Discovery of Chicken Proventricular Necrosis Virus from Transmissible Viral Proventriculitis Outbreak in Broilers, Thailand

Transmissible viral proventriculitis (TVP) is an infectious disease-causing retarded growth in chickens. In Thailand, many stunted chickens have been found on commercial broiler farms since 2017. Significant post-mortem lesions are found only in the proventriculus. This study aims to investigate the causative agents of TVP outbreaks focusing on chicken proventricular necrosis virus (CPNV), the possible significant cause of TVP. CPNV was reproduced in specific pathogen-free (SPF) chickens. Affected chickens that have undergone proventriculitis are CPNV-positive by RT-PCR and nucleotide sequencing followed by phylogenetic analysis. The result showed that proventriculitis could be experimentally reproduced by inoculation of proventricular homogenate obtained from the affected chickens in the amniotic sacs of embryonic eggs. However, no cytopathic effect in inoculated primary chicken embryo fibroblasts was found. The viral genomes could be detected at the first passage of both egg inoculation and the cell culture by RT-PCR. Thai CPNV was in the same group as the reference strain from the previous report. Histopathologically, proventriculitis with infiltration of inflammatory cells was found in the glandular part of the inoculated chickens. By in situ hybridization with a CPNV-specific probe, positive signals were found in mucosal epithelium and necrotic cells. This study is the first report on CPNV discovery in broilers in Thailand.