Venezuelan equine encephalitis virus: comparison of infectivity and virulence of strains V-38 and P676 in donkeys.

The research focuses on comparing the infectivity and virulence of two strains (V-38 and P676) of Venezuelan equine encephalitis (VEE) virus in donkeys. The study finds that the V-38 strain is significantly more lethal than the P676, despite both strains being roughly equally contagious.

Methodology and Strains

• The team studied two different strains of the VEE virus for this experiment. Strain P676, a low-passage variant, was originally discovered in Venezuelan mosquitoes. Conversely, strain V-38 was isolated from horse brain in 1938 and the exact number of laboratory passages it had undergone is unknown. This strain is usually used to formulate inactivated VEE vaccines.

Infectivity and Virulence

• Both strains showed almost equal abilities to infect donkeys. Infectivity relates to the virus’s capacity to enter host cells, reproduce, and spread.
• But when examining the fatality rate, the researchers found a stark difference between the two strains. A small quantity of strain V-38, as low as 50% hamster intraperitoneal infectious units, caused lethal infection in donkeys. Conversely, a much larger dose (about 631 million infectious units) of strain P676 did not cause fatal infection in one of the two donkeys tested.
• This disparity indicates that the V-38 strain is about 100 million times more virulent, or harmful, than the P676 strain in equine species.

Biphasic Pattern

• One of the donkeys infected with strain P676 reflected a biphasic pattern of clinical illness and viremia, indicating two separate phases of the disease manifestation and virus presence in the blood.
• There was also evidence suggesting that another animal experienced a second and fatal clinical response three weeks post-virus inoculation, further indicating a biphasic disease progression.