Contact with Wild Animals
Pets, especially hundreds of millions of cats and dogs, live in close contact with humans. They tend to get into contact with wild animals, especially birds and rodents. It may be for hunting, playing, feeding or just curiosity about a decaying carcass. This may become a serious issue if the virus circulating in birds would be better adapted to mammals, enabling mammal-to-mammal transmission on a large scale. One such H5N1 variant has been found in a red tailed hawk, but the results are not peer-reviewed yet. The almost simultaneous H5N1 outbreaks on more than 30 fur farms in Finland also suggests such a virus variant. A variant circulating in birds with a PB2-T271A mutation can be considered confirmed after the test results from the mixed farm in Brescia, Italy. The confirmed spillover from cows into wild birds is another risk.
One isolate, A/Red Tailed Hawk/ON/FAV-0473-4/2022, efficiently transmitted by direct contact between ferrets, resulting in lethal outcomes.
Here we report a case of influenza A(H5N1) infection in a domestic cat and five dogs living on a rural backyard poultry farm where an HPAI H5N1 outbreak was notified; the infection in poultry was caused by an HPAI H5N1 virus strain belonging to the BB genotype that was characterised by the presence of a PB2 mutation related to mammalian adaptation. (...) On the farm lived five domestic medium-sized crossbreed dogs and one cat that were allowed to roam freely inside and outside the farm. These animals did not present any clinical signs at the time mortality was observed for hens, nor in the following weeks. (...) Serological examinations detected antibodies against NPA, H5 and N1 in all sera collected from the dogs and the cat at the two sampling times.
It was surprising to observe that the virus characterised in this study, detected in hens, differed from all other HPAI A(H5N1) clade 2.3.4.4b viruses circulating in poultry and in birds by a mutation in the PB2 protein, T271A, which is a marker of virus adaptation to mammalian species; it has previously been shown to be associated with increased polymerase activity in mammalian cells and is present in the 2009 pandemic A(H1N1) virus. It should be noted that this mutation has never been observed in H5Nx viruses of clade 2.3.4.4b collected from birds in Europe since 2020. In contrast, it has been detected in ca 7% of clade 2.3.4.4b viruses identified in mammals in Europe, including the virus responsible for the outbreak on a mink farm in Spain. This molecular finding suggests that virus spread from mammals to birds cannot be excluded.
All three cats presented with neurological abnormalities and were euthanized due to a poor prognosis within 2 days (two cats) or 10 days (one cat) of known clinical disease onset. (...) To our knowledge, this report is the first to detail pathological findings in HPAI H5N1 naturally-infected cats during the widespread outbreak in North America beginning in 2021, and that describes a cat surviving for 10 days after onset of HPAI H5N1 encephalitis.
We detected antibodies to H5 and N1 subtype influenza A viruses in 4/194 (2%) dogs from Washington, USA, that hunted or engaged in hunt tests and training with wild birds. Historical data provided by dog owners showed seropositive dogs had high levels of exposure to waterfowl.
Four more cats have died of H5N1 bird flu in the United States, including two pets in South Dakota with no links to poultry or dairy cows, according to state and federal officials. At least 14 cats have recently died of bird flu.
Contact with Livestock
Exposure to infected cows and especially consumption of raw milk on dairy farms is a new and significant risk for cats. Many cats live on farms not as pets, but mostly to reduce the local rodent population.
The next day, cats on the farm that had consumed some of the raw milk from the sick cows also became ill. While the cows would go on to largely recover, the cats weren't so lucky. They developed depressed mental states, stiff body movements, loss of coordination, circling, copious discharge from their eyes and noses, and blindness. By March 20, over half of the farm's 24 or so cats died from the flu.
Three more cats have died of H5N1 bird flu in the United States, one of which was a domestic cat with no links to farms, according to state officials. At least 10 cats are now known to have died since bird flu spread to dairy cows earlier this year.
Two of the cats were found dead at a dairy farm in Curry County in New Mexico, according to the state’s veterinarian, Dr. Samantha Uhrig. Cows at the farm also tested positive after workers noticed a drop in milk production.
The third case was reported in Yellowstone County in Montana, where a domestic cat exhibited “neurologic signs” after the owner found a dead skunk on the property.
