Avian reovirus variants and lameness in broilers

Davor Ojkic, Marina Brash, Emily Martin, Emily Brouwer

Animal Health Laboratory, University of Guelph, Guelph, ON

AHL Newsletter 2020;24(1):12-13.

Avian reoviruses (ARV) are ubiquitous and often cause asymptomatic infections. Diseases associated with ARV infection are influenced by the virus pathotype, route of exposure, age and immune status. Certain ARV strains cause arthritis/tenosynovitis, respiratory disease, enteric disease, immunosuppression and malabsorption syndrome. Involvement of other infectious agents may also impact the nature and severity of reovirus-associated disease.

Prior to 2012, reovirus-associated leg issues occurred sporadically in Ontario broilers. However, in 2012-2013 and 2017-2018, outbreaks of reovirus-associated lameness resulted in significant morbidity and economic losses. Of 2,502 samples that were tested between 2012 and 2019 by real-time PCR, the majority (55%) were ARV-positive (Table 1).

Table 1.  Results of avian reovirus PCR tests conducted at AHL, 2012-2019.

Clinical presentation and intensity of histologic lesions varied and often appeared to be strain dependent, with cull rates ranging from 2% to 50%. In extreme cases, entire flocks had to be depopulated. Genotyping results determined that at least ten “variant” ARV strains were involved in cases with lameness issues in broilers. During the first outbreak in 2012, most variants were Variant A and Variant B. Since 2016 however, Variant D has been most frequently detected in affected birds, and it appears that introduction of genetically different viruses is still occurring (Table 2). Unfortunately, the source of introduction is unknown.  AHL

Table 2.  Avian reovirus genotypes identified at AHL, 2012-2019.