In March of 2014, less than two months after HPAI H5N8 erupted in South Korea, their Agricultural Ministry announced that a dog at a farm in Chungcheongnam-do province had tested positive for antibodies to this emerging avian flu virus.
Antibodies to a virus generally arise a couple of weeks after exposure, and are considered a solid indicator of past infection (either symptomatic or sub-clinical).
Ten days later (March 24th, 2014), local authorities announced the detection of H5N8 in eleven additional dogs (see Korea Finds More Dogs With H5N8 Antibodies).
Another report, published nearly a year later (see MAFRA: H5N8 Antibodies Detected In South Korean Dogs (Again)), suggested live virus had been isolated from an infected dog, not just antibodies.While not terribly common, we’ve seen dogs (and other non-avian species) infected with HPAI H5 avian influenzas in the past. The first report, from Thailand in 2004, was described in this 2006 Dispatch to the CDC’s EID Journal.
Dispatch Volume 12, Number 11–November 2006
Thaweesak Songserm,* Alongkorn Amonsin,† Rungroj Jam-on,* Namdee Sae-Heng,* Nuananong Pariyothorn,† Sunchai Payungporn,† Apiradee Theamboonlers,† Salin Chutinimitkul,† Roongroje
Avian influenza H5N1 virus is known to cross the species barrier and infect humans and felines.
We report a fatal H5N1 infection in a dog following ingestion of an H5N1-infected duck during an outbreak in Thailand in 2004. With new reports of H5N1 virus continuing across Asia, Europe, and Africa, this finding highlights the need for monitoring of domestic animals during outbreaks.
The following year, in:
(Maas R, Tacken M, Ruuls L, Koch G, van Rooij E, Stockhofe-Zurwieden N. Avian influenza (H5N1) susceptibility and receptors in dogs. Emerg Infect Dis. 2007 Aug; [Epub ahead of print]),
Researchers determined that dogs have susceptible receptor cells in their upper and lower respiratory tracts, and can shed the virus while not manifesting clinical symptoms of the disease.
Coincidentally, in 2004 H3N8 equine influenza – a strain that has been around nearly a half century in horses –also jumped,and adapted to dogs, creating a new dog-specific (canine) lineage of H3N8 (see EID Journal article Influenza A Virus (H3N8) in Dogs with Respiratory Disease, Florida).
All of this was somewhat surprising as prior to 2004, dogs were believed largely immune to influenza A. Over the past dozen years, we've gradually learned dogs are more susceptible to a greater range of influenza viruses than previously known.
- Again from Korea, in 2008 the CDC’s EID Journal carried a report on a newly emerging canine flu jumping from an avian source (see Transmission of Avian Influenza Virus (H3N2) to Dogs). That strain finally arrived in North America two years ago (see CDC Statement On Canine Influenza In Chicago).
- During the 2009 H1N1 pandemic, we saw several cases of reverse zoonosis, where dogs (and cats) contracted the `humanized’ H1N1 virus from their human contacts (see US: Dog Tests Positive For H1N1)
- In late 2012, in China: Avian-Origin Canine H3N2 Prevalence In Farmed Dogs, we looked at a study that found a newly emergent avian origin H3N2 virus prevalent in pet and farmed dog populations in southern China.
- More recently, in 2015, researchers reported finding Influenza A(H6N1) In Dogs, Taiwan.
In 2014, in Study: Dogs As Potential `Mixing Vessels’ For Influenza - we looked at the ability of different influenza strains (canine, equine and human) to infect, and replicate in, canine tracheal tissues. While in 2015, in Virology J: Human-like H3N2 Influenza Viruses In Dogs - Guangxi, China, we looked at the discovery two H3N2 CIVs possessing high homology with human/swine influenza viruses.
All of which makes understanding the susceptibility of dogs to novel flu strains, and their ability to transmit them, a high priority.
To that end we have a study, just 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.
Seong-Su Yuk, Dong-Hun Lee, Jae-Keun Park, Eredene-Ochir TO, Jung-Hoon Kwon, Jin-Yong Noh, Chang-Seon Song*
Avian Disease Laboratory, College of Veterinary Medicine, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 05029, Korea
Received: August 17, 2016; Revised: January 31, 2017; Accepted: February 7, 2017; Published online: April 6, 2017.
During the highly pathogenic avian influenza (HPAI) H5N8 outbreak in South Korea, a dog reared in layer farm contaminated by the virus was reported seropositive for HPAI H5N8. In order to investigate the possibility of the adaptation and transmission of HPAI H5N8 to dogs, we inoculated the H5N8 to dogs in experimental condition.
Weak viral genes in nasal swabs and seroconversions were detected even in contact dogs.
Although the H5N8 virus doesn’t seem to adapt to canine species fully, these results suggest that surveillance on farm dogs should continue as a species in which avian influenza virus may acquire infectivity to mammals through frequent contact with the virus.
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.
As the abstract points out, these dogs appeared only weakly infected and the virus doesn't appear fully adapted to a canine host.
Over the past two years, however, the H5N8 virus has undergone significant genetic changes (see EID Journal: HPAI A(H5Nx) Viruses With Altered H5 Receptor-Binding Specificity), so the results from this study may not apply to more recent incarnations of the virus.
The good news is, despite more than 1,000 farm outbreaks of HPAI H5N8 in Europe over the winter, we've not seen any evidence of infection in humans, or other mammals.
News that is tempered slightly by last January's study - Sci Rpts: H5N8 - Rapid Acquisition of Virulence Markers After Serial Passage In Mice - where researchers stated:
These results suggest that H5N8 viruses can rapidly acquire virulence markers in mammalian hosts; thus, rapid spread as well as repeated viral introduction into the hosts may significantly increase the risk of human infection and elevate pandemic potential.
As with all viruses, anything we can say about the behavior and public health threat from H5N8 is based on past observations, and is always subject to change.