Everything You Need to Know About Avian Metapneumovirus Infection in Poultry

 Dr. Ravi Sonwane, Dr. Pradip Doiphode, Dr. Deepak Koli and Dr. Shyam Vane

Hipra India Pvt Ltd.

Introduction:

Avian Metapneumovirus (aMPV) is a globally recognized viral pathogen that primarily affects poultry, causing significant economic losses in the industry. It is known by various names, including avian rhinotracheitis swollen head syndrome (SHS) and turkey rhinotracheitis (TRT) and is especially severe in turkeys and chickens (1). The disease leads to acute, highly contagious respiratory tract infections and can also impact egg production and quality.

Prevalence of aMPV in India:

In India, aMPV was first suspected in 2014 in Tamil Nadu in unvaccinated flocks (2). Later confirmed in 2018 and 2022 in multiple Indian states (3)(4). Sero-prevalence study shows 34% Broiler breeders, 85% commercial layers and 33% commercial broilers affected with aMPV (2). Highest seroprevalence observed in Monsoon season (3).

Disease overview and sub-types:

Avian Metapneumovirus (aMPV) is a single-stranded, RNA virus belonging to Family- Paramyxoviridae, Subfamily- Pneumoviridae and genus-Metapneumovirus. The virus is classified into four subtypes: A, B, C and D. Globally, Subtypes A and B are the most widespread, while in India, subtype B is predominant.

aMPV primarily targets the ciliated epithelium of trachea and oviduct, spreading rapidly through direct contact or aerosols transmission. Incubation period is about 4 days. The disease typically lasts for 7-14 days. Morbidity is high (30%), while mortality remains low (1-10%).

 Clinical findings and Lesions:

Avian metapneumovirus (aMPV) infection in chickens is generally characterized by mild respiratory manifestations, including ocular and nasal discharges, together with inflammation of the peri-orbital and infraorbital regions (Swollen head syndrome). In severe cases, neurological signs such as torticollis, disorientation and opisthotonos may also occur. In laying hens, aMPV is frequently associated with reproductive disturbances, including a reduction in egg production ranging from 30% to 70% and egg quality defects such as shell fragility and discoloration.

The severity of lesions depends on the course of infection and the degree of secondary bacterial involvement, from Light congestion to severe oedema with presence of mucus in nasal cavity in sinuses. These pathological alterations, combined with clinical signs, form the basis for diagnosis and highlight the economic significance of aMPV infection in poultry production systems.

Diagnosis:

Clinical signs and lesions caused by aMPV closely resemble those of other poultry diseases such as Newcastle Disease (ND), Infectious Bronchitis (IB), Infectious Laryngotracheitis (ILT), Infectious Coryza (IC), E. coli and Mycoplasma infections. The severity of aMPV infection is often complicated or exacerbated by the presence of secondary pathogens.

Diagnosis of aMPV infection begins with the recognition of compatible respiratory or reproductive signs. Molecular methods, such as PCR, are used limited due to short viral excretion period, which often precedes before onset of clinical signs. Therefore, Tracheal or choanal swab testing at early onset of clinical signs will be beneficial for diagnosis. Serological tests like ELISA are valuable for confirming past infection, assessing flock exposure and evaluate vaccine response.

Control and Prevention of aMPV through Vaccination:

• Vaccine with chicken origin demonstrate greater specificity and protective efficacy in chickens compared to turkey origin vaccines because Turkey origin vaccines replicate better in turkey, but chicken origin vaccine replicate in both.
• The effectiveness of an inactivated vaccine is directly related to the quality and quantity of the antigen. When selecting a vaccine, it is important to consider the antigen content and information about the vaccine virus. Additionally, using a well-validated vaccine with a high world market share can be a good approach.
• Suggested Vaccine schedule: primary dose- On 5^th to 7^th week First dose and 12^th to 14^th week booster.

Summary:

Avian metapneumovirus (aMPV) mostly underdiagnosed or underreported in Indian poultry, we are all familiar with respiratory diseases like ND, IB, IC, AI and many bacterial diseases when talking about respiratory disease complexes. Even when vaccines are administered for respiratory viral diseases that cause secondary infections—such as ND, IB, and AI—secondary infections may still occur. In such cases, it is important to consider whether the absence of vaccination against aMPV, a major cause of secondary infections, might be the reason. aMPV despite being a major contributor to respiratory problems, reduced productivity and leads to secondary infections, it is often ignored in discussions and vaccination programs. Unless we address aMPV Control, our control of respiratory disease in poultry will always remain incomplete.

 Reference:

1. https://pubmed.ncbi.nlm.nih.gov/39035438/
2. https://krishikosh.egranth.ac.in/assets/pdfjs/web/viewer.html?file=https%3A%2F%2Fkrishikosh.egranth.ac.in%2Fserver%2Fapi%2Fcore%2Fbitstreams%2F90a3f836-2ebc-4210-89e1-281fa89fbcb8%2Fcontent
3. https://www.indianjournals.com/article/ijps-53-1-022
4. https://arccjournals.com/journal/indian-journal-of-animal-research/B-4704
5. https://doi.org/10.1080/03079459708419215
6. https://www.msdvetmanual.com/poultry/avian-metapneumovirus-infection/avian-metapneumovirus-infection#Diagnosis_v3343988
7. https://www.hyline.com/Upload/Resources/TU%20AMPV%20ENG.pdf