Familial aggregation of Trypanosoma brucei gambiense trypanosomiasis in a very high incidence community in Zaire

Familial aggregation of Trypanosoma brucei gambiense human African trypanosomiasis (HAT) was investigated in 3 adjacent villages of central Zaire where 318/1431 inhabitants had previously suffered from HAT. Neither spatial nor familial aggregation was detected when analysing the distribution of cases in the whole community using Poisson, negative binomial and pairwise odds ratio models. However, clustering of cases was observed when specific familial relationships were examined. The risk of HAT for a child was significantly increased if the mother had also had HAT, but it was not influenced by a past history of HAT in the father. Sisters and brothers of cases of HAT had a higher risk of HAT than siblings of individuals who had never had HAT, but no such association was documented for half-sisters and half-brothers. Among married couples, a past history of HAT in one spouse had no impact on the other spouse's risk of HAT. Indirect arguments suggested that familial clustering was a consequence of shared exposure, either sequential or simultaneous, rather than of genetic susceptibility. The existence of familial clustering should be kept in mind when implementing passive or active case-finding activities.