A prospective study of the epidemiology and ecology of Lassa fever.
In studies of Lassa fever in Sierra Leone, the prevalence of human antibody to Lassa virus ranged from 8% to 52%. Mastomys natalensis, the reservoir of Lassa virus, constituted 50%-60% of the rodents captured in houses but only 10%-20% of those captured in surrounding agriculture and bush areas (chi 2 = 90.2, P less than 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 0% to 80%. The incidence of seroconversions in susceptible persons ranged from 5% to 22% per year; the ratio of illness to infection ranged from 9% to 26%, and the proportion of febrile illness associated with seroconversion was 5%-14%. Eightfold rises in titer of antibody occurred in 1%-18% of the antibody-positive population, a result suggesting reinfection. We estimate the ratio of fatalities to infection to be 1%-2%, a rate lower than estimates based on hospitalized cases. The high incidence of Lassa fever makes it a major problem in West Africa.
D000293:Adolescent; D000328:Adult; D000818:Animals; D000914:Antibodies, Viral / Q000032:analysis; D002648:Child; D002675:Child, Preschool; D004197:Disease Reservoirs; D005260:Female; D006801:Humans; D007835:Lassa Fever / Q000453:epidemiology* / Q000635:transmission / Q000662:veterinary; D007836:Lassa virus / Q000276:immunology; D008297:Male; D008875:Middle Aged; D009115:Muridae / Q000382:microbiology; D011446:Prospective Studies; D012376:Rodent Diseases / Q000453:epidemiology; D012807:Sierra Leone
D000914:Antibodies, Viral