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COLLECTION: GOAT HANDBOOK
ORIGIN: United States
DATE INCLUDED: June 1992
Extension Goat Handbook
This material was contributed from
collections at the National Agricultural Library.
However, users should direct all inquires about the
contents to authors or originating agencies.
DOCN 000000066
NO G-12
JOHNE'S DISEASE
D. M. Sherman; U. of Minnesota, St. Paul
S. B. Guss; Pennsylvania State U., University Park
Health and Disease Management
1 Johne's disease, also known as paratuberculosis,
is an infectious contagious disease of ruminant animals
affecting primarily the digestive tract. The causative
bacterium, Mycobacterium paratuberculosis localizes
in the wall of the intestines, producing an inflammatory
response which disrupts normal digestion and absorption
of nutrients. This leads to chronic progressive weight
loss with eventual debilitation and death. This disease
was first recognized in cattle in 1895, and in goats
in 1916. Since the disease has been studied more intensively
in cattle, many aspects of the bovine disease have
been assumed to hold true for goats. Following are
the differences and similarities between goats and
cattle discussed in terms of transmission, clinical
signs, postmortem lesions, laboratory diagnosis and
control.
2 Transmission The organism causing
Johne's disease is passed in the manure of infected
animals and contaminates the environment. Ingestion
of contaminated feed and bedding is the most common
mode of transmission. It has been shown that cattle
are most susceptible to infection as very young calves
and individual animals become more resistant to infection
as they grow older. This is confusing from the standpoint
that cattle do not show signs of the disease until
they are at least two years of age. Apparently, they
carry the infection in a dormant state until some
stress, such as calving, triggers the onset of clinical
signs. This same mode of transmission appears to hold
true also for goats.
3 However, it has been suggested
but not proven, that individual goats may be susceptible
to new infections throughout life, if the level of
environmental contamination is sufficiently high.
At least in cattle, there is evidence that occasionally,
infected dams may transmit the disease to offspring
in utero, with the result that newborns are already
infected.
4 Clinical Signs Johne's disease
in cattle is characterized by the appearance of a
chronic, profuse, watery diarrhea. A typical Johne's
cow is three to five years of age. Often, the onset
of diarrhea follows some stress such as calving, transport
or concurrent disease. The diarrhea which occurs may
continue intermittently or constantly for several
weeks to months. During this period the cow maintains
a good appetite. Despite her willingness to eat, however,
the animal progressively loses weight and may appear
as a walking skeleton as death approaches.
5 In goats, diarrhea is rarely a
prominent sign. If it occurs at all, it is usually
in the terminal stages after a prolonged period of
weight loss, lack of appetite and depression. This
absence of diarrhea makes the diagnosis of caprine
Johne's disease difficult. Animals showing progressive
weight loss should be suspected of having Johne's
disease. However, heavy parasitism, chronic viral
arthritis, internal abscesses, chronic pneumonia,
and an inadequate ration should also be considered
in the differential diagnosis. Herd outbreaks of diarrhea
are not likely to be Johne's disease. Salmonellosis,
Coccidiosis, Exterotoxemia and grain overload are
more likely causes of diarrhea in goats. Whereas the
typical Johne's goat is also an adult animal, terminal
cases have been seen in goats as young as fourteen
months of age.
6 Postmortem Examination Any animal
dying after a period of weight loss should be subjected
to a thorough postmortem examination by e.g., the
state diagnostic laboratory. This helps establish
the existence of Johne's disease in a herd.
7 It should be remembered that the
extent of grossly visible lesions is variable in animals
infected with Johne's disease. It is essential that
microscopic examination of selected tissues be performed
using special acid-fast stains to reveal the presence
of the Johne's organism. If tissues are to be submitted
by the local veterinarian to a pathology laboratory,
these should include sections of ileum, cecum, ileocecal
valve, ileocecal lymph node and enlarged mesenteric
lymph nodes, if present.
8 There is sometimes a thickening
and roughening of the wall of the small intestinal
tract (especially the posterior portion), the colon
and cecum. A more consistent finding is an enlargement
of the iliocecal-colic lymph node as well as the other
mesenteric lymph nodes. When the latter are cut, they
appear necrotic (consistency of cooked oatmeal), edematous
(wet and swollen) and sometimes irregularly reddened.
Microscopic examination of the intestinal wall and
lymph nodes reveal the proliferation of epitheloid
cells and the presence of macrophages. This is called
a granulomatous inflammatory reaction. When the sections
are stained by an ''acid-fast'' method, the small
organisms are stained red and can be seen within the
epithelioid cells and macrophages. There are sometimes
secondary lesions of amyloid and fibrinoid degeneration
in the kidney, adrenal glands and mammary glands.
9 As far as gross lesions are concerned,
there are differences between the cow and the goat.
