This is 4th article in a series of 4
University of Minnesota, Minnesota Veterinary Diagnostic Lab
Although many questions about turkey reoviral arthritis have been addressed in this four-part series, it is clear that despite several years of research and investigation there are many questions remaining to be answered. We are participating in a national effort to address industry concerns about reoviral arthritis.
Turkey reovirus subcommittee – A Reovirus Subcommittee of the National Turkey Federation has met during the last two years and seeks to organize both industry personnel and university researchers to address the TARV issue. The mission is to ensure transparency and collaboration to develop turkey-specific solutions to assist the industry in controlling turkey reoviral arthritis. This subcommittee met at the Minnesota Poultry Federation Convention meeting on March 13, 2019 to identify four focus areas:
- Define the economics of turkey reoviral arthritis/tenosynovitis in turkey production
- Determine what diagnostic tests are available, what lab offers the tests and what tests are being developed
- Methods for prevention of reovirus infection
- Current research needs, such as developing uniform terminology for reovirus identification across many labs.
What is new in research at the University of Minnesota?
1. Age susceptibility turkeys to TARV – we have received partial funding from Minnesota Turkey Research and Promotion Council (MTRPC) to support this study. We know very litte about the age at which turkeys are susceptible to reovirus infection and how easily reovirus can spread between turkeys.
2. Pathogenesis of selected strains in vivo – In this study, supported by the University of Minnesota Rapid Agricultural Response Fund (RARF) , we will determine if there are differences between reoviruses that cause lameness vs those that cause enteritis and aortic rupture. We will compare pathogenesis of reoviruses isolated from tendons, feces and heart.
3. Survey of chronically infected flocks: Based on our discussion with industry veterinarians, some farms see consistent TARV-associated lameness. It is not clearly understood why these farms experience repeated challenges. We will select four of these affected farms and compare with clean farms (n=2) by collecting and analyzing birds and environment samples (feces/litter) both before and after placing birds.
4. What are the optimum samples for detecting TARV by PCR or virus isolation? We are currently comparing different segments of the gastrocnemius and digital flexor tendons in order to optimize uniformity of sample collection and improve test accuracy. Additionally, we are assessing joint fluid as an alternative to tendons for reovirus testing.
5. Is TARV a seasonal problem? In 2019 the Minnesota Veterinary Diagnostic Laboratory (MVDL) continues to receive many turkey leg submissions from lameness cases throughout the U.S and several outside the U.S., including Germany. Based on the quality of submissions over several years it is clear that both producers and poultry veterinarians are better at recognizing the typical lesions and perhaps recognizing flock lameness at earlier ages. Case submissions received in in the first quarter of 2019 have been numerous and are often associated with severe clinical signs. We are now characterizing these 2019 viruses to see if there are differences from TARVs isolated in previous years.
Update on diagnostic test development:
1. ELISA – final validation of a turkey-specific ELISA is underway and we expect to offer this as an official VDL test by June 1, 2019. Prior to this date we can offer the ELISA as a non-validated test. We anticipate that this assay will be used to monitor antibody titers in breeder flocks as well as growing turkeys. It will be useful to gather more data on the typical reovirus titers observed in the field; from poults receiving passive immunity from vaccinated breeders, characterizing early field challenge titers in 9-weeks old turkeys (midgrowth), and determining typical titers in turkeys at the chronic stages of the disease.
2. Cross-neutralization assay – we have optimized this classic test and are finalizing a serum-virus panel to use in this test for differentiating TARV strains and identifying novel virus strains. We anticipate offering this testing service to our turkey clients by June 1, 2019.
3. Whole genome sequencing for genotyping- We are working on providing whole genome sequencing in a cheaper and more efficient fashion. The NGS project conducted by our group is in progress to search for gene sequences to differentiate both TARV strains as well as enteric reovirus strains. The funding for this research came from the UM-RARF and MTRPC.
Summary: The University of Minnesota TARV Research Group has created the following case definition for turkey reoviral arthritis/tenosynovitis.
Turkey reoviral arthritis is a progressive condition that appears as early as 10-12 weeks of age in male, and sometimes female, commercial turkeys. Younger birds are occasionally affected. The virus is distinct from chicken reovirus and the disease does not appear to be transmitted from chickens. Signs are most severe when the birds reach 15-16 weeks of age. Clinical signs include reluctance to move, recumbency and limping on one or both legs. There is often uni- or bilateral swelling of the hock (intertarsal) joint. Morbidity can be as high as 40% and mortality is usually a result of culling or aortic rupture. Lesions observed in acutely affected birds at necropsy are uni- or bilateral enlargement of the hock joints. Increased synovial fluid oftens fills the hock joint space and the sheaths of the gastrocnemius and digital flexor tendons. In chronic cases there is bruising of the skin of the hock, with prominent periarticular fibrosis, edema and occasional large flecks of fibrin within the subcutis and tendon sheaths. In a small percentage of cases there is partial or complete rupture of the proximal gastrocnemius tendon or a digital flexor tendon often accompanied by hemorrhage. Histological sections of gastrocnemius tendon and sheath reveal lymphocytic infiltrates in the subsynovium in acute cases, progressing to prominent subsynovial and peritendon fibrosis in chronic cases. Secondary bacterial infections (e.g., Staphylococcus) can occur and are accompanied by heterophilic inflammation. Definitive diagnosis is supported by 1) observation of typical gross and microscopic lesions, 2) ruling out other causes of lameness (e.g., osteomyelitis, bacterial arthritis, muscle rupture, footpad dermatitis, Mycoplasma synovitis) and 3) isolation of reovirus, referred to as turkey arthritis reovirus (TARV), from the gastrocnemius and/or digital flexor tendon in embryonated eggs or cell culture.