1. Poultry Industry in Vietnam

In Vietnam, one of the most important and rapidly expanding sectors of the country’s livestock economy is the chicken industry. Under the Ministry of Agriculture and Rural Development (MARD), the sector is vital to the country’s food security as a source of animal protein and rural revenue.

Population and Production Dynamics of Poultry

• Flock Inventory: The total number of chicken in Vietnam is between 510 and 530 million, showing consistent annual growth. Vietnam is one of the biggest producers of ducks in Southeast Asia, with more than 400 million hens and between 80 and 90 million ducks and waterfowl.
• Geographic Distribution: The Red River Delta in Northern Vietnam (including Ha Noi, Thai Nguyen, Hai Phong, and Phu Tho) and the Mekong River Delta/Dong Nai Province in Southern Vietnam are the two main agricultural zones where production is concentrated.

Per Capita Consumption Patterns

• Consumption of Poultry Meat: After pork, chicken and duck meat are the second most popular animal protein sources in Vietnam. The average annual consumption of poultry meat per person is between 17 and 19 kg due to urbanization and growing household incomes.
• Table Egg Consumption: The country produces more than 18 billion eggs annually thanks to growing commercial layer operations and duck-egg harvesting in the Mekong Delta. Between 130 and 150 eggs are consumed annually per person.

2. Newcastle Disease Brief

Newcastle disease was first officially identified clinically and reported by veterinarians in Vietnam in 1955. The virus has become hyper-endemic in both Northern and Southern regions since it was first officially documented.
Newcastle disease is caused by the Newcastle disease virus (NDV), a highly contagious member of the family Paramyxoviridae.
The three main pathotypes of Newcastle Disease Virus (NDV) strains in birds are lentogenic (low virulence, mild/no symptoms), mesogenic (moderate virulence), and velogenic (very pathogenic, causing severe respiratory/nervous manifestations and significant mortality).

• Etiology: The disease is caused by virulent strains of Avian Orthoavulavirus 1, family Paramyxoviridae (formerly known as Avian Paramyxovirus 1 or APMV-1). It is an enveloped, single-stranded, negative-sense RNA virus.
• Transmission: The virus spreads via inhalation or ingestion of contaminated secretions. Migratory birds act to introduce new strains into local poultry populations.
• Clinical Signs: Infected birds shows severe respiratory distress, greenish diarrhea, and neurological signs, as torticollis and leg paralysis.
• Pathology: Postmortem examinations typically shows proventricular, cecal tonsils, and intestinal lymphoid patches hemorrhages, in addition to catarrhal tracheitis

3. Most Prevalent Genotypes and Recent Outbreaks

Molecular epidemiological research on Class II Newcastle Disease viruses in Vietnam shows that virulent lineages are still circulating throughout the area and that viral evolution is ongoing.
The most common genotypes. The following dominant lineages in Vietnam are identified using phylogenetic sequencing that focuses on the hypervariable region of the viral fusion (F) gene:

• Class II, Subgenotype VII.2 (also VII.1.1, VIId, and VIIh): The main velogenic strain causing field outbreaks and immunization failures in Vietnam is genotype VII. The multi-basic cleavage site motif, which confers high systemic replication efficiency, is carried by isolates from commercial farms in Northern Vietnam (such as Ha Noi, Thai Nguyen, and Hai Phong), and molecular characterizations of these isolates confirm that circulating strains belong primarily to subgenotype VII.2.
• Genotype XII (Subgenotype XIId): These strains have historically co-circulated with Genotype VII and have strong genetic ties to outbreaks that have been documented in nearby Southeast Asian countries, such as Cambodia, Malaysia, and Indonesia.
• Genotype II: Almost exclusively linked to low-virulence, vaccine-derived lentogenic strains (such LaSota or B1 master seeds), yet frequently detected during routine diagnostic screening.

Outbreak Dynamics and Risk Factors

• Vaccine failure in Commercial Flocks: Severe ND outbreaks in completely vaccinated flocks are a persistent problem in commercial broiler and layer operations. Affected farms experience acute declines in egg production and mortality rates ranging from 15% to 50%, which clearly indicate antigenic divergence between circulating field strains and routine Genotype II vaccinations.
• Live Bird Markets (LBMs) & Transport Vectors: One of the main ways that viruses spread over provincial boundaries is through the uncontrolled movement of live poultry through traditional live bird markets.
• Backyard Reservoirs & Waterfowl Co-rearing: Raising native chickens alongside semi-scavenging ducks, who have the ability to transmit and shed NDV subclinically, creates a constant environmental reservoir for the virus.

4. Control, Recommendations, and Vaccination

Vietnam has to narrow the gap between traditional immunization practices and advanced, genotype-matched protection systems in order to control Newcastle disease.

Integrated Vaccination Strategies

• Resolving Antigenic Mismatch: LaSota, Hitchner B1, and Clone 30 are examples of commercial complexes that use standard live vaccinations that are Genotype II. They offer protection against clinical mortality, but they are unable to stop circulating Genotype VII field viruses from replicating and shedding into the environment.
• Homologous Inactivated vaccinations: Commercial operations are increasingly using a dual approach that combines oil-adjuvanted, inactivated Genotype VII-matched vaccinations with live lentogenic priming.

Biosecurity and Policy Recommendations

• Strengthening Live Bird Market Biosecurity: MARD and local Department of Animal Health (DAH) units should enforce mandatory rest days, routine sanitation, and molecular RT-PCR screening at major regional live bird transport hubs.
• Separation of Chickens and Waterfowl: Smallholders should be educated on physically isolating chicken flocks from duck populations to interrupt cross-species transmission chains.
• Active Molecular Surveillance: Regional Animal Health Offices (RAHOs) should perform routine F gene sequencing on field isolates to track genetic drift and detect emerging subgenotypes early.

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