Clinical

H5N1 updates and how to stay safe in your practice

AAHA will be hosting an upcoming webinar and sharing bimonthly updates about the H5N1 outbreak. Let us know what information is most helpful to include for your daily work in practice by filling out this form.

Terra Kelly, DVM, PhD, Dipl. ACZM, Carrie McNeil, DVM, MPH

Published Feb 21, 2025

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CDC recommendations

The CDC is recommending veterinary practitioners wear PPE when seeing cats with respiratory or neurologic signs in the 20 February 2024 MMWR. This report described two cats with clinical signs of and who tested positive for HPAI H5N1 with no known direct exposure to HPAI H5N1 infected farms but with potential indirect exposure via their owners who were dairy workers.

The piece also highlighted the importance of removing potentially H5N1 contaminated clothing prior to re-entering a household environment due to fomite risks. The authors also noted that while cat-to-human transmission has not been documented yet in this outbreak, suspected cat-to-human transmission of a low pathogenic H7N2 influenza virus in an animal shelter in 2016 suggests that contact with feline H5N1 cases could present a potential transmission risk to humans.

What can you do?

Strengthen surveillance and early detection

Remain vigilant for clinical signs of H5N1 in domestic animals, particularly cats, dogs, livestock–including backyard chickens, and wildlife patients.
Report suspected cases promptly to state animal health officials.
Encourage testing in high-risk settings, including farms, wildlife rehabilitation organizations, and households with sick animals that may have had contact with infected wildlife.

Enhance biosecurity measures

Advise clients on reducing exposure risks, including keeping cats indoors (away from livestock, poultry, and their environments and from sick or dead birds); preventing pets from scavenging wild bird carcasses and eating unpasteurized dairy products and uncooked meat-based foods and treats (including commercial raw and freeze-dried raw pet foods); implementing biosecurity protocols for backyard chickens; and washing hands and changing clothing (including footwear) after handling livestock, poultry, wild birds, and bird feeders. If cats can’t be kept indoors, considering use of bells on collars or removal of bird feeders may help in reduction of possible exposure.
Develop practice protocols for managing suspected cases, including isolation procedures, diagnostic testing, and official reporting to state authorities.
Use appropriate PPE when handling sick or deceased animals suspected of H5N1 infection or cats who may have been exposed to H5N1 to reduce the likelihood of human and animal exposure. The Centers for Disease Prevention and Control (CDC) provides guidance on PPE, including coveralls/ gowns, N-95 masks, goggles/face shields, boots or boot covers, a head covering, and gloves. Bring extra scrubs or clothes to work to change into after possible contamination to reduce risk of bringing home fomites.
The CDC also recommends that that veterinary professionals obtain occupational information from members of the household with animals suspected of H5N1 infection to help prevent unprotected exposures and inform public health investigations of potential animal-to-human transmission of HPAI A(H5N1) virus.

Educate and communicate risks

Provide science-based guidance to clients about the risks of H5N1 transmission in pets, livestock, and wildlife.
Understand who is at risk by keeping updated on information from the CDC and other public health agency sources. According to the CDC, individuals who work closely with domestic or wild animals (farmers or backyard poultry owners, veterinarians and animal care workers, and animal health responders) are at increased risk. Human health care providers are also at increased risk due to their contact with infected people.
Counter misinformation by sharing verified information from trusted sources such as the CDC, U.S. Department of Agriculture (USDA), and U.S. Geologic Survey (USGS).

