What are Metapneumovirus?

First noted in South Africa in the late 1970’s, avian metapneumovirus (aMPV) infection leads to disease in turkeys and chickens throughout the world (except Australia). Impacting birds of all ages, it targets the respiratory and reproductive tract. Avian metapneumovirus causes a variety of conditions to include:

  • Turkey rhinotracheitis (an infection of the respiratory tract in turkeys)
  • Swollen head syndrome in broilers and broiler breeders
  • A decrease in egg production

In addition to turkeys and chickens, aMPV has been found in pheasants, Muscovy ducks and guinea fowl. Through vaccination, aMPV infection can be well-controlled.

Avian metapneumovirus or aMPV, leads to turkey rhinotracheitis (a respiratory tract infection), swollen head syndrome in broiler chickens and a decrease in egg production.

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Symptoms of Metapneumovirus in Birds

Turkeys and chickens who have contracted aMPV can experience a very contagious upper respiratory tract infection. While it seems that younger birds are more apt to develop the infection, the disease impacts birds of all ages. 

In fattening turkeys, the main impact is on the upper respiratory tract. Symptoms include:

  • A watery discharge from their nose and eyes
  • Froth in eyes
  • Conjunctivitis
  • In later stages, mucous discharge from the nose, swelling below the eye sockets, sneezing and coughing
  • Lack of appetite
  • Ruffled feathers

In laying hens, typically a mild respiratory infection is seen;  however, there is a decrease in egg production and quality. Laying turkeys that experience coughing due to involvement of their lower respiratory tract may experience uterine prolapse.

Swollen head syndrome symptoms include the following:

  • Swelling in the sinuses below the eye and in the tissues surrounding the eye
  • Frothy eyes
  • Discharge from nose
  • Abnormal position of neck
  • Odd neck posture as a result of ear infection

In chickens and pheasants, infection may not lead to clinical symptoms. Lesions can be seen in some cases and are dependent on the course of infection (particularly in secondary bacterial infections); they are most seen at 4-10 days after infection.

Types 

aMPV is part of the Paramyxoviridae family and subfamily Pneumovirinae. aMPV has been isolated into subtypes A to D. How the glycoprotein or G protein is sequenced will be used to determine the subtype for each strain. Analysis of F protein sequences has led to the suggestion that European subtypes A, B and D are more similarly related than subtype C.

Causes of Metapneumovirus in Birds

It is thought that aMPV is very contagious. The extent of its spread seems to be connected to the density of the poultry population, how hygienic the conditions and the level of biosecurity. Spread of aMPV can be horizontal through direct contact or when the bird has contact with contaminated material. Transmission is most likely to be airborne, as it most impacts the ciliated epithelial cells in the upper respiratory tract. Ciliated cells from the reproductive tract can also be targeted by aMPV. Once the virus is released from the host and into the environment it will quickly be destroyed. The incubation period is between three and seven days. Shedding of aMPV appears to happen for only a few days after infection occurs.

Diagnosis of Metapneumovirus in Birds

Serologic assays have been developed that will confirm aMPV infection in commercial chickens and turkeys. There are multiple commercial ELISA kits that are regularly used, as well as virus neutralization and indirect immunofluorescence tests in order to confirm infection. When testing, acute and convalescent serum samples should be analyzed. 

It is important that samples be gotten from the upper respiratory tract in the disease’s early stages when attempting to isolate the virus. In broiler-type chickens, samples should be obtained prior to the sixth day after infection occurs as once symptoms are apparent it may not be possible to isolate replicating aMPV. The best way to obtain samples are through tracheal and choanal swabs. 

Antigen detection tests, to include immunofluorescence and immunoperoxidase assays on fixed and unfixed tissues are also utilized.

When diagnosing infection, paramyxoviruses, infectious bronchitis virus, influenza viruses and a range of bacteria and Mycoplasma spp will need to be ruled out as they can cause respiratory disease and problems with egg production in chickens and turkeys. These may be causing secondary infections, hiding the presence of aMPV.

Treatment of Metapneumovirus in Birds

Good husbandry will often greatly minimize the seriousness of infection, particularly in turkeys. The following are key:

  • Best possible ventilation
  • Appropriate density in regards to stocking
  • Proper temperature control
  • High quality of litter
  • Biosecurity

Also key in reducing the severity of the disease is keeping secondary bacterial infections under control through antibiotics.

Birds that don’t experience a secondary infection and have a good foundation of health can overcome the infection within 7-10 days. Should the bird become ill and not be properly managed, the disease can worsen and last longer due to the development of secondary infections.

Recovery of Metapneumovirus in Birds

Vaccinations are available (both live and inactivated types) to immunize chickens and turkeys and these are frequently used in places where the disease is endemic. Antibodies from the mother do not offer enough protection against aMPV infection. The first immunization is recommended to take place as soon as possible after the bird hatches. All birds must receive a sufficient dose to ensure that immunization is consistent among the flock and farm. Repeated vaccination is typical, as live vaccine may only offer short-term protection.