The risk of tropical spastic paraparesis differs according to ethnic group among HTLV-I carriers in Inongo, Zaire.

Following the finding in 1990 of six HTLV-I-positive cases of tropical spastic paraparesis (TSP/HAM) is a field survey carried out in the city of Inongo (Bandundu, Zaire), the prevalence of HTLV-I infection has been studied by detection of specific antibodies on a randomized sample of the general population. Among the 1,162 subjects surveyed, 36 (3.1%) were found to be HTLV-I seropositive, giving a seroprevalence of 3.2% (CI: 2.1, 4.3) estimated by direct standardization on age and sex distribution given by the census in the city. Among the five major ethnic groups, the Bolia showed the highest prevalence rate (6.5%) but with no detected TSP/HAM cases, while all six TSP/HAM cases were found among the Ntomba, who showed a prevalence rate of only 2.2%. This finding suggests that besides HTLV-I infection, critical environmental and/or genetic cofactors play a part in the development of TSP/HAM.