Avian influenza

Early recognition of avian influenza is important to stopping its spread.

Birds

Poultry with LPAI may have no signs at all, or they may have mild respiratory signs (e.g., nasal discharge or sneezing), decreased feed consumption, ruffled feathers, and decreased egg production.

Poultry with HPAI—and possibly pet birds—may have one or more of the following signs:

• Sudden death with no prior signs
• Low energy or appetite
• Purple discoloration or swelling of various body parts
• Hemorrhages on un-feathered parts of the legs or feet
• Decreased egg production, or soft-shelled/misshaped eggs
• Nasal discharge, coughing, or sneezing
• Lack of coordination
• Diarrhea
• Death

Companion animals

Clinical signs of HPAI in cats are better known than in dogs. Signs in either species may include the following:

• Fever
• Lethargy
• Inappetence
• Conjunctivitis
• Copious oculonasal discharge
• Dyspnea
• Neurologic signs (e.g., tremors, seizures, ataxia, or blindness)
• Death

In cats, the disease typically has been severe, with a high mortality rate. Because several of these signs are often encountered with common respiratory diseases of cats and dogs, laboratory confirmation of HPAI infection is necessary for a definitive diagnosis.

It would be prudent to consider HPAI infection on your list of differential diagnoses for dogs or cats with respiratory and/or neurologic signs with known exposure to infected animals or a recent history of exposure to or ingestion of dead birds or raw cow’s milk or colostrum. 

Avian influenza is most often spread by direct contact between infected birds and healthy birds. It may also be spread indirectly through contact with contaminated equipment and with biological secretions and/or excretions from infected birds. The virus can be found in secretions from the nares, mouth, and eyes of infected birds and in their excrement.

Contact with excrement from infected birds is the most common means of bird-to-bird transmission, although airborne secretions are another important mode of transmission, especially within poultry houses. Excrement from wild ducks can introduce avian influenza into domestic flocks raised on ranges or in open flight pens.

Transmission between poultry facilities

Spread of avian influenza between poultry facilities has almost always been attributed to the movement of infected birds or contaminated people and equipment (including clothing, boots, and vehicles). Both outdoor and indoor flocks are susceptible. Airborne transmission of avian influenza virus from farm to farm is highly unlikely because the virus cannot travel long distances through the air, and it is susceptible to the effects of sunlight and drying.

Transmission to other bird populations

Even though HPAI has been detected in the United States other bird populations that are housed indoors continue to have a very low risk of becoming infected. Birds housed outdoors, however, risk exposure to the virus, with numerous cases of HPAI reported in backyard flocks in the United States. Outdoor pet birds and birds kept in zoos or captive wildlife facilities are also at risk. These birds need to be protected from contact with wild migratory birds (especially waterfowl and shorebirds), their excrement, and water frequented by waterfowl and shorebirds. If pet birds become infected, they may be able to spread the virus.

Transmission to other animals

Certain mammalian species—including cats and dogs—may become infected if they eat sick or dead infected birds, as might occur when outdoors in an area experiencing an outbreak. The risk of mammal-to-mammal transmission, even with close contact, is considered low in most situations, but not zero. A noteworthy exception is the 2024 outbreak of H5N1 infection among U.S. dairy cattle herds, involving bovine-to-bovine and bovine-to-cat spread. Evidence is growing that milk is a major transmission route in these cases, as may occur when inadequately sanitized milking equipment is shared among cows or cats are fed raw milk or colostrum. There also is evidence that the virus can spread from dairy cattle premises into nearby poultry premises.

Transmission to people

HPAI viruses can spread from birds to people as a result of extensive direct contact with infected birds, such as during home slaughter or defeathering of infected poultry. Public health concerns center around the potential for the virus to mutate or combine with other influenza viruses to a form a new strain that could easily spread from person to person. Still, there is no evidence that this has happened yet when it comes to HPAI, and the U.S. Centers for Disease Control and Prevention (CDC) currently considers the public health risk low. The subtypes of HPAI associated with the majority of avian influenza infections in people worldwide are H5N1 and H7N9.