Cows may show a dramatic thickening of the intestinal
wall causing the lining of the intestine to be thrown
up into accordian-like folds. Goats almost never exhibit
this lesion, and at best, may show only some lymph
node enlargement. Appropriate tissues should always
be submitted for histopathological examination if
the history suggests Johne's disease, since the presence
of gross lesions is unreliable in the goat.
10 Diagnosis There are two major
problems associated with the successful control of
Johne's disease. First, it is peculiar to this disease
that for every clinically affected animal in a herd,
there are probably several animals which are infected
but not showing clinical signs. These are termed subclinical
carriers, and they are the major source of ongoing
environmental contamination and transmission. The
second problem is that there is no rapid, reliable,
inexpensive test for identifying these subclinical
carrier animals.
11 The current diagnostic method
of choice is the bacterial culture of feces on specialized
media. Unfortunately, the causative agent, Mycobacterium
paratuberculosis is a finicky organism, is hard to
grow on artifical media, culturing takes about 14
weeks but can take as long as twenty weeks for colonies
to appear. This makes the process of identifying and
removing infected animals from the herd a painfully
slow task. In addition, the number of organisms shed
in the feces of infected animals may vary with time,
meaning that several attempts at fecal culture may
be necessary before an infected individual is finally
identified as a shedder. The results of intradermal
injection of Johnin are inconsistent; however I.V.
injection of infected animals will often give a body
temperature elevation of 1.5 to 3F (but stay below
103.1F) and it will double the blood neutrophil to
lymphocyte ratio.
12 Many other diagnostic tests have
been tried in both cattle and goats with little success.
These include skin testing, the complement fixation
test and the hemagglutination test. All suffer to
a greater or lesser extent from the same problem.
Many infected animals are missed and many noninfected
animals are falsely identified as infected.
13 There may be some good news for
the goat industry in the diagnostic application of
the agar gel immuno-diffusion test (AGID). This test
involves the formation of a precipitation line in
semi-solid media (agar) between wells containing an
extract of the causative organism and antibodies against
the organism present in the serum of infected goats.
Surprisingly, the test has been of little value when
applied to the diagnosis of Johne's disease in cattle
but appears to be quite accurate when applied to goats
and sheep. Both clinical and subclinical goat cases
can be identified with an accuracy equal to the fecal
culture test. The test is inexpensive, requires a
small serum sample from each animal and can yield
results in only 24 hours. Though currently not an
accepted diagnostic test, AGID has potential for future
widespread application in the diagnosis of caprine
and ovine Johne's disease.
14 Treatment and Control Unfortunately
there is no satisfactory treatment available against
Johne's disease. Because the causative agent is in
the same bacterial genus as the organism causing tuberculosis,
various antitubercular drugs have been employed, but
with little or no success.
15 Vaccination holds some promise
for control, but several pitfalls have obstructed
progress in this area. Large draining nodules may
form at the vaccination site. These are especially
objectionable to owners of show animals. In addition,
vaccination may cause false positive reactions to
the tuberculosis skin test, thus interferring with
tuberculosis regulatory programs. At present, state
controlled cattle vaccination programs are underway
in several states but vaccination has not been approved
for use in goats.
16 Regulatory attitudes vary from
state to state concerning the identification and control
of Johne's disease. Some states have a voluntary control
program whereas others may have mandatory controls.
Regulations concerning Johne's disease in goats may
be less clearly defined than those concerning cattle.
It is best to check with the livestock regulatory
agency in your state to acquire accurate information
concerning the status of this disease.
17 Control programs may be aimed
at identification of infected individuals coupled
with rigid culling of animals identified as positive.
At present, identification is achieved by fecal culture.
Improved diagnostic techniques such as AGID can accelerate
the identification process. Along with identification
and culling, improved management and sanitation will
help reduce the incidence of new infections. Kids
should be taken immediately from does and raised in
separate quarters. Before removing, kids should receive
colostrum by bottle or by nursing a thoroughly washed
udder to limit oral contamination. Because of the
likelihood that adult goats may infect each other,
animals should not be overcrowded, manure should not
be allowed to build up and feed and water should be
provided in such a way that fecal contamination is
kept to a minimum. When possible, herd additions should
be purchased from known, Johne's free herds. If the
status of a herd is not known purchased animals should
be quarantined for several weeks before entering the
new herd.
18 At the present time, many goat
owners are resigned to living with Johne's disease
because of the frustration associated with trying
to eliminate it from their herds. Hopefully, continued
progress in understanding the mechanisms of this disease
along with improved methods of diagnosis and treatment
will allow us to develop a more aggressive attitude
toward this aggravating problem.
JOHNE'S DISEASE
COLLECTION;GOAT HANDBOOK
ORIGIN;United States
DATE_INCLUDED;June 1992
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