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Johne's disease, also known as paratuberculosis, is a contagious bacterial disease of
ruminant animals affecting primarily the intestinal tract. Due to the long
incubation period of the disease (typically more than 2 years), the disease
appears hidden within a herd and is usually perceived as an individual cow
problem, rather than a herd problem.
The bacterium that causes Johne's disease is Mycobacterium paratuberculosis that
localizes in the wall of the intestines, producing a inflammatory response which
disrupts normal digestion and absorption of nutrients. It
is a Gram-positive acid-fast bacteria that grows very slowly in culture media
typically used in diagnostic laboratories,.
M. paratuberculosis is a relative of the bacterium that causes
tuberculosis in humans (Mycobacterium tuberculosis), cattle (Mycobacterium
bovis), and birds (Mycobacterium avium.
In
general, animals with Johne's disease "waste away" despite their
continuing to eat well. The two cardinal signs of M. paratuberculosis
infection are: diarrhea and rapid weight loss. In
some animal species, like sheep and goats, diarrhea is less common.
Other diseases can also lead to similar clinical
signs (examples include internal parasites, salmonellosis, and hardware
disease). Since
Johne's disease is considered non-treatable, these animals are typically culled
from the herd and sold for slaughter.
M. paratuberculosis
can replicate only when it is in animals: it cannot multiply in nature, outside
the animal. However, if soil or water is contaminated with this bacterium, it
can survive there for over a year because of its resistance to heat, cold and
drying.
In the
U.S.
it is estimated that 7.8% of the beef herds and 22% of the dairy herds are
infected with M. paratuberculosis.
Control
Principles of Johne's disease control include:
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Reducing exposure and
infection of replacement cattle on farm.
Ø
Identifying and removing
the most highly infected cattle.
Ø
Preventing introduction
of infection by screening sources of off-farm replacements.
Johne's disease control programs require a
long-term commitment to prevention and must be adapted to individual herds. This
approach, however, has not yet been widely adopted by veterinarians and
producers.
Useful
Links:
USDA Disease Surveillance Information - Johne's Disease
DairyBusiness
- Controlling Johne's Disease step by step
University of Wisconsin - Johne's Information
Center
HorsePages.com -
Johne's Disease
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