Coordinate with public health and wildlife experts

Develop regular communication with local, state, and federal agencies to facilitate data sharing and coordinated response efforts.
Engage with One Health networks to facilitate a comprehensive approach to surveillance and outbreak management

Situational Update:

Species impacted:	Cases:	Where:	How is it transmitted/spread?*	What to look for:
Domestic cats	> 88 in U.S. since 2022	18 states: CA, CO, ID, IO, KS, LA, MI, MN, MO, NE, NM, OH, OK, OR, SD, TX, UT, WY	•Eating infected birds & rodents •Eating raw meat or poultry products/ commercial pet food or unpasteurized milk •Contact with infected cattle/poultry and their contaminated environments •Contact with infected people or contaminated clothing	•Anorexia •Lethargy •Fever •Oculonasal discharge •Difficulty breathing •Neurologic signs (ataxia, circling, tremors, seizures, blindness). •Can be rapidly fatal (up to 70% of infected cats die of their infections); however, serosurveys have reported antibodies to H5 viruses in ~12% of apparently healthy stray cats
Dogs (companion)	0 in U.S.	Thailand, Canada Washington study detected H5 and N1 antibodies in 2% of hunting dogs Thailand serosurvey found antibodies in 25% of stray dogs	•Eating infected birds	•Rare, mild disease to fatal infections •Anorexia •Fever •Conjunctivitis •Cough •Difficulty breathing
Poultry (includes backyard chickens and ducks)	> 160 million in U.S. since 2022	50 states & Puerto Rico (commercial and backyard flocks and live bird markets)	•Contact with infected poultry or wild birds •Contact with contaminated equipment •Contact with infected people or contaminated clothing •Poultry trade promotes spread	•Acute mortality •Respiratory signs (sneezing, coughing, oculonasal discharge) •Edema of the face and cyanosis of combs and wattles •Diarrhea •Skin hemorrhages •Decrease in egg production •Neurological signs (tremors, stargazing, paralyzed wings)
Cattle	> 970 herds since first detection in 2024	17 states: AZ, CA, CO, ID, IO, KS, MI, MN, OH, OK, NV, NM, NC, SD, UT, TX, WY	•Contact with infected animals •Contact with contaminated milking equipment and clothing (large amounts of virus shed in the milk) •Exposure to infected wild birds (Nevada and Arizona)**	•Many subclinical or mild infections (unlike poultry) making detection difficult •Thickened, abnormal milk •Loss of appetite •Lethargy •Low-grade fever •Mild respiratory signs •Diarrhea (less common)
Wildlife	> 500 species globally (485 avian and 48 mammalian species) U.S. wildlife cases are reported by the USDA and U.S. Geological Survey	50 states	•Consumption of sick prey (mammals and birds) •Direct transmission & contact with contaminated environments (including virus in water) for wild avian flocks •Rare reports of transmission between wild mammals	Clinical signs in sick wildlife are variable, but generally include neurologic and respiratory signs. Sick wild birds can have: •Eye swelling •Change in color of iris •Respiratory signs (sneezing, coughing, oculonasal discharge) •Gastrointestinal signs (diarrhea) •Neurologic signs (tremors/seizures) The most common clinical signs in sick wild mammals are: •Neurologic signs (tremors/seizures and ataxia) •Respiratory signs (nasal and ocular discharge and dyspnea)
People	70 cases in the U.S. in the past year	13 states: CA, CO, IO, LA, MI, MO, NV, OH, OR, TX, WA, WI, WY	•No sustained human-human transmission •Contact with sick cattle & poultry •One North American fatality had genotype primarily found in wild birds •CDC study detected H5N1 antibodies in 2% (3/150) of bovine veterinary practitioners	•Conjunctivitis •Fever •Cough •Sore throat •Runny or stuffy nose •Muscle aches •Fatigue •Shortness of breath or difficulty breathing •GI signs (diarrhea, nausea, vomiting - less common) •Seizures (less common)

* Information on modes of transmission are suspected or verified based on reported evidence for each species. In general, avian influenza viruses can be transmitted through direct contact, indirect contact (e.g., contaminated surfaces), and inhalation.

**The HPAI virus initially detected in dairy cattle, H5N1 clade 2.3.4.4b genotype B3.13, was the only strain known to infect dairy cattle. However, in early 2025, two spillover events involving a different genotype circulating in migratory birds, D1.1, occurred in dairy cattle in Nevada and Arizona. Ongoing new introductions will complicate efforts to control the virus in dairy cattle, underscoring the importance of robust surveillance and prevention measures.

View all the links used in the above table here.