First detection of D181 genotype of infectious bronchitis in poultry flocks of Morocco.

Background: This paper reports the first pathological and molecular characterization of the novel variant of infectious bronchitis virus (IBV) D181 in poultry flocks in Morocco and Africa.

Methods: The study includes six poultry farms, involving three flocks of layers aged between 28 and 67 weeks and three broiler flocks aged 27, 39 and 42 days from different regions of Morocco. In all affected layer flocks, a severe drop in egg production with poor eggshell quality was reported. Necropsy of dead birds was carried out, and samples of trachea, lungs, oviduct, ovaries, and kidneys were fixed in 10% neutral buffered formalin for histopathologic examinations, while other portions were stored at -20 °C for molecular analysis. Real time RT-qPCR for IBV gene group was performed, and IBV variants were identified. Partial S1 gene sequences were amplified by conventional RT-PCR, sequenced, and aligned for phylogenetic and amino acid similarity analysis.

Results: Necropsy of dead birds revealed misshapen and hemorrhagic ovarian follicles with an edematous oviduct and severe reaction in the cecal tonsils. A caseous material accumulation in the sinus was noted in few birds. In contrast, the broiler flocks exhibited respiratory clinical signs such as difficulty in breathing, sneezing, tracheal rales, watery eyes and lethargy, associated with a decrease in feed consumption. Mortality in broiler ranged from 2 to 15%. Histopathological analysis of samples showed a lympho-plasmocytic inflammation in the oviduct, trachea, and lungs. Individual necrosis of epithelial cells, with sloughing of the bronchial epithelium and accumulation of desquamated cells with mucus in the airways, was observed in some birds. Partial S1 gene sequencing and phylogenetic analyses showed that the Moroccan strains were very closely related to D181 strains isolated in Dutch layers and breeders in 2018. Nucleotide sequence identities reached 90.9-95% with the Dutch isolates (strain CK/NL/D181/2018).

Conclusion: Our sequencing results demonstrate for the first time that the D181 IBV genotype is circulating in Moroccan poultry. These findings justify permanent monitoring of circulating strains in order to appropriately adjust vaccination strategies to align with the evolving field situation.