Equine Influenza

Equine influenza is a common respiratory infection of horses caused by an orthomyxovirus of the genus Influenza A. Influenza A viruses can be divided into sub-types on the basis of the antigenic reactivity of the surface glycoproteins, the haemagglutinin (H1-H16) and the neuraminidase (N1-N9) molecules (Fouchier et al., 2005). Equine influenza (EI) is caused by two subtypes H7N7 and H3N8. Outbreaks due to H7N7 are limited as the isolation of the virus has not been reported since last two decades. Recent infection in India (2008-2009) was associated with H3N8 (Virmani et al., 2009). As per the seroservillance report of year 2012-13, 21 out of 1482 samples were found to be positive for equine influenza antibodies (NRCE, 2013). Even in 2016-17 seropositive samples (8 out of 1735) were observed by NRCE India (NRCE,2017). At present no cut-off point for EI antibodies level in positive samples has been decided for the haemagglutination inhibition (HI) test so, serum samples with low titres should be investigated further and at least four times increase in titre between paired serum samples should be considered for recent infection (OIE, 2016). It is usually a self-limiting disease characterised by pyrexia, coughing and nasal discharge (Van and Cullinane,2002). The mortality rate associated with EI is very low, unless disease is exacerbated by secondary bacterial infection or continued work of the horse. It is considered the most important respiratory virus of horses because it is highly contagious and has the potential to disrupt major equestrian events and cause significant economic loss (Timoney et al., 2000). Large outbreaks are
The first sample should be taken immediately after suspicion or onset of clinical signs and the second one approximately 15 days later. EI antibodies are determined by using HI test