Although people may become infected through exposure to birds with HPAI, this happens only occasionally, and typically involves close or prolonged, unprotected exposure to infected poultry. The risk of people catching the virus from infected mammals—including from other people—is considered extremely low in most cases. However, with the 2024 outbreak of H5N1 infection in dairy cattle, some dairy farm workers have developed mild signs of infection.  

The risk posed to veterinarians and other veterinary personnel by caring for animals with HPAI infection is unknown, but not negligible. In general, close, prolonged contact equates to increased risk.

Animal and human health authorities worldwide monitor avian influenza viruses for their potential to infect humans. The CDC and the World Health Organization provide information on avian influenza in people. So far, there’s no indication that HPAI viruses can be transmitted person to person.

BIRDS

Various tests and strategies are used to screen for avian influenza or confirm its presence in poultry species. These tests include antigen capture immunoassay (ACIA), direct RNA detection with molecular methods, and virus isolation. Consult your state animal health official to determine which test is preferred given the circumstances you’ve encountered.

ACIA: Rapid ACIA test kits are available from various commercial sources. These tests can be effective flock-based screening tools, as they have lower sensitivity than molecular assays but are highly specific for avian influenza when used for testing of clinically ill or dead birds. In areas with no known outbreaks, positive results must be confirmed by molecular methods. In areas with outbreaks, both positive results—and negative results for birds with clinical signs—must be molecularly confirmed per APHIS’s Veterinary Services Guidance 12001. Positive samples will be sent to the USDA’s National Veterinary Services Laboratories (NVSL) to determine the viral subtype and pathotype.

Direct RNA detection: This molecular method involves real-time reverse transcriptase polymerase chain reaction (rRT-PCR) to first detect influenza A and H5/H7 subtypes in biological specimens. Then, either sequencing is performed to determine the subtype and pathotype of the virus, OR virus isolation is performed with antigenic and/or molecular characterization. Tests are performed by all National Animal Health Laboratory Network (NAHLN) laboratories and other veterinary laboratories approved by the USDA’s NVSL.

Virus isolation: Many NAHLN laboratories perform virus isolation as well. Sequencing methods and in vivo testing are then used to characterize isolated virus where indicated. A substantial drawback to virus isolation is the delay in obtaining the results and the requirement for strict biocontainment during sample collection.

Both virus isolation and rRT-PCR can be applied, with caution, to specimens from non-poultry species. The rRT-PCR testing performed by NAHLN laboratories is specific for all influenza A viruses, and then further testing is performed for important subtypes. This test would be expected to detect infection in any species that is actively shedding virus. Test results can be available in as little as a half day (12 hours), and the USDA has indicated that the results of rapid screening can be expected within 4 to 7 hours after specimens are received by the NVSL.

View a directory of NAHLN laboratories and a Fact Sheet from the USDA on diagnostic tests for avian influenza in birds.

The types of specimens needed for detection or confirmation of HPAI depend on the bird species and situation. The USDA provides recommendations on this, although you’re encouraged to consult your state animal health official for specific advice. In some cases, necropsy of dead or euthanized birds may be advised to determine whether a bird or flock has HPAI. In others, certain swab samples may be recommended. If HPAI is suspected, necropsy is best performed at an NAHLN facility. Contact the facility before submitting any birds for necropsy.

NON-HUMAN MAMMALS

In the absence of formal protocols developed and recommended by such regulatory agencies, if a non-human mammal is suspected to have HPAI, it may be appropriate to submit samples to at least one NAHLN laboratory for preliminary diagnosis—before recommending euthanasia, particularly for companion animals (including pet birds). View the USDA’s testing guidance for influenza A in livestock, wildlife, and companion animal species. View the USDA’s testing guidance for influenza A in livestock, wildlife, and companion animal species. Contact your state animal health official for more information.

Treating HPAI in animals

If an animal is exhibiting clinical signs suggestive of HPAI, contact appropriate federal and state authorities before you initiate any treatment. Should a commercial poultry flock be affected, immediately quarantine the premises and birds, and limit exposure to birds, until regulatory officials can respond or direct you on an appropriate course of action.

Recovery of poultry from HPAI is extremely rare. Infected poultry typically are euthanized and poultry products destroyed when HPAI infection is confirmed. The outcome also may be influenced by the producer’s participation in secure food supply plans. If regulatory officials authorize you to treat, keep in mind that the FDA prohibits extralabel use of adamantine and neuraminidase inhibitor classes of antiviral drugs in chickens, turkeys, and ducks.

