.JPG)
Douwe Bakker and Peter Willemsen, CIDC-Lelystad, The Netherlands.Douwe Bakker and Peter Willemsen, CIDC-Lelystad, The Netherlands.
Mycobacterium paratuberculosis causes paratuberculosis (Johne's disease) in domestic ruminant livestock such as cattle, sheep, goats and farmed deer. Paratuberculosis in ruminants is characterized by a chronic granulomatous enteritis. The chronic enteritis results in malabsorption of essential nutients and accelerated protein loss. Clinical signs of the disease are decrease in milk production, progressive weight loss, intractable diarrhoea, wasting, and finally death. Paratuberculosis results in significant economic losses to the herd owner. These losses are mainly caused by a decreased milk production, early replacement of the animals, susceptibility to disease and direct expenditure on diagnosis and control.
Disease transmission is thought largely to occur via the faecal-oral route. Faecal contamination of teats, also resulting in the presence of mycobacteria in colostrum and milk are the major source of infection; contaminated pasture, water and feed may also be responsible for transmission of infection. The actual prevalence of paratuberculosis in most countries is unknown. Given the uncertainties in the performance with regard to sensitivity and specificity of the tests used, the true prevalence in the Dutch dairy herds is estimated to be between 50% and 80% at herd level.
In Europe, unsuccessful attempts have been made to control the disease by
vaccination, or by culling or removing animals that test positive, usually
by faecal culture or serum antibody test. Inadequate diagnostic tools are regarded
to be the main cause of this failure. Inter-species transmission of paratuberculosis
has been demonstrated through experimental infection of domestic ruminants
with different strains of M. paratuberculosis isolated from different domestic
species and there are reports of natural disease of sheep and goats grazing
with infected cattle. Wildlife ruminant species reported to be infected with
M. paratuberculosis are white-tailed deer, red deer, roe deer, exotic deer,
tule elk, and bighorn sheep.
Recently, the known host range of M. paratuberculosis has been increased to
include non-ruminant wildlife species, in particular the rabbit. Foxes, weasels,
ferrets and birds that predate or scavenge on rabbits also have been shown
to be infected.
In general, wildlife reservoirs are regarded to pose a threat to the efficacy of various disease control strategies in domestic livestock systems. However, early indications from recent studies in the Netherlands show that thusfar paratuberculosis is not yet widespread in Dutch wildlife. Therefore, the high prevalence of paratuberculosis in Dutch dairy herds could pose a threat to a wide variety of wildlife, not vice versa.
Establishment of a wildlife reservoir of paratuberculosis will not only greatly affect the little wildlife left, but will also interfere with any conceivable control programme for paratuberculosis in domestic livestock in the future.
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