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Metapneumovirus Epidemiology and Seasonality

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Avian Metapneumovirus (aMPV)

Respiratory diseases are a constant challenge for poultry producers and veterinarians since they do not show pathognomic signs, making diagnosis more complex.

Distribution and epidemiology of aMPV

The aMPV affects turkeys and chickens and can also be found in guinea fowl, ducks, and pheasants.

It is an enveloped negative-sense RNA virus included in the genus Metapneumovirus of the Pneumoviridae family.

The global impact of aMPV is significant. Six viral subtypes of aMPV are recognized worldwide, each with its unique distribution.

Schematic figure representing aMPV: (G) Glycoprotein, (F) Fusion protein, (SH) Small hydrophobic protein and other structural proteins, (M) Matrix protein, (N) Nucleocapsid protein, (P) Phosphoprotein, (L) RNA-dependent RNA polymerase and RNA strand.

 

Currently, subtype B is the most prevalent worldwide. However, subtypes A and B are causing outbreaks in several states in the USA, following a prolonged period without aMPV detection.

The recent introduction of aMPV-A and -B into the US has coincided with the increased spread of H5N1 HPAI by migratory waterfowl.

The presence of aMPV has been confirmed in wild migratory birds in several countries, indicating that this factor must be considered in epidemiological studies, as well as seasonality and biosecurity to prevent it. Horizontal transmission through aerosol is the most common route of infection, and no vertical transmission has been reported.

Pathogenesis

Common symptoms include:

In chickens, it causes swelling of the periorbital and infraorbital sinuses, torticollis, disorientation, and opisthotonos. The clinical manifestation may progress to reddening of the conjunctiva with edema of the lacrimal gland.

Vaccination and selective pressure

There are contradictory reports regarding the evolution of aMPV.

Some studies report that aMPV is a relatively slow-evolving virus compared to other avian RNA viruses, and others estimate that its rate of viral evolution is within the normal range.

The phylogenetic relationships among the aMPV-B strains, reconstructed using the maximum likelihood method in the Molecular evolutionary genetics analysis (MEGA X) software, showed that aMPV-B has evolved in Europe since its first appearance.

Diagnostic tests and discovery of new viral strains

All experts recommend monitoring birds by serology to detect antibodies by ELISA and detect the virus to identify the prevalence of the subtype and determine the best vaccine to use.

The following commercial ELISA kits are available:

  1. Idexx Avian Pneumovirus antibody test kit to detect subtypes A, B, and C
  2. BioChek Avian rhinotracheitis (ART) antibody test kit to detect subtypes A and V

AMPV subtypes A, B, C, and D can be detected by traditional real-time PCR or RT-qPCR. However, virus isolation and genome sequencing of the G gene region can be necessary to identify subtypes.

Common samples for analysis are oropharyngeal, nares, and sinus cavity swabs that should be submitted in transport media. For asymptomatic birds, the nares are the most reliable sample site for molecular diagnosis of aMPV, with the choanal cleft and trachea being secondary options. Symptomatic birds normally have detectable virus in the choanal cleft, nares, and trachea.

The control of aMPV requires correct identification of the agent, epidemiological surveillance, effective diagnosis, adequate immunoprophylactic programs, and constant biosecurity.

A

B

Figure 1. (A) Turkey showing swollen infraorbital sinuses, ocular discharge, and conjunctivitis (courtesy of Dr. Ashley Mason); (B) five-week-old chicken showing swollen head, swollen infraorbital sinuses, plugged nostrils, and opaque crusted ocular discharge (courtesy of Dr. William McRee). Source: Luqman et al., 2024. Viruses 16 (4): 508.

 

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