Avian Influenza A(H5) Outbreak
Current US Outbreak
As of March 13, 2025
Critical Updates:
- The rare PB2 E627K mutation, which allows for more efficient transmission in humans, has been detected in dairy cows. San Bernardino County cattle are the suspected source. This detection raises alarms that H5N1 has become more adapted to humans and may be more likely to spread via human-to-human transmission, although this has not yet been reported.
- Experts from Harvard Medical School-led Massachusetts Consortium on Pathogen Readiness and Johns Hopkins University join the growing number of experts warning to prepare the potential of an H5N1 pandemic.
- Critical activities needed include: enhancing the National Milk Testing Strategy, improving data sharing, increasing public and worker awareness through product labels and engagement strategies, rapid testing development and deployment, and improved testing and research
- Arcturus, a San Diego biotechnology company, reports continuing to plan their phase 1 clinical trial for an H5N1 mRNA vaccine funded by the Biomedical Advanced Research and Development Authority (BARDA), despite a similar H5N1 mRNA contract between Moderna and BARDA for their phase 3 clinical trial being under review by the federal government. Continued progress with clinical trials for mRNA vaccines is an essential aspect of H5N1 preparedness.
- The National Governors Association published a commentary on H5N1 Emergency Preparedness and Response, highlighting the current CORI risk assessment and the work of state health departments who had responded to H5N1 in their jurisdiction.
Routine Surveillance Updates
- The Centers for Disease Control and Prevention (CDC) is reporting 70 confirmed human cases of H5 in the United States Outbreak as of March 13, 2025 (Figure 1). For the duration of the outbreak, there have been three cases that have not had a known source of infection and reported no contact with animals or raw milk, while 24 have had contact with poultry, 43 have had contact with dairy cows, and two have had exposure to a backyard flock.
- CDC reports that for the duration of the outbreak, 217 tests have been conducted for individuals with exposure to dairy cows, and 620 tests have been conducted for individuals exposed to birds and other animals, resulting in a positivity rate of 18.89% (41/217), 3.87% (24/620) respectively, since March 2024.
- Commercial and wild birds continue to be gravely impacted by H5N1, with 31 commercial flocks and 52 backyard flocks affected in the last 30 days.
The United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) has reported 16 new infected cattle herds from four states (CA, NV, AZ, ID) in the last 30 days, bringing the total for the outbreak to 985 cattle herds in 17 states.
Resources
Risk Assessment
Factsheet
Archived Risk Assessment
Communication Resources
H5N1 Question & Answer
Pet Owners
Question: I heard that there are house cats dying of H5N1. Should I be concerned?
Answer: Bird flu infection among cats still appears rare but infections have been fatal. In late 2024 bird flu killed 20 big cats at an animal sanctuary in Shelton Washington and at least three house cats have died from bird flu after drinking raw milk or consuming recalled raw canned cat food. For indoor cats, the best protection against bird flu is to not consume raw animal products of any kind, including commercially prepared raw meats and raw milk. Outdoor cats are at greater risk of infection through contact with wild infected birds or other infected animals, though the likelihood of infection depends on the environment and certain areas such as farms, ponds where waterfowl, and areas experiencing outbreaks in wild birds may be higher risk.
Question: I have created a "catio" (an enclosed patio made for cats to enjoy outdoor spaces). Is it safe for my cat to continue to use?
Answer: Several of the most recent cats known to be infected with H5N1 have become infected from drinking raw milk or eating raw food. Cats may also be infected by coming in close contact with infected animals or surfaces. If the “catio” is enclosed so that wild animals cannot enter, it is less likely for the cat to be exposed than if that cat is otherwise free outdoors. When using this type of space, be sure that there is no bird feeder or other source of food that could draw infected birds or mice and that the cat’s food and water remain indoors.
Question: My cat is an indoor/outdoor cat, which means they go on walks with me and have some unsupervised outdoor time. Should I still allow this time for my cat?
Answer: To limit the risk of infection, consider keeping your cat indoors. If your cat does go outdoors, whenever possible, try to limit their exposure to wild birds, backyard poultry, or waterfowl, as these are known reservoirs for H5N1.
Question: I have a dog and I’ve heard the recent news about cats being infected with H5N1. Is this something I should be concerned about?
Answer: Dogs, as well as cats, are susceptible to infection with H5N1. Although no infections in dogs have been reported by the United States Department of Agriculture for the current outbreak, Canadian health officials reported an H5N1 infection in a pet dog in Oshawa, Ontario in 2023. The dog became sick after chewing on a dead goose and later died. The strain is believed to be the same 2.3.4.4b clade that continues to circulate in wild birds, cattle, and a number of other wild and domestic mammalian species. This strain has also caused 66 infections in humans, most of which have had contact with infected animals. To keep your dog(s) safe, it is important not to feed them raw food (e.g., meat, eggs, etc.) and to keep them away from wild birds. If your dog spends time outside off leash in areas where waterfowls or other wildlife gather (e.g., lakes, ponds), closely supervise them to ensure they are not coming in contact with bird feces or other animal products (bones, flesh, etc.).
Backyard Flock Owners
I have a backyard flock/small backyard coup of chickens. Is there anything I should be doing to protect my animals, my family, or myself?
Be sure to protect your flock/birds from contact with wild birds and rodents. You can do this by covering the tops of chicken coops and securing food and water bins. You can also protect yourself and your family by wearing boot covers, gloves, and even masks when accessing the backyard flock. If you notice birds are dying suddenly and without another known cause, contact your state health agency.
Friends of Farmers
Is it safe to consume eggs I'm offered from local farmers or neighbors with backyard chickens?
Eggs are safe to consume as long as they are cooked to an internal temperature of 165°F. According to the FDA, this means that both the egg whites and the yellow center should be firm and that scrambled eggs should not be runny. Eggs should be properly cooked when consumed by humans as well as pets. As always, it is also important to wash your hands thoroughly after touching or cooking with raw eggs, including when touching the eggshell. It is also important to thoroughly clean workspaces and utensils that have touched raw eggs with soap and hot water.
Hunters and Bird Enthusiasts
Question: I hunt wild birds and other animals. Are there any additional precautions I should take?
Answer: In the current outbreak in the US, hunting wildlife has not been associated with any infections, however there are certain precautions you can take to protect yourself and your family from H5N1 currently circulating in wild animals. H5N1 infections in birds is widespread and have been observed in other wild animals such as opossums, bears, skunks, and even marine wildlife. Foxes are also believed to be susceptible to the virus, and wild animals that consume birds as part of their diet may be at a greater risk of infection in general. When hunting, it is important not to touch animals that are already dead. If you come across large groups of dead birds or other animals, you can help your community by reporting it to your state health agency. When handling animals that you have killed, consider that some animals can be infected with H5N1 or other disease and not exhibit symptoms; therefore, it is important to package animal meat appropriately and wash your hands after touching any carcasses or raw meat.
Question: I have a bird feeder at my house and like to feed local birds at the park. Are there any additional precautions I should take?
Answer: Songbirds, the types of birds that are most often attracted to bird feeders, are much less likely than waterfowl (ducks, geese, swans, etc) to contract avian influenza and less likely to shed large amounts of virus, meaning they do not transmit the disease easily. As a result, there is no recommendation to take down bird feeders unless you also take care of poultry. It is still important to routinely clean bird feeders or bird baths to reduce the risk of infection from other types of infections. Conversely, feeding birds directly (eg throwing breadcrumbs or seeds) at ponds or other areas where waterfowl gather may be a higher risk activity as waterfowl are known to carry the H5N1 infection and can be ill without showing symptoms.