A prospective longitudinal study of naturally infected horses to evaluate the performance characteristics of rapid diagnostic tests for equine influenza virus.

This study explores the performance of rapid diagnostic tests in detecting equine influenza virus in horses, revealing that viral RNA lasts longer in nasal swabs than traditionally thought and that antibodies can be detected for extended periods post-infection.

Overview of the Research

• This research paper discloses the results of a longitudinal study to evaluate the performance of two types of diagnostic tests for equine influenza (EI), a highly contagious and hazardous disease affecting horses.
• The researchers took advantage of a real-life outbreak of equine influenza in Australia in 2007 to conduct this study.
• The methods used to detect the EI virus were real-time reverse transcriptase polymerase chain reaction (qRT-PCR) assays and a blocking enzyme-linked immunosorbent assay (bELISA), both of which had not been used for diagnosing EI before this study.

Study Methodology

• The study was conducted on 36 horses that were naturally infected with EI, from which nasal swabs and blood samples were collected daily.
• The primary objective of the study was to determine how soon after infection these tests would yield positive results and how long these results would remain positive.

Main Findings of the Study

• The study found that EI viral RNA was detected in all horses by the qRT-PCR method, from the first to tenth day after clinical signs were evident, extending up to 34 days in some horses.
• The bELISA methods detected antibodies against EI virus by the third day, with the median time to seroconversion being 5 days.
• Interestingly, the results showed that viral RNA could be detected from nasal swabs for much longer than previously supposed for the virus shedding period in horses.

Further Findings and Conclusion

• Beyond the immediate infection detection, the bELISA method successfully detected antibodies for 139 days post-infection and could detect antibodies in approximately 50% of tested horses 12 months following infection.
• Using the haemagglutination inhibition testing method, antibodies against H3 antigens were found in the horses for 28 days post-infection; however, two horses tested negative by 35 days following infection.
• The research hence concludes these rapid diagnostic tests can detect the virus and antibodies for a much longer period than typically thought, providing valuable insights for future disease management and control measures.