Description:
<p>In studies of Lassa fever in Sierra Leone, the prevalence of human antibody to Lassa virus ranged from 8Vo to 52(7o. Mastomys natalensis, the reservoir of Lassa virus, con-stituted 50^0-60^0 of the rodents captured in houses but only 10^0-20^0 of those cap-tured in surrounding agriculture and bush areas (x2 = 90.2, P< 10"6, df = 1), a finding suggesting that houses are the most-important location for transmission of Lassa virus. Viral infection of Mastomys from houses ranged from O^o to 80^0. The incidence of seroconversions in susceptible persons ranged from 5a7o to 22^0 per year; the ratio of ill-ness to infection ranged from 9^0 to 26^0, and the proportion of febrile illness associated with seroconversion was 5(7o-14(7o. Eightfold rises in titer of antibody occurred in l^o-lS^o of the antibody-positive population, a result suggesting reinfection. We estimate the ratio of fatalities to infection to be l(Vo-207o, a rate lower than estimates based on hospitalized cases. The high incidence of Lassa fever makes it a major problem in West Africa.</p>