#19,359
Last May, in MMWR: Serologic Evidence of HPAI A(H5N1) Virus Infection in a Veterinary Professional Exposed to an Infected Domestic Cat we looked at a probable cat-to-human transmission of HPAI H5N1.
While long considered possible, actual evidence of cat-to-human transmission of avian flu viruses has been pretty sparse. Two notable exceptions being:- In 2005, the CDC's EID Journal Probable Tiger-to-Tiger Transmission of Avian Influenza H5N1, reported that while no humans tested positive by RT-PCR, 2 close human contacts (3.5%) tested positive via serology (microneutralization) for the virus 4 weeks later.
- In 2018 we saw evidence suggesting several employers had been infected by LPAI H7N2 during an outbreak in 2016 (see J Infect Dis: Serological Evidence Of H7N2 Infection Among Animal Shelter Workers, NYC 2016).
In April of 2024, less than a month after the first detection of H5N1 in cattle, the CDC released Guidance for Veterinarians: Evaluating & Handling Cats Potentially Exposed to HPAI H5NI.
After our summer lull, we are seeing an uptick in North American avian flu outbreaks in poultry, which typically increases when southbound migratory birds return from their high-latitude roosting areas.
That suggests that the risks of domestic cats being infected are likely rising, and with that come exposure risks to their owners, veterinarians, and animal rescue staff.
Last week the AVMA (American Veterinary Medical Association) Journal published an updated - albeit, unofficial - best practices article penned by researchers at the CDC.
Although this is a public domain article (produced by U.S. government employees) I've only posted extended excerpts. Follow the link to read it in its entirety.
I'll have a bit more after the break.
How can veterinary personnel recognize and protect themselves from domestic cats infected with highly pathogenic avian influenza A(H5N1) viruses?Lizette O. Durand, VMD, PhD1* ; Sonja J. Olsen, PhD1 ; Natalie M. Wendling, DVM, MPH2 ; Timothy M. Uyeki, MD, MPH, MPP1 ; Grazia Mirabito, PhD1 ; Tom T. Shimabukuro, MD, MPH, MBA1 ; Colin A. Basler, DVM, MPH2
Abstract
Highly pathogenic avian influenza A(H5N1) viruses circulate globally in wild birds, causing poultry outbreaks and spillover infections in mammals and sporadic human infections. Recent detections in domestic cats highlight occupational risks for veterinarians handling cats in areas where A(H5N1) virus is circulating. Although the potential risk for cat-to-human A(H5N1) virus-transmission is currently low, vigilance is warranted. Veterinarians can use published recommendations to evaluate exposure risks, implement infection control practices, use recommended personal protective equipment, train staff, and coordinate with health officials. The One Health approach can help reduce risks of A(H5N1) virus infection to veterinary staff, cat owners, and other animals.
Keywords: avian influenza; cats; PPE; One Health; H5N1
Viewpoint articles represent the opinions of the authors and do not represent AVMA endorsement of such statements.
Introduction
(SNIP)
Between March 2024 and March 2026, A(H5N1) viruses were detected in 137 domestic cats in the US.5 While detailed information is not available on all affected cats, they represent owned indoor only cats, owned indoor/outdoor cats, and feral domestic cats (including barn cats).
Detections were associated with exposure to sick or A(H5N1) virus–infected dairy cattle or contaminated fomites from dairy farms, contact with wild birds, eating raw meat, commercially produced raw pet food products and/or consuming raw milk contaminated with A(H5N1).6–10
Reported clinical signs of A(H5N1) illness in cats have included nonspecific signs, such as fever, lethargy, and loss of appetite; respiratory signs, including coughing, sneezing, labored breathing, nasal and ocular discharge; and neurologic manifestations, including abnormal gait, circling, tremors, seizures, and blindness.11 In documented fatal feline cases, cats deteriorated quickly, progressing from onset of clinical signs to death in a few days.9
During the same 2-year period, 71 human cases of influenza A(H5Nx) virus infection were confirmed in the US. Most cases occurred in people with occupational exposure to A(H5N1) virus-infected animals, including 41 in dairy farm workers and 24 in poultry depopulation workers. Three human cases were linked to backyard flocks and 3 had unknown exposures.12,13
While transmission of low pathogenic avian influenza A(H7N2) virus from domestic cats to humans has been documented,14–16 there have been no virologically confirmed human cases of A(H5N1) in the US transmitted from an infected cat. However, the recent report from Los Angeles County, California, provides serologic evidence of possible transmission of A(H5N1) virus from an infected cat to a veterinary professional who remained asymptomatic17. This newly identified possible source of A(H5N1) virus transmission from cats to humans is particularly relevant for veterinarians.
Although the overall risk of human A(H5N1) virus infection from cats or other companion animals is low, it is important for veterinarians to recognize and protect themselves and their staff from A(H5N1) virus transmission. When there is clinical suspicion for A(H5N1) virus infection in cats or other companion animals, a four-step One Health approach19 is available to protect veterinary personnel, pet owners, and other animals.
