Human Bancroftian filariasis: loss of patent microfilaraemia is not associated with production of antibodies to microfilarial sheath

Antisheath antibodies have been incriminated in elimination of circulating microfilariae in human filariasis since a very significant inverse associat ion has been consistently demonstrated between the two parameters. An attem pt was made in the present study to seek empirical proof for the above prop osal. Two cohorts of 43 and 73 microfilariae (mf) carriers were examined af ter 13 and 10 years, respectively, for mf as well as antisheath antibodies. The first cohort was also examined for the presence of circulating filaria l antigen (CFA). Of the 43 mf carriers examined after 13 years, 62.8% were free of circulating mf although only 3.7% of them had demonstrable antishea th antibodies. Approximately 93% of this cohort (with or without current mi crofilaraemia) tested positive for CFA after 13 years indicating continued presence of adult filarial worms in the host after loss of mf in circulatio n. When the second cohort of 73 mf carriers were examined after 10 years, 3 0 were found to be amicrofilaraemic and only 6.66% of them had demonstrable antisheath antibodies. We conclude that, in human Bancroftian filariasis, elimination of circulating microfilariae may not be mediated by antibodies to microfilarial sheath.