Avian Reoviruses from Clinical Cases of Tenosynovitis: An Overview of Diagnostic Approaches and 10-Year Review of Isolations and Genetic Characterization

Reoviral-induced tenosynovitis/viral arthritis is an economically significant disease of poultry. Affected birds present with lameness, unilateral or bilateral swollen hock joints or shanks, and/or reluctance to move. In severe cases, rupture of the gastrocnemius or digital flexor tendons may occur, and significant culling may be necessary. Historically, vaccination with a combination of modified live and inactivated vaccines has successfully controlled disease. Proper vaccination reduced vertical transmission and provided maternal-derived antibodies to progeny to protect against disease, at an age when they were most susceptible. Starting in 2011-2012, an increased incidence of tenosynovitis/viral arthritis was observed in chickens and turkeys. In chickens, progeny from reovirus-vaccinated breeders were affected, suggesting commercial vaccines did not provide adequate protection against disease. In turkeys, clinical disease was primarily in males, although females can also be affected. The most significant signs were observed around 14-16 wks of age and include reluctance to move, lameness, and limping on one or both legs. The incidence of tenosynovitis/viral arthritis presently remains high. Reoviruses isolated from clinical cases are genetically and antigenically characterized as variants, meaning they are different from vaccine strains. Characterization of the field isolates reveals multiple new genotypes and serotypes that are significantly different from commercial vaccines and each other. In 2012, a single prevalent virus was isolated from a majority of the cases submitted to the Poultry Diagnostic and Research Center at the University of Georgia. Genetic characterization of the σC protein revealed the early isolates belonged to genetic cluster (GC) 5. Soon after the initial identification of the GC5 variant reovirus, many broiler companies incorporated these isolates from their farms into their autogenous vaccines and continue to do so today. The incidence of GC5 field isolates has decreased significantly, likely because of the widespread use of the isolates in autogenous vaccines. Unfortunately, variant reoviruses belonging to multiple GCs have emerged, despite inclusion of these isolates in autogenous vaccines. In this review, an overview of nomenclature, sample collection, and diagnostic testing will be covered, and a summary of variant reoviruses isolated from clinical cases of tenosynovitis/viral arthritis over the past 10 yrs will be provided.