small mammals that also existed during the time.

Of their striking dissimilarity to modern fleas though, is the non-existence of rear jumping legs in these ancient forms. With the lack of springy legs, and the addition of a thick elongate mouth, led scientists like Engel to suggest that Pseudopulex ambushed their large victims. Pseudopulex would have spent much of their lives anchored to hosts with their claws and mouthparts and possessed little running or jumping ability.

The exciting discovery of these three flea-like species has resulted in a massive re-think of scientific theory concerning flea evolution, and finally closes the circle on Mesozoic biodiversity and the intricacies of ancient food chains.

Reference:
Gao, T., Shih, C., Xu, X., Wang, S., & Ren, D. (2012). Mid-Mesozoic flea-like ectoparasites of feathered of haired vertebrates. Current Biology 22, 732-735.

This post was written by Maxine Walter

That does it for ZOOL329 class of 2015 - I'd like to thank all the students for their posts! Next month, it's back to writing my usual posts about newly published and interesting parasite papers which you might have missed, and/or not as widely covered by the usual news and media outlets - so stay tuned!

Polysphincta boops

This is the sixth post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2015. This particular post was written by Rebecca-Lee Puglisi about not one, but THREE spider-zombifying and how they differ in their host preference, as well as what kind of web they make their spider hosts weave (you can read the previous post on how parasites mess with the Monarch Butterfly's migration here).

Photo of Polysphincta boops by Hectonichus

We all know that the natural world is amazing, and we all know that I hate horror movies! But what if losing ones self control and being manipulated by another was actually happening today and not just something you saw in movies? Let’s set the scene here. You are minding your own business when a six legged monster jumps upon your back, stabbing and poisoning you, knocking you unconscious for a few moments. When you wake up, you're no longer yourself and under control by the monster until the day you die. This nightmare happens on a daily basis to Orb-Weaver Spiders (Araneus and Araniella) in nature thanks to parasitoid wasps (Polysphincta and Sinarachna) that use them as hosts.

A study published last year in the journal Ecological Entomology aimed to identify whether the variations in host response to manipulation is a result of differences among parasitoids or among the spiders themselves. Spiders and wasps were collected at four different locations over Europe by shaking trees and catching the spiders and wasps in large nets underneath. The researchers collected four species of spiders (Araneus diadematus, Araniella cucurbitina, Araniella displicata, and Araniella ophistographa), and three species of parasitoid wasps (Polysphincta boops, Polysphincta tuberose, and Sinarachna pallipes), and 417 spiders were collected in total and placed into a laboratory in separate arenas where different species of wasps were introduced.

They found that while Polysphincta boops only parasitised one spider species - A. ophistographa, its relative P. tuberose was less picky and parasitised three spider species - A. cucurbitina, A. opisthographa, and A. diadematus. The same goes for S. pallipes, which parasitised A. cucurbitina, A. displicata, and A. opisthographa. All these wasps sting the spiders, paralysing them to lay an egg on their abdomen. The spider awakes with the egg that then hatches and feeds on the spiders' hemolymph (its blood), and the spider continues its life as normal.

Left: Web woven by spider parasitised by Polysphincta. Right: Web woven by spider parasitised by Sinarachna
Photos from Fig. 2 of the paper 

Their experiments showed that the parasitised spider’s webs changed from a two-dimensional to a three-dimensional structure with difference in the densities of the webs and the cocoons created. The differences between the webs / cocoons are determined by the final instar larva of the wasp species when neuromodulator chemicals are injected in the host spider by the larva. The spiders parasitised by Polysphincta wasps created a high density silk web with a low density cocoon web, whereas spiders parasitised by the Sinarachna wasps created the opposite structures, with a low density silk web and a high density cocoon web.

Higher density webs and cocoons provided better protection for the developing larva. After manipulating the spider to make the web and cocoon for the wasp larva, the larva then develops into its final stage where it kills the spider host, and eats all its internal organs before retreating into the web cocoon where it will grow into adult wasp. After the it reaches maturity, it will then find a mate to start the whole cycle again. This whole process takes roughly 20-30 days.

This whole circle of life and host manipulation interactions is both amazing and horrifying! I mean, have you seen the ‘chest buster’ scene from the movie ‘Alien’? If movie writers decide to make another big blockbuster about parasitoid creatures like those wasps, but have them attack humans, I will never sleep again!

Reference:
Korenko, S., Isaia, M., Satrapova, J., & Pekar, S. (2014). Parasitoid genus‐specific manipulation of orb‐web host spiders (Araneae, Araneidae). Ecological Entomology 39, 30-38.

This post was written by Rebecca-Lee Puglisi

Ophryocystis elektroscirrha (revisited 2)

This is the fifth post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2015. This particular post was written by Kate Ives and it is about how a parasite messes with the migratory journey of monarch butterflies (you can read the previous post about hyena poop and tapeworms here).

