What is Reovirus?
Reovirus is a very common virus in broilers and broiler breeders. There are many different strains of reovirus. The most common disease associated with reovirus is tenosynovitis (inflammation and swelling of one major tendon of the leg). Currently, it is not known which serotype(s) or strain(s) are causing tenosynovitis in Saskatchewan. Broiler flocks with tenosynovitis may also have increased pericarditis (inflammation around the heart) condemnations.
Tenosynovitis
Tenosynovitis is either unilateral or bilateral swelling in the tendon causing lameness. Birds limp or hesitate to get up and walk. In severe cases, the tendon can actually rupture. Mortality is typically not high however; heavy culling due to lameness is seen.
Control of Reoviral Infections
Broiler breeder vaccination is currently the method of control for reovirus infections. Unfortunately, vaccines do not contain all the strains or they contain strains that are not causing the disease seen in the field. The goal of our research is to determine which strains are causing infections in the field, and in the future develop a broiler breeder vaccine specific to the strains we find.
Our Research
How do we confirm Reoviral infections?
We look at a few things: antibody titers as we explained above, clinical signs (lame birds, swollen tendons), microscopic examination of the tendons, and virus growth in cell culture. Cell culture is used to further identify reovirus types. A sample of tendon is homogenized and put into a plate containing chicken cells. We look at the cells and tendon mixture - if the cells demonstrate a pattern associated with reovirus growth and there is cell death, then we know there is live reovirus in the tendon. After we know that, we can look at the genetic code of reovirus to determine the strain. This takes few weeks of work!
Our results so far:
Serological survey at Saskatchewan broiler farms
We collected sera at processing from 59 broiler farms. We found that 98.3% of farms were positive for reovirus. It is important to understand that just because farms were positive based on testing their sera does not necessarily mean that it was due to infection by disease causing reoviruses! The test used for this survey is not capable of differentiating between the reoviruses that cause disease and those that do not. It simply tells whether birds were exposed to reovirus or not. Currently there is no blood test available that can differentiate between pathogenic (disease causing) and non-pathogenic (non-disease causing) reoviruses.
Reovirus field cases
The clinical signs in infected birds in the field was ruffled feathers, splayed legs and reluctance to stand up. These birds had either unilateral (one side) or bilateral (both sides) inflammation of the tendons. Tendon samples were collected from these birds for microscopic examination. The most common microscopic finding was the presence of high number of immune cells.
Virus isolation from field cases of reovirus
Tendons were collected from infected birds. Of these samples, 82% were positive for disease causing reoviruses and a total of 37 reoviruses were isolated.
Genetic Analysis of the reovirus isolates
The 37 different reoviruses isolated were grouped into 4 distinct groups, based on each virus’s genetic make-up. The viruses were genetically different from the vaccine and vaccine-related field strains. This can be one of the main reasons why the vaccines currently used in the Saskatchewan industry fail to protect birds from reovirus associated disease caused by these emerging new reoviruses.
Evaluation of broiler breeder antibodies
Broiler breeders are currently vaccinated against reovirus so neutralizing antibodies (i.e. proteins that can get rid of the virus) are passed to broilers. When we tested sera from broiler breeders in Saskatchewan, we found that they did have neutralizing antibodies against the vaccine strain. However, those antibodies were unable to stop the newly emerging reoviruses from causing disease.
From our results so far, it is suggestive of the presence of reovirus infections in broiler flocks in Saskatchewan.
Current Work
We are in the process of developing a broiler breeder vaccine for control of reovirus infection.