Successful Transmission of Visna by Intrapulmonary Inoculation

Visna virus was successfully transmitted to susceptible sheep by intrapul-monary injection. Of 5 sheep inoculated within the first 24 hours of life and surviving over 2 weeks, 1 contracted paralytic visna 22 months after inoculation, and the other 4 all had repeatedly elevated cell counts in the cerebrospinal fluid for a period up to 28 months after inoculation. From 2 of these 4 sheep visna virus was isolated from the cerebrospinal fluid. Of 10 sheep inoculated at the age of 5 months 6 have had elevated cell counts in the cerebrospinal fluid, 1 repeatedly. Visna virus was isolated from the cerebrospinal fluid of 2 sheep in this group and from 1 choroid plexus, yet there has been no paralytic case of visna. Neutralizing antibodies against visna virus were found in sera from all the injected sheep. Lung lesions resembling the lesions found in maedi were seen in 3 cases. The relationship of visna virus and the maedi agent is discussed.