When it comes to the spread and evolution of influenza A viruses - birds, pigs, and humans top our list of primary hosts - but over the years we've also looked at a growing list of other (presumably less important) players in the flu world.
Since the early 2000's it has become apparent that both canines and felines are susceptible to a variety of influenza A viruses (see HPAI H5: Catch As Cats Can), with 2015's transmission of avian H7N2 to a veterinarian in New York City and the recent arrival of a new canine H3N2 virus to North America from Asia bit of a wake up call.While canine H3N2 (a formerly avian virus) has not been shown to infect humans, numerous reports coming out of China and Korea suggest it may be adapting to other hosts, and that it continues to reassort with other avian and human flu viruses. Including:
A Canine H3N2 Virus With PA Gene From Avian H9N2 - Korea
Canine H3N2 Reassortant With pH1N1 Matrix Gene
Virology J: Human-like H3N2 Influenza Viruses In Dogs - Guangxi, China
Interspecies Transmission Of Canine H3N2 In The Laboratory
Two months ago we looked at a study (see J. Virology: Zoonotic Risk, Pathogenesis, and Transmission of Canine H3N2) where researchers created and tested canine H3N2 - pdmH1N1 reassortants, and concluded some `may pose a moderate risk to public health and that the canine host should be monitored for emerging IAVs'.
But dogs (and cats) can also be exposed to novel HPAI viruses like H5N1 and H5N6 in the wild.In 2014 we saw multiple reports of farm dogs infected with HPAI H5N8 in South Korea (see Korea Finds More Dogs With H5N8 Antibodies) while over the summer we saw a report from the Arch. Of Virology: Novel Reassortant H5N6 Isolated From Cats - Eastern China.
In April of this year, in J. Vet. Sci.: Experimental Canine Infection With Avian H5N8, we saw a study published in the Korean Journal of Veterinary Science, where researchers inoculated dogs with the 2014 Korean strain of HPAI H5N8, in order to document its pathogenicity and ability to be transmitted to other dogs.
While producing only mild illness in these experimental animals, 2 of 4 that were inoculated shed small quantities of the virus and seroconverted, and at least one contact dog became infected. The authors wrote that these dogs appeared only weakly infected and the virus didn't appear fully adapted to a canine host.All of which brings us to a new study, published this past week in Transboundary and Emerging Diseases, where researchers experimentally infected dogs with two different clades of HPAI H5N1 (1.1.2 & 220.127.116.11c) and clade 18.104.22.168. H5N6.
While the bulk of the study is behind a paywall, we get the highlights from the abstract below:
Experimental infection of clade 1.1.2 (H5N1), clade 22.214.171.124c (H5N1) and clade 126.96.36.199 (H5N6) highly pathogenic avian influenza viruses in dogs.
AbstractSince the emergence of highly pathogenic avian influenza (HPAI) H5N1 in Asia, the haemagglutinin (HA) gene of this virus lineage has continued to evolve in avian populations, and H5N1 lineage viruses now circulate concurrently worldwide.
Dogs may act as an intermediate host, increasing the potential for zoonotic transmission of influenza viruses. Virus transmission and pathologic changes in HPAI clade 1.1.2 (H5N1)-, 188.8.131.52c (H5N1)- and 184.108.40.206 (H5N6)-infected dogs were investigated.
Mild respiratory signs and antibody response were shown in dogs intranasally infected with the viruses. Lung histopathology showed lesions that were associated with moderate interstitial pneumonia in the infected dogs. In this study, HPAI H5N6 virus replication in dogs was demonstrated for the first time.
Dogs have been suspected as a "mixing vessel" for reassortments between avian and human influenza viruses to occur. The replication of these three subtypes of the H5 lineage of HPAI viruses in dogs suggests that dogs could serve as intermediate hosts for avian-human influenza virus reassortment if they are also co-infected with human influenza viruses.
The idea that dogs could be a `mixing vessel - producing a hybrid human-avian (or human-swine) reassorted virus - is something we've looked at before (see Study: Dogs As Potential `Mixing Vessels’ For Influenza).
While perhaps not the most likely host for viral reassortment - is is certainly plausible.With H5N6's breakout performance in Asia last year, and the huge strides H5N8 has made in the past year (see ECDC/EFSA Joint Report: Avian Inﬂuenza Overview Oct 2016–Aug 2017) the potential threat that these viruses pose to non-avian species cannot be ignored (see J. Virulence Editorial: HPAI H5N8 - Should We Be Worried?).
It is worth noting that - while currently quantified as a relatively low-risk virus - over the summer the CDC added Canine H3N2 to their IRAT (Influenza Risk Assessment Tool) listing of novel flu subtypes/strains that circulate in non-human hosts and are believed to possess some degree of pandemic potential. Their evaluation reads:
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).