Enterite viral em frangos de corte naturalmente infectados

Abstract

Runting Stunting Syndrome (RSS) in commercial chickens has been reported worldwide and, although several studies have been carried out to clarify the etiology, there are some gaps in relation to the epidemiological, pathogenic and etiological aspects. In order to characterize the intestinal lesions in the different segments and age from diseased chicks, in addition to investigating the etiology of RSS, naturally infected chicks presenting growth retardation, apathy, poorly digested food in the feces or diarrhea were collected from four different commercial farms located in three municipalities in the in the state of Minas Gerais. Chicks without clinical signs were used as control. The total number of examined chicks were 243. The average weight of affected chicks was lower than expected for their flocks. Macroscopically, the small intestine of these chicks had paler serosa, with a watery, mucous or foamy content in the lumen associated with poorly digested food. Histologically, there was mild to marked dilation of the crypt with flattening of the crypt epithelium and necrotic crypts. Jejunum was the segment more affected histologically. The histologic morphometry of the intestines revealed villous atrophy especially in jejunum and ileum. Histological changes in other organs were not observed. Next-generation sequencing (NGS) detected avian nephritis virus (ANV), avian rotavirus (AvRV) and picornavirus in jejunum from 7-days-old chicks. In the one-day-old chicks no viruses were detected in the jejunum. Molecular sequence analysis of the picornavirus revealed genetic similarity with Gallivirus (GV) genus. In Fisher's exact test, only the GV was statistically significant (p <0.05), comparing chicks with and without histological lesions. In situ hybridization (ISH) for GV was performed and no association between virus and lesion was found, in other words, this virus was present only in crypt cells without histological lesion, although adjacent to them. Chicks, including those negative in NGS and without jejunal lesions, presented ISH positive signals for GV, in spite of low number of label in comparison with animals with jejunal lesions. Besides the exact etiology of RSS is not well understood and several viruses have been described, the results suggest that GV may plays a role in RSS in association with the other detected viruses, such as ANV and AvRV.