Johne's Disease Research

A two-year project involving the University of Otago to develop new diagnostic tests involving biomarkers to identify animals that express extremes for resilience or susceptibility following exposure to infection with paratuberculosis (or Johne’s disease) in deer.

Johne’s disease is a common cause of death and reduced growth rates among deer. It also affects sheep and cattle.

The disease is caused by bacterial infection with Mycobacterium avium subspecies paratuberculosis. The infection starts in the small intestine and spreads to the lymph nodes. If the disease advances, the intestinal walls can thicken, interfering with digestion and absorption of nutrients and causing loss of serum proteins.

Johne’s disease is most often introduced onto an uninfected farm through newly purchased deer. On farm, infection occurs through deer eating pasture or drinking water contaminated with contaminated faecal material. Hinds can also pass the bacteria on to their fawns through the placenta, colostrum or milk.

Clinical signs are muscle wasting, ill thrift and diarrhoea. Stress can bring on clinical effects. Sometimes enlarged lymph nodes or cheese-like abscesses can be seen. Typically infected deer show only subclinical symptoms (slow growth rates) rather than obvious symptoms. This means it can be hard to recognise the problem.

Johne’s disease outbreaks typically affects young deer aged 8-15 months, with losses of up to 20% recorded. Sporadic cases in mixed age deer occur in 1%-3% of adult animals per annum.

There are several immune diagnostic tests currently available. Some involve taking a blood sample. These are best used for confirming Johne’s in a deer with clinical signs of the disease. However the test are still not 100% accurate. This is because other bacteria can cause lesions or immune sensitization producing False (+) results.

Faecal samples can be cultured but it takes up to 60 days. As shedding of the bacteria in the faeces is intermittent, not all infected animals (especially those with minor infections) will show up as positive. Culture can be used to identify different strains of the bacterium. A recently developed molecular test (Polymerase Chain Reaction – PCR), which detects bacterial DNA, can provide results within one day.

If the animal is going to slaughter, Johne’s can be confirmed by culturing intestine and lymph nodes, or by carrying out a PCR test. Often the first indication of Johne’s in a herd is from the processing plant. Meat inspectors note animals with enlarged lymph nodes at slaughter, and the number of animals with lesions are reported back to farmers. Johne’s Management Limited, who has a register of all animals showing enlarged lymph nodes at meat inspection, supervises this programme. Farmers can use this information to help put a control programme into place.

The research project has received $500,000 for a two-year project to look at ways of developing new diagnostic tests to identify individual animals that express extremes for resistance or susceptibility following exposure to infection. It is a partnership between the New Zealand Deer Farmers’ Association, Callaghan Innovation, and the University of Otago, with funding provided by the deer industry through the Deer Farmers Association (DFA), Deer Industry New Zealand levy payments received in trust for science funding by the Deer Industry New Zealand Research Trust (DINZRT) and Callaghan Innovation (Government). Experimental field studies will be carried out under subcontract to AgResearch and governance of the project will be provided by DEEResearch, which has oversight for the Deer Industry’s research portfolio.

Professor Frank Griffin, who for three decades has led a University of Otago-based research team devoted to solving animal health problems in the deer industry, says elective breeding of animals with increased resistance to infection was now widely recognized as a future strategy to increase the health, welfare and productive capacity of our livestock. He says the science was ”quite fundamental” and unlike most agribusiness research, it was built on a genetic resource not available anywhere else in agriculture worldwide. They have access to Peel Forest Estate Deer Farm, which has maintained a number of pure breeds of deer that express extreme levels of resistance or susceptibility to Johne’s disease. The unique patterns of resistance or susceptibility for each deer breed became evident after the herd had been exposed to high levels of Mycobacterium avium subspecies paratuberculosis infection for a number of years. These animals will be the basis of the research.

The findings were potentially translatable to other species, such as cattle and sheep, and other infectious diseases. It’s thought the work had ”significant” implications for the likes of the dairy industry.

Frank believes the deer industry had provided a unique genetic resource in terms of purity and the foundation genetics, which when combined with the new molecular technology, created exciting opportunities to chart the underlying pathways of immunity associated with, either resistance or susceptibility to infection.

Scientists had been able to access ”incredibly pure breeds of deer” where the purity of the foundation genetics allowed them to customise future breeding programmes to produce progeny for experimental studies of disease resistance or susceptibility.

The use of assisted reproductive techniques meant the genetic pool could be expanded very quickly.

There was now a new concept for managing disease or health because there was access to susceptible and resistant animals. Technology around genetics had ”come of age”, as it was now possible to map individual genetic traits to breed animals with multiple traits for production, reproduction and disease resistance.

The deer industry had always been self-sufficient and remarkably innovative in finding solutions to emerging problems. “Its members were always looking for opportunities and it had been a very progressive industry to work with”, he said. He had enjoyed the interaction with the leaders in the industry, who had given ”unequivocal support” to the project.

Ultimately, the goal is to select the best breeds that would produce the most product with the smallest carbon footprint.

New Zealand is ”beautifully placed” in the high-value primary food production market. It is perceived as being clean, green and chemical-free and that image had to be protected and enhanced through the production of food products, that maximize animal health and welfare, reduce our carbon footprint, and mitigate environmental damage.