Researchers target wasting disease in livestock

Researchers aiming to control or even eliminate a disease in farm livestock which costs the nation up to $88 million a year are probing where some genetic types of animal are particularly susceptible -- or resistant.

A micro-organism with the tongue-twisting scientific label of Mycobacterium avium subspecies paratuberculosis -- also known as MAP -- causes Johne's disease, a chronic wasting intestinal disease in a range of animals, including cattle, deer and sheep.

Johnes is spread by the faeces of infected animals and blocks the absorption of food, causing them to waste away and die. Bacteria infect the walls of the intestines, causing a malabsorption syndrome, protein loss from the inflamed bowel, anaemia, and the collapse of the immune system.

It can not only mimic other health problems such as chronic parasitism, trace element deficiency and poor nutrition, but also interfere with tests for bovine tuberculosis.

The disease can also infect mustelids such as ferrets and stoats, and New Zealand scientists are also looking at whether such species are spreading Johne's disease between different species of farm animals, and different farms. Johne's Disease Research Consortium chairman Dr Andrew MacPherson said the science was focused on fundamentals of Johne's disease, developing better diagnostic tools that enable farmers and veterinarians to more easily identify infected animals, and examining how the disease spreads.

"Genetics is another important research area," he said. "We are working to identify a gene marker that does not compromise production but will allow farmers to select for stock that are resistant".

Increasing use of DNA screening would make it relatively easy for animals to be selected according to their level of susceptibility to the wasting disease.

Researchers were also aware of theories that there may be links been Johne's disease in animals and a very similar illness in humans, Crohn's disease.

But Dr MacPherson said the push to control Johne's on New Zealand farms was based on reducing costs and improving animal health, rather than trying to protect the industry against any future research which might show MAP causes Crohn's in humans, such as by surviving pasteurisation of milk.

"I've got a lot of faith in the dairy industry's ability to pasteurise," he said. The consortium was relaxed about the robust science underpinning pasteurisation.

Dr MacPherson, who was a cattle and sheep veterinarian for 20 years and has a sheep station near Gisborne, said the incidence of Johne's had fallen in cattle, but was causing concern in deer.

The consortium has set up a website to provide farmers with the latest information on Johne's disease, and the work being done by the consortium.

It has just lost a chunk of its budget as a result of sheep farmers voting not to pay levies on wool to fund industry-good work such as research.The $250,000 of farmer money would have been matched dollar-for-dollar by taxpayers.

NZ scientists doing world-class work, such as Geoff DeLisle, Bryce Buddle and Frank Griffin have contributed heavily to global knowledge about the disease.

Dr MacPherson said the website was helping researchers in different groups collaborate.