Avian flu outbreak in domestic cats raises new concerns

Our beloved cats are facing a new source of concern: a tiny microscopic entity known as the H5N1 virus, more commonly known as avian flu or bird flu.

Researchers at the University of Pittsburgh have uncovered compelling evidence that domestic cats have adapted to avian flu.

Experts investigated a rural outbreak in South Dakota, where several outdoor cats succumbed to the virus after exhibiting severe neurological and respiratory symptoms.

Spread of bird flu

The highly pathogenic avian influenza virus (HPAIV) H5N1 first appeared in China in 1996.

Over the years, the virus has diversified into several clades, with clade 2.3.4.4.b appearing to be the most geographically widespread. This clade has infected more than 90 bird species and 21 mammal species worldwide, including humans, in recent years.

Infections in domestic cats were initially documented in 2004 and linked primarily to respiratory illnesses. However, clade 2.3.4.4.ba showed an alarming capacity for neurological impacts in various mammalian hosts, such as sea lions, red foxes, and now domestic cats.

Outbreak in South Dakota

In April 2024, ten outdoor cats in rural South Dakota were reported dead after exhibiting respiratory and neurological symptoms.

Researchers performed necropsies on two of the cats at the North Dakota Veterinary Diagnostic Laboratory.

Tissue samples were subjected to a comprehensive suite of analyses, including histopathology, quantitative RT-PCR, whole genome sequencing, phylogenetics, and lectin histochemistry. Pseudovirus binding assays further assessed receptor compatibility.

Avian flu in domestic cats

The H5N1 clade 2.3.4.4.b was confirmed in the brains and lungs of infected cats.

Genetic analysis revealed a close relationship between the cat isolates and H5N1 sequences previously identified in South Dakota dairy cattle.

This suggests a risk of spread from infected cattle or birds. Importantly, unique mutations in the cat isolates suggest potential adaptation of the virus.

Neurological impact of the virus in cats

The study revealed severe neurological damage in infected cats, with significant lesions in the cerebellum and hippocampus. Key findings include:

• Neuronal necrosis: Death of nerve cells in critical regions of the brain.
• Gliosis: Proliferation of glial cells in response to injury.
• Perivascular inflammation: Immune responses surrounding blood vessels in the brain.
• High viral antigen concentrations: It is mainly found in the cerebellum and hippocampus.

The viral load in the brain far exceeded that observed in respiratory tissues, favoring the neurotropic tendencies of the virus.

Cats demonstrated co-expression of sialic acid receptors in their lung and brain tissues, consistent with avian and human influenza viruses.

This receptor compatibility could enable cross-species transmission and highlights the risks of domestic cats acting as potential bridges for virus adaptation.

Role of cats in virus adaptation

The study, entitled “Marked neurotropism and potential adaptation of H5N1 Clade 2.3.4.4.b virus in naturally infected domestic cats” raises significant public health concerns.

The researchers noted that cats could serve as hosts for reassortment between avian and mammalian influenza viruses. This scenario could facilitate the emergence of new influenza strains capable of infecting humans.

“Cats could act as mixing vessels for mutations,” the study warns, posing a risk of genetic reassortment and possible transmission from cats to humans. Although no human cases linked to cats have yet been reported, this possibility calls for vigilance.

Wider implications of the epidemic

The conclusions of the University of Pittsburgh This study mirrors previous reports from Texas, where H5N1 outbreaks on cattle farms were linked to cat and bird deaths.

Such cases highlight the need for enhanced surveillance of H5N1 in domestic and wild species to assess and mitigate the risk of animal-to-human transmission.

The adaptation of H5N1 in domestic cats highlights the ability of the virus to cross species barriers and adapt to mammalian hosts.

With unique mutations identified in key viral proteins and evidence of systemic infections in cats, the potential for zoonotic transmission cannot be ignored. Enhanced surveillance and preventative measures are essential to curb this emerging threat.

Vigilance and proactive measures can help mitigate the risks posed by adaptation to H5N1 in domestic and wild animals.

Protecting cats from bird flu

The following tips can help protect cats from the deadly virus:

1. Keep cats indoors: Prevent exposure outdoors, especially in areas where outbreaks of H5N1 in birds or mammals are reported.
2. Monitor wildlife: Reduce interactions between domestic cats and wildlife, such as birds or small mammals, to reduce the risk of infection.
3. Hygiene practices: Wash your hands thoroughly after handling birds or cleaning areas where wild birds may have been.
4. Avoid feeding raw meat: Make sure cats do not eat raw or undercooked poultry or wild game, as they can harbor the virus.
5. Stay informed: Keep track of local updates on H5N1 and follow advice from veterinarians or public health authorities.
6. Vaccine research: Consult your veterinarian about developments in flu vaccines for pets if you live in high-risk areas.

The study is published in the journal Emerging microbes and infections.

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