>80% of farms have cats present
>50% of farms with cats observed sick or dead
cat
Stray and Feral Populations
Large numbers of cats and dogs live to some degree as strays or feral. Those animals could act as a reservoir for a virus adapted to mammals. For example there could be long chains of transmission in the stray cat population before the virus occasionally reaches free roaming cats living in households.
Of the 701 stray cats examined, 83 were found to have antibodies to the bird flu virus. Some of the stray cats examined had mild symptoms of illness, but not specific to bird flu. Eating contaminated dead birds is a plausible route of infection for these stray cats. An analysis into different risk factors showed that stray cats originating from nature reserves had, on average, more frequent antibodies against the bird flu virus stray cats from other habitats, such as a livestock farm, holiday park or industrial area.
In domestic cats, 4 of the 814 blood samples examined had antibodies to the avian flu virus. The blood samples from the domestic cats were sent to the Faculty for blood testing for various reasons. These were therefore not part of the castration project, but were added to this part of the study as a control group. Among the domestic cats, there was an overrepresentation of cats from urban areas in the Randstad, and it is not known whether these cats went outside and thus may have had contact with (wild) birds. With the new study in domestic cats that go outdoors, the faculty aims to gain more insight into this. The study is expected to be completed by mid-2024.
We experimentally inoculated cats with H5N1 virus intratracheally and by feeding them virus-infected chickens. The cats excreted virus, developed severe diffuse alveolar damage, and transmitted virus to sentinel cats. These results show that domestic cats are at risk of disease or death from H5N1 virus, can be infected by horizontal transmission, and may play a role in the epidemiology of this virus.
Our study also shows that infected cats excrete H5N1 virus via the rectum, suggesting that cat-to-cat transmission of H5N1 virus could occur through infected feces.
In an unpublished study carried out last year by the National Institute of Animal Health in Bangkok, researchers led by virologist Sudarat Damrongwatanapokin tested 629 village dogs and 111 cats in the Suphan Buri district of central Thailand. Out of these, 160 dogs and 8 cats had antibodies to H5N1, indicating that they were infected with the virus or had been infected in the past. “That's a lot,” says Albert Osterhaus, a virologist at the Erasmus University in Rotterdam, the Netherlands. “This is definitely something to look into.” So far, researchers at Bangkok's Chulalongkorn University have isolated the virus from at least one of the dogs.
Food Contamination
Cat food contaminated with H5N1 has infected cats in South Korea. The cat food based on poultry was not properly disinfected. The risk from commercial cat or dog food is very low, as it is usually properly cooked and disinfected.
Another case in Poland may have been caused by contaminated raw poultry meat being fed to the cats, but the cause is not confirmed. It is worth reading this post for further details.
On 27 June 2023, the IHR National Focal Point of Poland notified WHO of unusual deaths in cats across the country. As of 11 July, 47 samples have been tested from 46 cats and one captive caracal, of which 29 were found to be positive for influenza A (H5N1). Fourteen cats are reported to have been euthanized, and a further 11 died, with the last death reported on 30 June. The source of the exposure of cats to the virus is currently unknown and epizootic investigations are ongoing.
Sporadic infection of cats with A(H5N1) has previously been reported, but this is the first report of a high numbers of infected cats over a wide geographical area within a country.
As of 12 July, no human contacts of A(H5N1) positive cats have reported symptoms, and the surveillance period for all contacts is now complete.
The risk of human infections following exposure to infected cats at the national level is assessed as low for the general population, and low to moderate for cat owners and those occupationally exposed to H5N1-infected cats (such as veterinarians) without the use of appropriate personal protective equipment.
While there may be more than one route of infection, with dozens of indoor and outdoor cats affected, H5N1 contamination from raw poultry has to be considered. (...) As a result, we received five meat samples for testing and conducted molecular tests for the presence of the virus. The analysis showed that one of the 5 samples contained the virus. Further analysis showed that the meat contains not only the genetic material of the virus, but also the infectious virus – we were able to isolate the virus in cell cultures. While it cannot be ruled out that the virus found its way into the meat samples later, or even the meat was contaminated by the owners with the virus developing in the cat's body, it is also possible that the raw meat was the source of infection.
Earlier this week, the H5 AI strain was found in two kinds of cat food -- Balanced Duck and Balanced Chicken manufactured by Nature's Raw -- used at the shelter in Seoul's Gwanak district, and follow-up tests found that they were contaminated with the highly pathogenic H5N1 AI strain, according to the Ministry of Agriculture, Food and Rural Affairs.
