Marker characteristics of Venezuelan encephalitis virus strains isolated before and after epidemics and equine epizootics in Middle America.

The researchers examined 94 Venezuelan encephalitis virus strains from Central America and found these strains had differing features before and after the epidemics and equine outbreaks in the region. While similar to harmful strains in appearance, the dominant strains were similar to the enzootic, or locally occurring, strains from North Central America, disproving the theory that epidemic strains emerge from a mix of enzootic and epidemic strains.

Methodology

• The researchers studied 94 strains of Venezuelan encephalitis (VE) virus. These viruses had been isolated from sentinel hamsters exposed in Central American nations including Mexico, Guatemala, Belize, and Honduras.
• They segregated and compared these strains based on when they were isolated, whether that was before or following the regional epidemics and equine epizootics between 1966 and 1972.
• The team then further characterised 23 virion clones that resembled contagious (epizootic) strains using hydroxylapatite chromatography and Vero monkey kidney cell plaque size determinations.

Findings

• The study revealed that most of the virions in these clones were not similar to epizootic VE strains from Central America. Instead, they closely resembled enzootic strains found northwards of the Panama Canal region.
• These predominant virions were categorised under the hemagglutination-inhibition antigenic subtype IE and typically exhibited optimal hemagglutination at a pH level of 6.2. Furthermore, these strains proved to be harmless (avirulent) for English shorthair guinea pigs when inoculated subcutaneously.

Implications

• The results of the research contradict a popular theory about the origin of VE virus strains. This theory suggests that virions causing regional outbreaks (epizootic virions) evolve in Central America from strains that combine both endemically persistent (enzootic) and outbreak-causing (epizootic) virions.
• The researchers’ findings offer evidence that this is not the case, as they discovered the dominant virions in the studied strains were more akin to enzootic rather than epizootic strains.