Astroviruses as Causative Agents of Poultry Enteritis: Genetic Characterization and Longitudinal Studies on Field Conditions

Abstract

Astroviruses (AstVs) are nonenveloped RNA small round viruses (SRVs) with a genome of 6.8-7.9 kb. Known avian AstVs are spread worldwide; they have been associated with poult enteritis and mortality syndrome in the United States and reported in Italy in intensive turkey and guinea fowl flocks. Nevertheless, their real prevalence and their pathogenic role in avian enteritis affecting Italian flocks is far from clear. Negative staining electron microscopy (nsEM) is used for the routine diagnosis of avian enteric SRVs, although it cannot distinguish morphologically similar particles. Enzyme-linked immunosorbent assay (ELISA), reverse-transcription PCR (RT-PCR), and genomic sequencing are now used for this specific purpose. We analyzed 329 samples of chicken, turkey, and guinea fowl intestinal contents from Italian poultry flocks. Most samples were from enteritis outbreaks, but we also included samples from three longitudinal studies (one on 11 broiler flocks and the other two on a guinea fowl flock). We first examined the samples with nsEM. SRVs, including AstVs, are often associated with rotaviruses and were the most commonly detected morphotypes in avian enteric diseases. We then analyzed 124 of the samples with an RT-PCR targeting the open reading frame (ORF)-1b of AstV. This gene codes for an RNA-dependent polymerase. We then sequenced and genetically analyzed the RT-PCR positive samples. Phylogenetic analysis distinguished three defined clusters: the first included guinea fowl AstVs and turkey AstVs-2; the second, chicken AstVs; and the third was formed by avian nephritis viruses (ANVs). No strains clustered with turkey AstVs-1. The results indicate that ORF-1b presents certain genetic variability, even among AstVs from the same species. In longitudinal studies, samples retrieved from the same shed were homogeneous, with some exceptions suggesting possible coexistence of different genetic types in the same unit. The finding of ANV-like viruses in commercial guinea fowls underlines the genetic variability of AstVs and strengthens the hypothesis of a varied intraherd situation.

Detection and molecular characterization of enteric viruses in enteritis-affected commercial broiler chickens in India

“…Our observations of varying levels of nt and aa identities of ANV compared with previously published polymerase gene sequences of ANV from abroad are consistent with the earlier reports (Canelli et al, 2012;Kang et al, 2012). Phylogenetic analysis revealed that all ANVs of this study clustered together.…”

Human Astroviruses

“…However, later on, two genera were established based on their hosts of origin: Mamastrovirus (MAstV) and Avastrovirus (AAstV), infecting mammalian and avian species, respectively. Although initially detected in children's stool, AstVs have been found in the feces of a wide variety of mammalian species, i.e., cats (6), cattle (7), deer (8), dogs (9), mice (10), rats (11), pigs (12), sheep (13), mink (14), bats (15), cheetahs (16), rabbits (17), and even sea lions and dolphins (18), as well as in avian species, i.e., turkeys (19), chickens (20), ducks (21), pigeons (22), and guinea fowl (23) and other wild aquatic birds (24).…”

The Use of Convalescent Sera in Immune-Electron Microscopy to Detect Non-Suspected/New Viral Agents

“…To better characterize and identify those particles observed using ns-EM methods that were morphologically classified as small round viruses (SRVs), AstVs and enterovirus-like viruses (ELVs), we further analyzed samples of different avian commercial species, including turkey, with RT-PCR targeting the open reading frame (ORF)-1b of AstV, which encodes an RNA-dependent polymerase. We then sequenced and genetically analyzed the RT-PCR positive samples, and we performed a phylogenetic analysis to distinguish and type them [ 37 ]. This study also permitted us to compare the results obtained by the two diagnostic methods (RT-PCR vs .…”