Isolation and Identification of Western Equine Encephalomyelitis Virus from Mosquitoes by Tissue Culture Methods

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  • Viral and Rickettsial Disease Laboratory, California State Department of Public Health, Berkeley 4
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A chick embryo tissue culture method for the isolation of viruses from mosquitoes, and perhaps other arthropods, is described. The application of this method to mosquito surveillance studies concerned with the prevalence of WEE and SLE virus infections in C. tarsalis led to the recovery of 75 virus strains from 545 pools of this arthropod. Of the 75 agents, 66 proved to be WEE virus and 9 were found to represent a new arthropod-borne virus previously described from this laboratory. No recoveries of SLE virus were made.

Because of the high incidence of non-specific cellular degeneration encountered in the inoculated cultures, sub-passages were necessary. Presumably, only two passages of the mosquito pool suspensions were required to recover all of the strains of WEE virus detectable by this method, since additional sub-culture through the third passage did not yield any additional strains. This did not hold true in the case of the new arthropod-borne virus, as it was found that the presence of this agent became apparent in a number of instances only in third passage materials. It thus seems conceivable that decisions as to the number of passages to be undertaken routinely in any given epidemiologic or field study may depend upon the pathogenetic properties of the virus under study.

A method was devised for the rapid colorimetric identification of the WEE virus. The simplicity of the method resides in the fact that a single dilution of the viral isolate is tested against a single dilution of specific immune sera.