Key result
Novel avian orthoreovirus genotypes IV and V infect ~30% of symptomatic chickens, revealing severe vaccine mismatch.
Why the study?
The molecular epidemiology and pathogenic landscape of Avian orthoreovirus strains circulating in Upper Egypt remain largely unexplored.
Novel ARV Genotypes IV and V circulating in Upper Egypt show severe vaccine mismatch and high virulence in chicks, highlighting the need for regionally-tailored vaccines.
May signal need for ARV surveillance and vaccine review in poultry; leaves open efficacy of current vaccines against genotypes IV/V.
Avian orthoreovirus (ARV) imposes substantial economic losses on the global poultry industry, primarily through runting-stunting syndrome and viral arthritis. Despite its global prevalence, the molecular epidemiology and pathogenic landscape of ARV strains circulating in Upper Egypt remain largely unexplored. This study investigated the molecular characteristics, phylogenetic relationships, and pathogenic potential of ARV in broiler flocks across Assiut, Sohag, and New Valley governorates. Out of 140 clinical samples from chickens showing stunted growth and tendon swelling, 42 (30%) were positive by RT-qPCR targeting the σC gene. Phylogenetic analysis of 11 representative isolates using MEGA X revealed a complex co-circulation of two genetically distinct genotypes. Notably, this study provides the first report of ARV Genotypes IV (GC IV) and V (GC V) in Upper Egypt governorates. Nine isolates clustered within Genotype V, forming a unique regional sublineage, while two isolates belonged to Genotype IV, showing high homology to contemporary Asian strains. Crucially, these field isolates exhibited extreme genetic divergence from commercial vaccine strains, sharing as little as 38% amino acid identity, indicating a severe vaccine mismatch. Experimental infection of young chicks confirmed high virulence, characterized by significantly impaired growth, reduced tibial length, and elevated feed conversion ratios (p <0.05). High viral loads were quantified in the tendons, pancreas, and proventriculus (p < 0.01). These findings underscore the urgent emergence of novel ARV variants in Upper Egypt and highlight the critical need for developing regionally-tailored vaccination strategies to mitigate these evolving threats.
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Ahmed et al. (2026) studied Avian orthoreovirus (ARV) infection (n=140). Avian orthoreovirus (ARV) Genotypes IV and V was evaluated on ARV positivity by RT-qPCR targeting the σC gene. Novel Avian orthoreovirus Genotypes IV and V were detected in 30% of symptomatic chickens in Upper Egypt, showing severe vaccine mismatch and high virulence in experimental infection (p<0.05).
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