Cats As Potential Vectors/Mixing Vessels for Novel Flu
#18,547
Just over a month ago (Dec 12th) the LA County Department of Public Health announced two cats had died after consuming raw milk, and H5 was strongly suspected. A week later, the LADPH confirmed H5 infection in two cats in a second household, and announced they were investigating 3 other sick cats at the same location.
Unlike the first event - which was linked to raw milk - the second outbreak was tentatively linked to the consumption of two brands of commercial raw meat pet food (see recall notices).
While LADPH's attentions have understandably been focused primarily on their wildfire crisis, yesterday their Veterinary Health division issued their first H5N1 HAN of 2025, announcing 3 more confirmed feline H5N1 infections.
As this HAN alert reminds us, feline infections and/or deaths from H5N1 are underreported. They cite `multiple H5 bird flu probable and suspected cases', which were never tested, and are urging Veterinarians to report suspected cases.
Due to its length, I've only posted some excerpts. Follow the link to read the Animal Health Alert in its entirety.
1.13.2025
Key Points:
• Five indoor-only cats in one household experienced acute onset of illness after consuming two brands of commercially available raw pet food. Four of the cats had severe clinical signs and two of them died. One cat had mild clinical signs. One of the severely affected cats was tested and later confirmed to be infected with H5N1 (aka H5bird flu). Both raw pet food diets were tested, and one of the two raw pet foods, Monarch Raw Pet Food, was confirmed to contain live, infective, H5N1 virus.
• In a second single-cat household, the indoor-only cat had acute onset of illness after consuming three different brands of commercially available raw pet food. This cat was tested and confirmed to be infected with H5 bird flu. The investigation is ongoing and testing of the raw pet food by the US Food and Drug Administration (FDA) is currently underway.
• Influenza A is rarely detected in cats. These are the first cats in LA County to be confirmed positive for H5 bird flu after consuming raw pet food products.
• Five other cats from two different households in LA County have also been confirmed with H5 bird flu after drinking raw milk for human consumption that was part of a recall due to H5 bird flu contamination. All five of these cats died from H5 bird flu.
• H5 bird flu is a One Health issue that significantly affects human health, animal health and the environment. Veterinarians should strongly advise pet owners to not consume nor feed raw dairy, raw meat, raw poultry, and raw pet food diets to pets.
- • REPORT suspected cases of H5 bird flu in cats and other animals. See the Guidance for Veterinary Practices with Suspect H5 Bird Flu Cases in Pets. Influenza A testing is available through commercial diagnostic laboratories. Testing through Public Health may be available for certain cases. Take a complete dietary history (including any raw dairy, raw poultry and/or meat including raw pet food diets, and wild bird exposure).
Dear Veterinary Colleagues:
In Los Angeles County, there have now been 7 laboratory confirmed cases of H5 bird flu in cats. Five cats with confirmed H5 bird flu consumed raw milk that was part of a recall due to H5 bird flu contamination. Two cats with confirmed H5 bird flu consumed commercially available raw pet food products.
There have been multiple H5 bird flu probable and suspected cases in cats that either consumed raw pet food or raw milk and became acutely ill, but not all cats were able to be tested.
As part of the epidemiologic investigation and when available from the owners, the pet foods fed to the suspected and confirmed cases of H5 bird flu are being tested through federal partners. One commercially available raw pet food, Monarch Raw Pet food, tested positive for H5 bird flu, with live infective virus isolated from the samples. The product is sold at several farmers markets in southern California, and do not have lot numbers, nor Best Before dates.
Testing is still pending on several additional commercially available raw pet foods that were consumed by cats that became acutely ill and then tested positive for H5 bird flu.
Testing options if you suspect a case:
Commercial testing for influenza in cats is available through veterinary diagnostic laboratories.
Public health is offering testing in cases that are highly suspicious for H5 bird flu – those with a clear epidemiologic link plus acute onset of significant compatible clinical signs. A clear epidemiologic link includes confirmed history of consumption of raw milk, raw pet food, or raw poultry/meat. Significant compatible clinical signs include fever, severe lethargy, loss of appetite, acute respiratory disease, acute neurologic disease, hepatopathy/icterus, uveitis.
Please reach out to Veterinary Public Health for further assistance with testing. See the Guidance for Veterinary Practices with Suspect H5 Bird Flu Cases in Pets.
