Encephalitis and chorioretinitis associated with neurotropic African horsesickness virus infection in laboratory workers. Part IV. Experimental infection of the vervet monkey (Cercopithecus pygerythrus).

Neurotropic vaccine strains of African horsesickness (AHS) virus types 1 and 6 were implicated as the possible aetiological agents in 4 cases of encephalitis and uveochorioretinitis in laboratory workers accidentally exposed to the freeze-dried vaccine preparations of the virus. To date, AHS virus has not been known to infect man. To ascertain whether or not primates were susceptible to infection with AHS virus, vervet monkeys (Cercopithecus pygerythrus) were inoculated, either transnasally or intraconjunctivally, with vaccine strains of AHS virus types 1 and 6. The course of infection was monitored using parameters such as behavioural changes, febrile reaction, cerebrospinal fluid pleocytosis, serology, magnetic resonance imaging and autopsy. Encephalitis, manifested by varying degrees of fever, behavioural changes and pleocytosis, but no chorioretinitis was detected in all 6 transnasally infected monkeys. This was confirmed by autopsy, where a meningo-encephalitis affecting the medial temporal lobe but no lesions in the eyes was demonstrated. Neither virus appeared to infect the animals after intraconjunctival inoculation. These findings support the theory that the patients were infected by the inhalation of freeze-dried vaccine preparations. The pathogenesis of the eye lesions, however, remains uncertain.