An immunoepidemiological study of Wuchereria bancrofti in Muhaka, Kwale District, south coastal Kenya
Description
This study was designed to determine the relationship between Wuchereria bancrofti infection status, levels of circulating microfilarial, parasite antigenemia and antifilarial antibody responses. The effects of transmission season and concurrent helminth infections on filarial infection and antifilarial antibody responsiveness were also examined. The study was conducted in a population of 328 life-long residents aged $\geq$1 yr, in Muhaka, Kwale District, south coastal Kenya, an area endemic for bancroftian filariasis. Wuchereria bancrofti microfilaremia and circulating antigenemia were determined before the long rains, a time coinciding with a low transmission season. Acute and chronic manifestations of filariasis were also assessed. The prevalence of microfilaremia increased gradually with age and was significantly higher, p $<$.001 in Kilore (24%) than in Mvumoni (6.3%). The prevalence of antigenemia increased with age and also was significantly higher in Kilore (48.9%) than in Mvumoni (20.5%), p $<$.001. Hydrocele and acute manifestations of filariasis were also significantly more common in Kilore than in Mvumoni. Baseline antifilarial antibody levels at a time coinciding with a low transmission season, were dependent on W. bancrofti infection status, locality, age and clinical status of the participants. Levels of IgG4 were higher in the antigen-positive than antigen-negative persons (p $<$.001) in both communities. In contrast, the levels of IgG3 were lower in microfilaria-positive than microfilaria-negative persons in Mvumoni (p =.053) and in Kilore, levels of IgG2 antifilarial antibody responsiveness were lower in antigen-positive than antigen-negative persons (p =.014). In antigen-negative persons, all four isotypes were significantly higher in Kilore than Mvumoni (p $<$.001, for IgG1, IgG2, IgG4 and p =.055 for IgG3). Follow up serum samples were available from a subset of 123 participants after the transmission season. Comparing antifilarial antibody responsiveness in all pre- and post-transmission samples in Mvumoni, the low prevalence community, there were no significant changes in IgG1, IgG2 or IgG3 levels but IgG4 antibody responses increased significantly (p =.023). Qualitative analyses of seasonal shifts in stage-specific anti-Brugia pahangi IgG1 and IgG4 isotypes in paired sera by immunoblot showed similar antigen recognition profiles. Despite increased exposure to infective larvae following the onset of the rainy season, very few individuals showed new reactivity with previously unrecognized filarial antigens. Antifilarial IgG responses were dependent upon filarial infection status but were not significantly influenced by the presence or absence of infection with either S. haematobium or intestinal helminths