Photo by David R. Tribble

We have all experienced that sluggish lack of energy when we’re ill – it’s much easier to hit the couch and rest up for a few days than get out and run a marathon, right? Well for the Monarch Butterfly, the choice is not always that easy! In order to find the best breeding and feeding sites, and avoid freezing in cold temperatures, most Monarchs undertake long and energetically costly migratory journeys during autumn each year.

Monarchs are commonly parasitised by the protozoan Ophryocystis ktroscirrba. The spores of this parasite are ingested by the Monarch caterpillars and asexually reproduce within the host's intestinal tract. When ingested in high numbers, these parasites have been shown to have considerable detrimental effects on the fitness and migration ability of the Monarchs. A pair of researchers set out to explored how monarchs infected by parasites exhibited different patterns in their flight endurance, speed, deceleration ability, and loss of body mass over their relative migration distances.

They raised 100 Monarch caterpillars in captivity and infected them with parasitic O. ktroscirrba. When they metamorphosed into adult butterflies, they were placed on an automated flight mill apparatus which was used to calculate the above mentioned parameters. The flight trials found that parasitised monarchs flew 14% shorter distances, at 16% slower speeds, and lost almost twice as much body mass as unparasitised Monarchs undertaking the same journey.

Just like a viral infection may sap our energy, O. ktroscirrba has a similar resource-consuming effect on Monarchs. The parasites inhibit the host’s ability to absorb nutrients and utilise stored energy for powered flight. Along with parasite-induced damage to tissues, muscles and membranes, this makes powered flight a much more effort-demanding activity. The parasites live in clusters inside the host’s intestinal walls, leading to water loss and faster dehydration. This is thought to account for the greater loss in body mass with each kilometre flown, as compared to unparasitised monarchs. These  constraints contribute to overall reduced larval survival rates, smaller adult body size, shorter lifespans, and therefore the inability to migrate efficiently or survive long enough to migrate or reproduce. It becomes a sheer battle of survival – the host throwing every defence at the rapidly reproducing parasites living inside it.

Photo by Dwight Sipler

But if all this energy is used in defences, how much  left  for migration? Quite often, the story ends with the death of the Monarch - an alarming occurrence that has thrown the species into a threatened status in many parts of the world. However, in a different light, these long-migratory journeys can be seen as a mechanism for reducing parasite prevalence in the Monarchs. The eradication of human diseases provides a perfect analogy for the pathogen-monarch dynamics. Whether through the cycle of life and death, or advancements in vaccines and modern medicine, when a disease is reduced or eliminated from a human population, the remaining population experiences increases in fitness and survival. In the same way, if Monarch migrations are energetically costly, and diseased hosts experience lower successful migrations, with each death the prevalence of the pathogens also decreases, and the remaining Monarch population becomes more adapted to fight off infections.

This insight into host-pathogen interactions also gives rise to possible areas of further research. Throw the effects of climate change and human activities into the mix, and we have the potential to develop a deeper understanding of the mighty Monarch, and its risk of parasitism. But let us not forget the importance of continuing research into the Monarch itself – its physiology and its behaviour. After all, we cannot truly study a parasite without first understanding its host!

Reference:
Bradley, C. A. & Altizer, S. (2005). Parasites hinder monarch butterfly flight: implications for disease spread in migratory hosts. Ecology Letters 8, 290-300.

This post was written by Kate Ives

Dipylidium sp.

This is the fourth post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2015. This particular post was written by Courtney Hawkins and it is about hyena poop and tapeworms (you can read the previous post about monarchs, milkweeds, and parasite here).

I think we can all agree that parasitologists don’t always have the most glamorous jobs in the world. But how about combing through hyena faeces for nine years looking for intestinal parasites? It may not be your dream job but it is for five German scientists. Let me explain…

Photo of spotted hyenas from Fig. 1 of this paper

Dipylidium caninum is an intestinal parasite often found in domestic dogs (Canis familiaris) and cats (Felis catus). This parasite is believed to also infect wild carnivores in both the Canidae and Hyaenidae families. The lifecycle of D. caninum, or canine tapeworm, begins as an adult who sheds segments of its body called proglottids, filled with packets of egg and are excreted with the faeces of the hyenas. Fleas act as the main intermediate host and ingest these eggs during their larval stage. The eggs then hatch and migrate into the body cavity of the flea. The parasite larvae begin developing when the adult fleas emerge from their cocoons and encounter a mammalian host. These mammalian hosts are then infected by consuming the fleas during grooming and the life cycle begins again.

