Eight laboratory-contracted infections in man with Rift Valley fever virus are reported. The outstanding symptoms were headache, backache, anorexia, prostration and fever. The duration of fever ranged from 2 to 6 days. All the patients recovered without exhibiting any permanent sequelae, but the rapidity of convalescence was variable. The enforced total or partial cessation of normal activities varied from 2 to 28 days.

Rift Valley fever virus was isolated from the blood of each patient during the febrile stage of the illness. The development of neutralizing antibody during convalescence was demonstrated in all the cases.

Two of the patients, one of whom had had vivax malaria 4 months previously, had malaria parasites in their blood at the onset of illness.

Although quantitative tests for virus were not made on freshly drawn blood specimens, the first-day serum of one patient contained 1,458,540 intracerebral LD50 of virus after 82 days' storage in the refrigerator. The presence of viable Rift Valley fever virus was demonstrated in this same blood after storage for 2 years in the fluid state. The sera of other patients exhibited viable virus after even longer periods of storage in the refrigerator (up to 1,048 days).

Three African employees who were not known to have had Rift Valley fever were found to be immune. In the absence of evidence showing recent activity of the virus among human beings residing in this locality, this was interpreted as indicating that the 3 individuals had experienced subclinical infections as result of contact with the virus in the laboratory.

The experiences reported indicate that the risk of infection is very great among persons engaged in investigations on Rift Valley fever virus, but they also show that the probability for complete recovery from the disease is high.

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From the Yellow Fever Research Institute, Entebbe, Uganda.

This Institute is financed by means of grants made by The Rockefeller Foundation and by the Secretary of State for the Colonies under the Colonial Development and Welfare Acts and by contributions from the Governments of Uganda, Kenya, Tanganyika, Northern Rhodesia, Nyasaland and Zanzibar.

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