Avian Metapneumovirus
Terminology
The following terms may be used to refer to the disease caused by avian metapneumovirus.
- Avian Metapneumovirus (AMPV)
- Swollen Head Syndrome (SHS)
- Avian Rhinotracheitis (ART)
- Turkey Rhinotracheitis (TRT)
- Avian Pneumovirus (APV)
This document will use "avian metapneumovirus" or "AMPV" throughout.
Overview of the 2024 Avian Metapneumovirus Outbreak
At the time of writing, the 2024 outbreak of avian metapneumovirus in the United States is continuing to develop.
Avian metapneumovirus (AMPV) is a viral upper respiratory disease of poultry including turkeys, broilers, layers, and breeders. AMPV may also affect other poultry and avian species such as pheasants, Muscovy ducks, pigeons, and various wild birds. The 2024 outbreak consists of two distinct groups. Eastern states, including Pennsylvania, have been affected by avian metapneumovirus subtype B. Western states have been affected by avian metapneumovirus subtype A. All detections from previous AMPV outbreaks in the US were subtype C. There is no treatment for AMPV, but treatment of secondary infections may reduce the severity of disease. At the time of writing, no licensed commercial AMPV vaccines are available for use in the United States. Prevention and control are best achieved through biosecurity, proper cleaning, disinfection, and downtime between flocks. AMPV is reportable at the state level in some states, but detection in any state is reportable at the federal level to the United States Department of Agriculture (USDA). Producers and veterinarians are encouraged to contact their state animal health officials if they suspect avian metapneumovirus.
In Pennsylvania, avian metapneumovirus is reportable to the Pennsylvania Department of Agriculture (PDA). Although AMPV in Pennsylvania is a reportable disease, it is not an actionable disease. There are no current policies from PDA or USDA that will disrupt domestic movement of birds or poultry products due to AMPV detection. Producers from other states are encouraged to check with their state agricultural agencies.
Avian metapneumovirus does not cause disease in humans.
Contact your veterinarian or diagnostic laboratory with any questions regarding avian health and disease.
Clinical Signs and Gross Lesions
Birds of any age can be infected by avian metapneumovirus, although the disease is typically more severe in younger birds. AMPV primarily affects the upper respiratory tract, causing inflammation of the nares (nostrils), sinuses, and trachea. Clinical signs may include coughing, mucus or discharge from the nares, swollen heads, and general signs of an unthrifty bird. At later stages, disease may progress to include torticollis (twisted neck or stargazing) or other neurological signs due to involvement of the inner ear. In severe cases, vent prolapse may occur due to straining from coughing. In layers or breeders, there may be reduced egg production and misshapen eggs, soft-shelled eggs, or thin-shelled eggs. Infection by AMPV makes other secondary infections much more likely to occur, such as E. coli. When AMPV is complicated by secondary infections, mortality rates may increase substantially (up to 50% mortality has been reported in some turkey flocks).
On post-mortem examination, the sinuses or trachea may be filled with excessive mucus. Depending on the severity of the infection, edema (seen as gelatinous fluid) may be present under the skin around the skull or neck. Layers and breeders may have folded egg membranes in the reproductive tract, or yolk peritonitis. Additional lesions may be observed if secondary infections are present.
Avian metapneumovirus cannot be distinguished from other respiratory diseases based solely on clinical signs or gross lesions. AMPV can mimic diseases such as Mycoplasma gallisepticum (MG), Ornithobacterium rhinotracheale (ORT), infectious bronchitis (IBV), infectious coryza, and others. Diagnostic testing at a laboratory is required to diagnose AMPV. If you suspect AMPV, please contact your veterinarian and/or your veterinary diagnostic laboratory.
Diagnostic Testing
PCR and serology (ELISA) are commonly used in the diagnosis of avian metapneumovirus. There are pros and cons to each of these testing methodologies.
Before submitting samples to a laboratory, please call ahead and confirm that the samples you have chosen are appropriate for the testing required. The laboratory staff can provide specific testing recommendations and will also help interpret the results. Please call your laboratory if you have any questions about laboratory results.
Treatment
There is no treatment for avian metapneumovirus. However, treatment may be important in controlling secondary bacterial infections. The earlier any secondary diseases are identified and treated, the better the prognosis. Contact your veterinarian as soon as any infection is suspected.
Prevention
Wild birds are thought to be reservoirs for avian metapneumovirus. However, if AMPV becomes present on a farm, the virus may persist in a poultry house for a long time under ideal conditions. The current best practices to prevent avian metapneumovirus infection and spread include cleaning, disinfection, adequate downtime between flocks, appropriate stocking densities, and strict biosecurity measures.
Transmission
Avian metapneumovirus spreads readily through direct contact of respiratory secretions. The virus can survive in rodents for several days, and rodent, human, insect, or inanimate fomites can readily spread infective secretions from one house to another. Although transmission via aerosolization cannot be discounted, it is much less likely to occur than direct contact. There are no published records of direct vertical transmission (spread from breeder hen to chick/poult).
Vaccination
At the time of writing, there are no available commercial avian metapneumovirus vaccines licensed for use in the United States. USDA is investigating the possibility of importing AMPV vaccines from outside the US. Production of an autogenous vaccine may become a possibility if avian metapneumovirus is successfully isolated from an infected flock.
Regulatory Impacts
Although avian metapneumovirus is reportable to the Pennsylvania Department of Agriculture (PDA) and USDA, it is not an actionable disease in Pennsylvania. From the federal regulatory perspective, AMPV is not treated like highly pathogenic avian influenza (HPAI). Trade will not be restricted by PDA or USDA; however, foreign nations, states importing products, and/or private trading partners may institute their own policies. Check with your trading partners and relevant regulatory agencies for their requirements.
Producers from outside the Commonwealth of Pennsylvania are encouraged to check with their state agricultural agency to confirm their regulatory requirements.
Final Notes
The 2024 US outbreak of avian metapneumovirus is continuing to develop.
If you have questions or are seeking further information about avian metapneumovirus, please contact us at the Penn State Animal Diagnostic Lab and Penn State Extension.
Note on Highly Pathogenic Avian Influenza (HPAI): Avian metapneumovirus may lead to high mortality and may appear similar to highly pathogenic avian influenza (HPAI).
Pennsylvania residents who have sick birds or suspect highly pathogenic avian influenza (HPAI) should contact the Pennsylvania Department of Agriculture via the hotline 717-772-2852 and select option 1 to reach the on-call veterinarian, or the United States Department of Agriculture (USDA) Healthy Birds Hotline at 866-536-7593.
Authors: Dr. Jonathan Elissa, DVM; Dr. Kayla Niel, DVM, MS; Dr. Megan Lighty, DVM, PhD, DACPV
