Assessing the risk of avian influenza

Highly pathogenic avian influenza (HPAI) has been spreading across North America since January 2022.¹ As of November 2023, more than 72 million cases of HPAI have been reported in wild birds and poultry flocks, and the virus has been confirmed in every state except Hawaii.² Cases have also been documented in several species of mammals, including humans, with 1 case reported in the US.^3,4

Understanding the pathogens

HPAI is an influenza A virus. These viruses are further classified by variants of the surface proteins, hemagglutinin (HA) and neuraminidase (NA). Of the 18 HA subtypes and 11 NA subtypes that are known, those numbered 16 and 9, respectively, have been identified in birds.⁵ The virus involved in the current outbreak has an HA 5 protein and an NA 1 protein and is designated H5N1, a strain that has not been detected in the US since 2016.¹ It is highly transmissible and very durable in the environment, and it is able to survive in water for 102 days at 28 0C or up to 207 days at 17 0C. In feces, the virus can survive for 7 days at 20 0C and 30 to 35 days at 4 0C.⁶ Viral particles can be found in secretions from the eyes, respiratory tract, and mouth, as well as in feces of infected birds. The virus also can be carried on feathers, skin, clothing, equipment, dirt, and other fomites.⁷

In contrast to low pathogenic avian influenza (LPAI), HPAI viruses cause severe disease in infected birds, with the exception of waterfowl (ducks, geese, swans, shorebirds, etc). Waterfowl are considered natural carriers for avian influenza viruses and serve as a reservoir for the virus in the wild.⁸ Most waterfowl do not develop clinical signs of disease, though they may shed the virus for long periods of time and are one of the main sources of transmission to the pet bird population.^6,8 HPAI outbreaks in other species, however, can result in morbidity and mortality of 90% to 100%.⁸

Disease typically manifests as severe neurologic and respiratory signs, though other signs can be present. Infected birds may also die without displaying clinical signs beforehand. Although cases in mammals have been increasing, birds remain the primary at-risk population for HPAI. The current H5N1 outbreak appears to be particularly deadly to wild birds, especially birds of prey. The incubation period is generally 1 to 7 days, during which birds may transmit disease without showing outward physical signs.⁹ Note that longer incubation periods may occur, and the World Organisation for Animal Health recognizes HPAI incubation as 21 days, although this can vary by strain.

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Recognizing avian flu

Veterinarians who primarily or exclusively treat wild and outdoor companion birds are most likely to encounter HPAI in their patients. Nevertheless, any clinician seeing indoor or outdoor birds of any species must be aware of HPAI and of steps they can take to minimize the risk of spread within their facility. The first step is to be aware of HPAI outbreaks in your area. The CDC maintains a current situation web page with regularly updated information on cases in wild birds, poultry flocks, and mammals. This page also tracks human cases and overall public risk.³

Patients should be screened with prioritized biosecurity according to risk. Although any bird can become infected with HPAI, birds that live outdoors are at higher risk of exposure. Backyard chickens, turkeys, and other poultry can be exposed to viral particles through direct contact with wild birds, their droppings, or contaminated soil and water.

Infected poultry can present with increased respiratory effort, lethargy, ataxia, stargazing, purple discoloration of the comb and wattles, and sudden death.¹⁰ A bird can be contagious without showing clinical signs during the incubation period, and waterfowl can carry the disease and be contagious without showing any clinical signs.^6,8 Waterfowl with outdoor exposure should be considered potentially infectious, even if they are not displaying clinical signs of illness.

Reducing risk of transmission

Birds that live outdoors should be examined in isolation from other patients, and facilities and equipment used for examination should be thoroughly disinfected. Use of personal protective equipment (PPE), including masks, hair covers, gloves, shoe covers, and gowns or coveralls, helps reduce risk of carrying viral particles on clothing or skin. PPE should be double-bagged and disposed of after use. Any non-disposable clothing, towels, or other objects used during examination should be thoroughly washed (with bleach) and dried (under high heat), separately from other laundry.

Examining outdoor birds at the end of the day, after handling other avian patients, may also help reduce the risk of disease spread. Viral particles can survive on contaminated surfaces for up to 7 days at room temperature,⁶ so even if your practice does not see birds every day, the risk of transmission is still present if infectious viral particles are allowed to remain in the environment.

Birds that live exclusively indoors are unlikely to be exposed to avian influenza. However, taking a thorough history of each indoor bird before performing a physical examination can be helpful in assessing HPAI risk. An owner with an indoor bird who also owns outdoor poultry or waterfowl, or who regularly interacts with these species, could potentially carry HPAI into their home and to their indoor birds.

After incubation, psittacine birds infected with HPAI may show severe respiratory and neurologic signs and sometimes die suddenly. After signs present, death usually follows quickly, often within a few days. Recovery is rare.¹¹ Birds that are actively showing clinical signs, or that have had known exposure to outdoor poultry or wild birds within the last 2 weeks, should be treated as potentially infectious, and similar PPE and disinfection efforts should be taken.

An indoor-only bird with no exposure to the outdoors or to outdoor birds is unlikely to be exposed to avian influenza. Although infection cannot be ruled out in birds with severe neurologic or respiratory signs or sudden death, other differential diagnoses may be more likely, depending on patient history.