With scientific evidence of the linkage between contaminated raw products and cats developing severe or fatal H5 bird flu infection, Los Angeles County Department of Public Health (LAC DPH) recommends veterinarians strongly advise pet owners not to feed pets raw pet food diets, raw meat, raw poultry, and raw milk due to the risks associated with H5 bird flu.
H5 bird flu in cats that consumed raw pet food
Approximately 1-2 weeks after beginning to consume two commercially available raw food pet diets, all cats in a household of five strictly indoor-only cats became ill. Two of the five cats experienced acute respiratory distress and were humanely euthanized. Clinical signs in the cats included: upper respiratory symptoms, lethargy, reduced appetite, pollakiuria, ataxia, corneal edema, uveitis, and retinal detachment leading to permanent vision loss. As part of initial diagnostics, one severely ill cat had a respiratory PCR panel performed by a commercial veterinary laboratory, which came back positive for influenza A. The cat’s sample was retested and influenza A positive at the California Animal Health and Food Safety Laboratory (CAHFS).
The sample was then sent to the USDA’s National Veterinary Services Laboratory (NVSL) where whole genome sequencing (WGS) was performed and was confirmed to be positive for H5 bird flu (H5N1). The owner had unopened and opened packages of both commercially available raw pet foods that were fed to the cats. These samples were provided to the Animal Diagnostic Center laboratory of Cornell University where testing was performed in partnership with the FDA. Testing confirmed that product samples of both the opened and unopened Monarch Raw Pet food were infected with live and infective influenza A H5N1 virus.
In a separate single-cat household, a strictly indoor-only domestic cat was confirmed positive for H5 bird flu on December 31, 2024. The cat was fed three different brands of commercially available poultry-based raw pet foods. No pre-existing illness was identified prior to the cat becoming sick. Symptoms in this cat included fever, lethargy, anorexia, and acute wheezing.
The cat remained hospitalized on oxygen for several days, was released and is recovering from illness. A respiratory PCR panel resulted positive for influenza A at a commercial laboratory, and both oropharyngeal and rectal swabs tested through Los Angeles County DPH were confirmed by NVSL as positive for H5 bird flu. The investigation is ongoing and testing of the raw pet food diets is currently underway by the FDA. Household members and veterinary clinic staff who had contact with the cat are also being monitored for symptoms of flu.
H5 Bird Flu in cats that consumed raw milk products
To date, in LA County, there have been two separate households with confirmed positive H5 bird flu in cats following the consumption of recalled raw milk products. In early December 2024, seven cats from one household became ill and five died in LA County after drinking the recalled raw milk sold for human consumption. On December 22, 2024, a cat from a different household was submitted for rabies testing after it died following the acute onset of severe neurologic signs (anorexia, disorientation, ataxia, confusion, circling, and seizures). Following a negative rabies test, a brain swab was collected and confirmed by NVSL to be positive for H5N1.
Further investigation revealed that this cat lived in a household of eight indoor/outdoor cats that also had been offered milk from Raw Farm LLC in late November 2024; however, it was unclear how many cats had consumed the raw milk in this household. Over a period of three days, three of the eight cats in this household had become acutely ill and died, and only the one cat referenced above was tested for influenza.
Veterinary Public Health extends sincere condolences to the families and pet owners of these cats that passed or that were affected by bird flu. We sincerely appreciate the time and efforts from pet owners who provided information about their households and provided samples of raw products for testing with the goal of protecting other animals and other families from contracting this disease.
In early December, in Emerg. Microbes & Inf.: Marked Neurotropism and Potential Adaptation of H5N1 Clade 2.3.4.4.b Virus in Naturally Infected Domestic Cats, we looked at a report on the HPAI H5 infection of a house full of domestic cats in South Dakota last April.
Isolates from the two cats that were tested showed signs of viral adaptation to a mammalian host. The authors wrote:
Cat H5N1 genomes had unique mutations, including T143A in haemagglutinin, known to affect infectivity and immune evasion, and two novel mutations in PA protein (F314L, L342Q) that may affect polymerase activity and virulence, suggesting potential virus adaptation.
Dead cats showed systemic infection with lesions and viral antigens in multiple organs. Higher viral RNA and antigen in the brain indicated pronounced neurotropism.
While the H5 virus currently lacks the ability to transmit efficiently from human-to-human, every mammalian infection is another opportunity for the virus to hone its abilities.
