Avian Influenza

TL;DR. Avian influenza is a highly contagious, legally reportable viral disease of birds that causes severe respiratory, digestive, and neurological damage, frequently resulting in sudden death.

Strict biosecurity, including covered enclosures, is the most effective way to protect domestic birds from wild bird transmission.

What is it?

Avian influenza, commonly known as bird flu or fowl plague, is a highly contagious viral infection caused by Influenza A viruses. This virus can infect virtually all species of birds, including domestic poultry (such as chickens, turkeys, and ducks), wild waterfowl, and companion pet birds (such as parrots, finches, and cockatiels). Because the virus is highly adaptable and capable of mutating rapidly, it represents one of the most significant infectious disease threats to avian populations worldwide.

Veterinarians and regulatory agencies categorize avian influenza into two distinct forms based on how severely the virus affects domestic poultry:

• Low Pathogenic Avian Influenza (LPAI): These strains typically cause mild disease. Affected birds may show subtle respiratory signs, a temporary drop in egg production, or ruffled feathers. While LPAI is less severe, some strains (specifically those in the H5 and H7 subtypes) have the ability to mutate into the highly destructive highly pathogenic form.
• Highly Pathogenic Avian Influenza (HPAI): These strains cause severe, systemic disease with extremely high mortality rates, often approaching 100% within 24 to 48 hours. HPAI viruses replicate rapidly throughout multiple organ systems, causing widespread vascular damage, internal bleeding, and organ failure.

Because avian influenza is a zoonotic disease—meaning it can, in rare instances, be transmitted from birds to humans—and because it poses a massive threat to the global food supply, it is a strictly regulated disease. Any suspected case must be reported immediately to state or national veterinary authorities.

Causes & risk factors

Avian influenza is caused by Influenza A viruses, which are classified into subtypes based on two proteins on the surface of the virus: hemagglutinin (H) and neuraminidase (N).

Wild waterfowl (such as ducks, geese, and swans) and shorebirds are the natural reservoirs for these viruses. These wild species can carry and shed the virus in their saliva, nasal secretions, and feces without showing any outward signs of illness.

Transmission to domestic or pet birds occurs through several pathways:

• Direct Contact: Healthy birds coming into contact with infected birds or their secretions.
• Indirect Contact (Fomites): The virus is highly resilient in the environment. It can easily be carried into a bird's environment on contaminated shoes, clothing, equipment, feed, water, or the hands of caretakers.
• Aerosol Transmission: Close-range inhalation of viral particles coughed or sneezed into the air by infected birds.

There are no specific breed predispositions for avian influenza, as the virus is capable of infecting any avian species. However, susceptibility and the severity of clinical signs vary significantly by species. Domestic poultry like chickens and turkeys are highly susceptible to HPAI and experience rapid, devastating mortality. Waterfowl may tolerate infection better but still shed massive quantities of the virus. Companion birds kept outdoors or in aviaries with open tops are at an exceptionally high risk if wild birds can fly overhead and defecate into their enclosures.

Signs to watch for

The clinical signs of avian influenza can appear suddenly and progress with devastating speed, particularly in cases of Highly Pathogenic Avian Influenza (HPAI). Because companion birds often mask signs of illness until they are critically ill, any change in behavior must be treated with urgency.

• Sudden death (Cardinal): Often, the very first sign of HPAI is the sudden, unexplained death of one or multiple birds without any prior signs of illness.
• Dyspnea / Difficulty breathing (Common): Birds may breathe with an open beak, stretch their necks out to inhale, or exhibit rapid, labored chest movements.
• Nasal discharge (Common): Clear to mucoid discharge from the nostrils (nares), sometimes accompanied by coughing, sneezing, or wet-sounding respiration.
• Cyanosis of the comb and wattles (Common): In poultry, the comb, wattles, and skin of the head may turn a distinct blue, purple, or dark red color due to a lack of oxygen and systemic vascular damage. Swelling (edema) of the head, eyelids, comb, and wattles is also common.
• Neurological signs (Occasional): The virus can cross the blood-brain barrier, leading to tremors, twisting of the neck (torticollis), loss of balance, circling, or paralysis.
• Diarrhea (Occasional): Profuse, watery, often bright green or yellow diarrhea due to gastrointestinal tract involvement.
• Systemic signs (Common): Extreme lethargy, complete loss of appetite (anorexia), ruffled feathers, and a sudden drop in egg production or the production of soft-shelled or misshapen eggs.

Dyspnea and open-mouth breathing are common, severe signs of avian influenza infection.

How vets diagnose it

Diagnosing avian influenza requires extreme caution. Because of the highly contagious nature of the virus and the strict biosecurity protocols surrounding it, your veterinarian will likely instruct you not to bring a suspected bird into a standard clinic waiting room. Instead, they will coordinate diagnostic sampling under strict quarantine conditions or refer you directly to state agricultural or wildlife diagnostic laboratories.

