Filariasis

This is an infestation with thread-like helminths (Latin "Filum"—a thread). They are widely distributed in many species and live in the lymphatics and connective tissue. Fertilised eggs develop into embryonic worms—microfilariae. These are taken up by insect vectors that act as intermediate hosts in which further development occurs. They are then inoculated into a human host when next bitten by the insect.

Myiasis—papule

Three diseases are caused by filarial worms:

• Lymphatic filariasis due to Wuchereria bancrofti, which liberate microfilariae into the blood stream.

• Onchocerciasis due to Onchocera volvulus. The microfilariae are liberated into the skin and subcutaneous tissues.

• Loiasis due to Loa loa, in which microfilariae are found in the blood.

Lymphatic filariasis affects 120 million people in 73 countries (34% in sub-Saharan Africa). It causes lymphoedema of the legs, genitalia, and breasts. It may be asyptomatic for a long period and the adult worms live for four to six years in the lymphatic vessels and lymph nodes producing thousands of microfilaria each day. These are picked up by mosquitoes when they take a blood meal and are passed on to the next victim when they feed again.

Treatment

• In endemic areas the whole community should be treated with a single dose of two of the following three drugs once a year for four to six years:

(a) Ivermectin 400 micrograms/kg body weight

(b) Diethylcarbamazine (DEC) 6 mg/kg body weight

(c) Albendazole 600 mg.

• The chronic lymphoedema can be improved by keeping the legs moving, raising the legs when sitting, and prevention of secondary bacterial infection by regular washing and moisturising of the skin.

Lymphoema of the legs in filariasis
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