Newcastle Disease is one of the most important infectious poultry diseases worldwide and is associated with high morbidity, mortality, and economic loss. In several countries, vaccination is applied to prevent and control outbreaks; however, information on the ability of vaccines to reduce transmission of ND virus (NDV) is sparse. Here we quantified the transmission of velogenic NDV among 42-day-old broilers. Chickens were either vaccinated with a single dose of a vector vaccine expressing the F protein (rHVT-ND) at day-old in the presence of maternally derived antibodies or kept unvaccinated. Seeders were challenged 8 h before the co-mingling with the corresponding contacts from the same group. Infection was monitored by daily testing of cloacal and oro-nasal swabs with reverse transcription-real-time PCR and by serology. Vaccinated birds were completely protected against clinical disease and virus excretion was significantly reduced compared to the unvaccinated controls that all died during the experiment. The reproduction ratio, which is the average number of secondary infections caused by an infectious bird, was significantly lower in the vaccinated group (0.82 (95% CI 0.38–1.75)) than in the unvaccinated group (3.2 (95% CI 2.06–4.96)). Results of this study demonstrate the potential of rHVT-ND vaccine in prevention and control of ND outbreaks.

Two avian reovirus strains (A and B) from clinically affected poultry flocks, belonging to the same genetic cluster based on a partial sequence of the sigmaC coding region, were compared for molecular and pathogenicity aspects including intra-host dissemination and inter-host transmission capabilities, microscopic lesions and viral load in different organs. Strain B caused a 10% mortality and more severe liver and heart lesions, with slower transmission to contact animals. In contrast, Strain A showed rapid transmission and lower pathogenicity, without mortality. Whole genome sequence analysis revealed mosaicism in both strains, with gene segments of vaccine-like or vaccine origin. High nucleotide and amino acid sequence identities were noted, except for the lambdaC, muB, and sigmaC genes. LambdaC gene of Strain B grouped with vaccine strains, whereas Strain A branched with wild-type reoviruses. The muB gene of Strain B resembled alleles found in some Hungarian and Chinese chicken-origin strains and a pheasant-origin reassortant. Despite similar S1 genes, the strains exhibited different pathogenicity and transmission abilities. These findings suggest that sigmaC-based genotyping can obscure pathogenicity differences. Whole genome sequencing and characterization are essential to identify molecular markers of pathogenicity, reinforced by a curated sequence and standardized pathogenicity database.Research highlights ARV strains of the same genotype had distinct pathogenic and transmission traits.( LambdaC, muB, and sigmaC genes made a difference. SigmaC-based genotyping obscures pathogenicity differences.

Background/Objectives: Effective control of Newcastle disease (ND) requires a reduction in virus shedding and transmission. While recombinant herpesvirus of turkey vectored Newcastle disease (rHVT-ND) vaccines induce strong systemic immunity, their ability to generate early mucosal immunity and limit transmission may not be optimal when used alone. Methods: Day-old layer chicks with maternally derived antibodies were vaccinated with the rHVT-ND vaccine alone or in combination with conventional live ND vaccines administered either at hatch or in a booster program. Birds were challenged with a genotype VII.2 velogenic ND virus strain at 3, 4 or 6 weeks of age. Humoral immune responses, clinical protection, challenge virus shedding and transmission to vaccinated contact groupmates were assessed. Results: All vaccination programs provided strong clinical protection (85–100%); however, combined vaccination strategies induced earlier immunity and reduced virus shedding more efficiently than the rHVT-ND vaccine alone. Booster vaccination further accelerated the onset of immunity and decreased shedding. By 6 weeks of age, differences among vaccination regimens had mainly disappeared, with all vaccinated groups showing minimal or no challenge virus shedding. Transmission to vaccinated contact birds was significantly reduced in the combined vaccinated groups, whereas unvaccinated controls efficiently spread the challenge virus and consequently caused high mortality in the contact groupmates. Conclusions: Both the rHVT-ND vaccine alone and in combination with live ND vaccines provided similar clinical protection against genotype VII.2 NDV challenge; however, combined vaccination programs accelerated immunity and more effectively reduced virus shedding and transmission, supporting their use for improved ND control, particularly in endemic regions.