• RT-PCR (Reverse Transcription Polymerase Chain Reaction) [GOLD STANDARD]: This molecular test is the gold standard for diagnosing avian influenza. It detects the genetic material (RNA) of the Influenza A virus from tracheal, cloacal, or oropharyngeal swabs. RT-PCR is highly sensitive, specific, and provides rapid results, which is critical for containing an outbreak.
• Viral Isolation: This test involves inoculating embryonated chicken eggs with samples from the bird to grow and isolate the live virus. While highly definitive, it must be performed in high-security biosafety level 3 (BSL-3) laboratories and takes several days to complete.
• ELISA (Enzyme-Linked Immunosorbent Assay): This serological test detects antibodies against the influenza virus in the bird's blood. It is primarily used for screening and surveillance in flocks rather than diagnosing acute, highly pathogenic infections, as birds with HPAI often die before they can mount a detectable antibody response.

If a bird tests positive for a highly pathogenic strain or an H5/H7 subtype, the diagnosing laboratory is legally required to notify state and federal veterinary authorities immediately.

RT-PCR testing of tracheal or cloacal swabs is the gold standard for rapid, accurate diagnosis of avian influenza.

Treatment options

There are no approved antiviral drug treatments for avian influenza in birds. Because of the extreme risk of viral mutation, the potential for the virus to jump to humans, and the highly contagious nature of the disease, treatment is not legally permitted or medically recommended for birds suspected of carrying Highly Pathogenic Avian Influenza (HPAI).

Regulatory Depopulation

In almost all jurisdictions, if HPAI is confirmed in a flock (whether it is a commercial poultry farm, a backyard flock, or a collection of pet birds), agricultural authorities will mandate immediate depopulation (humane euthanasia) of all birds on the premises. This drastic measure is legally required to halt the spread of the virus to neighboring flocks, wild bird populations, and humans.

Supportive Care (LPAI Only)

In rare cases involving Low Pathogenic Avian Influenza (LPAI) in non-poultry companion birds (such as indoor-only pet parrots), and under strict quarantine guidelines dictated by local veterinary authorities, supportive care may be attempted. This is highly dependent on local regulations and requires isolation from all other birds.

• Fluid Therapy: Administering subcutaneous or intravenous fluids to support hydration.
• Nutritional Support: Tube feeding or offering highly palatable, easily digestible foods.
• Secondary Infection Control: Broad-spectrum antibiotics may be prescribed to treat or prevent secondary bacterial infections that can take advantage of the bird's compromised respiratory tract.

Prognosis

The prognosis for birds infected with Highly Pathogenic Avian Influenza (HPAI) is grave. The virus causes rapid, multi-organ failure, and mortality rates approach 100%, often within hours of the first symptom. For any birds that survive the initial viral onslaught, regulatory mandates will almost always require euthanasia to control the outbreak.

For birds infected with Low Pathogenic Avian Influenza (LPAI), the prognosis is guarded to fair. While many birds can recover from LPAI with supportive care, they may remain carriers and shed the virus into the environment for weeks. Additionally, the risk of the virus mutating into a highly pathogenic strain within a flock means that even LPAI diagnoses are met with strict quarantine and potential depopulation mandates depending on local agricultural laws.

Prevention

Because there is no treatment, prevention through strict biosecurity is the single most important tool for protecting your birds from avian influenza.

• Exclusion of Wild Birds: Keep pet birds indoors. For backyard poultry, ensure runs are completely enclosed with solid roofs and fine mesh wire to prevent wild birds, their feathers, or their droppings from entering the enclosure.
• Protect Food and Water: Store bird feed in rodent-proof, sealed containers. Never use open water sources (like ponds or rain barrels) that wild waterfowl can access to water your birds.
• Sanitation and Hygiene: Wash your hands thoroughly with soap and water before and after handling your birds. Dedicate a specific pair of boots or shoes for use only inside your bird enclosures, or use a disinfectant footbath at the entrance.
• Quarantine Protocols: Always quarantine any new birds in a completely separate building for a minimum of 30 days before introducing them to your existing birds.
• Limit Visitors: Avoid allowing visitors who own birds or work with poultry near your flock. If you visit feed stores or poultry swaps, change your clothes and shoes before returning to your own birds.

When to call your vet

Avian influenza is a veterinary emergency of the highest order. You must contact a veterinarian or your state animal health official immediately if you observe any of the following red flags:

• Sudden, unexplained death of one or more birds in your flock.
• Severe respiratory distress, such as open-mouth breathing or gasping.
• Neurological signs, including head tilting, tremors, or loss of balance.
• Swelling or blue/purple discoloration of the head, comb, or wattles.

If you suspect avian influenza, do not transport your bird to a veterinary clinic without calling ahead first. The clinic must prepare isolation protocols to prevent contaminating their facility and risking the lives of other avian patients.

Sources

• USDA Animal and Plant Health Inspection Service (APHIS) Avian Influenza Response Guidelines, pages 12-24.
• Association of Avian Veterinarians (AAV) Biosecurity and Infectious Disease Control Standards, pages 45-52.
• Standard of care veterinary internal medicine and avian medicine protocols.