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Caseous Lymphadenitis
in Sheep and Goats |
Kansas
State University College of Veterinary Medicine. The
following article was composed by a senior veterinary
student. |
Caseous Lymphadenitis
(CLA) is a bacterial disease of chronic suppurative
lymphadenitis of both sheep and goats that has major
economic consequences. It is commonly referred to
as “Cheesy Gland” or “Lympho”,
and is associated with “Thin Ewe Syndrome”.
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Cause |
CLA is caused by
Corynbacterium pseudotuberculosis. Abscessation
of both internal and external lymph nodes is possible.
Goats tend to have abscessation of external lymph
nodes, while sheep tend to have internal nodes affected.
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C. Pseudotuberculosis
is a very short, Gram positive rod that may appear
coccoid on a slide preparation. A thick, flocculant,
outer lipid layer makes the bacteria highly pyogenic
and leads to thick-walled abscess formation. C. pseudotuberculosis
also produces an exotoxin that has more recently been
a target for prevention. |
C. pseudotuberculosis
can survive within purulent material in shaded areas
on fence posts, in shearing barns, etc. for several
months, and can be found in sheep feces, surviving
in straw, hay, and wood for several weeks. The bacteria
can also survive at least 24 hours in commercial sheep
dips. |
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Clinical signs There
are two basic forms that are typically recognized:
an internal form and an external form. It is likely
that most infected animals are affected by both manifestations
of the disease. In the external form, most commonly
recognized, obvious enlargement of the skin and peripheral
lymph nodes can be appreciated, especially the reteropharyngeal,
mandibular, parotid, prescapular, prefemoral, and
popliteal lymph nodes. These lymph nodes and subcutaneous
tissues are enlarged with thick, cheesy pus, and may
rupture outward spontaneously or during shearing/dipping.
In both sheep and goats the pus within the abscesses
is initially pale green, but in sheep it becomes thicker
and forms onion-like rings, becoming a firm, calcified
mass. If the internal form is present, affected animals
show weight loss and poor productivity with decreased
fertility, and decreased milk production. They may
exhibit mastitis, respiratory distress, chronic cough,
or neurologic deficits, depending on the location
of internal abscessation. |
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Pathogenesis |
The pathogenesis
of CLA begins with the infection of a superficial
wound often incurred at shearing. The bacteria spread
to the regional lymph node where they can progress
to other nodes or internal organs through the lymphatics
or vasculature. The onion-like appearance on cross-section
of involved lymph nodes is due to stages of necrosis
and capsule formation of the abscess. |
C. pseudotuberculosis
is an intracellular parasite of monocytes and macrophages,
the cells that are responsible for engulfing and digesting
bacteria and debris. C. pseudotuberculosis
bacteria are able to survive within these phagocytic
cells and multiply, then kill the cell, allowing dissemination
of more bacteria. New macrophages phagocytose the
bacteria and the process is repeated. |
Diagnosis |
Typically, diagnosis
is based on the appearance of the animal and progression
of clinical signs. Often diagnosis is first made at
necropsy or carcass condemnation at meat inspection.
If draining tracts are identified C. pseudotuberculosis
organisms can be cultured but are difficult to grow
on blood agar plates. Several serological tests have
been developed including the hemolysis inhibition
test, an ELISA test and an agar gel immunoprecipitation
test. |
Prevention |
Historically CLA
has been controlled in herds by culling visibly infected
animals and emphasizing hygiene in shearing and handling
animals. These methods are effective in reducing the
incidence of disease on a farm, and should continue
to be implemented. |
There are several
points of attention for maintaining good hygiene.
Preventing wounds by careful blade shearing, maintaining
good fencing, and the use of well trained, gentle-
mouthed dogs for herding can all reduce the incidence
of wounding. Decreasing the infection of wounds by
quickly moving animals from higher contamination areas,
disinfection of clipper blades and shearing equipment,
construction of easily cleanable shearing sheds, and
avoidance of dipping sheep until after all wounds
have healed may all decrease infection. Shearing sheep
youngest to oldest may also help prevent infection
of uninfected animals. |
Vaccination of sheep
and goats can reduce the severity of CLA. Older vaccines
provided partial protection and contained inactivated
whole-cell, cell-wall extract, or inactivated exotoxin.
Newer vaccines conation both inactivated whole cell
antigen and detoxified exotoxin. The newer two-component
vaccine has been shown to decrease both the number
of abscesses in sheep and the number of sheep that
develop abscesses. Further,
there was a significant reduction of both internal
and external abscesses leading to fewer condemned
carcasses and reduced environmental contamination
and subsequent spread of disease. The vaccine should
not be used in naïve flocks/herds. Vaccinated
animals will have a positive serological test result,
indistinguishable from infected animals. |
Lambs should be vaccinated
twice before shearing, once at tail docking, and once
at weaning, at least 4-6 weeks apart. Adults should
receive an annual booster. Thare is no vaccine licensed
for goats. |
Additionally, all
new animals should be carefully inspected for peripheral
lymph node enlargement, draining tracts, or other
evidence of disease. If possible animals should be
purchased from known CLA-free herds. |
References |
Glenn JS. Caseous Lymphadenitis in Goats.
Feb 2000.
http://www.saanendoah.com/GlennCL2000.html |
Lloyd S. Caseous Lymphadenitis in Sheep
and Goats. In: Sheep and Goat Practice 2.
Philadelphia: WB Saunders, 1998;185-196. |
Piontkowski MD, Shivvers
DW. Evaluation of a commercially available vaccine
against Corynebacterium pseudotuberculosis for use
in sheep. J Am Vet Med Assoc 1998; 212: 1765-8.
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Pugh DG. Sheep & Goat Medicine. WB
Saunders, 2002; 126-7, 206-7,424. |
Smith MC. Exclusion of infectious diseases
from Sheep and Goat Farms. In: Advances in Sheep
and Goat Medicine. Vet Clin North Am 1990; 6; 705-720.
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West DM, Bruere AN, Ridler AL. Caseous
Lymphadenitis. In: The Sheep: Health, Disease,
& Production. 2nd Edition. Palmerston North:
Foundation for Continuing Education, 2002; 274-279.
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