Wuchereria bancrofti in a community with seasonal transmission:: stability of microfilaraemia, antigenaemia and filarial-specific antibody concentrations

The effect of seasonal transmission on microfilaraemia, antigenaemia and filarial-specific antibody levels in individuals infected with Wuchereria bancrofti was investigated in a follow-up study in an endemic community in north-eastern Tanzania. The subjects were 37 adult male residents who were found to be positive for circulating filarial antigen (CFA) at the beginning of the study (26 of whom were also found microfilaraemic with W. bancrofti at this time). Blood samples were collected from each subject in July 1998, January 1999 and July 1999, during the seasons when transmission intensity was high, low and high, respectively. The mean intensities of microfilaraemia and the mean concentrations of CFA were each slightly higher during the low-transmission season than during the two high-transmission seasons but the differences were not statistically significant (P>0.05). Similarly, the mean levels of filarial-specific IgG(1), IgG(2), IgG(3), IgG(4) or IgE did not differ to a statistically significant degree between the three examination times. Microfilaraemias and the levels of CFA and filarial-specific antibodies all therefore appeared to be remarkably stable and largely unaffected by the seasonal variation in transmission. That no variation in the mean IgG(4)/IgE ratio was observed over the study period may indicate that the level of resistance to W. bancrofti infection in the study subjects was also unaffected by the transmission season.