SEARCH FOR SOURCES AND CARRIERS OF EQUINE ENCEPHALOMYELITIS VIRUS

Abstract

Brains of 112 ground squirrels (Citellus richardsoni), 10 hawks, one burrowing owl, three pheasants, four crows, nine rats (eight Mus decumanus and one M. rattus) two wild ducks, two jack rabbits, three hens, three pigs, and two cats were examined for the presence of virus. Spleens of 15 ground squirrels and livers of three others, also spleens of five hawks and six rats were examined. Six assassin bugs (one Zelus audax and five Sinea diadema), 133 mosquitoes, 30 Stomoxys sp., 10 Tabanidae, 30 crickets, 64 grasshoppers, and 12 ticks (Dermacentor andersoni Stiles) were also examined in suitable sized lots.Two guinea pigs were injected with a suspension of each lot. If suspicious temperature reactions occurred, these animals were destroyed and suspensions of their brains were injected into other guinea pigs. All the injected animals that survived, regardless of whether or not they had shown any temperature reaction, were given a challenge inoculation of 25 M.L.D. of Western virus three weeks or longer after the first injection.Lot 21, consisting of two ground squirrel brains, was the only group to give any evidence suggestive of the presence of virus. Virus could not be isolated from this lot but temperatures of the injected guinea pigs, and subsequent resistance of the survivor to a challenge inoculation, were very suggestive of its presence. This is the second occasion on which results suggested the presence of virus in very small amount in ground squirrel brains.