Pathogenicity of GI-23 Avian Infectious Bronchitis Virus Strain Isolated in Brazil

Abstract

IBV variants belonging to the GI-23 lineage have circulated since 1998 in the Middle East and have spread to several countries over time. In Brazil, the first report of GI-23 occurred in 2022. The study aimed to evaluate the in vivo pathogenicity of exotic variant GI-23 isolates. Biological samples were screening by real-time RT-PCR and classified in to GI-1 or G1-11 lineages. Interestingly, 47.77% were not classified in these lineages. Nine of the unclassified strains were sequenced and showed a high similarity to the GI-23 strain. All nine were isolated and three, were studied for pathogenicity. At necropsy, the main observations were the presence of mucus in the trachea and congestion in the tracheal mucosa. In addition, lesions on the tracheas showed marked ciliostasis, and the ciliary activity confirmed the high pathogenicity of isolates. This variant is highly pathogenic to the upper respiratory tract and can cause severe kidney lesions. This study confirm a circulation of GI-23 strain in the country and report, to first time, the isolation of an exotic variant of IBV in Brazil.

Keywords: Brazil GI-23 isolate; IBV variant; S1 complete sequence; South America; chicken disease.

Figure 1

Phylogenetic relationships based on partial spike gene nucleotide sequences of avian infectious bronchitis virus (IBV) detected in Brazil. The inferred evolutionary history using the Maximum Likelihood method and Tamura 3-parameter model [35]. It showed the tree with the highest log likelihood (−4060.44). The percentage of trees in which the associated taxa clustered is shown next to the branches. The initial tree(s) for the heuristic search were obtained automatically by applying Neighbor-Join and BioNJ algorithms to a matrix of pairwise distances estimated using the Tamura 3 parameter model and then selecting the topology with superior log likelihood value. The rate variation model allowed some sites to be evolutionarily invariable ([+I], 45.19% sites). This analysis involved 54 nucleotide sequences. There were a total of 1807 positions in the final dataset. MEGA11 was used for evolutionary analyses [30]. The Genbank sequence I.D. OP113954.1 (IBV SB2805), was the first IBV sequence that showed a pattern similar to other sequences of the GI-23 group in Brazil [26]. * Indicate the sequences obtained from the samples isolated and analyzed in the present study.

Figure 2

Embryo development at 17 days following inoculations with IBV GI-23 Brazilian field. Note evidence of dwarfing, winding, and hyperemia in the three IBV-infected embryos (bottom of figure) compared to a non-infected control embryo (two larger embryos at the top).

Figure 3

Gross pathology in kidney. The arrows in (A) indicate the enlarged kidney lobes and in (B) they indicate the presence of urates in kidney lobes.

Figure 4

Gross pathology in air sacs infected with Brazilian GI-23 IBV. The arrow in (A) indicate the presence of foam and opacity at 6 dpi, and the arrow in (B) shows the presence of yellowish material in the air sac 13 dpi.

Figure 5

Histopathology of tracheal mucosa and kidney. (A) indicates the tracheal mucosa with lymphoplasmacytic infiltration, epithelial cell hyperplasia, ciliary loss and degeneration of epithelial cells; (B) indicates kidney interstitial lymphoplasmacytic infiltration.