Up until a dozen years ago, most veterinarians would have told you that cats (and dogs) are not generally susceptible to human influenza viruses. That notion began to change in 2004, when we saw two unrelated events; the jump of equine H3N8 influenza from horses to Florida greyhounds, and the infection of more than 100 tigers by avian H5N1 in Thailand.
Just six weeks ago we saw history repeat itself, with the announcement from the Guangxi Zoo: Reports 2 Tiger Deaths Due To H5N1.
Although poultry and pigs get most of our attention, over the past decade we’ve a growing body of evidence confirming a wide spectrum of influenza carriage by both dogs and cats. A few examples include:
- In 2006, Dr. C.A. Nidom demonstrated that of 500 cats he tested in and around Jakarta, 20% had antibodies for the H5N1 bird flu virus.
- Findings that prompted the FAO in 2007 to warned that: Avian influenza in cats should be closely monitored,
- In 2008 the CDC’s EID Journal carried a report on a newly emerging canine flu in Korea jumping from an avian source (see Transmission of Avian Influenza Virus (H3N2) to Dogs).
- In 2011, we saw the plot thicken yet again, when it was announced that this canine H3N2 had jumped to cats (see Korea: Interspecies Transmission of Canine H3N2).
- And during the 2009 H1N1 pandemic, we saw 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 2012 the OIE reported on Cats Infected With H5N1 in Israel, although so far no sustained virus transmission in cats or from cats to humans has been observed.
- Dogs have also been found to be susceptible to (apparently asymptomatic) infection with the recently emerged H5N8 virus (see MAFRA: H5N8 Antibodies Detected In South Korean Dogs (Again).
- Companion animals like dogs and cats are increasingly being viewed as potential `mixing vessels’ for influenza reassortment (see Study: Dogs As Potential `Mixing Vessels’ For Influenza).
In late 2012, in China: Avian-Origin Canine H3N2 Prevalence In Farmed Dogs, we saw a study that found more than 12% of farmed dogs tested in Guangdong province carried a strain of canine H3N2 similar to that seen in Korea. The authors cautioned:
As H3N2 outbreaks among dogs continue in the Guangdong province (located very close to Hong Kong), the areas where is densely populated and with frequent animal trade, there is a continued risk for pets H3N2 CIV infections and for mutations or genetic reassortment leading to new virus strains with increased transmissibility among dogs.
Further in-depth study is required as the H3N2 CIV has been established in different dog populations and posed potential threat to public health.
Today, in a similar vein, we’ve a study out of China that looks at the seroprevalence of (avian origin) canine H3N2, along with two seasonal human flu viruses, in cats in Northern China.
Xuxiao Zhang†, Ye Shen†, Lijie Du, Ran Wang, Bo Jiang, Honglei Sun, Juan Pu, Degui Lin, Ming Wang, Jinhua Liu and Yipeng Sun*
Virology Journal 2015, 12:50 doi:10.1186/s12985-015-0285-5
Published: 1 April 2015
Background The close contact between cats and humans poses a threat to public health because of the potential zoonotic transmission of influenza viruses to humans. Therefore, we examined the seroprevalence of pandemic H1N1/09, canine H3N2, and human H3N2 viruses in pet cats in northern China from 2010 to 2014.
Finding Of 1794 serum samples, the seropositivity rates for H1N1/09, canine H3N2, and human H3N2 were 5.7%, 0.7%, and 0.4%, respectively. The seropositivity rate for H1N1/09 in cats was highest in 2010 (8.3%), and then declined continuously thereafter. Cats older than 10 years were most commonly seropositive for the H1N1/09 virus.
Conclusions Our findings emphasize the need for continuous surveillance of influenza viruses in cats in China.
Different subtypes of influenza viruses are reported to be naturally transmitted to cats from other species worldwide, including avian viruses (H5N1), canine viruses (H3N2), and human viruses (pandemic H1N1/09, seasonal H1N1, and H3N2) [1-3]. The close contact between cats and humans possesses a threat to public health because of the potential zoonotic transmission of influenza viruses to humans. In China, the canine H3N2 and H1N1/09 influenza viruses circulate in dogs , and the seasonal H3N2 and H1N1/09 viruses are prevalent in humans [5,6], any of which might be transmitted to cats. Therefore, we examined the seroprevalence of the pandemic H1N1/09, canine H3N2, and human seasonal H3N2 influenza viruses in cats in northern China from January 2010 to June 2014.
The complete article is available as a provisional PDF. The fully formatted PDF and HTML versions are in production.
For a virus, successfully jumping to a new species is akin to hitting the lottery. A fresh supply of hosts not only increases its odds of long-term survival, it may also provide new opportunities for evolution and/or reassortment with other viruses.
Last summer, in Canine H3N2 Reassortant With pH1N1 Matrix Gene, we looked at exactly that scenario, in a report appearing in the journal Epidemiology & Infection, that found a new reassortment of the canine H3N2 virus – one that has picked up the M (matrix) gene from the 2009 H1N1 pandemic virus.
If this sounds vaguely familiar, it is because we’ve seen this same M gene showing up regularly in all three North American swine variant viruses (H1N1v, H1N2v, H3N2v), which caused more than 300 human infections to be reported in 2012. The CDC has speculated that:
`This M gene may confer increased transmissibility to and among humans, compared to other variant influenza viruses.’ – CDC HAN 2012
Whether any of this means that canine H3N2 is on the fast track towards `humanization’ is anyone’s guess, but this does illustrate just how intertwined avian, canine, and human influenza viruses really are.
Something that the American Society for Microbiology warned about last summer, in a press release on a study of canine influenza viruses:
CONTACT: Jim Sliwa
WASHINGTON, DC – June 19, 2014 – Equine influenza viruses from the early 2000s can easily infect the respiratory tracts of dogs, while those from the 1960s are only barely able to, according to research published ahead of print in the Journal of Virology. The research also suggests that canine and human influenza viruses can mix, and generate new influenza viruses.
All of which highlights the importance of continued surveillance – and not just of pigs and poultry – for emerging novel influenza viruses all over the world.