Experimental infection of rhesus monkeys with Lassa virus and a closely related arenavirus, Mozambique virus.

As a model for the pathogenesis of Lassa fever in humans, nine rhesus monkeys were inoculated with Lassa virus. Three monkeys had had a previous asymptomatic experimental infection with Mozambique virus, a closely related arenavirus; these monkeys were protected from illness and viremia and manifested only mild pathologic lesions. The other animals developed severe disease and viremia. At necropsy, hepatocellular necrosis, interstitial pneumonia, a unique pulmonary arteritis, adrenal gland necrosis, encephalitis, and uveitis were prominent pathologic lesions which correlated with the organ titers of virus. One animal infected with Lassa virus developed prolonged viremia, a typical immune response, and sudden onset of lower limb paralysis after recovery; at necropsy chronic proliferative arteritis of the spinal cord, brain, and heart was evident. Similarities and differences in the pathologic lesions in this model and Lassa fever in humans indicate that care must be taken in interpreting the results of experiments concerning immune prophylaxis, pathogenesis, and treatment in rhesus monkeys.