Influenza A(H3N8) Virus in Pigs

Influenza A(H3N8) is endemic in birds. About 50 years ago, the Influenza A(H3N8) virus unexpectedly jumped from birds to horses, spawning a new system of notation: Influenza A/Equine-2 (caused by H3N8). See here. The location: Florida, USA.

Then, in 2004 that equine Influenza A(H3N8) virus had mutated enough to be able to jump from horses to dogs. See here. The location: Florida, USA.

The next target of the ever mutating Influenza A(H3N8) virus were harbor seals, who started dying in 2012. See here. The location: New England, USA.

We can easily follow the trail of the virus: jumping from birds to horses, jumping from race horses to race dogs, spreading through population, expanding across the USA. Another strain jumped from birds to seals.

Research indicated that the virus in seals had recently adapted to bind to alpha 2,6 receptor cells, the type found in the human upper respiratory tract.

We can ask ourselves the question which species will be next in line of the Influenza A(H3N8) virus. Novel research indicates that avian and seal viruses replicated substantially and caused detectable lesions in inoculated pigs[1]. Surprisingly, researchers could not detect specific antibodies against HA in any H3N8-infected pigs. Therefore, special attention should be focused towards viruses of the H3N8 subtype as they could behave as stealth viruses in pigs.

Now we could have stealth viruses circulation in pigs without us knowing about it. While the Influenza A(H3N8) virus doesn’t currently appear to be established in swine populations, nobody knows for sure, because pigs aren't tested.

[1] Solórzano et al: Cross-species infectivity of H3N8 influenza virus in an experimental infection in swine in Journal of Virology – 2015