Microfilaraemia, serum antibody and development of clinical disease in microfilaraemic subjects infected with Wuchereria bancrofti and treated with diethylcarbamazine citrate.

A seroepidemiological survey of bancroftian filariasis was carried out in 2 townships in Sri Lanka with the objectives of determining the microfilaraemia rates, dependence on age and sex, susceptibility to re-infection, effect of diethylcarbamazine therapy on serum antibodies to microfilarial surface antigens, and the predictive value of the indirect fluorescent antibody test. The mean microfilaraemia rate was 5.4%. Microfilaraemia was not sex-dependent but a marginally elevated incidence was seen in the 6-35 year age groups. In up to 58% of the microfilaraemic patients who had been treated for microfilaraemia previously, a second phase of microfilaraemia was seen 2-7 years after treatment. This was unlikely to have been due to incomplete parasite elimination. Antibodies to microfilarial surface were found in 24-35% of microfilaraemic patients and in 14-63% of amicrofilaraemic symptomatic subjects. Serum anti-microfilarial surface antibody levels did not alter with chemotherapy with diethylcarbamazine citrate. The findings of follow-up investigations of microfilaraemic subjects were compatible with the notion that microfilaraemia does not necessarily lead to clinical disease.