Educational
Information
What is Johne’s
Disease?
What are the signs of Johne’s Disease?
How is Johne’s Disease Controlled?
How is Johne’s Disease Diagnosed?
Is Johne's Disease a risk to small ruminants like sheep and goats?
Are there any human health issues?
Links to MSU Extension Publications
Links to Johne's Disease Information Sites
What is Johne’s Disease?
Johne’s
Disease, or paratuberculosis, is an untreatable, chronic,
progressive, infectious disease caused by the bacteria Mycobacterium
avium paratuberculosis (MAP) that primarily affects the intestinal
tract of cattle and other ruminant species. The infection
causes a gradual thickening of the lining of the intestine
over a period of several years; slowly compromising the digestive
capability of the animal eventually resulting in decreased
production, weight loss, intermittent to chronic diarrhea
and finally death. Transmission of the infection to uninfected
animals occurs early in life, generally through consumption
of the organism from the environment or contaminated colostrum
or milk. Animals can also become infected prior to birth if
the dam is in an advanced stage of the disease. Due to the
slowly progressive nature of the disease, diagnosing infected
animals is challenging especially during the early, pre-clinical
stages of disease. Control of Johne’s disease depends
on management practices that limit exposure of susceptible
animals to MAP.
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What are the signs
of Johne’s Disease?
Clinical signs of Johne’s disease rarely
appear in cattle until they are approximately two or more
years of age. Infection generally occurs early in life from
ingestion of contaminated fecal material from either the environment,
udder of the dam, or thru contaminated milk or colostrum.
Animals exposed at an older age, or exposed to a very small
dose of bacteria at a young age, are not likely to develop
clinical disease until they are much older than two years
of age. The bacteria that causes Johne’s disease invades
the cells that line the wall of the small intestine. The animal’s
body then produces an inflammatory response. The resulting
bacteria and immune response lead to a thickening of the gut
wall and, eventually, an inability to absorb water and essential
nutrients, resulting in chronic diarrhea. Cattle gradually
lose weight and become emaciated, while still maintaining
a good appetite. They may also develop 'bottle jaw', a soft
swelling under the mandible due to protein loss from the bloodstream
into the intestinal tract. Signs may appear after a period
of stress such as calving, poor nutrition, heavy milk production
or any other cause. Once such signs occur, death generally
follows within a matter of weeks.
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How is Johne’s Disease Controlled?
Controlling
Johne's disease can be a difficult goal. Johne's disease is
particularly difficult to control because animals can be infected
with MAP and yet appear perfectly healthy. Most cattle become
infected with Johne's disease as young calves, but do not
exhibit signs until the age of two or greater. It is highly
recommended that producers attempting to control or eliminate
Johne's disease from their herds begin by performing, or having
a veterinarian perform a risk assessment on the farm. Once
a risk assessment has been done, producers can begin to make
changes to decrease further spread of the disease. Producers
can also work with veterinarians to institute a herd testing
program in order to determine the prevalence of the disease
on the farm.
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How is Johne’s Disease Diagnosed?
Identifying
cattle infected with Johne’s disease is a critical component
of managing the disease. There are two basic ways to diagnose
Johne’s disease in cattle. The first is to identify
the organism in the feces of an infected animal. This is most
commonly done by culturing feces for the Johne’s bacteria.
The second method of diagnosing Johne’s disease is to
look for an immune response by the infected animal to the
Johne’s organism. Currently, the most commonly used
test is called a Johne’s ELISA. This test can be performed
on either blood or milk. However, because of the nature of
the disease, interpretation of test results is not always
straightforward. A broad understanding of Johne’s disease,
how the tests work, and how the results are to be used is
necessary in interpreting the test results.
To
view a list of Michigan laboratories offering USDA approved
Johne’s testing, click
here.
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Is Johne's Disease a risk for small ruminants like sheep and goats?
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Is
Johne’s disease a threat to the human population?
Many
animal diseases have zoonotic significance in that they may
also induce human infection. There is some evidence that the
bacteria that cause Johne’s disease in cattle may also
be associated with Crohn’s disease in humans. However,
this relationship is unclear. As early as 1913 similarities
were noted between Johne’s and chronic granulomatous
enteritis in humans, later named Crohn’s disease. While
the body of research increases, it is safe to say that more
needs to be known about both diseases before any firm conclusions
are drawn. Below are some links to more detailed information
of the potential connection between Johne’s and Crohn’s
disease.
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Links to MSU Extension Publications
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Links to Johne's Disease Information Sites
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