Immunity and the prospects for vaccination against filariasis

Abstract

Lymphatic filariasis and onchocerciasis are tropical diseases caused by filarial nematode parasites which affect about 90 million and 20 million people respectively. Although very little mortality is associated with these diseases, infection frequently leads to debilitation and disfigurement. Onchocerciasis is caused by a single species, Onchocerca volvulus, transmitted by blackfly and endemic in regions of West Africa and Central America. Infection can result in a variety of skin lesions and blindness, hence the generic name «river blindness». Lymphatic filariasis is more broadly distributed, as there are three causative agents (Brugia malayi, Brugia timori and Wuchereria bancroftl) which are transmitted by a variety of mosquito species. B. malayi is restricted to India and South East Asia, and B. timon· to the Lesser Sunda archipelago of islands in Indonesia. W. bancrofti is more cosmopolitan, and is found throughout the tropical zone, particularly in India, South East Asia, Africa, parts of Central and South America and a number of the Pacific Islands. As one of the mosquito vectors (Culex quinquefasciatus) can breed in polluted water, large foci of urban Bancroftian filariasis may develop. Symptoms of lymphatic filarial infection include painful attacks of lymphadenitis and chronic obstructive lesions such as hydrocoeles and elephantiasis. A profound social stigma may be associated with disfigurement which compounds the physical discomfort and debilitation. An additional and quite distinct syndrome called Tropical Pulmonary Eosinophilia (TPE) may also result from infection. This is essentially an occult form of filariasis, characterized by extremely high levels of IgE, eosinophilia and asthmatic attacks. The syndrome is believed to be caused by immediate hypersensitivity to first stage larvae (microfilariae) which have become trapped in the lungs, although it is unclear why certain individuals are predisposed to this type of pathology (1).