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Avian Metapneumovirus

Avian Metapneumovirus


Avian Metapneumovirus (aMPV) is a contagious infection of turkeys and, to a lesser extent in most parts of the world, chickens. The virus is capable of producing a variety of disorders including rhinotracheitis and swollen head. The virus is a member of the family Paramyxoviridae, genus Metapneumovirus, and subfamily Pneumovirinae. Unlike other members of the family, pneumoviruses are not associated with hemagglutination.

Host range

Clinical infection with aMPV virus appears to affect chickens and turkeys of all age groups. Experimental studies suggest other avian species, such as pheasants, may also be susceptible. However, many avian species, such as geese and ducks, appear to have natural resistance to the virus. There is no known public health concern for humans exposed to this virus.


The aMPV virus is spread primarily through direct contact between birds. Contaminated feed, water, equipment, and personnel are probably also important in the spread of the virus. The role of airborne transmission is not fully understood but appears to be less important. In regions where outbreaks of aMPV have been documented, the virus has typically spread rapidly. aMPV is found in all major turkey-producing countries of the world, with the exception of Canada and Australasia.

Clinical Signs

The clinical signs are extremely variable and depend on host species, age, concurrent infection, and environmental factors.

In growing turkeys, infection with aMPV is sometimes called "turkey rhinotracheitis". The clinical signs are primarily respiratory in nature and include sneezing, nasal discharge, coughing, snicking, rales, conjunctivitis, swollen infraorbital sinuses, and submandibular edema. In older turkeys, coughing and head shaking are frequently observed. This coughing may lead to a prolapse of the uterus in breeding turkeys. In laying turkeys, there may be a drop in egg production (up to 70%), poor eggshell quality, and peritonitis. Mortality in turkeys ranges from 0 to 50% and depends on age and presence of secondary infections. Turkeys typically recover from the infection within 10-14 days.

In chickens, infection with aMPV is sometimes called "swollen head syndrome". However, aMPV infection in chickens does not always result in clinical disease. Immunosuppression and secondary invasion of opportunistic pathogens appear to play a significant role in the expression of clinical signs in chickens. Concurrent Escherichia coli and infectious bronchitis virus infectious often appear to be associated with "swollen head syndrome". This syndrome is characterized by swelling of the periorbital and infraorbital sinuses, as well as torticollis, opisthotonos, and disorientation. In broiler breeders, egg production may be compromised and in layers, the quality of eggs may be poor. Mortality in chickens is usually less than 2%.

Gross Lesions

In turkeys, gross lesions may be present in the trachea and include deciliation of the mucosa and the presence of watery to mucoid exudate. In the reproductive tract, findings may include ovary regression, egg yolk peritonitis, misshapen eggs, and abnormalities of the albumin and yolk. When secondary infections are present, other lesions may be present including airsacculitis, pneumonia, pericarditis, and perihepatitis.

In chickens, gross lesions are less prominent and are typically confined to the head. The subcutaneous tissues of the head, neck, and wattles may have yellow gelatinous to purulent edema and the infraorbital sinuses may be swollen.

Differential Diagnosis

A number of avian viruses such as Newcastle disease, avian paramyxovirus (APMV)-3, infectious bronchitis, and avian influenza, may cause respiratory disease and egg production problems in chickens and turkeys resembling aMPV infection. Paramyxoviruses and some avian influenza virions are similar in morphology but can be easily distinguished from aMPV in the laboratory as they posses HA and neuraminidase activity. Infectious bronchitis virus can be differentiated from aMPV by morphological and molecular (polymerase chair reaction [PCR]) characteristics. A number of bacteria and Mycoplasma species can cause signs very similar to aMPV infection. Laboratory isolation and identification of aMPV is required for a definitive diagnosis.


Diagnosis of aMPV is usually based on the observation of compatible clinical signs in the field followed by confirmation through laboratory testing.

The isolation of aMPV virus can be difficult due to the transient nature of the virus in the tissues of infected birds. Collect nasal secretions or tissue scrapings, taken from the nasal sinuses and turbinates of birds in the early stages of infection, and submit them to the laboratory for virus isolation. Additionally, submit sections of fresh and formalin-fixed trachea, lung, and other affected viscera.

Paired serum samples, taken during the acute and convalescent stages of infection, should also be submitted to the laboratory.

In the laboratory, aMPV virus testing may include immunohistochemistry on formalin-fixed tissues, real-time polymerase chain reaction (RT-PCR) to detect viral RNA in secretions, and enzyme linked immunosorbent assay (ELISA) or serum neutralization to detect pneumovirus-specific antibodies in the blood. Tracheal organ cultures, prepared from chicken embryos, are useful for the diagnosis of virus types that produce ciliostasis.

Prevention and Control

Good biosecurity and excellent management practices including disinfection during the downtime period, adequate ventilation, temperature control, stocking densities, and litter quality, are critical to controlling the severity of aMPV infection.

Live attenuated and inactivated aMPV vaccines are available for use in turkeys and chickens. Live vaccines are used for first vaccination in laying birds, followed by oil-adjuvanted inactivated aMPV. Live infectious bronchitis vaccines can interfere with the replication of aMPV in chickens.

Selected References

  1. Charlton, B. R. (ed). 2006. Avian Disease Manual, 6th ed. American Association of Avian Pathologists (AAAP), 953 College Station Road, Athens, Georgia 30602-4875.
  2. Cook, J.K.A. 2000. Avian pneumovirus infections of turkeys and chickens.
    Vet J. Sept 160(2):118-25. Review.
  3. Cook, J.K.A. and D. Cavanagh. 2002. Detection and differentiation of avian pneumoviruses (metapneumoviruses). Avian Pathology 31:117-132.
  4. Cook, J.K.A., M.B. Huggins, S.J. Orbell, K. Mawditt and D. Cavanagh. 2001. Infectious bronchitis virus vaccine interferes with the replication of avian pneumovirus vaccine in domestic fowl. Avian Pathology 30:233-242.
  5. Gough, R.E. and R.C. Jones. 2008. Avian Metapneumovirus. In Diseases of Poultry, 12th ed. Y.M. Saif. et al. (ed.). Blackwell Publishing, Ames, Iowa.
  6. Gough, R.E. and J.C. Pedersen. 2008. Avian Metapneumovirus. In A Laboratory Manual for the Isolation and Identification of Avian Pathogens, 5th edition. American Association of Avian Pathologists. L. Dufour-Zavala Louise et al. (ed.) OmniPress, Inc., Madison, Wisconsin.
  7. Njenga, M.K., H.M. Lwamba, and B.S. Seal. 2003. Metapneumoviruses in birds and humans. Virus Res Feb;91(2):163-9. Review.
  8. Villegas, P. 1998. Viral diseases of the respiratory system. Poult Sci Aug;77(8):1143-5. Review.
  9. World Organization for Animal Health (OIE) website. 2008.

Thank you to the following individuals for reviewing these materials:

Jaime Ruiz
Morella DeRosa

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