Malignant catarrhal fever
Malignant catarrhal fever is less common than it used to be, but is a severe disease that cannot be treated and usually causes death. In deer it is associated with a herpes-type virus and probably comes from a form that affects sheep. Stags are more susceptible than hinds, and winter is the worst time for infection. Prevention is the best approach, and this is done by separating sheep from deer, feeding deer well and minimising their stress.
Bovine tuberculosis (TB) probably poses the biggest threat to the deer-farming economy, and also risks the health of farmers and slaughterers. New Zealand has a scheme aimed at controlling and eventually eradicating the disease. The Animal Health Board is responsible for controlling TB and accredits farms after tests are clear. Eradicating TB in farmed deer is complicated because it can be transmitted back to them by cattle, possums and ferrets.
Johne’s disease was first identified in farmed deer in the late 1990s. It is caused by the bacterium Mycobacterium paratuberculosis, which can be passed to deer by cattle and sheep. It is related to TB and their symptoms are similar, which complicates diagnosis of both. Johne’s disease affects the intestines, leading to failure to thrive and in many cases death (up to 20% of infected animals die quickly). In cattle and sheep it does not affect young animals, but in deer it does, especially at the end of winter and other times of stress. In a herd of deer, some infected animals show little or no signs of the disease, but can pass it on to others.
Deer Industry New Zealand and the New Zealand Deer Farmers’ Association (NZDFA) support research and practical activities towards controlling the disease. The NZDFA Johne’s Research Group has written a manual on how to manage the disease and minimise its effects on farms.
Mad deer disease?
A mysterious disease of deer and elk in Canada and the central US appears to be spreading. It riddles the brain of infected animals, which lose condition and die. There is no evidence yet of humans contracting the disease.
Young deer are generally more susceptible to leptospirosis than adults, and some can die. The bacteria can infect humans, and there is always a risk of infection for those working at slaughtering plants. Animals with the disease are treated with antibiotics.
Clostridial diseases (blackleg, pulpy kidney) in deer have similar symptoms to those in sheep and can be prevented by vaccination. Yersiniosis strikes sporadically, and cryptosporidiosis is a recent disease of newly weaned deer.
Lungworm and internal parasites are major problems in young deer, causing failure to thrive and death. Problems are worse when nutrition is inadequate and animals have been poorly managed. These parasites can be treated with regular doses of anthelmintics, given to young deer orally or as a pour-on drench. Drenching can start before weaning in January and should continue every three to six months until natural immunity occurs around 11–12 months of age.
Internal parasites in deer are becoming resistant to drenches. Research is being done to modify drenching programmes and find alternative methods of control.
External parasites of deer include ticks and lice. Nymph (larval) ticks can be a major problem on newborn fawns, causing some deaths. Tick infestations of velvet antler during growth in the spring can be a problem in some years. Shower and spray treatments are available, but these are licensed for cattle and sheep and not usually for deer. An insecticide worn as an ear tag, effective for up to eight weeks, has recently been developed for hinds during the fawning season where there is high risk of infection.