Runting and Stunting Syndrome in Broiler Chickens: Histopathology and Association With a Novel Picornavirus

Abstract

Runting stunting syndrome (RSS) in commercial chickens has been reported worldwide, and although several studies have attempted to clarify the cause and describe the lesions, there are gaps in knowledge of the epidemiology, pathogenesis, and etiology. The study objective was to use commercial chicks naturally affected by RSS to describe the histologic changes of RSS in all segments of the small intestine in chicks of different ages and to identify viral gene sequences in affected chicks and their association with histologic lesions. Chicks lacking clinical signs but from the same houses and from unaffected houses were used as controls. The average weight of affected chicks was significantly lower than expected for their flocks. Macroscopically, the small intestines had paler serosa, with watery, mucoid, or foamy contents and poorly digested food. Histologic lesions were characterized by necrotic crypts, crypt dilation, and flattening of the crypt epithelium. Histomorphometry of the intestines revealed villous atrophy especially in the jejunum and ileum. Histologic changes in other organs were not observed. Random next-generation sequencing of total RNA extracted from formalin-fixed paraffin-embedded tissues detected avian nephritis virus, avian rotavirus, and picornavirus in jejunal segments from 7-day-old chicks. No viruses were detected in the jejunum of 1-day-old chicks. Detection of picornaviral reads was significantly associated ( P < .05) with histologic lesions of RSS. Sequence analysis of the picornavirus revealed genetic similarity with the genus Gallivirus. Using in situ hybridization for galliviral nucleic acid sequences, the signal was associated with crypt lesion severity, although signal was detected both in chicks with and without RSS.

Differential Viral Genome Diversity of Healthy and RSS-Affected Broiler Flocks

“…The last 4 picornavirus genomes belong to the genus Gallivirus, with one genome closely related to species A2, and 3 genomes sharing only 69% with A2, suggesting a new species. Galliviruses were previously detected in two consecutive flocks in the same building, indicating high stability, even with good hygiene [7]. Overall, picornaviruses are widely identified in chicken samples, with frequent co-infections with several different picornaviruses, which may lead to fast evolution, high diversity, and recombination events [46,47].…”

“…Studies in recent years to identify the causative agent were limited mainly to PCR analysis of selected viruses. Heretofore, many viruses were associated with RSS, i.e., astroviruses, avian nephritis viruses, reoviruses, rotaviruses, and parvoviruses [7]. A recent metagenomic study on affected and unaffected broilers did not find any association between detected viruses and RSS; however, the study was limited by the low number of animals [8].…”

“…Viral reads belonging to Picornaviridae were found in 43 samples. A previous study showed that picornaviruses are significantly associated with histological lesions [7]. However, a metagenomic study reported that picornaviruses were the most abundant viruses in both healthy and sick chickens [41].…”

“…Previous studies to associate specific viruses with RSS concluded that the disease is polyetiological with the involvement of several different viruses, including avian nephritis virus (ANV), astrovirus (CAstV), parvovirus, rotaviruses (RVs), and avian orthoreovirus (ARVs) [7]. Recently, picornaviruses and calicivirus have been detected in RSS-affected chickens as well [8].…”

Microbiological and pathological studies of concurrent infections associated with retarded growth in broilers in Behira governorate

“…Accordingly, this study was done to identify some of the concurrent possible causes and their histopathological pictures in some broiler's flocks. Malabsorption syndrome (MAS), viral arthritis/tenosynovitis and runting-stunting syndrome (RSS) that are caused by ARV, are characterized by growth retardation (De Carli et al 2020;Kim et al 2020;De Oliveira et al 2021). At arthritis/ tenosynovitis disease, poor growth and feed conversion can occur due to inability of lame bird to reach feed.…”