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Canine Influenza Virus

In 2004 H3N8 influenza was isolated from racing greyhounds in the USA. Both molecular and antigenic characterisation of the virus showed that it was highly related to equine influenza and that therefore equine influenza had crossed the species barrier to a new mammalian host – the dog.

In the UK there have been two cases of equine influenza infecting packs of foxhounds. In both cases diagnosis was confirmed by the AHT retrospectively; the first by immunohistochemistry from post-mortem samples and serology, and the second by serological screening. Following investigations into these two outbreaks, it appears that the first case of equine influenza infecting dogs in the UK was in 2002. However, unlike in the USA where canine influenza has become endemic and passes from dog to dog, in the UK both cases have been isolated and have not spread.

Research has shown that dogs share the same a2-3 sialic acid receptors in the respiratory tract as found in horses and this could explain why dogs have become infected with the equine virus.

The route of infection has not been confirmed, however it is thought to have been from a high concentration of aerosolised virus excreted from infected horses sharing a relatively close air space with the dogs.

The Animal Health Trust has been carrying out sero-surveys to establish the prevalence of, and therefore the risk of, canine influenza to the UK dog population.

Related articles:

Emerging Infectious Diseases, in press, 2007. Daly et al. Factors involved in the interspecies transmission of equine influenza viruses to dogs.

Science. 2005 Oct 21;310(5747):482-5. Crawford et al.
Transmission of equine influenza virus to dogs.

Vet Rec. 2005 Oct 22;157(17):527. Smith et al.
Canine influenza virus.
Vet Rec. 2005 Nov 5;157(19):599. Newton et al.
Canine influenza virus: cross-species transmission from horses.