Hawks Mountain Ranch
INFORMATION ABOUT:
CASEOUS
LYMPHADENITIS
(CLA, CL, Abscesses, Boils)
Information from the American
Sheep Industry Association
6911
S. Yosemite·
Englewood, Colorado 80112-1414 ·
Phone (303) 771-3500
SPH Update: Caseous Lymphadenitis ~ 1997
INTRODUCTION
Caseous
lymphadenitis (CLA) is a chronic, infectious, contagious disease of
sheep and goats caused by the bacterium Corynebacterium pseudo-tuberculosis that
results in abscesses of the lymph nodes and less frequently of the
internal organs. Once an animal becomes infected, it is at high risk of
spreading the disease to others through contact with other sheep and by
contaminating the environment. Because the organism can survive for long
periods on infected premises and in soil, eradication of CLA can be a
lengthy and frustrating process. Eradication should be considered,
however, because of the economic impact and human health risks of the
disease.
ECONOMIC IMPORTANCE
Losses
from CLA are difficult to quantify and are due to a large number of
factors. The visceral form (abscesses of internal organs) is the cause
of significant economic loss in the sheep industry due to condemnation
of carcasses. One source ranks CLA as the third most important cause of
condemnation at slaughter. The superficial form (abscesses of peripheral
lymph nodes and shearing cuts) is the cause of abscess scars that
decrease pelt value. Other causes for loss include unthriftiness,
decreased weight gain and wool growth, and reduced milk production and
reproductive efficiency. In addition, affected animals are frequently
culled prematurely, and some even die. Increased somatic cell counts in
dairy animals and decreased value of breeding stock have also
contributed to economic losses.
ZOONOTIC
POTENTIAL
Corynebacterium pseudotuberculosis infections in humans are rare but can occur,
particularly where infected sheep and goats are skinned by hand. The
most common scenario involves puncturing of the human skin with infected
knives. The
disease also has been spread to humans consuming raw milk from infected
sheep and goats. Precautions should always be taken to prevent the
contact of purulent exudate or contaminated objects with human skin, and
milk should always be adequately pasteurized prior to consumption.
DISEASE CHARACTERISTICS
Lesions
of CLA can be found in animals less than six months old but may occur
and recur throughout the lifetime of an animal. The incidence of disease
increases with age. This is most likely due to repeated exposure to the
organism. Two forms of the disease have been described. The superficial
form involves abscessed and enlarged lymph nodes that are located
closest to the skin surface. Most commonly, the lymph nodes around the
head (intermandibular, parotid, retropharyngeal, and cervical) and lymph
nodes near the origin of the limbs (prescapular, prefemoral, and
supramammary) are affected. The second form of the disease involves
abscesses of the internal organs and lymph nodes, and is often
associated with chronic debilitation. The organs most likely to be
affected are the lung and associated lymph nodes, kidney, liver, and
mesenteric lymph nodes. Both forms are found in sheep and goats; the
superficial form is more common in goats in nodes around the head and
neck, and the visceral form is more common in sheep.
The
involved lymph nodes are distended by thick and often dry purulent
exudate that is a greenish color. If external lymph nodes are affected,
there is a well-defined, non-painful swelling that grows larger over
time. If left untreated, the skin covering the node will become thin and
the abscess will eventually rupture to the outside, releasing exudate
and bacteria into the environment.
TRANSMISSION
The
mode of transmission is not known for certain; however, it appears that
mechanical inoculation through
the skin is essential for development of the superficial form of the
disease. In both sheep and goats, direct contact with the bacteria
results in infection. Such contact can occur when the purulent material
of a draining abscess from one animal touches another animal, allowing
the bacteria to enter through the skin. Since the bacteria are capable
of surviving for extended periods of time (months to years) in the
environment, surfaces can harbor organisms and continuously infect
animals as they come in contact with them. It is believed that feed
bunks become easily contaminated, particularly in goat herds, resulting
in the high incidence of abscesses around the head and neck in this
species.
In
sheep, the bacteria are spread most commonly at shearing through
contaminated equipment. Contaminated sheep dips have also been
implicated. Crowding during shearing is another mode of transmission.
This level of congregation is sufficient for the bacteria that are
aerosolized by sheep that have lung lesions to infect shearing cuts.
Numerous routes of infection have been studied experimentally.
Researchers
have shown that the organism is capable of entering the lungs by
inhalation, can disseminate to internal organs by injection into the
bloodstream, cross mucous membranes of the digestive tract and vagina,
and does not need a break in the skin to become infected by contact with
the bacteria. Once the organism enters the body it travels to local
lymphatics, where it forms an abscess in the local lymph node. The
bacteria release an exotoxin (a toxic phospholipase D or PLD) that not
only enables initial bacterial movement to lymph nodes but it also
causes an intense inflammatory reaction. The healing process results in
the development of a thick wall surrounding the bacteria. The bacteria
continue to multiply inside the abscessed lymph node.
DIFFERENTIAL DIAGNOSES
It
is important to consider other causes of abscesses such as Staphylococcus,
Streptococcus species,
and Actinomyces and to confirm that the cause is truly Corynebacterium pseudotuberculosis before initiating stringent control or
eradication measures. When the internal form is present, a chronic
wasting disease may be all that is apparent. In such cases, one must
consider the possibility of other diseases such as abnormal or poor
teeth, Johne’s disease, chronic pasteurella pneumonia, ovine
progressive pneumonia, scrapie, internal parasites, neoplasia, or
inadequate nutrition.