For cats and dogs, treatment typically needs to be started before HPAI has been confirmed, as other diseases may cause similar clinical signs. The recommended treatment approach is generally one of supportive care. No specific antiviral agents are available for cats or dogs with HPAI, and drugs used to treat humans with influenza (e.g., neuraminidase inhibitors such as zanavimir or oseltamivir) have not been adequately evaluated in pets.

Biosecurity is the first line of defense against transmission of avian influenza to birds, including companion birds and commercial and backyard poultry, and to cattle. Early detection allows actions to be taken quickly to protect poultry and cattle, and prevent infections from spreading.

What to do if you suspect avian influenza

When it comes to birds, two general scenarios are common when it comes to suspicions of avian influenza.

If the primary veterinarian suspects the disease due to the signalment/clinical signs and contacts their state animal health official (SAHO) or APHIS veterinarian in charge (AVIC), then the SAHO or AVIC will then determine next steps:

• If this is the first case in the state, they will send out a foreign animal disease diagnostician to investigate and collect and submit samples to the appropriate laboratories.
• If this is not the first case, the SAHO or AVIC may instruct you on how to properly collect and submit samples, including where to send them for testing.

If the primary veterinarian does not initially suspect avian influenza, but submits routine samples to the laboratory of their choice, the test results may lead to suspicion of avian influenza by the laboratory and/or veterinarian. In this case, the primary veterinarian or laboratory contacts the SAHO or AVIC, who then determines next steps as indicated for the first scenario.

If you suspect a bird of any kind has avian influenza, immediately contact your state animal health official. If directed to collect samples, be sure to take appropriate precautions to protect yourself and others.

If a commercial poultry flock is affected, the premises and bird(s) need to be immediately quarantined, and exposure to birds limited, until regulatory officials can respond or direct the veterinarian regarding an appropriate course of action. If HPAI—or LPAI—is confirmed at a poultry farm, federal and state animal health officials will respond to the disease. Visit the USDA’s website for details on what that response involves.

Contact a NAHLN laboratory for specific, up-to-date information on the appropriate collection and submission of samples and carcasses. View AVMA’s webpage describing training and other requirements for shipping biological specimens. Also visit the USDA’s webpage for other HPAI resources.

For information on what to do for cattle with suspected HPAI infection, view the AVMA’s webpage on H5N1 in U.S. dairy cattle.

See more information on what to do for cattle with suspected HPAI infection.

Precautions to protect veterinarians and other animal care workers

When animals are suspected of having HPAI infection, it’s important that veterinarians and others handling those animals take steps to minimize the risk of becoming infected themselves. Read up on the CDC’s recommendations to reduce the risk of infection for people working with or exposed to infected animals, and for veterinarians and other veterinary personnel evaluating or handling cats with potential viral exposure. View National Animal Health Emergency Management System Guidance on personal protective equipment related to zoonotic diseases, and the veterinary infection control guidelines issued by the National Association of State Public Health Veterinarians.

Birds brought to veterinary clinics

Owners may bring backyard birds with suspected HPAI to companion animal or mixed animal clinics. When this happens, certain precautions can help protect people and other animals:

• Take the bird to an examination or isolation room, or examine it outside the clinic.
• Perform all treatments and diagnostics there.
• Limit staff access to the bird.
• Use personal protective equipment (gown, gloves, face shield or safety goggles, and N95 respirator—or, if unavailable, surgical mask—and disposable head/hair cover).
• Practice hand hygiene after glove removal.
• Clean and disinfect contaminated surfaces.
• Disinfect items that cannot be disposed of.
• Report the case to the USDA and state authorities, who may direct you to collect samples for testing.
• Consult with state or local health officials on how to dispose of contaminated waste. Ensure that wild animals can’t access the waste.
• Recommend to the owner that the bird, and any other animals that might have had contact with it, be quarantined when returned home.

Companion animals

While you’re awaiting test results, animals suspected of having HPAI need to be quarantined. Family members, pets, and other animals that may have been exposed should be monitored for signs of illness. Animal owners and veterinary staff need to be made aware of risks to themselves and other individuals with whom the animal may have come in contact.