Equine influenza in the United Kingdom in 1998.

The research article investigates an outbreak of equine influenza in the UK in 1998 and uses diagnostic tools and detailed analysis to understand the cause, impact on horses, and potential strain of the virus.

Research Motive and Methods

• The research was motivated by the occurrence of equine influenza in the UK in 1998, amongst both vaccinated and unvaccinated horses. The goal was to understand the cause of this respiratory disease and its impact.
• Diagnostics undertaken included serology, a blood test that identifies antibodies in response to an infection in the bloodstream, and a nucleoprotein enzyme-linked immunosorbent assay – a test that detects proteins in the context of an immune response.

Findings and Observations

• The research found that the symptoms were generally milder in vaccinated horses, but more severe in unvaccinated horses. The severe symptoms included fever, loss of appetite, coughing, mucopurulent (involving mucus and pus) nasal discharge, and secondary bacterial pneumonia.
• There was a detailed investigation of an outbreak among 52 vaccinated thoroughbreds in a flat racing yard. The researchers found that more than 60% of these horses seroconverted (developed antibodies in response to an infection) based on tested serum samples.

Analysis of the Virus Strain

• The researchers performed preliminary sequencing and characterization of an isolate from this outbreak. They found that it was ‘American-like’, suggesting its genetic sequence resembled those often found in an American strain.
• However, they found a large proportion of horses with preinfection serohemolysis (a test indicating the level of antibodies) titers that were higher than expected. These horses seroconverted following the outbreak. Typically, this response was seen in outbreaks involving ‘European-like’ strains.
• The study hypothesized that the protective effect of the currently used ‘European-like’ A/equine-2 vaccines against circulating ‘American-like’ strains could be decreasing, indicating a potential increase in the risk of influenza outbreaks among horses.