Johne’s disease is a common cause of death and reduced growth rates among deer. The disease is caused by a bacterial infection (Mycobacterium avium subsp. paratuberculosis or MAP) in the gut and is closely related to the organism that causes tuberculosis.
MAP, which causes Johne’s disease, is a tough and persistent organism that may be found in slurry or dung. Therefore, infection could be present on pasture for at least a year after slurry or manure has been applied or has been contaminated by grazing cattle. Even if manure has been well composted, MAP may still be present.
All deer can be infected by cattle and sheep strains of MAP and since the primary route of infection is through the ingestion of contaminated food and drink, co-grazing between species should be avoided where possible.
Actiphage® rapid blood test for early detection
PBD Biotech was established to commercialise the work on an improved test for mycobacteria developed by Drs Cath Rees, at the University of Nottingham, and Ben Swift of the Royal Veterinary College.
Actiphage is a simple blood test that is able to detect the presence of viable mycobacteria and accurately identify the strain. As it can distinguish between live and dead mycobacteria, it also promises a DIVA test (differentiating between infected and vaccinated animals) for the industry.
The Actiphage test is able to identify animals at an early stage of infection from MAP or bovine TB (caused by Mycobacterium bovis) before they start to transmit the disease. This enables more effective disease management within the herd.
Actiphage is currently undergoing UK and international trials towards OIE validation, which would enable it to be used routinely by vets. It already has Animal and Plant Health Agency (APHA) permission for exceptional private use in English cattle herds that have undergone chronic bovine TB breakdowns.
Testing for TB
Red deer are susceptible to bovine TB. Infected animals have no symptoms until the disease is well established so the disease can spread through herds, either through close contact or from hinds to calves in milk. In utero transmission from hinds to foetus more common than in cattle.
The standard test for M.bovis is the skin test Single Intradermal Comparative Cervical Tuberculin (SICCT), which measures the immune response to tuberculin. This is a complex mix of proteins extracted from lab cultures of M. bovis and killed by heat.
If an animal is infected, its immune system will have been ‘sensitised’ (primed) and the injection of tuberculin incites an inflammatory response with a swelling developing at the injection site.
The vet injects the tuberculin and then returns three days later to inspect the animals for a reaction. The ‘reactors’ are removed from the herd and destroyed.
However, the main limitation of the tuberculin skin test is its sensitivity ie. the probability that it will correctly identify an infected animal as positive. Studies have shown on average 20% of bovine TB-infected cattle can be missed by one round of skin testing using standard interpretation.
The SICCT test can be used for deer, but an additional issue is the amount of handling required. The deer need to be seen twice by the vet within three days, which is stressful for the animals – and also expensive to have a vet on stand-by while containing the stags.
Actiphage as a test in deer
The benefits of Actiphage were apparent to Sarah Arden of Arden Farms, and the farm has been supporting the development of the MAP test for use in venison farming.
Sarah has particular interest in using Actiphage to screen animals before they are used as breeding stock, and has undertaken comprehensive testing on breeding animals over the summer in conjunction with a PhD student.
Johne’s disease testing is the main application for Actiphage in deer herds today. However, PBD Biotech would also welcome expressions of interest from any farmer or herd-owner interested in trialing its TB test on their herd.
If you would like to discuss using or helping to trial Actiphage in deer or another species, please get in contact touch.