Leo A. Thomas

Overwintering of Western Equine Encephalomyelitis Virus in Experimentally Infected Garter Snakes and Transmission to Mosquitoes

Summary Garter snakes were inoculated in September and November with Western equine encephalomyelitis (WEE) virus and were caused to hibernate under simulated natural conditions. They emerged during March, April, May and June. After varying periods when no virus was detectable in their blood, virus was detected in concentrations as high as 106, and for a period up to 70 days following emergence of snakes. Normal mosquitoes became infected by feeding on these snakes and after an extrinsic incubation period of approximately 3 weeks transmitted WEE virus to 1-day-old chicks. These data demonstrate that snakes may serve as a natural overwintering mechanism for WEE virus. The technical assistance of Jack Cory and Edward Patzer is gratefully acknowledged.

Overwintering of western equine encephalomyelitis virus in garter snakes experimentally infected by Culex tarsalis.

Summary Garter snakes were infected with western equine encephalomyelitis (WEE) virus by the bites of experimentally infected Culex tarsalis. The snakes hibernated overwinter under simulated natural conditions and viremia was detected up to 69 days after emergence the following spring. Snakes which were maintained at room temperature after emergence developed viremia within a few days, while those maintained under simulated natural conditions required up to approximately 5 weeks. As shown in previous studies, circulating virus was detected in concentrations sufficient to infect C. tarsalis. The use of fish tags proved satisfactory in assuring positive identification of individual snakes.

Susceptibility of Garter Snakes (Thamnophis Spp.) to Western Equine Encephalomyelitis Virus

Summary 1) It has been demonstrated that garter snakes are susceptible to infection with WEE virus. This is the first evidence, to the best of our knowledge, that a virus which is an important parasite of avian and mammalian hosts can infect a cold-blooded vertebrate and cause viremia of high titer and long duration. 2) The possibility that snakes may play a role in overwintering of the virus is being investigated.

Isolation of a virus closely related to Powassan virus from Dermacentor andersoni collected along North Cache la Poudre River, Colo.

Conclusions A virus closely related, if not identical, to Powassan virus has been isolated from Dermacentor andersoni from northern Colorado. A nonreciprocal relationship between RSSE virus and 791A-52 virus is indicated by the cross neutralization tests. The importance of Dermacentor andersoni in maintenance of this virus is unknown. Although thousands of this tick species collected in many areas in the western United States have been examined for viruses in this laboratory, this is the only isolation of this agent. Since these prior studies of ticks at the Rocky Mountain Laboratory were directed specifically toward study of the ecology of Coloradotick fever virus, the ecology of the 791A-52 virus is unknown. Field and laboratory studies on this subject are in progress.

Isolation of a Soldado-like virus (Hughes group) fromOrnithodorus maritimus ticks in Ireland

Three isolations of a virus of the Hughes group were obtained from seabird ectoparasites,Ornithodoros (Alectorobius) maritimus, on Great Saltee Island, Ireland. The agent is closely related to Soldado virus, originally obtained from related ticks near Trinidad, West Indies, and represents the second recorded tickborne arbovirus in Ireland.