AVIAN INFLUENZA VIRUS
CSU laboratory is tracking the disease as it spikes in housecats
Sept. 23, 2025
A highly pathogenic form of avian influenza virus, or bird flu, was first detected in wild birds in the United States in early 2022, and it became a concern among consumers as commercial poultry flocks were stricken across the country, leading to a scarcity of eggs and high prices for those available.
The virus didn’t stop there: It sickened dairy cattle nationwide – and, in some cases, crossed species to afflict dairy workers. In this instance, consumers were spared because pasteurization kills potentially harmful microbes in milk.
Yet, detection work continues with avian influenza virus, as, most recently, it has caused increasing illness in pet cats.
Colorado State University’s Veterinary Diagnostic Laboratories plays a key role in nationwide testing and monitoring to protect animal and human health. In recent months, the lab has run as many as 600 bird flu tests per day on samples from birds, cattle, cats, and other species. Understanding how disease affects wild and domestic animals is a mission of the lab in Fort Collins, and the information it gleans is essential for animal and public health officials, food-animal producers, and others who work to halt the spread of disease and curb potential impacts to human health.
The lab works closely with state and federal agencies and is part of the U.S. Department of Agriculture’s National Animal Health Laboratory Network, a collection of 65 public veterinary labs across the country charged with collaborating to monitor disease.
Avian influenza viruses have been detected for decades in wild waterfowl and shorebirds, such as ducks and geese. These birds are considered the “reservoir species” for the virus, hosts that harbor and transmit the pathogen. Some influenza viruses can spill over and infect other populations. The current virus, scientifically known as H5N1 clade 2.3.4.4b, can infect wild birds, domestic poultry, and mammals, including humans.
The Centers for Disease Control and Prevention has reported 70 cases in humans, including one death, the result of people interacting with infected animals. There is no known person-to-person spread at this time, and the current public health risk is low, according to the CDC.
Dr. Kristy Pabilonia, executive director of CSU’s Veterinary Diagnostic Laboratories, recently discussed highly pathogenic avian influenza virus. She is a microbiologist, a veterinarian, and an expert on poultry diseases, including avian influenza viruses.
Dr. Kristy Pabilonia, executive director of CSU’s Veterinary Diagnostic Laboratories.
What species is your laboratory detecting the virus in?
Since early 2022, we’ve detected highly pathogenic avian influenza virus, or HPAIV, in many species. We’ve detected outbreaks in commercial poultry and backyard poultry flocks, dairy cattle, domestic pet cats, wild birds, and a variety of wild mammal species, including mountain lions, foxes, mice, and many others. Recently, we’ve had many positive tests on wild raptor birds, and our number of pet cat positives continues to increase. Luckily, we have not detected HPAIV in Colorado cattle for many months, due to the hard work of our state and federal partners and the dairy producers.
How high is the mortality rate in birds?
It depends on the bird species. We know that, traditionally, wild birds are the reservoir of influenza viruses. As a reservoir, they will get infected and shed the virus into different environments, but they typically don’t show clinical signs of disease. The currently circulating avian influenza virus is different. One of the reasons this is such a pesky virus is that it does kill wild birds, depending on the species. Certain birds are more susceptible, and in some species, you can see really large mortality events. In Colorado, we have experienced large mortality events in some wild bird populations, such as snow geese.
This version of the virus has been around for a while. When the virus was detected in cattle, was that the moment when people started paying more attention?
The broader public tends to pay closer attention when there is something new or unexpected, like detection of the virus in a new species, but veterinarians, scientists, and state and federal officials are fighting to control spread of influenza viruses all the time.
What do you see as the most recent significant avian influenza event here in Colorado?
Every detection is meaningful and important. Our job is really impactful because it provides state and federal officials with the information they need to know where the virus is so they can respond. Our laboratory always works to support animal producers and protect the U.S. food supply. In Colorado, we’ve detected quite a lot of cat positives, and the numbers have been increasing. That’s been one of our focuses.
How common is it for this virus to infect cats in a significant way?
We’ve known for many years that cats can be infected with influenza viruses. In Colorado, we’ve detected HPAIV in wild and captive large cats, such as mountain lions, tigers, and domestic pet cats. This is really concerning because those are people’s pets. We also know that preventing cases in pets can prevent cases in their human owners.
We know dogs are also susceptible to influenza viruses, but we’ve had very few detections of avian influenza globally in domestic dogs. There are many scientists studying the differences in susceptibility that we see in different species. We are hopeful that our work in rapid detection of the virus will prevent as much spread as possible to people’s pets.
What are the symptoms for cats?
Early in the outbreak, all the samples we received were from cats with severe neurologic disease, causing incoordination and an inability to walk. More recently, we’ve been detecting HPAIV in cats that have had more mild clinical signs, and a couple of cases where cats have been sick but have survived. The course of disease in an individual cat may be dependent on their original infectious dose and their route of exposure. I’m very interested in studying more about this.
Your lab recently detected avian influenza in a cat that consumed raw pet food. What should pet owners know about this?
Our laboratory has detected the virus in cats that live on dairies, cats that have consumed raw milk, cats that have scavenged on dead birds, and we’ve even had some cats with no known exposure. It’s very interesting that we are seeing cats exposed to the virus by so many different routes. Our recent detection of a positive cat that ate raw pet food is very important because it gives us information that we can pass along to pet owners. It is really important that cat owners do not feed their cats raw pet food or raw dairy products. They should also minimize their cat’s exposure to any wild birds.
With domestic cats, when should testing for HPAIV be considered?
If cats have neurologic symptoms, we always recommend testing for rabies. Now, we recommend also testing for avian influenza. If you have a cat with neurologic disease, unexplained respiratory disease, or an unexplained severe illness, particularly if it’s consumed raw pet food or raw milk, or has had contact with a dairy, or contact with wild birds, these could all be reasons to get influenza testing. We recommend you talk to your veterinarian.
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