Photo of Dipylidium egg capsule and proglottids in hyena faeces from
Fig. 1 of this paper

The spotted hyena is infected with an unknown species of Dipylidium, neither its genetic identity nor the factors influencing infection are known. This study aimed to provide the first genetic data for this species infecting hyena hosts in East Africa, and to investigate the ecology, demographic, behavioural and physiological factors that influence this species to infect this social carnivore.

Much like D. caninum, it is assumed that the intermediate host is a flea and is most likely the ‘stick fast flea’ (Echidnophaga larina) which is often found on spotted hyenas. Spotted hyenas are social carnivores that often share a communal den inside the clan’s territory with both sexes visiting to socialise and scent mark. It is here that provides the perfect microenvironment for the intermediate host population due to its low temperature, low light and relative humidity.

This study was conducted from 2003 – 2012 on three large clans with the mean population being 89 animals. In total, 146 faecal samples were collected from 124 individuals between the ages of 48 days to about twelve years old. Thirteen of those animals were sampled when they were juveniles and again when they reached adulthoods. Now there are some pretty complicated statistical and genetics analysis taking place and if you are interested feel free to read the journal article (which is Open Access). But here are the major findings:

Adults were less infected than juveniles. This is possibly because as a hyena ages, it acquires immunity from Dipylidium. It was also discovered that the chance of infection decreased the more pups are in the den, because with more pups to go around, there are fewer fleas on each pup, and therefore they also have lower chances of ingesting an infected one. But the chances of infection increases as the total number of adults and older juveniles visiting the den rises and this is because of the increase in possible hosts for the fleas.

It can be seen from this study that host age and denning behaviour are important factors that influence the abundance of Dipylidium infections in wild carnivores. However more genetic information is required to clarify whether this hyena tapeworm is D. caninum or a related, but different, species.

Who knew a little bit of faecal matter could tell us so much!

This post was written by Courtney Hawkins

References:
East, M., Kruze, C., Wilhelm, K., Benhaiem, S. & Hofer, H. (2013). Factors influencing Dipylidium sp. infection in a free-ranging social carnivore, the spotted hyaena (Crocuta crocuta). International Journal of Parasitology: Parasites and Wildlife 2: 257-265.

Ophryocystis elektroscirrha (revisited 1)

This is the third post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2015. This particular post was written by Aimee Diamond and it is on how the Monarch Butterfly can keep pesky parasite-induced blemishes at bay (you can read the previous post about a deadly parasite that causes rabbits to tilt their head like they are being animated by Shaft Studio here).

Photo by Derek Ramsey

The monarch butterfly, dubbed one of the most beautiful species of butterfly on the planet, has a beauty secret that helps reduce signs of pesky imperfections. BUT HOW, you may cry? You might see those ads for make-up and skincare products and they are always talking about visible pores, so how do you think butterflies feel about all these SPORES?

The imperfections I am talking about on these butterflies are caused by the protozoan parasites Ophryocystis elektroscirrha. These parasitic spores cover the surface of infected butterflies and get scattered onto the host plant - the milkweed - or onto the butterfly’s eggs. Once the eggs hatch, the caterpillar feeding off the contaminated milkweed plants end up ingesting these spores, which reside and mature in their gut.

The parasite then penetrate the intestinal wall and begin to clone multiple copies of themselves. They then undergo a sexual phase and form spores around the scales of the developing butterfly. And so, when the butterfly emerges from its cocoon, it is already infected.

Now, many studies have shown that virulence (how harmful a parasite is) is a parasite trait, and that its expression depends on the interactions between the genes of the host and the parasite. However, there is another factor that determine how virulent a parasite can be. It all comes down to host ecology; in this case, the species of milkweed that the monarch butterfly chooses for its host plant. There are over 100 species of milkweed, of which 27 are used by the monarch butterfly to lay their eggs for their little ones to feed on. What makes many species of milkweed relevant in determining O. elektroscirrha virulence is the fact that these plants contain toxic chemicals known as cardenolides which varies in quantity, depending on the milkweed species, but is used by the caterpillar in defense against predators, as well as parasites.

Photo by April M. King

In short, depending on which species of milkweed these butterflies land on, the amount of cardenolides that their caterpillar ingest can aid in defending them against those pesky parasite-induced imperfections.

A study was done to test how parasite virulence varies according to host ecology. For this, two milkweed species were used; Asclepias incarnata and Asclepias curassavica, and caterpillars were infected with cloned parasites and fed with either of the two milkweed species. These two species were chosen as they contain different amounts of cardenolides; A. curassavica has a much greater amount of these toxic chemicals than A. incarnata. If we put the pieces of the puzzle together, it can be assumed that the butterflies reared on A. incarnata will be more heavily infected with the parasite than those reared on A. curassavica.

