Avian Flu Diary: EID Journal: Spread of Canine Influenza A(H3N2) Virus, United States

#12,739

Earlier this summer the CDC added canine H3N2 - which arrived to North America in April of 2015 - to their list of (n=14) novel flu viruses with pandemic potential (see Updating the CDC's IRAT (Influenza Risk Assessment Tool) Rankings), albeit with relatively low impact and emergence scores.

Note: The CDC uses two sets of criteria to evaluate novel viruses. One to estimate a virus's potential for sustained human-to-human transmission, and another to gauge it's potential for significant impact on public health.

Their summary read:

H3N2: [A/canine/Illinois/12191/2015]
The H3N2 canine influenza virus is an avian flu virus that adapted to infect dogs. This virus is different from human seasonal H3N2 viruses. Canine influenza A H3N2 virus was first detected in dogs in South Korea in 2007 and has since been reported in China and Thailand. It was first detected in dogs in the United States in April 2015. H3N2 canine influenza has reportedly infected some cats as well as dogs. There have been no reports of human cases.

Summary: The average summary risk score for the virus to achieve sustained human-to-human transmission was low risk (less than 4). The average summary risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was in the low risk range (less than 4).

As we recently reviewed much of the history of this virus, along with canine H3N8, just two weeks ago in J. Virology: Zoonotic Risk, Pathogenesis, and Transmission of Canine H3N2, I'll skip over most of that preamble today.

In that study, published online last month in the Journal of Virology, researchers created and tested canine H3N2 - pdmH1N1 reassortants, and found some `may pose a moderate risk to public health and that the canine host should be monitored for emerging IAVs'.

In a similar study, a little over a year ago (May 2016) in the Archives of Virology called Virulence Of A Novel Reassortant Canine H3N2 In Ferret, Dog and Mouse Models researchers found `significantly enhanced virulence' in mice infected with an H3N2/H1N1pdm reassortant virus. They wrote:

Thus, we speculate that the natural reassortment between pdm H1N1 and CIV H3N2 can confer virulence and that continuous surveillance is needed to monitor the evolution of CIV in companion animals.

As companion animals, dogs (and cats) are continually exposed to human influenza viruses, and for that reason are increasingly viewed as potential `mixing vessels’ for influenza reassortment (see Study: Dogs As Potential `Mixing Vessels’ For Influenza).

And in the summer of 2014 saw evidence of just such an event, in a report appearing in the journal Epidemiology & Infection, that found a new reassortment of the canine H3N2 virus – one that had picked up the M (matrix) gene from the 2009 H1N1 pandemic virus (see Canine H3N2 Reassortant With pH1N1 Matrix Gene) – in china.

All of which brings us to a new synopsis report published this week in the CDC's EID Journal on Canine H3N2. I've only included the abstract and some excerpts, so follow the link to read it in its entirety.

Spread of Canine Influenza A(H3N2) Virus, United States

Ian E.H. Voorhees, Amy L. Glaser, Kathy Toohey-Kurth, Sandra Newbury, Benjamin D. Dalziel, Edward J. Dubovi, Keith Poulsen, Christian Leutenegger, Katriina J.E. Willgert, Laura Brisbane-Cohen, Jill Richardson-Lopez, Edward C. Holmes, and Colin R. ParrishComments to Author

Abstract

A canine influenza A(H3N2) virus emerged in the United States in February–March 2015, causing respiratory disease in dogs. The virus had previously been circulating among dogs in Asia, where it originated through the transfer of an avian-origin influenza virus around 2005 and continues to circulate.

Sequence analysis suggests the US outbreak was initiated by a single introduction, in Chicago, of an H3N2 canine influenza virus circulating among dogs in South Korea in 2015. Despite local control measures, the virus has continued circulating among dogs in and around Chicago and has spread to several other areas of the country, particularly Georgia and North Carolina, although these secondary outbreaks appear to have ended within a few months.

Some genetic variation has accumulated among the US viruses, with the appearance of regional-temporal lineages. The potential for interspecies transmission and zoonotic events involving this newly emerged influenza A virus is currently unknown.

(SNIP)

H3N2 CIV Disease, Host Range, and Zoonotic Potential

Similar to H3N8 CIV infections, H3N2 CIV infections in dogs are associated with mild upper respiratory tract disease, including frequent coughing and fever, although infection of the lungs and more severe disease and death occur on occasion and are probably associated with mixed infections by other viruses or bacteria (14).

Although CIV epidemics pose a clear threat to canine health, the risks to other animals and humans are largely unknown. Unlike H3N8 CIV, H3N2 CIV appears to have a relatively broad host range, infecting ferrets, guinea pigs, and cats after experimental challenge (15,16). Nevertheless, experimental inoculation of strains of H3N2 CIV from South Korea and United States (17) into swine resulted in poor replication, suggesting that sustained transmission of the virus after a canine-swine transfer is unlikely, despite swine being a common host of other H3N2 IAVs.

Natural spillover of the virus from dogs to cats has been documented in South Korea and the United States, but those outbreaks were largely confined to the shelter populations where they emerged, and the viruses do not appear to undergo prolonged transmission in household cats, despite high levels of viral shedding (18,19).

To our knowledge, no transfers of either CIV subtype to humans have been documented. However, human pandemic IAVs, including the H1N1 (both seasonal and the 2009 pandemic) (20) and the H3N2 (21) subtypes, appear able to occasionally infect dogs based on results of serologic testing or isolation of the virus. Although none of these infections is known to have resulted in major onward transmission among dogs, this might provide the opportunity for human IAVs to reassort with CIVs through natural coinfections in dogs.

In 2010, a novel H3N1 CIV resulting from the reassortment of an H3N2 CIV (HA segment) and pandemic H1N1/09 virus (the other 7 genomic segments) was isolated in a dog from South Korea (22), and in 2012 an H3N2 carrying only the pandemic H1N1/09 matrix segment was isolated from a dog in South Korea (23,24). In 2015, a novel reassortant H3N2 CIV containing the polymerase acidic (PA) genomic segment from an H9N2 pandemic avian IAV was also isolated from a dog in South Korea (25). Additionally, dogs and humans express a similar diversity of sialic acid variants and linkages, which have been demonstrated to be important determinants of IAV infection and host range (26), including N-acetyl neuraminic acid and both the α2–3 and α2–6 linkages (27,28).

Given these key biologic and physiologic features and the close contact that exist between human and dog populations, the potential for dogs to act as virus “mixing vessels” or as sources of zoonotic infections by IAVs should not be overlooked.

Until a dozen years ago, dogs (and cats) were both viewed as being relatively immune to influenza viruses. That perception began to change in 2004 and 2005 when equine H3N8 was detected in dogs, and avian H5N1 began to show up in both dogs and cats in Asia.

While we worry primarily about birds or swine producing the next pandemic virus, we can't discount the possibility of being blindsided by a virus coming from another host species.

Dogs, cats, seals (and other marine mammals), horses, bats, and a variety of peridomestic animals (rabbits, skunks, mink, etc.) - even cattle - have all been found to carry flu viruses.

For a `walk on the wild side', you may wish to revisit some earlier blogs on some plausible - if not particularly likely - novel flu hosts to keep an eye on.