Johne's disease is an infection of the small intestine by the bacteria Mycobacterium avium subspecies paratuberculosis (MAP for short). It is most common in farmed ruminants but can occassionally be found in other species too. Initial infection generally occurs when the animal is very young. Following this is a 'latent' period where the animal is infected but apparently healthy as the bacteria is essentially dormant within it. The latent period may be short or extend for years. Clinical signs of disease may emerge after times when the animal has been under stress.
Animals developing Johne's disease pass through a range of worsening clinical signs. The signs begin with a drop in productivity which may mean a failure to gain live weight, or weight loss, and a drop in milk production in dairy animals. This is followed by scouring and particularly foul smelling diarrrhoea which leads to severe emaciation and eventually death.
They can go from healthy looking to severely ill in a couple of months.
In weaner and yearling deer outbreaks of Johne's disease are occassionally severe, affecting around 20 - 30% of a mob. In adult deer the disease usually only causes sporadic cases.
It is a major cause of economic and productivity loss at the farm and industry level. Sporadic serious outbreaks on infected farms are a major animal health issue.
It is also difficult to control and it is present on many sheep, beef, and dairy farms in New Zealand. The complex nature of the infection cycle means a concerted effort is needed to control it.
It can cause false positive reactions to the test for bovine tuberculosis (Tb) plus lesions caused by Johne's disease have an identical appearance to Tb lesions too which complicates the control of this other important disese.
If you notice well managed deer in your herd losing weight JD should to be ruled out as a cause, given the many possible reasons for a loss of productivity. If those deer also have foul smelling diarrhoea you can be far more confident the cause is in fact JD. Get your veterinarian to confirm a diagnosis. The diagnosis should include some or all of the following tools:
DeerPRO recommends veterinarians who are members of the New Zealand Veterinary Association Deer Special Interest Branch. For information on the member nearest you, please email deer@vets.org.nz.
Yes.
Johne’s disease can be successfully and cost effectively controlled.
Over a decade of experience has repeatedly shown control outcomes that the farmer, veterinarian, and DeerPRO feel were successful.
A control programme will involve the following steps:
The bottom line is more animals, heavier sooner and better which is exactly the aim for the New Zealand Deer Industry.
The main way that JD spreads between farms is through the trading of healthy looking but infected deer.
The main way that JD is transmitted between animals is when young calves ingest the MAP bacteria which can be found in high numbers in the faeces of diseased animals and may also be in their milk. This is most likely when it is suckling from an infected hind (calves may suckle from hinds other than their mother) but can also happen when grazing contaminated pasture or eating contaminated supplementary feeds. The calf’s gut system matures in the months post birth and this process is likely to make it particularly susceptible to infection by MAP.
Calves may also be infected before birth in the uterus.
Drinking water contaminated with MAP infected faeces is another potential source of infection.
There is no transmission risk through nose-to-nose contact through fences.
Wildlife are not generally considered a major source of transmission of JD. However the bacteria have been found in multiple wildlife species in New Zealand including rabbits, hedgehogs, ferrets, cats and gulls. The role of these species in the persistence of MAP is unknown at this point but probably very low.
The importance of transmission of JD between deer and other species of livestock is not yet well understood.