At least one cat there died after being infected with the H5N1 AI strain.
In June and July 2023, feline AIV infections, confirmed to be caused by H5N1, occurred at two different shelters in Seoul, South Korea, with no confirmed human cases involved. The source of infection in the first case remains unclear; in the second case, the infection originated from infected poultry feed. (...) Three out of 40 cats housed in a non-profit private shelter in Seoul, South Korea between June 24 and 27, 2023 died of high fever and anorexia. Subsequent mortality persisted at 1–2-day intervals, and 38 of the 40 animals finally died; however, the exact cause of death was not revealed.
Dr Tom Peacock, a virologist and fellow at the Pirbright Institute agreed: “This latest case wouldn’t be the first time there have been concerns H5N1 could be moving through different mammals via contaminated feed,” citing the outbreak of avian flu in cats in Poland last year, which experts suspected might have been transmitted through mink byproducts used in raw cat food.
The next day, cats on the farm that had consumed some of the raw milk from the sick cows also became ill. While the cows would go on to largely recover, the cats weren't so lucky. They developed depressed mental states, stiff body movements, loss of coordination, circling, copious discharge from their eyes and noses, and blindness. By March 20, over half of the farm's 24 or so cats died from the flu.
The study involved five ferrets from one household in Poland, comprising three sick 9-week-old juveniles, their healthy mother, and another clinically normal adult, admitted to the veterinary clinic in June 2023. The juvenile ferrets displayed significant lethargy and a pronounced unwillingness to move with accompanying pulmonary distress. Prompted by concurrent outbreaks of A/H5N1 influenza virus infections in Polish cats, point-of-care tests were conducted that revealed type A influenza antigens in the throat swabs of all five ferrets. Despite treatment, one juvenile ferret exhibited dyspnea and neurological symptoms and eventually died. The two remaining ferrets recovered fully, including one severely affected showing persistent dyspnea and incoordination without fever that recovered after 11 days of treatment. (...) To our best knowledge, this is the first documented natural A/H5N1 avian influenza in domestic ferrets kept as pets. (...) Though other routs cannot be excluded, for example, the owners’ shoes contaminated with faeces of infected birds, the alimental infection is much more probable, as the affected ferrets were kept strictly indoors, and fed raw poultry meat.
Prevention
The most effective measures to prevent infection of your pet are keeping it away from birds and not feeding raw meat, especially poultry. This means keeping cats indoors and dogs on leashes. While H5N1 infections in dogs can be mild, a more recently infected dog died from H5N1. This may depend on the exact virus strain or type of dog. However, documented cases of dogs infected with H5N1 are very rare. A preventive measure that won't bother your pet is keeping shoes outside the home to avoid dragging in any infectious material, especially bird feces. Another one is to prevent contamination of food and water sources by placing them under a cover. Guidelines on how to keep birds and other pets safe can be found here, here and here.
Inoculation of influenza (H5N1) into beagles resulted in virus excretion and rapid seroconversion with no disease. Binding studies that used labeled influenza (H5N1) showed virus attachment to higher and lower respiratory tract tissues. Thus, dogs that are subclinically infected with influenza (H5N1) may contribute to virus spread.
To elucidate the susceptibility of dogs to this pathogen, we infected two groups of 6 beagles with 106 50% egg-infectious dose of H5N1 AIV A/bar-headed goose/Qinghai/3/05 (BHG/QH/3/05) intranasally (i.n.) and intratracheally (i.t.), respectively. The dogs showed disease symptoms, including anorexia, fever, conjunctivitis, labored breathing and cough, and one i.t. inoculated animal died on day 4 post-infection. Virus shedding was detected from all 6 animals inoculated i.n. and one inoculated i.t. Virus replication was detected in all animals that were euthanized on day 3 or day 5 post-infection and in the animal that died on day 4 post-infection. Our results demonstrate that dogs are highly susceptible to H5N1 AIV and may serve as an intermediate host to transfer this virus to humans.
