RIFT-VALLEY FEVER IN RURAL NORTHERN SENEGAL - HUMAN RISK-FACTORS AND POTENTIAL VECTORS

To investigate past infection in and transmission of Rift Valley fever (RVF) virus to humans within an endemic focus, we undertook a retrosp ective cohort study of the seminomadic Peul people living in sub-Sahar an northcentral Senegal. Residents of the rural settlement of Yonofere five years of age or older were studied during February-May 1989. Ant i-RVF virus IgG was found in blood samples of 22.3% of 273 persons who responded to a standard questionnaire; none had IgM antibodies. Serop ositivity was similar for males (25.4%) and females (21.1%), increased markedly with age for both sexes, and varied considerably among compo unds (groups of huts) (0-37.5%). Risk factors for past RVF virus infec tion were nursing sick people, assisting animals during abortions/birt hs, and treating sick animals. In all age groups, odds ratios (ORs) fo r RVF viral antibody among females who reported treating sick animals were three to six times greater than for those who did not. The ORs fo r males who reported assisting with animal births/abortions and nursin g sick people were approximately five times those for males who did no t. Serologic prevalence of RVF viral antibody among sheep averaged 30. 1% overall (0.8% IgM), but varied among compounds (0-66.7%) in a manne r different from that of humans. The seasonal abundance and relative d ensity of potential mosquito vectors were estimated by monthly samples captured in Centers for Disease Control and Prevention-type traps. Mo squito abundance varied seasonally with rainfall (> 90% captures durin g four months). Species diversity was large (28 spp.), dominated by Ae des and Culex. Rift Valley fever virus was not isolated from 142 pools of 2,956 unengorged mosquitoes tested, although three other arbovirus es were found. Results indicate that RVF is endemic in this region, pe ople are at considerable risk of infection, and that a heretofore unre cognized mode of human infection under nonepizootic conditions may be transmission via contact with infected animals or humans.