Avian reovirus in Italy: three episodes of abnormal losses in offspring of vaccinated broiler breeders.

Avian reovirus (ARV) is an important pathogen of poultry and the causative agent of viral arthritis/tenosynovitis. The disease can cause severe clinical signs in broiler flocks at an early age, resulting in major welfare issues and substantial economic losses for the poultry industry. Vaccination of breeders is widely used to control the disease, aiming to reduce vertical transmission and provide maternal antibodies to offspring. However, in recent years the number of clinical cases has increased in several countries. This study describes the clinical presentation, gross and histological lesions, and laboratory findings in three Italian broiler flocks in which ARV was identified. Sequencing of a partial fragment of the sigma C (σC)-econding gene enabled genetic characterization of the viruses, which showed a low degree of homology with vaccine strains used in breeders in Italy, belonging to genotypic cluster I. The isolates were instead assigned to clusters II and IV. These findings confirm the circulation of genetically distinct ARV genotypes in Italian poultry farms and underline the need for broader investigations of suspected cases to improve understanding of ARV epidemiology and to refine control strategies.