11 Reovirus Infections

Avian reoviruses are members of the orthoreovirus genus in the Reoviridae family (4, 6). Ubiquitous in commercial poultry, they can be differentiated by antigenic configuration, pathotype, relative pathogenicity, growth in cell culture, sensitivity to trypsin, and host specificity (2, 3, 4, 5, 8, 9, 10, 11, 12).1 Reoviruses have been isolated from a variety of tissues in chickens affected by assorted disease conditions, including viral arthritis/tenosynovitis, stunting syndrome, respiratory disease, enteric disease, immunosuppression, and malabsorption syndrome (9, 10, 11, 12). They have frequently been found in chickens that were clinically normal. The nature of the disease that occurs following reovirus infection is very much dependent upon host age, immune status, virus pathotype, and route of exposure. Interactions with other infectious agents have been documented (9, 11, 12) and may result in differences in both the nature and severity of reovirusinduced disease expression. In young meat-type chickens, economic losses related to reovirus infections are frequently associated with increased mortality, viral arthritis/tenosynovitis (9), and a general lack of performance including diminished weight gains, poor feed conversions, uneven growth rates, and reduced marketability of affected birds (1). Breeder flocks that develop viral arthritis just prior to the onset of or during egg production may in addition to lameness be characterized by increased mortality, decreased egg production, suboptimal hatchability/fertility, and vertical transmission of virus to progeny—all of which can contribute to increased costs for poultry producers.