Highly Pathogenic Avian Influenza
by Jenny Alonge
In February 2022, The United States Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) confirmed that highly pathogenic avian influenza (HPAI) had been detected in a Dubois County, Indiana, commercial turkey flock that experienced increased mortality rates. Samples from the affected birds were tested at the Indiana Animal Disease Diagnostic Laboratory at Purdue University, part of the National Animal Health Laboratory Network, and HPAI was confirmed at the APHIS National Veterinary Services Laboratories (NVSL) in Ames, Iowa—the first confirmed HPAI case in commercial poultry in the United States since 2020. In the ensuing months, additional outbreaks have been identified in commercial and backyard poultry flocks in multiple states across the country.
Avian influenza
Avian influenza is caused by influenza type A virus, and avian-origin influenza viruses are broadly classified based on two protein groups—hemagglutinin or “H” proteins and neuraminidase or “N” proteins—on the virus’ surface. The 16 “H” proteins and nine “N” proteins proteins can occur in many different combinations, and each combination is considered a different virus subtype. Avian influenza virus subtypes are classified as low pathogenic or highly pathogenic, based on their genetic features and the disease’s severity in poultry. While most avian influenza viruses are low in pathogenicity (LPAI), and cause no signs or only minor clinical signs in poultry, HPAI virus is extremely contagious and can cause high mortality in affected poultry populations. Both viruses can spread rapidly through poultry flocks. Transmission occurs through direct contact with infected birds, as well as contact with contaminated surfaces. Avian influenza outbreaks in domesticated poultry are concerning for several reasons:
- Evolving viruses — LPAI viruses have the potential to evolve into HPAI viruses, causing major agricultural implications.
- Outbreaks — HPAI outbreaks spread rapidly and cause significant disease and death in poultry flocks.
- Economic impact — HPAI outbreaks lead to significant economic impacts and trade restrictions.
- Zoonosis — Avian influenza A viruses have the potential for transmission to humans exposed to infected birds.
Highly pathogenic avian influenza distribution
The current HPAI virus outbreak in the U.S. is classified as H5N1, and preliminary genetic sequencing data obtained from infected poultry suggests that the virus belongs to clade 2.3.4.4b. This strain is descended from a Eurasian strain that has been circulating in Asia for several years and in mainland Europe and the United Kingdom for more than a year. Since HPAI was first detected in North America in December 2021 in Newfoundland and Labrador, Canada, the virus has spread across the U.S., affecting wild aquatic birds, commercial poultry, and backyard or hobbyist flocks. Data updated on July 12, 2022, demonstrated that HPAI had affected 40,089,232 birds across the U.S., with 385 reported outbreaks in 200 counties across 37 states.
Highly pathogenic avian influenza testing
If you suspect commercial poultry or a backyard flock is affected by avian influenza, you must immediately contact your state animal health official. Avian influenza is considered a reportable disease by the World Health Organization for Animal Health and must be reported to the USDA and state authorities. Depending on the situation, the official may send a regulatory representative to collect samples, or direct you to take specimens. If so, you should contact the National Animal Health Laboratory Network (NAHLN) for specific, up-to-date information on appropriate collection and submission of samples and carcasses. Many tests are available and validated for poultry species, including:
- Virus isolation — Viral isolation can be performed by many NAHLN laboratories, but results take several days.
- Real-time reverse transcriptase polymerase chain reaction (rRt-PCR) — The rRT-PCR is performed by all NAHLN laboratories and is specific for all influenza A viruses. Further testing is then performed for important subtypes. This test can detect infection in any animal actively shedding the virus, and results can be available in about 12 hours.
- Agar gel immunodiffusion (AGID) — Serologic testing using AGID can demonstrate a flock’s virus free status.
- Necropsy — For suspected HPAI cases, a necropsy should be performed by a NAHLN facility, and the laboratory notified before the bird is submitted for necropsy.
Protecting flocks from highly pathogenic avian influenza
Educate your clients to help protect their flocks from HPAI. Tips include:
- Dedicated footwear — Avian influenza most commonly enters poultry barns on workers’ footwear. Wear shoe covers or clean boots when entering the birds’ pen to prevent tracking HPAI virus.
- Control wildlife — Rodents can spread HPAI, so take steps to control the rodent population on your farm, and plug and patch holes in building exteriors to prevent wild birds from nesting or sheltering in your facilities.
- Separate species — Ducks are known reservoirs for HPAI virus and typically carry the virus without exhibiting signs. Separate chickens, turkeys, quail, guineas, and other poultry species from ducks.
- Eliminate standing water — HPAI virus lives for a long time in cool, moist conditions, so eliminate standing water sources. In addition, ensure your birds cannot access water sources that wild birds may use, because this could result in virus transmission.
- Sanitize feeders and waterers — Frequently sanitize your flock’s feeders and waterers to help prevent virus spread.
- Do not share equipment — Don’t share equipment among flocks.
- Quarantine new birds — When you purchase new birds, buy only from a reputable National Poultry Improvement Plan (NPIP) dealer, and quarantine the newly purchased birds from your existing flock for at least three weeks to rule out infection.
- Monitor your flock — Monitor your flock closely for any infection signs, including lethargy, decreased appetite, decreased water intake, decreased egg production, soft or misshapen eggs, discolored wattle or comb, incoordination, diarrhea, and sudden death.
HPAI is a concerning issue, but you can take measures to control this disease to protect poultry populations and the public health. Immediately contact your state animal health official if you suspect an HPAI case.
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