Lymphatic filariasis, commonly known as elephantiasis, is a neglected tropical disease. Infection occurs when filarial parasites are transmitted to humans through bites of mosquitoes. Currently, 886 million people in 52 countries are living in areas that require preventive chemotherapy to stop the spread of infection. At least 36 million people remain with these chronic disease manifestations. Eliminating lymphatic filariasis can prevent unnecessary suffering and contribute to the reduction of poverty.
Lymphatic filariasis is caused by infection with parasites classified as nematodes (roundworms) of the family Filariodidea. There are 3 major species of filarial worms causing human disease: Wuchereria bancrofti(90% of cases), Brugia malayi, and Brugia timori. They are transmitted by members of Anopheles, Culex, Aedes, Mansonia, and Ochlerotatus genera of mosquitoes, depending on the geographical location and biological peculiarities of each species. Adult worms nest in the lymphatic vessels and disrupt the normal function of the lymphatic system. The worms can live for approximately 6-8 years and may produce millions of microfilariae (immature larvae) that circulate in the blood during their life time. Mosquitoes are infected with microfilariae by ingesting blood when biting an infected host. Microfilariae mature into infective larvae within the mosquito. When infected mosquitoes bite people, mature parasite larvae are deposited on the skin from where they can enter the body. The larvae then migrate to the lymphatic vessels where they develop into adult worms, thus continuing a cycle of transmission.
Lymphatic filariasis infection involves asymptomatic, acute, and chronic conditions. The majority of infections are asymptomatic, showing no external signs of infection while contributing to transmission of the parasite. These asymptomatic infections still cause damage to the lymphatic system and alter the immune system. Acute episodes of local inflammation involving skin, lymph nodes and lymphatic vessels often accompany chronic lymphoedema or elephantiasis. When lymphatic filariasis develops into chronic conditions it leads to lymphoedema (tissue swelling) or elephantiasis (skin or tissue thickening) of limbs and hydrocele (scrotal swelling). Involvement of breasts and genital organs is common. Medical treatment include administration of diethylcarbamazine citrate (DEC) and albendazole. Morbidity management and disability prevention include surgical approach. Clinical severity and progression of the disease, including acute inflammatory episodes, can be reduced and prevented with simple measures of hygiene, skin care, exercises, and elevation of affected limbs.
Elimination of lymphatic filariasis is possible by stopping the spread of the infection through preventive chemotherapy through mass drug administration (MDA). MDA involves administering an annual dose of medicines to the entire at-risk population. The medicines used have a limited effect on adult parasites but effectively reduce the density of microfilariae in the bloodstream and prevent the spread of parasites to mosquitoes. The MDA regimen recommended depends on the co-endemicity of lymphatic filariasis with other filarial diseases. Mosquito control is a supplemental strategy to reduce transmission of lymphatic filariasis and other mosquito-borne infections. Depending on the parasite-vector species, measures such as insecticide-treated nets (ITNs), indoor residual spraying or personal protection measures may help protect people from infection. The use of ITNs in areas where Anophelesis the primary vector for filariasis enhances the impact on transmission during and after MDA. Historically, vector control has in select settings contributed to the elimination of lymphatic filariasis in the absence of large-scale preventive chemotherapy.
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World Health Organization. Lymphatic filariasis [updated 12 April 2019]. Available from: https://www.who.int/news-room/fact-sheets/detail/lymphatic-filariasis.
