Venezuelan Equine Encephalitis Virus: Comparison of Infectivity and Virulence of Strains V-38 and P676 in Donkeys

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  • Instituto de Investigaciones Veterinarias, Apartado 70, Maracay, Venezuela

Two strains of Venezuelan equine encephalitis (VEE) virus were examined for the ability to replicate in, as well as to produce death among donkeys. One, a low passage strain known as strain P676, was originally isolated from mosquitos in Venezuela. The other, strain V-38, was isolated from a horse brain in 1938 and had undergone an unknown number of laboratory passages; it is used extensively for the preparation of inactivated VEE vaccine. Both strains were found to be approximately equal in their ability to infect donkeys. However, a quantity as small as 50% hamster intraperitoneal infectious units of strain V-38 resulted in fatal infection. On the other hand, as much as 631 million infectious units of strain P676 were nonfatal in one of two donkeys. It appears that strain V-38 is approximately 100 million times more virulent than strain P676 in equine species. One donkey which received strain P676 demonstrated a biphasic pattern of clinical illness and viremia, and there is suggestive evidence that another animal experienced a second and fatal clinical response 3 weeks after virus inoculation.

Author Notes

Present address: 330 The Village, No. 306, Redondo Beach, California 90277.

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