|
Johne's (pronounced "Yo-nees") disease is a contagious, slowly developing and fatal bacterial disease of the intestinal tract. A German veterinarian first described it in a dairy cow in 1895 and the disease was named after him. The disease is also called paratuberculosis. Johne's disease primarily occurs in domestic and wild ruminant species such as sheep, goats, cattle, bison, deer, llama, etc. It has also infrequently been reported in non-ruminant species e.g. rabbits, primates, fox and stoat.
This disease
is hard to detect. The signs of Johne's disease are vague and months
can pass after infection before they appear. Weight loss in animals
with a good appetite may be the only indication as diarrhea is not
a common sign in sheep, unlike what is seen in cattle. Infected
sheep may appear unthrifty and wool break/poor fleece condition
may also be noted. The signs of Johne's disease can be confused
with the clinical indications of other conditions such as parasitism,
OPP (ovine progressive pneumonia), CLA (caseous lymphadenitis) or
malnutrition. Of course, more than one problem may be occurring
- for example, sheep eventually succumbing to Johne's disease had
improved clinically after treatment for parasites. Because of the
slowly progressive nature of the infection, signs of Johne's disease
are usually not seen until animals are adults.
Knowledge
on the prevalence of this disease in the approximately 8.5 million
sheep and lambs in the U.S. is limited, due both to lack of testing
and reporting. However, valuable information on the prevalence of
Johne's disease in sheep managed in the United States will be collected
through the confidential "Sheep 2001" survey to be conducted by
the National Animal Health Monitoring System of the USDA. BM_1_(Please
consider participating in the survey if asked - the results likely
will guide U.S. sheep health and welfare programs.)
Johne's disease typically enters a flock when an apparently healthy, but infected, animal is introduced. This animal contaminates the premises (feed, ground, water) by shedding the organism in its manure. The organism is then ingested by other sheep. Lambs are thought to be most susceptible to infection and their suckling manure-contaminated teats is another route of infection. It is also possible that a ewe in the later phases of the infection can shed M. paratuberculosis into her milk and colostrum, thus transmitting it to her lambs.
The best
way to avoid this chronic infectious disease of course is to be
as certain as possible that animals brought into the flock are not
infected with M. paratuberculosis. Johne's disease test-negative
flocks are the best sources of animals for purchase. Since many
flock managers do not yet test for the infection, assess the entire
flock (not just the animals you intend to buy) for body condition.
Ask the owner about the cull rate and common cause for culling -
how many animals were thin/unthrifty for no confirmed reason? Check
the body condition of the dam of lambs you intend to purchase and
have her tested if you have suspicions (tests on sheep less than
one year old are not likely to be informative unless exhibiting
signs of the infection).
There are two common ways to test sheep for Johne's disease: culture of fecal samples and blood tests for antibodies to M. paratuberculosis. The biology of the disease can make it difficult to detect infected animals, especially those in an early stage of infection. A truly infected sheep in this "sub-clinical" phase may neither be shedding the organism consistently (thus the fecal culture may be negative) nor be making antibody in response to the infection (thus the blood test will be negative). Despite this, collecting manure for culture and/or blood for either the ELISA or AGID, as the blood tests are called, can provide useful information needed to control the infection.
Although few studies have been reported, Johne's disease is not considered a curable disease. As with most diseases caused by mycobacteria, the course of therapy is very long (months) and expensive. For most animals, treatment is cost prohibitive and the best that can be expected is an improvement in clinical signs while under treatment, not a cure.
This is a very controversial subject. There is a human disease called Crohn's disease that in some ways resembles Johne's disease. The cause of this chronic inflammatory bowel disease is not known and there is no known cure. A few laboratories have grown M. paratuberculosis from a few Crohn's patients' specimens but there is no evidence that the organism caused the disease. No connection has been shown between contact with animals with Johne's disease or milk consumption and Crohn's disease. |
   |
||||||
 |
||||||
 |
 |
 |
|
 |
|
 |