Case-Control Study of Mastomys Natalensis and Humans in Lassa Virus-Infected Households in Sierra Leone

Richard A. KeenlysideU.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, Center for Infectious Diseases, Atlanta, Georgia

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Joseph B. McCormickU.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, Center for Infectious Diseases, Atlanta, Georgia

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Patricia A. WebbU.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, Center for Infectious Diseases, Atlanta, Georgia

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Ethleen SmithU.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, Center for Infectious Diseases, Atlanta, Georgia

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Luanne ElliottU.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, Center for Infectious Diseases, Atlanta, Georgia

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Karl M. JohnsonU.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, Center for Infectious Diseases, Atlanta, Georgia

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Lassa virus infection and antibodies were studied in households where Lassa fever cases occurred, and compared to those in nearest neighbor houses and “far” houses located across the village from case houses. Seventy-nine percent of all rodents caught in the houses were Mastomys, the natural reservoir of Lassa virus. Rodent infection was not randomly distributed, but rather focal. Thirty-nine percent of the Mastomys in case houses were viremic, compared to 3.7% in control houses. Human antibody prevalence in case houses was 30%, compared to 20% in non-case houses (P < 0.05, chi-square test, df = 2). Neither seroconversions nor antibody prevalence rates were associated with household size or number of persons per room. Trapping of rodents in half of the case and control houses resulted in a Mastomys reduction ranging from 2.2- to 3.3-fold. This reduction failed to significantly reduce the seroconversion rate to Lassa virus in the people of trapped houses compared to those in untrapped ones. More complete trapping will be needed in order to better evaluate this procedure as a means of interruption of Lassa virus transmission in endemic villages.

Author Notes

Present address: Rhode Island Department of Health, 75 Davis Street, Providence, Rhode Island 02908.

Present address: Vector-Borne Diseases Division, Center for Infectious Diseases, P.O. Box 2087, Fort Collins, Colorado 80522.

Present address: U.S. Army Medical Research Institute for Infectious Diseases (USAMRIID), Fort Detrick, Frederick, Maryland 21701.

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