Four-Step One Health Approach
Recognize cases
In most cases, domestic cats with A(H5N1) virus infection have presented with respiratory (eg, nasal discharge, tachypnea or breathing quickly, dyspnea or trouble breathing, sneezing, or coughing) or neurologic signs (eg, ataxia, circling, tremors, seizures, or blindness).4,9,17 Although other diseases, such as rabies, can present with respiratory and neurologic signs, in areas where A(H5N1) virus is circulating in animals,5 a detailed history can help narrow clinical suspicion for A(H5N1) virus infection. Before the appointment, clinic staff could consider conducting a prescreening interview to obtain a thorough exposure history.9,18 This history can include information about environmental exposures (eg, do owners work on a dairy farm or with domestic poultry, live on a farm, own a backyard flock) animal exposures (eg, unsupervised outdoor access, hunting wild birds or other animals, contact with farm animals), and dietary risk factors (consumption of raw meat, commercially produced raw pet food, or raw milk).
Protect clinic staff
If there is clinical suspicion for A(H5N1) in a sick cat, implementing infection prevention and control measures can help protect veterinary healthcare workers.18,20 These include, when possible, conducting exams in an isolation room to prevent contamination of other clinic areas and limiting the number of staff interacting with the cat. Personal protective equipment (PPE) use will depend on exposure level (high, medium, low). When interacting with or handling a potentially A(H5N1) virus–infected cat (high exposure), staff are advised to wear a National Institute for Occupational Safety and Health–approved particulate respirator (requires prior fit-testing), fluid resistant gowns (single-use disposable or reusable cloth gowns, or laboratory coats that are laundered after contact with the patient), eye protection, disposable gloves, shoe covers or dedicated footwear, and hair/head cover (Figure 1).18,20,21 It is recommended that clinical staff adhere to proper hand-washing protocols20–22 after touching a potentially infected cat, or contaminated equipment or surfaces18 and disinfect contaminated surfaces after use.20 Staff that do not have contact with potentially infected animals (low exposure) do not have to wear PPE.
Since there is limited information on the potential transmission of A(H5N1) viruses from cats to humans, it is suggested that sick cats be isolated from people and other animals until a negative real-time reverse transcription–PCR test result for influenza A(H5N1) is returned or until resolution of clinical signs.18 During this time, it is important for clinical staff to understand how to properly don and doff PPE, which may require refresher training.20,21
Contact public health and animal health officials
When there is clinical suspicion of A(H5N1) in a cat, veterinarians should contact their state or local public health officials or state public health veterinarian.18 While the decision to isolate a cat potentially infected with A(H5N1) virus at home or at a veterinary clinic should be made by the veterinarian and cat owner, local public health and animal health officials may have additional protocols for isolating, testing, and managing of A(H5N1) virus–infected animals as well as monitoring of exposed persons.
Guidance from the CDC recommends that all persons exposed to an animal infected with A(H5N1) viruses self-monitor their health for signs and symptoms of A(H5N1) virus infection up to 10 days after the last known exposure.23 They can contact their health-care provider and designated state or local public health official if they develop any clinical signs or symptoms (eg, acute respiratory illness and/or conjunctivitis)23 to discuss testing and treatment options for people exposed to confirmed A(H5N1) virus–infected animals. The CDC currently recommends antiviral treatment with oseltamivir for symptomatic persons who are confirmed, probable, or suspected cases of novel influenza A virus infection associated with severe human disease such as A(H5N1) virus infection.24 Oseltamivir for post-exposure prophylaxis using treatment dosing (twice daily for 5 days) as soon as possible can be considered for persons exposed to sick cats confirmed or suspected with A(H5N1) virus infection.25 Additionally, persons who are symptomatic should stay home and limit contact with others until the test results are known.23
Educate owners
Veterinarians may consider educating cat owners about the potential exposure risks for A(H5N1) viruses. Strategies such as keeping cats indoors and discouraging consumption of raw milk, raw meats, and commercially produced raw pet foods, can reduce risk.18 When A(H5N1) virus infection is suspected, veterinarians should consider providing information on safe handling of cats and suggest that owners contact their public health department for more information on self-monitoring of their symptoms.18
Implementing the One Health19 approach in veterinary clinics can protect both humans and animals. The CDC provides recommendations to protect veterinary staff managing cats exposed to A(H5N1) virus, emphasizing the importance of considering influenza A(H5N1) virus infection in the differential diagnosis, implementing infection prevention and control protocols, and using proper PPE by veterinarians and clinic staff.18 Given the potential transmission risk, veterinarians should remain cautious when interacting with cats potentially infected with A(H5N1) viruses.
Acknowledgments
The authors would like to thank Reid Harvey and Alice Shumate for their thoughtful discussions around worker safety within a veterinary practice.
Since its arrival in late 2021, the amount of HPAI H5 virus in the environment has sharply increased during the fall and winter, making now a good time to think about how you will protect your companion animals (dogs and cats) during the months ahead.Disclosures
The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the CDC.
The CDC offers the following advice to pet owners on how they may keep their animals safe from avian flu, and what to do if they suspect infection.
While cat-to-human transmission of influenza viruses has only rarely been documented, HPAI H5 continues to exceed our expectations, and we should treat it as an evolving threat.
