Influenza A Virus in Dogs

Influenza is a versatile virus, forever changing and adapting to new species. Still, it was a bit of a surprise to discover that dogs can also become inflected with Influenza A. When some Greyhounds fell ill and died from a respiratory illness in 2004 it was discovered that they were infected with Influenza A(H3N8), a virus subtype known as Equine Influenza virus. Because these dogs raced at a horse race track, it was thought that that must have been the place where they were infected.

Influenza A(H3N8) virus was also responsible for a major outbreak in New York state. Multiple outbreaks around the US in pet dogs now suggest that the Influenza A(H3N8), virus may now be endemic.

Because of the lack of previous exposure to this virus, dogs have no natural immunity to this virus. A vaccine has recently become available.

Analysis has shown that Influenza A(H3N8) virus was first transferred from horses to dogs[1] and then adapted to dogs through some tiny mutations[2]. It has changed so much that there’s not yet any evidence that the virus can be transferred to people, horses, cats, or other species.

What this means is that Nature has created yet another vessel to mix the Influenza virus in and it increases the danger of new subtypes of the virus.


Recently however, there has emerged some disturbing news from South Korea: Korea’s Ministry of Agriculture announced that a dog has tested positive for antibodies to Influenza A(H5N8) Virus[3]. This is the first time that evidence of an Influenza A(H5N8) Virus infection has been found in a non-avian species.

To soften the impact of this worrying news, Korean government officials mentioned that the dog lived on a bird flu affected farm, that the dog was reportedly only asymptomatic and that the dog must have acquired the virus from after eating an infected chicken at the farm.

But they cannot hide the fact that Influenza A(H5N8) Virus was previously known to only infect birds and now seems capable of infecting a mammalian species too. Health authorities reassuringly say it is very unlikely that humans could be susceptible to Influenza A(H5N8) Virus, although the farm's workers are being tested.

The reason for this sudden change in behaviour is the realisation that this version of Influenza A(H5N8) Virus is the result of a recent reassortment involving three different viruses[4]. Which proves again that Influenza viruses remain as unpredictable as ever before.

Other recent research[5] revealed that infected dogs in China have elevated antibodies against Influenza A(H1N1)pdm09 virus. This high seroprevalence of Influenza A(H1N1)pdm09 virus among dogs without clinical signs of influenza support the premise that dogs may play a role in human influenza ecology in China.

There are two different influenza A canine influenza viruses: one is an H3N8 virus and the other is an H3N2 virus. Canine influenza A(H3N2) viruses are different from seasonal influenza A(H3N2) viruses that spread annually in people.

Reports suggest that Influenza A(H3N2)virus is circulating widely among dogs in Los Angeles County (USA) since late 2021. From July to December 2021 there were 1284 confirmed and probable cases of Influenza A(H3N2)virus. The death toll has risen to 13 dogs.

[1] Rivailler et al: Evolution of canine and equine influenza (H3N8) viruses co-circulating between 2005 and 2008 in Virology - 2010
[2] Crawford et al: Transmission of equine influenza virus to dogs in Science - 2005
[3] Korea Times: Bird flu found to be transmitted to dog (March 14th, 2014) 
[4] Lee et al: Novel Reassortant Influenza A(H5N8) Viruses, South Korea, 2014 in Emerging Infectious Diseases - 2014
[5] Su et al: Evidence for Subclinical Influenza A(H1N1)pdm09 Virus Infection among Dogs, Guangdong Province, China in Journal of Clinical Microbiology - 2014