Phylogenetic characterization of a highly attenuated strain of equine arteritis virus from the semen of a persistently infected standardbred stallion.

This research article delves into the genetic analysis and characterization of a weakened or ‘attenuated’ strain of the equine arteritis virus (EAV) named CA95G. It was found in the semen of a Standardbred stallion that was persistently infected with the virus. Despite its weakened form, this strain was capable of causing a non-symptomatic infection and an immune response in susceptible horses.

Analysis of the CA95G Strain

• The researchers isolated the novel CA95G strain of EAV from the semen of a persistently infected Standardbred stallion.
• This strain was found to cause subclinical infection, meaning the horses showed no apparent symptoms, however, the immune response was evident as seroconversion took place. Seroconversion is the process of developing detectable antibodies in the blood that are specifically directed towards an invading pathogen.
• Interestingly, the CA95G virus was only isolated once from the blood and nasal secretions of 6 horses that were deliberately infected as part of the study.

Comparative Genetic Analysis

• The researchers conducted a sequence analysis of the genes that code for known EAV structural proteins. This was done to compare the genetic material of the CA95G strain with that of virulent field strains of EAV.
• They discovered that the highly attenuated CA95G strain was genetically similar to virulent strains of EAV, particularly one strain that was isolated during an outbreak of equine viral arteritis in western Canada in 1986.

Persistent Infection and Virus Diversity

• The study also underlined that carrier stallions act as natural reservoirs for EAV. This means that the horses can harbor the virus for an extended period, helping in its spread.
• Moreover, genetic diversity of the virus is generated during the course of persistent infection in carrier stallions. In other words, as the virus remains in the stallion’s system for longer, its genetic makeup undergoes changes.
• These subtle genetic changes that maintain the persistent EAV infection in the stallion’s reproductive tract are likely to influence the behavior of the virus, for instance, its virulence or severity.