Lassa Fever, a New Virus Disease of Man from West Africa

Lassa Fever, a hitherto unknown virus disease from Nigeria, caused the death of two missionary-nurses and the grave illness of a third. The onset is gradual with fever, weakness, myositis and ulcerative pharyngitis, progressing to symptoms of myocarditis, pneumonitis and pleuritis, encephalopathy, and evidences of a hemorrhagic diathesis. It is characterized in the early stages by moderate leukopenia, with increase of immature neutrophilic elements. It may be transmitted directly from person to person; the incubation period is about a week. It is likely to be of increasing public-health importance as travel to the interior parts of Nigeria increases, and as the area is developed because of future population pressures.