Lymphatic filariasis
One of the most common causes of disability

Lymphatic filariasis is a human disease caused by parasitic worms that enter the body after being bitten by an infected mosquito. Some people develop a syndrome called elephantiasis, which is marked by severe swelling in the arms, legs, breasts, or genitals. Infection is usually acquired in childhood causing hidden damage to the lymphatic system.

Lymphatic filariasis affects 120 million people and one billion people at risk for infection. About 40 million people are disfigured or incapacitated by the disease, making it one of the most common causes of disability.

What causes Lymphatic filariasis

Lymphatic filariasis is a disease caused by filarial parasites, classified as roundworms, being transmitted by mosquitoes from human to human. It is a type of helminth infection with Wuchereria bancrofti the most common cause (90% of cases), but also Brugia malayi, and Brugia timori are known to cause disease. Culex, Anopheles and Aedes mosquitos are involved in the transmission of the disease.

Adult worms disrupt functionality of hosts’ lymphatic system after nesting in the lymphatic vessels, where they subsequently produce millions of immature larvae circulating in the blood. Upon biting an infected host, the immature larvae enter mosquitoes through blood and will mature into infective larvae within them. When the infected mosquitoes subsequently bite a person, the mature larvae deposited on one’s skin enter into the body. Once entered the body of a new host, the larvae migrate into the host’s lymphatic vessels, where they mature into adult worms and cause abnormal functionalities of the lymphatic system.

Photo: Wuchereria bancrofti, the most common cause of Lymphatic filariasis.

Where is Lymphatic filariasis found

It is considered endemic in tropical and subtropical regions of Africa, Asia, Central and South America, and Pacific Island nations. Out of 73 countries where the disease occurs, 37 are in Africa.

  • In the Americas, it is present in Brazil, Costa Rica, the Dominican Republic, Guyana, Haiti, Suriname, and Trinidad and Tobago.
  • In Asia, it is present in Bangladesh, Cambodia, India, Indonesia, Laos, Malaysia, Maldives, the Philippines, Sri Lanka, Thailand, Timor-Leste, and Vietnam.
  • In the Middle East, it was present only in Yemen until 2019.
  • In the Pacific region, it is endemic in American Samoa, the Cook Islands, Fiji, French Polynesia, Micronesia, Niue, Papua New Guinea, Samoa, Tonga, Tuvalu, and Vanuatu.

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In many of these countries, considerable progress has been made towards elimination of filariasis.

Image: Countries with endemic Lymphatic filariasis (2020).

What are the symptoms of Lymphatic filariasis

Most cases are asymptomatic but contribute to the transmission of the parasite. These asymptomatic infections can still cause damage to the lymphatic system and the kidneys, and 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). Involvement of breasts and genital organs is common.

Acute episodes of local inflammation involving skin, lymph nodes and lymphatic vessels often accompany chronic lymphoedema or elephantiasis. Some of these episodes are caused by the body’s immune response to the parasite. Most are the result of secondary bacterial skin infection where normal defenses have been partially lost due to underlying lymphatic damage. These acute attacks are debilitating, may last for weeks.

Photo: typical swelling of elephantiasis in legs.

How can Lymphatic filariasis be prevented

The present objective of prevention is the eradication of lymphatic filariasis, which is achievable since the disease has no known animal reservoir. This consists of systematic mass deworming of entire populations with a single annual dose of two medicines, namely albendazole in combination with either ivermectin or diethylcarbamazine citrate.

Avoiding mosquito bites, such as by using insecticide-treated mosquito bed nets, also reduces the transmission of lymphatic filariasis.

How is Lymphatic filariasis diagnosed

The standard method for diagnosing active infection is by finding the microfilariae via microscopic examination in nocturnally collected blood. The blood sample is typically in the form of a thick smear and stained with Giemsa stain.

Testing the blood serum for antibodies against the disease may also be used.

How is Lymphatic filariasis treated

Treatments for lymphatic filariasis differ depending on the geographic location of the area of the world in which the disease was acquired.

Anthelmintics

In sub-Saharan Africa, albendazole is used with ivermectin to treat the disease, whereas elsewhere in the world, albendazole is used with diethylcarbamazine. Geo-targeting treatments is part of a larger strategy to eventually eliminate lymphatic filariasis.

Antibiotics

Doxycycline is also effective in treating lymphatic filariasis but with the disadvantage that it requires 4 to 6 weeks of treatment. The reason for success of antibiotic treatment is that the parasites depend on symbiotic bacteria.

The medications do not kill the adult worms but prevent further spread of the disease until the worms die on their own. Adult worms have a lifespan of 6 to 15 years.

Supportive treatment

In some cases surgery may be needed.

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