Evaluation of transmission potential and pathobiological characteristics of mallard originated Avian orthoavulavirus 1 (sub-genotype VII.2) in commercial broilers

Abstract

Newcastle disease (ND), caused by Avian orthoavulavirus 1 (AOAV-1), affects multiple avian species around the globe. Frequent disease outbreaks are not uncommon even in vaccinates despite routine vaccination and, in this regards, viruses of diverse genotypes originating from natural reservoirs (migratory waterfowls) play an important role in a disease endemic setting. Though genomic characterization of waterfowl originated viruses has been will-elucidated previously, there is a paucity of data on clinico-pathological assessment of mallard-originated sub-genotype VII.2 in commercial chickens. Hence, the current study was designed to evaluate its transmission potential, tissue tropism and micro-and macroscopic lesions in commercial broilers. Based on complete genome and complete F gene, phylogenetic analysis clustered the study isolate within genotype VII and sub-genotype VII.2 in close association with those reported previously from multiple avian species worldwide. The study strain was found to be velogenic on the basis for typical residue pattern in the F-protein cleavage site (112 R-RQ-K-R↓F 117), sever disease induction in chicken, tissue tropism and subsequent clinico-pathological characteristics. Giving a clear evidence of horizontal transmission, a 100% mortality was observed by 4 th and 6 th day post infection (dpi) in chickens challenged with the virus and those kept with the challenged birds (contact birds), respectively. The observed clinical signs, particularly the greenish diarrhea, and macroscopic lesions such as pinpoint hemorrhages in proventriculus and cecal tonsils were typical of the infection caused by an AOAV-1 in chickens. The virus exhibited a broad tissue tropism where genomic RNA corresponding to study virus was detected in all of the tissues collected from recently mortile and necropsied birds. The study concludes that mallard-originated Avian orthoavulavirus 1 is highly velogenic to commercial chicken and, therefore, ascertain continuous vaccine monitoring in vaccinates and routine 3 surveillance of migratory/aquatic fowls to better elucidate infection epidemiology and subsequent potential impacts on commercial poultry.

Detection of Avian Orthoavulavirus-1 genotypes VI.2.1 and VII.1.1 with neuro-viscerotropic tropism in some backyard pigeons (Columbidae) in Eastern Saudi Arabia

“…Regarding genotype VII.1.1 (VIId), it has been shown that pigeons are an efficient source of infection with this virus for in-contact chickens. Similarly, the mallard-originated VII.2 strain was shown to be readily transmissible to and between chickens ( 51 ). Recently, Hicks and colleagues conducted a phylodynamic analysis of the complete F gene sequences of AOAV1.…”