Cats As Potential Vectors/Mixing Vessels for Novel Flu
#17,984
Yesterday afternoon CIDRAP was able to confirm that 3 cats had tested positive for HPAI H5 on at least one of the Texas dairy farms where cattle have been infected, and Cornell University - whose Animal Health Diagnostic Center has done some of the preliminary testing - reported:
Grackles and pigeons were found dead at the same facilities, alongside some farm cats. While samples from cows were being sequenced, tests from the birds and a cat performed in the Molecular Diagnostics Laboratory at the AHDC came back positive for HPAI. Analysis of the NGS data then detected influenza sequences in the nasal swabs and milk samples from the sick cows.
It's not exactly breaking news that cats can be infected with avian influenza, although prior to 2004 cats (and dogs) were thought to be unlikely hosts.
That perception was abruptly changed by two unrelated events; the jump of equine H3N8 influenza from horses to Florida greyhounds, and the H5N1 infection of captive tigers in Thailand fed infected chicken (see below).
The following comes from a World Health Organization GAR report from 2006.
28 February 2006
(EXCERPTS)
Several published studies have demonstrated H5N1 infection in large cats kept in captivity. In December 2003, two tigers and two leopards, fed on fresh chicken carcasses, died unexpectedly at a zoo in Thailand. Subsequent investigation identified H5N1 in tissue samples.
In February 2004, the virus was detected in a clouded leopard that died at a zoo near Bangkok. A white tiger died from infection with the virus at the same zoo in March 2004.
In October 2004, captive tigers fed on fresh chicken carcasses began dying in large numbers at a zoo in Thailand. Altogether 147 tigers out of 441 died of infection or were euthanized. Subsequent investigation determined that at least some tiger-to-tiger transmission of the virus occurred.
Since then we've seen an avian H3N2 virus jump to dogs in South Korea, before spreading globally (see 2008 EID Journal Transmission of Avian Influenza Virus (H3N2) to Dogs), along with occasional spillovers of avian & human influenza viruses into canines, including:
Canada CFIA & PHAC: Domestic Dog Tests Positive for Avian Influenza in Canada
Korea Detected H5N8 Antibodies In asymptomatic Farm Dogs
- In 2006, Dr. C.A. Nidom demonstrated that of 500 cats he tested in and around Jakarta, 20% had antibodies for the bird flu virus.
- In 2007 the FAO warned that: Avian influenza in cats should be closely monitored,
- and in 2012 the OIE reported on Cats Infected With H5N1 in Israel.
In the middle of the last decade China reported several spillovers into captive lions and tigers:
Fatal H5N1 Infection In Tigers By Different Reassortant Viruses - China
And in late 2016, New York City reported hundreds of cats across several city-run animal shelters contracted avian H7N2 (see NYC Health Dept. Statement On Avian H7N2 In Cats).
Studies later showed that two shelter workers were infected while 5 others exhibited low positive titers to the virus, suggesting possible infection (see J Infect Dis: Serological Evidence Of H7N2 Infection Among Animal Shelter Workers, NYC 2016).
More recently, the United States has reported a number of spillovers of HPAI H5N1 into cats (see Nebraska Veterinary Diagnostic Center (NVDC) Report: 2 Domestic Cats Infected With HPAI H5N1), and last year both South Korea and Poland reported significant outbreaks in felines.
WHO Update & Risk Assessment On H5N1 In Cats - Poland
Emerg. Microbes & Inf.: Characterization of HPAI A (H5N1) Viruses isolated from Cats in South Korea, 2023
Detections of AI A(H5N1) in domestic cats (in France, Italy and Poland) and 5 dogs on a single poultry establishment (in Italy) have been reported, although such instances remain rare. The Poland cases have created a lot of interest as the source of infection has not been identified and the companion animals concerned (33 tested positive to date) were from multiple sites across Poland, were both indoor and outdoor cats, some exposed to raw pet food or wild birds and others not. Sequences of viral isolates from infected cats contain the common mutation, E627K in the PB2 gene, as well as the less common K526R, which has been detected in wild bird viral isolates.
Note: The E627K mutation is the same as mentioned last night by the CDC in their analysis of the human infection with H5N1 in Texas.
While the risks of infection to dogs and cats (and their owners) is considered low, it is not zero (see J. Virulence: HPAI H5N1 Virus Infection In Companion Animals), and cat-to-human transmission has been reported.In recent weeks we've seen guidance from both the CDC (see Bird Flu in Pets and Other Animals) and the UK's DEFRA on the importance of keeping pets safe from H5N1.
The growing diversity of H5N1 in the wild, and the increasing frequency of mammalian infections, provides the virus with new opportunities to adapt (or reassort) into a bigger threat (see below).
