Culex tarsalis Coquillett as a Vector of an Attenuated Strain of Western Equine Encephalomyelitis Virus. ∗

Summary

Culex tarsalis can be infected with a non-neuroadapted strain of western equine encephalomyelitis virus and an attenuated variant with low neuropathogenicity derived from this strain. The infective threshold of the attenuated variant for C. tarsalis was greater than 10^3.0 suckling mouse intracranial LD₅₀ of virus/0.01 ml of blood. The original and attenuated strains multiplied equally in mosquitoes and both were transmitted to chicks by mosquito bite. The mouse pathogenicity or plaque size of the attenuated virus was not altered after a single passage in chicks and mosquitoes. The attenuated variant developed lower levels of viremias in chicks than the original strain.