Lymphatic filariasis is a parasitic disease that can result in an altered lymphatic system and the abnormal enlargement of body parts, causing pain, severe disability, and social stigma. Infection occurs when filarial parasites are transmitted to humans through mosquitoes. The majority of infections show no external signs of infection, but they still cause damage to the lymphatic system and the kidneys, as well as alter the body’s immune system. When lymphatic filariasis develops into chronic conditions, it leads to lymphoedema (tissue swelling) or elephantiasis (skin/tissue thickening) of limbs and hydrocele (scrotal swelling).

In the Western Pacific Region, 24 of 37 countries and areas were endemic for lymphatic filariasis as of 2000. Since then, 13 of the 24 countries and areas have eliminated the disease as a public health problem. These countries include the following: Cambodia, China, Cook Islands, Kiribati, the Lao People's Democratic Republic, Niue and Vanuatu, Kiribati, the Marshall Islands, Palau, Republic of Korea, Tonga, Viet Nam, and Wallis and Futuna. Other endemic countries are making progress toward elimination. Almost all the remaining endemic countries use a triple drug regime composed of three drugs for preventive chemotherapy campaigns called Mass Drug Administration (MDA). Brunei and the Federated States of Micronesia are in the last stages and are positioning for submitting dossiers for validation of elimination of the disease as a public health problem if the surveys show that the disease is no longer a public health problem.

Whereas the disease was once thought to affect only adults, it now appears that most infections are acquired in childhood. Initial infection is followed by a long period of subclinical disease, which progresses in later life to clinically manifest disease. Lymphatic filariasis can cause a variety of clinical manifestations, that can be grouped into three categories: acute attacks, lymphoedema, and hydrocoele.

The adult filarial worms cause inflammation of the lymphatic system leading to lymphatic vessel damage, even in asymptomatic people, and lymphatic dysfunction, which predispose the lower limbs in particular to recurrent bacterial infection. These secondary infections provoke “acute attacks”, which are the commonest symptom of lymphatic filariasis and play an important role in the progression of lymphoedema. Acute attack is usually associated with local pain, swelling, fever, and chills.

Lymphoedema occurs primarily in the lower limbs and is common in women. In its most advanced form, lymphoedema may prevent people from carrying out their normal daily activities. Lymphatic filariasis may also evolve towards a genital disease (hydrocoele) that is characterized by a swelling of the scrotum and penis.

The vast majority of infected people are asymptomatic, but virtually all of them suffer from damage to the lymphatic system and the kidneys and from an altered body's immune system.

People infected with filariasis who have microfilaraemia or a positive antigen test should receive antifilarial drug treatment to eliminate microfilariae. Unfortunately, the medicines available have limited effect on adult worms.

Treatment also involves the Management of Morbidity and Disability Prevention (MMDP) that includes simple hygiene measures, such as basic skin care and exercise prevent acute attacks and progression of lymphoedema, and prevention of skin infections. For management of hydrocoele, surgery may be appropriate. MMDP also includes psychological and socioeconomic support for people with disabling conditions to ensure that they have equal access to rehabilitation services and opportunities for health, education and income. Activities beyond medical care and rehabilitation include promoting positive attitudes towards people with disabilities, preventing the causes of disabilities, providing education and training, supporting local initiatives, and supporting micro- and macro-income-generating schemes.

Preventive chemotherapy is used at the community level to eliminate microfilariae from the blood of infected individuals in order to interrupt the transmission of infection by mosquitoes.