Surveillance of Lassa fever in missionaries stationed in West Africa.

To determine the distribution of Lassa virus in West Africa, a serological survey was undertaken. A number of mission hospital supplied sera from patients admitted with a history of fever and specimens were also collected in New York from missionaries who had experienced an unusual febrile illness while working in Africa. More cases of Lassa fever were detected among missionaries than among Africans, possibly because many African patients had left hospital before the complement fixation tests had become positive. Although most adults had fairly high fever and some were prostrated, fever was less severe in the children examined. In general the findings confirm that not all Lassa fever patients have the severe syndrome described in the original reports.