PARASITE ANTIGENEMIA WITHOUT MICROFILAREMIA IN BANCROFTIAN FILARIASIS

The term ''endemic normal'' in the context of filariasis refers to peo ple who are amicrofilaremic and free of clinical signs or symptoms of filariasis despite regular exposure to the parasite. Some sera from en demic normals contain soluble Wuchereria bancrofti antigens that are d etectable by enzyme-linked immunosorbent assay. We now report evidence that filarial antigenemia in these people is not an artifact and that it is indicative of active W. bancrofti infection. Filarial antigenem ia was first detected within one month of the onset of microfilarial p atency in experimentally infected primates. Human sera from antigen-po sitive endemic normals contained the same filarial antigens (by Wester n blot) as sera from people with microfilaremia. Sera from antigen-pos itive endemic normals also contained significantly higher levels of im munoglobulin G(4) antibodies to native and recombinant filarial antige ns than sera from antigen-negative controls matched for age and sex. T he epidemiology of filarial antigenemia in endemic normals was studied with sera from a population-based study of filariasis in an Egyptian village with a microfilaria prevalence of 29%. Seventeen percent of en demic normals had antigenemia, and this group comprised 11% of the tot al village sample. Filarial antigenemia was significantly more common in endemic normals more than 30 years of age than in younger people. T hese results suggest that amicrofilaremic and asymptomatic W. bancroft i infections are relatively common in endemic areas. Additional studie s are needed to determine the clinical significance, prognosis, and op timal management of such infections.