Body cavity filariasis

Filariasis is a parasitic disease caused by thread-like filarial nematodes (roundworms) in the family Filarioidea (also known as 'filariae'). Of the hundreds of described filarial parasites, only 8 species cause natural infections in humans (see separate articles Lymphatic Filariasis e Cutaneous Filariasis).

Body cavity filariasis is caused by the worms Mansonella perstans, Mansonella streptocerca e Mansonella ozzardi, and is often referred to as mansonellosis.¹

Life cycles^{2 3}

• Infective larvae are transmitted by infected arthropods during a blood meal. The larvae migrate to the appropriate site of the host's body, where they develop into microfilariae-producing adults.

• The adult worms of M. ozzardi live in the abdominal cavity of the human host, living within the mesenteries, peritoneum and in the subcutaneous tissue. The adult worm can live for several years.

• M. perstans adult worms live in body cavities, most often the peritoneal cavity or pleural cavity and, less frequently, in the pericardium .

• The female worms produce microfilariae which circulate in the blood. The microfilariae infect biting arthropods (midges for M. perstans and both midges and blackflies for M. ozzardi).

• Inside the arthropod, the microfilariae develop within 1 to 2 weeks into infective filariform (third-stage) larvae. During a subsequent blood meal by the insect, the larvae infect the vertebrate host.

• The larvae then migrate to the appropriate site of the host's body, where they develop into adults.

Among the known human filarial infections, mansonellosis is probably the most frequent filariasis in sub-Saharan Africa as well as a northern part of the Amazon rainforest.

It has been estimated that 114 million people may be infected and as many as 581 million people in 33 countries are at risk for M. perstans infection in Africa alone.

It is one of the most common human helminthiases in endemic areas, and it is more prevalent and more neglected than other filarial diseases such as lymphatic filariasis, onchocerciasis, and loiasis. In endemic areas, the probability of infection increases with age, with the prevalence reaching 100% in highly endemic areas.

Mansonellosis infections are thought to have little pathogenicity and to be almost always asymptomatic, but occasionally causing itching, joint pains, enlarged lymph glands, and vague abdominal symptoms.

• Identification of microfilariae in peripheral blood or skin by microscopic examination is the most practical diagnostic procedure.

• Examination of blood samples will allow identification of microfilariae of M. perstans e M. ozzardi. A thick smear, stained with Giemsa or haematoxylin and eosin is often used.

• Antigen detection using an immunoassay for circulating filarial antigens is useful because microfilaremia can be low and variable.

• Antibody detection is of limited value. Substantial antigenic cross-reactivity exists between filaria and other helminths, and a positive serological test does not distinguish between past and current infection.

• The combination therapy of diethylcarbamazine plus mebendazole for M. perstans microfilaremia is presently one of the most widely used, but the use of ivermectin has also been proven to be very effective against microfilariae.

• Doxycycline has shown excellent efficacy and safety when used as an antimicrobial against endosymbiotic Wolbachia bacteria harboured by some strains of M. perstans e M. ozzardi.

• Diethylcarbamazine and ivermectin have been used effectively to treat M. streptocerca .

• Prevention of morsi di insetto by wearing long-sleeved shirts, not wearing short trousers and the use of insect repellents.

• Widespread application of insecticides to specific breeding sites has been used.

• The ivermectin and mebendazole-based mass drug administration treatment regimens (iMDA and mMDA) deployed by the WHO's Elimination of Neglected Tropical Diseases (ESPEN) programme and its forerunners have likely impacted significantly on the mansonellosis disease burden, principally by reducing the transmission of M. streptocerca in Africa.

• The plan of using iMDA to control malaria could also affect M. ozzardi parasite prevalence and transmission in Latin America in the future.

• A potentially far greater mansonellosis disease burden impact is likely to come from short-course curative anti-Wolbachia treatments, which are presently being developed for onchocerciasis and lymphatic filariasis treatment.