Genetic epidemiology of host predisposition microfilaraemia in human loiasis

Evidence is accumulating from experimental and human studies that genetic factors are involved both in the control of infectious diseases and in the regulation of infection levels and clinical presentation. So far few studies have investigated the role of these genetic factors in human infection by the filarial parasite Loa loa. We present a segregation analysis on 74 nuclear families who live in the tropical rainforest of southern Cameroun and are exposed to homogeneous loiasis transmission. The results indicate that there is a genetic predisposition to be microfilaraemic and that predisposed subjects might be genetically unable to mount an efficient immune response against loiasis antigens. This individual susceptibility could explain at least in part why the prevalence of infection (microfilaraemic individuals) does not usually exceed 30% of the exposed population in hyperendemic regions. Further genetic studies, based on linkage analysis using both familial information and genetic markers, will help to identify the nature of the genetic factors predisposing to microfilaraemia.