IAV was detected in 2.8% of the samples (13/458), whereas influenza B virus was not detected during this study. Genetic analysis revealed the presence of A (H1N1) and A (H3N2). (...) Interestingly, a higher detection rate (84.61%) was observed in samples collected during autumn and winter, which could be linked to the peak flu season in Kunshan and Shanghai. Clinical signs, including sneezing, dyspnea, and coughing, varied from mild to moderate among influenza-positive cats. No deaths were reported among the positive cats. Based on molecular and serological testing, we demonstrated human seasonal IAV-infected cats in this study. This is the first report to assess the reverse zoonotic events of influenza viruses in cats in Kunshan, China, and highlights the potential risk of catching IAV in cats living in close contact with their owners.
In pets, there's no specific antiviral treatment available; only supportive care.
If you suspect your pet has bird flu, it's important to alert your vet right away, because they need to take precautions ahead of time. (...) Jeromin adds that those who are feeding raw beef, chicken, or wild bird game to their pets should start cooking it, because freezing does not kill the virus. If you tend to walk through wild bird droppings and have indoor house cats, she also advises not to wear your shoes inside, because that can potentially spread the virus, as well.
An outbreak of influenza A(H7N2) virus in cats in a shelter in New York, NY, USA, resulted in zoonotic transmission. Virus isolated from the infected human was closely related to virus isolated from a cat; both were related to low pathogenicity avian influenza A(H7N2) viruses detected in the United States during the early 2000s.
We describe the first case of cat-to-human transmission of influenza A(H7N2), an avian-lineage influenza A virus, that occurred during an outbreak among cats in New York City animal shelters. We describe the public health response and investigation.
So far, domestic poultry and dairy cows have proved to be imperfect vessels. So too have the more than 48 other mammal species that have become infected by eating infected birds and then died.
But researchers say there is one population of animal floating under the radar: Pets. The risk may be low, but the opportunities for transmission are abundant.
Felids, known as felines or cats, are susceptible to avian influenza virus infection. Felines prey on wild birds and may serve as a host for avian influenza virus adaptation to mammals. Feline-to-feline transmission has been demonstrated experimentally, and real-world outbreaks have been reported. Domestic cats are a popular human companion animal and thus provide a potential pathway for zoonotic spillover of avian influenza viruses to humans.
Through our systematic review, we identified 486 avian influenza virus infections in felines, including 249 associated feline deaths, reported in the English scientific literature from 2004 – 2024. The reports represent cases from 7 geographical regions, including 17 countries and 12 felid species. Of particular interest are domestic cats infected with H5N1 clade 2.3.4.4, which represents a variant in the hemagglutinin serotype 5 gene of IAV which became the dominant IAV H5 serotype among poultry in 2020. Clade 2.3.4.4b was first reported in felines in 2022, and among the feline infections reported, it has yielded a mortality rate of 67%. Clade 2.3.4.4b is also responsible for the ongoing AIV outbreaks among dairy cattle in the U.S., representing a significant threat to feline companion animals. Furthermore, subclinical infections of H5N1 in cats have been reported. Thus, we argue that surveillance among domestic cats is urgently needed.
But researchers say there is one population of animal floating under the radar: Pets. The risk may be low, but the opportunities for transmission are abundant.
Six feline cases of Influenza A (HPAI H5N1) have been diagnosed in domestic cats in Colorado during 2024. One of these cases was directly associated with a known infected commercial dairy facility. Two of the six cases were indoor only cats with no direct exposures to the virus. Three of the six cases were known indoor/outdoor cats that hunted mice and/or small birds as prey and also spent time indoors with their owners. Five of the six cases have presented with similar clinical signs and disease progression: an initial complaint of lethargy and inappetence, followed by progressive respiratory signs in some and fairly consistent progressive neurologic signs in most. Several of these cases were tested for rabies preceding diagnosis with H5N1 infection due to the indistinguishable presentation once neurologic signs presented. HPAI H5N1 infection should be considered in domestic felines even if all of the risk factors or clinical signs are not present.
For the new cases, there aren’t many details available, and it’s possible that even the indoor cats did spend time outdoors or that they consumed raw milk or meat from infected animals. But if not, the possibilities are concerning: these cats might have caught the virus from an infected mouse inside the home or perhaps even picked it up from a human with an unknown, asymptomatic infection from contact with other animals. Either of these scenarios suggests that bird flu is even more entrenched than we realized.
This identification of H5N1 in indoor-only cats is a big concern.
