Filariasis

Abstract

Filarial infections are caused by parasitic nematode worms of the superfamily Filarioidea. These parasites are transmitted by biting insect vectors and cause a range of pathology, from asymptomatic or mild disease, to severe clinical disease and premature death. Infection in those living in endemic regions is usually asymptomatic, and disease generally occurs only after prolonged exposure and accumulation of worms. Travellers may develop more severe disease at lower levels of exposure to infection. The three major human filarial diseases are lymphatic filariasis, onchocerciasis and loiasis. More than 200 million individuals worldwide are estimated to have at least one of the human filariases. Host immune responses to circulating microfilariae lead to acute lymphatic filariasis with lymphadenitis, lymphangitis and epididymo-orchitis. The pathogenic mechanisms of chronic lymphatic filarial disease leading to hydrocele and elephantiasis are not fully understood. Immune responses to microfilariae in onchocerciasis produce itchy skin disease and eye pathology, sometimes leading to blindness. Loiasis causes transient allergic subcutaneous swellings and eye worm through the passage of adult worms. Individual specific treatment includes diethylcarbamazine for lymphatic filariasis and loiasis, and ivermectin for onchocerciasis. Diethylcarbamazine is contraindicated in onchocerciasis. Management of chronic lymphatic filariasis requires strict hygiene, antifungal drugs and antibiotics to prevent secondary infection. Control programmes using single-dose annual treatment of the entire population, regardless of infection status (mass treatment) with combinations of diethylcarbamazine, albendazole and ivermectin are in progress for the many poor populations affected by lymphatic filariasis and onchocerciasis.