Whole Genomic Constellation of Avian Reovirus Strains Isolated from Broilers with Arthritis in North Carolina, USA

Abstract

Avian reovirus (ARV) is an emerging pathogen which causes significant economic challenges to the chicken and turkey industry in the USA and globally, yet the molecular characterization of most ARV strains is restricted to a single particular gene, the sigma C gene. The genome of arthrogenic reovirus field isolates (R18-37308 and R18-38167), isolated from broiler chickens in North Carolina (NC), USA in 2018, was sequenced using long-read next-generation sequencing (NGS). The isolates were genotyped based on the amino acid sequence of sigma C (σC) followed by phylogenetic and amino acid analyses of the other 11 genomically encoded proteins for whole genomic constellation and genetic variation detection. The genomic length of the NC field strains was 23,494 bp, with 10 dsRNA segments ranging from 3959 bp (L1) to 1192 bp (S4), and the 5′ and 3′ untranslated regions (UTRs) of all the segments were found to be conserved. R18-37308 and R18-38167 were found to belong to genotype (G) VI based on the σC analysis and showed nucleotide and amino acid sequence identity ranging from 84.91–98.47% and 83.43–98.46%, respectively, with G VI strains. Phylogenetic analyses of individual genes of the NC strains did not define a single common ancestor among the available completely sequenced ARV strains. Nevertheless, most sequences supported the Chinese strain LY383 as a probable ancestor of these isolates. Moreover, amino acid analysis revealed multiple amino acid substitution events along the entirety of the genes, some of which were unique to each strain, which suggests significant divergence owing to the accumulation of point mutations. All genes from R18-37308 and R18-38167 were found to be clustered within genotypic clusters that included only ARVs of chicken origin, which negates the possibility of genetic pooling or host variation. Collectively, this study revealed sequence divergence between the NC field strains and reference ARV strains, including the currently used vaccine strains could help updating the vaccination regime through the inclusion of these highly divergent circulating indigenous field isolates.

Detection of avian reovirus (ARV) by ELISA based on recombinant σB, σC and σNS full-length proteins and protein fragments

“…The authors also observed that antiserum from vaccinated chickens with strains from distinct lineages had smaller litres of antibodies or did not recognize the S1133 σC protein. Since the commercial ELISA plates are coated with a viral lysate, other more conserved proteins could be recognized by the antisera of the unvaccinated birds, such as λA, λC and σA, which show conservation rates above 90% in some reports [16, 19], although recent work has added new information about the variability of reovirus proteins, highlighting λC [56, 57]. The presence on the ELISA plate of similar proteins between the vaccine and circulating strains would explain the similar OD values between the antisera of vaccinated and unvaccinated chickens in the commercial ELISA.…”