Intrafamilial clustering and 4-year follow-up of asymptomatic human T-cell leukaemia virus type I (HTLV-I) infection in Benin (West Africa).

BACKGROUND: Few data exist concerning familial human T-cell leukaemia virus type I (HTLV-I) carrier states and transmission in African countries. Two previous surveys performed in Benin in 1989 and 1990 using a three-level cluster sampling method allowed us to identify HTLV-I positive subjects. The evolution of HTLV-I within the families of these subjects is described over a 4-year period, 1991-1995. METHODS: Since 1991, 37 HTLV-I seropositive subjects, six subjects with indeterminate Western-Blot pattern, and their relatives have been followed up once a year clinically and biologically. RESULTS: Twenty-three mothers in the study group gave birth to 27 children between 1991 and 1995. Among the 13 infants born to the 12 seropositive mothers, two seroconverted before their second birthday. One adult woman whose husband was seropositive developed seropositivity 4 years after marriage. In March 1992, a family case-control study (proband study) was conducted. A seroprevalence of 27.5% was found among 138 relatives of 32 infected subjects and 1.4% among 142 relatives of 32 control subjects. CONCLUSIONS: There is clearly an intrafamilial clustering of HTLV-I in Benin. The annual incidence density of HTLV-I in this cohort is estimated at 6 per thousand.