#18,020
Up until 20 years ago, cats (and dogs) were thought relatively immune to influenza A viruses. All that changed when an equine H3N8 virus jumped to greyhounds at a racetrack in Florida in 2004, and half-way around the world, big cats in Asian zoos began to succumb to avian H5N1.
A small sampling includes:Since then we've seen a second (avian H3N2) influenza A virus jump to dogs and begin a world tour, and dozens of reports of dogs and cats infected with a variety of (mostly novel) influenza A viruses.
Microorganisms: Case Report On Symptomatic H5N1 Infection In A Dog - Poland, 2023
J. Virology: Zoonotic Risk, Pathogenesis, and Transmission of Canine H3N2
Access Microbiology: Inter-Species Transmission of Avian Influenza Virus to Dogs
WHO Update & Risk Assessment On H5N1 In Cats - Poland
Nebraska Veterinary Diagnostic Center (NVDC) Report: 2 Domestic Cats Infected With HPAI H5N1
The most obvious concern is that a dog or a cat might pick up a novel influenza A virus (like H5N1) from exposure to birds, or a contaminated environment, and bring it home (zoonotic transmission).
Reverse zoonosis may help explain how SARS-COV ended up in North American deer and other peridomestic animals, and almost certainly how human influenza A viruses have spread so widely in swine (see Reverse zoonosis of influenza to swine: new perspectives on the human-animal interface).
While we've seen a fair number of studies on novel flu infection in companion animals, relatively little is known about the spread of seasonal flu viruses to cats.
- During the 2009 H1N1 pandemic we did see several reports of feline infection
- In late 2010 we saw a study (see EID Journal: Pandemic H1N1 Infection In Cats) that looked at the pathogenesis of novel H1N1 in domestic felines.
- Six years ago we looked at two rare fatal infections in cats from a single household in Connecticut. Reportedly, both cats had pre-existing conditions, and the owner of the cats had recently been sick with a flu-like illness. (see Connecticut: Two Cases Of Fatal H1N1 In Cats)
First, some excerpts from the letter (follow the link to read it in its entirety), after which I'll return with a postscript.
Evidence of Reverse Zoonotic Transmission of Human Seasonal Influenza A Virus (H1N1, H3N2) Among Cats
Sajid Umar, Semin Kim, Di Gao, Pu Chen
First published: 18 April 2024
https://doi.org/10.1111/irv.13296
Dear Editor,
Human–animal interactions are closely intertwined. The connection between animal, human, and environmental health is becoming increasingly complicated with globalization, industrialization, and climate change. Since the beginning of the 20th century, the number of domestic cats has increased rapidly worldwide, including in China. There are approximately 600 million domesticated cats worldwide, including 65 million cats in China, most of whom have close human contacts.These close contacts create more chances for pathogen spillover among humans and cats, which could lead to the emergence of new pathogenic strains or variants. Cats living in proximity to their owners carry a particular risk of catching pathogens, as they often share snuggles, kisses, dining, and beds [1, 2]. We share hundreds of pathogens with our animals, which they serve as intermediate or reservoir hosts for pathogens that affect human health. Cats, owing to their genetic similarity to humans, are more susceptible to catching diseases from their owners. Recently, it has been estimated that humans spillover far more pathogens to animals than animals transmit to humans [2, 3].
(SNIP)
The high susceptibility of cats to IAVs generates the possibility of zoonotic and reverse-zoonotic transmission events and can serve as a mixing vessel for the emergence of new IAV variants (Figure 1). A large population of animals and humans makes China an ideal location for the emergence of future IAV pandemics.(SNIP)
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). Among the positive strains, there were nine strains of A (H1N1) virus and four strains of A (H3N2) virus. A/H1N1 and A/H3N2 positive cats showed HAI titers against these viruses, which also supported the evidence of reverse zoonosis. 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. Despite some limitations, such as the small sample size and geographical area, our study provides useful information to veterinarians, pet owners, and policymakers.
Cats could act as additional intermediate or reservoir hosts for endemic IVA evolution and thus may contribute to major public health issues. There are several reports on the natural transmission of different IAV subtypes in cats, including avian H5N1, canine H3N2, human H1N1, and H3N2 [8]. Anthroponotic spillover events for IAV have been documented among cats, suggesting close interactions between cats and owners suffering from influenza-like illness [1, 8-11]. In addition to cats, a variety of other animals (swine, dogs, turkeys, and ferrets) has been naturally infected with Influenza A/H1N1. Human-to-pig transmission of IAV is the most studied anthroponotic event. More IAVs jump from humans to swine than from swine to humans [1].
Several suggestions have been made to minimize the risk of IAV-reverse zoonosis.
First, flu vaccine shots are recommended to owners and susceptible cats to reduce anthroponotic events.Second, people who are sick with seasonal flu need to modify their behaviors and should be more vigilant about the health of their cats. Pet owners can minimize reverse zoonotic transmission by keeping nasal discharges and other bodily secretions away from cats during the sickness period.Third, owners can minimize their playing time and petting activities with their cats while they are sick.Finally, they can also limit reverse zoonotic transmission by regularly cleaning and disinfecting the bedding area and providing fresh and healthy feed to their cats.
Reverse zoonotic events in IAV can pose significant health risks for cats and possibly human health if left unchecked. Therefore, it is important to keep the IAV under control before it imposes deadly consequences on the human population. Keeping in mind the close association of cats with humans and the high pandemic potential of IAV warrants a more integrated research approach to minimize reverse zoonoses. This could include greater testing and continuous human pathogen surveillance at the human-animal contact interface. This type of data could facilitate the mitigation, prevention, prediction, and preparation of future IAV pandemics.
Twice in my lifetime (H2N2 in 1957 & H3N2 in 1968) pandemic influenza viruses have emerged from China that were a combination of avian and human flu viruses. Presumably, some unknown host was co-infected with a seasonal flu virus and and avian flu virus, and produced a hybrid via reassortment.
While that host might have been a human, it could just as easily have been a pig, a dog, a cat, or some other non-human host.
All reasons why, with the elevated amount of HPAI H5N1 virus in wild birds and the environment, it is more important than ever to heed the CDC's advice on how to keep your pets (and your family) safe.