And that was exactly the outcome of the study. The lower the chemical defense in the host plant species, the higher the parasite virulence in the caterpillar/butterfly. Host ecology, can sometimes drive parasite virulence more so than genetic traits and interactions between the host and parasite alone. The monarch butterfly can now have gorgeous spore-­free scales, as long as it chooses a milkweed species with greater chemical defense as their larval host plant.

The search for radiant, parasite-free exoskeleton is over. Maybe she’s born with it, maybe it’s cardenolides.

De Roode, J. C., Pedersen, A. B., Hunter, M. D., & Altizer, S. (2008). Host plant species affects virulence in monarch butterfly parasites. Journal of Animal Ecology, 77(1), 120-126.

This post was written by Aimee Diamond

Encephalitozoon cuniculi

This is the second post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2015. This particular post was written by Brenda Cornick and it is about an outbreak of a microsporidian parasite that causes rabbits to look like they were being animated by Shaft Studio (you can read the previous post about a parasitoid that commandeer a spider to weave a tangled web for it here).

An Encephalitozoon cuniculi spore
From Figure 7 of this paper

For those with pet rabbits, Calicivirus and Myxoma virus are generally thought to be the main dangers to bunny's health. However, there is another nasty lurking within our little furry friends that you may not be aware of - the parasite Encephalitozoon cuniculi. The vast majority of rabbits that carry this parasite show no symptoms at all, and can live a normal healthy life. But for the unlucky few that are affected, the symptoms are particularly unpleasant, and usually fatal. There was an outbreak of E. cuniculi in a rabbit colony at a Japanese zoo between 1999-2001 that claimed the lives of 42 rabbits. But before we look at the study surrounding this outbreak, a summary of how this parasite operates would be helpful.

Encephalitozoon cuniculi is a type of microsporidian, a single-cell parasite equipped with a structure called a polar tube, which is curled inside the infective spore. Spores are the infectious stage, and are either inhaled or consumed by the host. When it comes into contact with a host cell, the spore discharges its polar tube and penetrates the cell membrane, allowing the parasite to enter. It is an intracellular parasite that lives inside its host's cell, and this species also attacks the host's central nervous system. The most common means of transmission is from the urine of an infected rabbit.

Dat Shaft head-tilt
From Figure 1 and 2 of this paper

In rabbits that develop disease from E. cuniculi infection, clinical symptoms include head tilt, loss of balance, weakness in the hind legs, depression, stunted growth, and lesions results from inflammation caused by the rupturing cells releasing spores. Rabbits showing some or all of these symptoms, can have nodules and cysts on their internal organs such as brain, heart, liver, and kidneys. This parasite has also been known to be transmitted to humans with compromised autoimmune systems, such as those suffering from AIDS, and was listed by the World Health Organisation as an emerging infectious agent. Encephalitozoon cuniculi spores are able to survive pretty well in the external environment, but can be eradicated with the use of standard disinfecting routines.

In Japan, this nasty little parasite has also been found in squirrel monkeys and domestic dogs living in close quarters with humans. The E. cuniculi outbreak at the Japanese facility prompted the study featured in this post, which involved clinical and pathological examinations, and biosecurity countermeasures. The alarm was first raised when two young bunnies showed signs of a central nervous system problems. Blood tests were conducted, and those bunnies were diagnosed with encephalitozoonosis. Following these cases, biosecurity measures were put in place included monitoring, isolation, and transport limitation. Any rabbits even suspected of harbouring E. cuniculi were humanely euthanized. Despite these measures, periodic infections were still occurring, leading to the entire rabbit colony being euthanized. In total, 32 out of the 42 (76.2%) rabbits were found to be infected with E. cuniculi.

Following this incident, the facility was closed and all the equipment, such as cages, feeders, floors were thoroughly sterilized using burners, 70% ethanol solution, and boiled water. New rabbits were introduced back into the facility two months after this procedure. and there has been no recurrence of E. cuniculi outbreaks.

It became clear during this study that the original infection had come from eight rabbits that were introduced to the colony with no quarantine period. Due to the lack of simple biosecurity measures, the act of introducing new bunnies became a death sentence for the whole colony. For this particular facility, the rabbits were a popular interactive attraction for visitors, many of whom were infants or the elderly whose immune systems may not be as strong as others. This highlights the importance of adequate biosecurity and husbandry techniques when dealing with readily transmissible parasites that can be harboured by multiple host species, and can have such devastating effects.

Reference:
Fukui, D., Bando, G., Furuya, K., Yamaguchi, M., Nakaoka, Y., Kosuge, M., & Murata, K. (2013). Surveillance for an Outbreak of Encephalitozoon cuniculi Infection in Rabbits Housed at a Zoo and Biosecurity Countermeasures. Journal of Veterinary Medical Science, 75(1), 55-61.

This post was written by Brenda Cornick