Although transmission to humans is very rare, HPAI is zoonotic. If there is any suspicion of HPAI, be sure to maintain a high standard of personal hygiene during and between clinic appointments. Protection with a face mask (N95 or greater protection), safety goggles, gloves, and covering garments is strongly recommended to reduce both zoonotic transmission and the chance of spreading infection throughout a facility.¹²

Creating awareness of the disease

Educating your clients, whether they own outdoor poultry or indoor birds, will help to prevent exposure and spread of HPAI. The US Department of Agriculture (USDA), for example, has numerous resources available to advise on biosecurity practices.

In general, indoor birds should be kept indoors, and outdoor birds should be protected from wild bird exposure as much as possible. Unfortunately, it is not possible to protect outdoor birds 100% from potential exposure, given the durability of the virus in the environment and the ease with which it is spread from wild birds. Nevertheless, good biosecurity practices can help reduce, if not eliminate, exposure risk.

Suspected cases of HPAI must be immediately reported to the Animal and Plant Health Inspection Service of the USDA as well as to state animal health officials. Each state has its own guidelines for reporting suspected cases of HPAI. Contact your state veterinarian’s office for further guidance.

Veterinarians are on the front lines for detecting this virus, and only through accurate and consistent reporting can we fully follow this disease’s progression. Polymerase chain reaction and agar gel immunodiffusion testing—both recommended for detection in poultry—are available for HPAI at select USDA-approved laboratories. By following these guidelines, practices should be able to not only screen patients for suspicion of HPAI but also keep the facility, patients, and staff safe.

Laurie Hess, DVM, DABVP (Avian Practice), is 1 of approximately 150 board-certified avian specialists worldwide. After graduating from Yale University, she earned her veterinary degree at Tufts University. She is the owner and medical director of the Veterinary Center for Birds & Exotics in Westchester County, New York, and serves as a professional services veterinarian for pet product retailer Chewy. Hess is also the author of Unlikely Companions: The Adventures of an Exotic Animal Doctor–a memoir about life as an exotic animal veterinarian.

Michael Huffaker, DVM, completed his veterinary education at Midwestern University in Phoenix, Arizona. He then completed an internship in raptor medicine and surgery at the Raptor Center in Minneapolis, Minnesota, where he triaged, treated, and rehabilitated birds of prey including hawks, owls, falcons, osprey, and eagles.

Now pursuing board-certification in avian medicine and surgery, Huffaker works closely with Hess and her veterinary team in New York on all manner of exotic pets. When not treating patients, Huffaker enjoys spending time with his own exotic animals: a rabbit, a snake, a frog, and a 3-legged hamster.

References

1. Highlights in the history of avian influenza (bird flu) timeline – 2020-2023. Centers for Disease Control and Prevention. Updated February 27, 2023. Accessed December 14, 2023. https://www.cdc.gov/flu/avianflu/ timeline/avian-timeline-2020s.htm
2. 2022-2023 detections of highly pathogenic avian influenza in wild birds. US Department of Agriculture Animal and Plant Health Inspection Service. Updated December 12, 2023. Accessed December 14, 2023. https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/ animal-disease-information/avian/avian-influenza/ hpai-2022/2022-hpai-wild-birds
3. H5N1 bird flu: current situation summary. Centers for Disease Control and Prevention. Updated December 13, 2023. Accessed December 14, 2023. https://www.cdc.gov/flu/avianflu/avian-flu-summary.htm
4. U.S. case of human avian influenza A(H5) virus reported. News release. Centers for Disease Control and Prevention. April 28, 2022. Accessed December 14, 2023. www.cdc.gov/media/releases/2022/s0428-avian-flu.html
5. Avian influenza type A viruses. Centers for Disease Control and Prevention. Updated April 28, 2023. Accessed December 14, 2023. https://www.cdc.gov/flu/ avianflu/influenza-a-virus-subtypes.htm
6. Si Y, de Boer WF, Gong P. Different environmental drivers of highly pathogenic avian influenza H5N1 outbreaks in poultry and wild birds. PLoS ONE. 2013;8(1):e53362. doi:10.1371/journal.pone.0053362
7. Avian influenza. American Veterinary Medical Association. Accessed December 14, 2023. https://www.avma.org/ resources-tools/animal-health-and-welfare/animal-health/ avian-influenza
8. Current bird flu situation in wild birds. Centers for Disease Control and Prevention. Updated March 11, 2022. Accessed December 14, 2023. https://www.cdc.gov/flu/ avianflu/wildbirds.htm
9. Case definition: avian influenza (AI). US Department of Agriculture Animal and Plant Health Inspection Service. March 2022. Accessed December 14, 2023. https://www.aphis.usda.gov/animal_health/monitoring_surveillance/ avian-influenza-case-definition.pdf
10. Avian influenza in birds. Centers for Disease Control and Prevention. Updated June 14, 2022. Accessed December 14, 2023. www.cdc.gov/flu/avianflu/avian-in-birds.htm
11. Wellehan JFX Jr, Lierz M, Phalen D, et al. Infectious disease. In: Speer BL, ed. Current Therapy in Avian Medicine and Surgery. 1st ed. ; 2015:22-106.
12. Prevention and antiviral treatment of bird flu viruses in people. Centers for Disease Control and Prevention. Updated October 31, 2022. Accessed December 14, 2023. https://www.cdc.gov/flu/avianflu/prevention. htm#Protective-actions-wild-birds