RABBITS AND deer could be involved in the spread of Johne’s disease, but a new, more reliable test could be on its way to help tackle the disease.
Moredun, Edinburgh, researcher Karen Stevenson said a survey of Scottish wildlife conducted with SAC found Johne’s in rabbits in a region where there were farms with both large rabbit populations and Johne’s in cattle.
“This raises the potential of wildlife acting as reservoirs for Johne’s infection, even where a herd is clear of the disease. A further survey also found 2% of Scottish deer were infected with Johne’s.
“There is also evidence of the bacteria in most species, such as foxes and stoats, which feed on rabbits, although this appears to be a dead-end infection. However, rabbits are diseased and may spread Johne’s.
“These potential wildlife reservoirs have significant implications for disease control. A closed herd which has tested free of Johne’s could be reinfected by rabbits. But more work is needed to investigate the interspecies transmission of the disease and the epidemiology of infection,” she said.
However, there is hope on the horizon, with work ongoing to develop a more accurate and reliable test for Johne’s. “Recently, using modern technologies, Moredun has identified a number of proteins specific for Johne’s that could be incorporated into diagnostic tests.
“The current ELISA blood test for Johne’s is non-specific for Johne’s and can result in false positive reactions. It also relies on detecting antibodies to the bacteria, but animals do not develop antibodies until the disease is well advanced.
“Faecal culture is more reliable, but this takes up to 16 weeks for cattle and even longer for sheep. Controlling disease on farm is equally difficult as for every one clinically infected cow there are likely to be another 25 sub-clinically infected. These sub-clinical animals are a real problem as they shed the disease in their faeces without showing infection themselves,” said Dr Stevenson.
The recent work is likely to lead to the development of three to four new tests for Johne’s, although more work is needed on the type of test to be developed. “It will take three to four years to show that the proteins are suitable for developing a test and a further, unknown, period to develop the test,” she added.