Lymphatic filariasis

Endemic in over 80 countries in Africa, Asia, South and Central America and the Pacific Islands. More than 40% of all infected people live in India and one-third live in Africa.

	W. bancrofti China Japan Vietnam India Malaysia B. malaya India China Korea Malaysia Indonesia Philippines

Parasitic nematode worms of the family filariidae.

Three species are of significance,

Parasite	Definitive host
Wuchereria bancrofti,	Man only
Brugia malayi	Man and animals
Brugia timori.	Man and animals

Adult worms (Macrofilaria)	4-10 cm long, longevity 10-15 years
Microfilaria	300 micometers

Macrofilaria are present in the lymphe fluids

• They give rise to a constant production of microfilaria
• Adaptation to the intermediate host has led to the nocturnal appearance of of microfilaria in the blood (microfilaraemia)

Via the bite of blood-feeding female mosquitoes which transmit immature larval forms of the parasitic worms from human to human.

	Vectors: mosquitoes Anopheles Culex Aedes Mansonia Only the female mosquitoes are haemotophgous and bite only at night
W. bancrofti parasites are mainly transmitted by Culex quinquefasciatus mosquitoes and some species of Anopheles. Brugia parasites are mainly transmitted by Mansonia mosquitoes.

In humans, adult worms can live for many years, producing large numbers of larval forms (known as microfilariae) which circulate in the lymphatics and blood where they can be ingested by blood-feeding mosquitoes, so completing the transmission cycle.

The disease can be diagnosed by the identification of microfilaria in a blood sample that has preferably taken at night.

Infective larvae develop into adult worms (known as macrofilariae) in the afferent lymphatic vessels, causing severe distortion of the lymphatic system. Adult Wuchereria are often lodged in the lymphatics of the spermatic cord, causing scrotal damage and swelling. Elephantiasis - painful, disfiguring swelling of the limbs - is a classic sign of late-stage disease.

There are three basic disease stages:

• 1. Asymptomatic: patients have hidden damage to the lymphatic system and kidneys.
• 2. Acute: attacks of 'filarial fever' (pain and inflammation of lymph nodes and ducts, often accompanied by fever, nausea and vomiting) increase with severity of chronic disease.
• 3. Chronic: may cause elephantiasis and hydrocoele (swelling of the scrotum) in males or enlarged breasts in females.

The foot of an elderly man who had to give up his job due to to his elephantiasis

The global elimination strategy has two major components:

• Mass administration of drugs to 'at-risk' populations with once-a-year, one-day treatment (to interrupt transmission)
• Promotion of rigorous, simple hygiene techniques for lymphoedema (to alleviate and prevent suffering of affected individuals).
• Interruption of transmission by the use of insecticides

Lymphatic filariasis used to be treated with a 12-day treatment regimen using the drug diethylcarbamazine (DEC), but recent work has shown that a single dose of DEC is equally effective. Ivermectin has also been registered for treatment of filariasis, and albendazole was shown to have additional antifilarial effects. 

The treatment strategy is now based on annual, single-dose, 2-drug regimens of

• ivermectin+albendazole in countries that are co-endemic for onchocerciasis, and of
• DEC+albendazole in all other countries. 

A health worker dispensing DEC tablets at a local distribution point. Bacillus sphaericus to control Culex mosquitos and mass distribution of DEC tablets are being used to help control Bancroftian filariasis in favelas around Recife.

Transmission can also be reduced by avoiding mosquito bites in endemic areas , e.g. through use of

• repellents,
• bednets,
• insecticides.

Mosquito vectors often breed in polluted urban waters (such as blocked drains and sewers) so good sanitation and environmental management to minimize mosquito breeding places can play a major role in reducing the risk of the disease.

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