DIAGNOSIS
Diagnosis
of the superficial form of CLA is usually based upon the presence of
abscessed lymph nodes and culture of C. pseudotuberculosis from
their contents. Enlargement of one or more superficial lymph nodes with
purulent discharge is suggestive of the disease but should not be
assumed. Necropsy may reveal internal abscesses which can also be
cultured for confirmation. If CLA is suspected, a gram stain to reveal
gram-positive, pleomorphic, club-shaped rods may aid in determining if
an animal should be isolated while awaiting culture results.
The
only commercially available serologic test today is the ELISA test,
which supposedly will detect subclinical infections as early as 30-60
days postinfection and has been shown to have a specificity and
sensitivity of 85%. False
positives will occur in animals vaccinated against the disease. The
serum can be tested and costs about $5 per sample.
TREATMENT
There
is no effective antibiotic therapy for CLA due to the way the animal
encapsulates the bacteria within the lymph node and isolates it from the
rest of the animal’s body. Treatment of this disease should always be
accompanied by control methods to prevent the spread of the bacteria to
other animals, and affected animals should be immediately isolated in
all circumstances. The abscess can be lanced and flushed daily with a
strong povidone iodine solution, or the entire lymph node can be removed
surgically, thereby eliminating environmental contamination. Another
alternative is to aspirate the abscess free of pus and infuse it with
10% formalin.
VACCINATION
There are two types of vaccines now available
for immunization against C.
pseudotuberculosis. One
contains a toxoid of C. pseudotuberculosis alone. The other is in combination with Clostridium perfringens type D and Clostridiurn
tetani toxids.
It is thought that the vaccine for CLA alone will be the most effective.
Although there is little research data currently available to confirm
their effectiveness, reports indicate that vaccines help prevent and
lessen the effects of the disease as shown by fewer abscesses in
infected herds. Vaccination,
however, should not be utilized as the sole protective measure against
CLA and should be used in conjunction with other control measures to
prevent and eliminate the disease.
The
first vaccination can be given at 3-4 months of age, after passive
immunity fades, and a booster administered four weeks later and repeated
annually. The vaccines may cause formation of a sterile granuloma at the
injection site, which may persist for many years, and can induce a fever
of one-two days duration and other side effects occasionally.
CONTROL AND ERADICATION
An
effective control program for this disease requires a great deal of
dedication, patience, and daily observation. Eliminating the organism
from an infected herd will primarily involve eliminating it from the
environment. While the goals of eradication may differ among operations,
from simply decreasing the incidence of disease to its complete
elimination, similar steps will be required.
· First and foremost, immediate isolation of
affected animals prior to rupture of the abscess is necessary to reduce
environmental contamination. An option for these individuals can then
be chosen (lancing, surgical removal, or culling).
· If an abscess drains into the environment,
the entire area including feeders, waterers, gates, walls, and floors
should be thoroughly cleaned and disinfected. Almost all commercially
available disinfectants such as Nolvasan, iodine, and bleach are
effective in killing the bacteria if used after a thorough
cleaning of the environment, because excess organic material mactiyates
many disinfectants. Orthophenyl phenols are the best disinfectants to
use on porous surfaces and with hard water.
· Once an animal develops an abscess, it should
be considered infected for life and permanently isolated from
non-infected animals even if it has been treated and resolved. Animals
with recurrent abscesses should be culled from the herd or flock.
· Newly purchased sheep and goats should be
obtained from CLA-free flocks/herds and kept isolated from infected
animals.
· Control external parasites and keep the
environment clear of potentially sharp objects. This may decrease the
chance for the bacteria to penetrate the skin.
· Provide your own shearing board or carpet for
shearing crews, since the previous farm(s) where these surfaces were
used may have the disease and may have contaminated these surfaces.
· Disinfect all shearing gear before starting
to shear.
· Shear affected animals last and shear from
youngest to oldest since older animals are more likely to be infected,
and disinfect contaminated shearing equipment immediately.
· Decrease crowding, thereby decreasing contact
among animals.
· Cull and necropsy suspect (thin, poor-doing)
animals.
· Vaccinate the entire herd/flock.
· Use serological (ELISA) test to detect
carriers of internal abscesses as a diagnostic tool for thin animals and
to screen purchases.
GLOSSARY
Aspirate
—
The collection of fluid
from a mass via needle suction
Necropsy —
A systematic examination
of tissues and organs of a dead animal after used to confirm the cause of
disease and even death
Chronic —
Of long duration
Neoplasia —
A cancer
Debilitated —
Weakened
Povidone Iodine —
A mild form of iodine
Encapsulated —
Walled-off
Purulent —
Pus-like
ELISA —
Enzyme Linked
Immunosorbent Assay; a blood test
using a specific kind of technology
Serologic Test —
A blood-based test
Exudate —
A thick fluid that is
spontaneously produced in response to a bacterially—based
disease
Zoonosis —
A disease of animals that
can infect humans
Mesenteric —
Associated with the
mesentery,
which is a structure inside the abdomen that suspends the small
intestine
FOR FURTHER READING
Augustine, J.L. and H.W. Renshaw. “Survival of Corynebacterium pseudotuberculosis on Axenic Purulent Exudate on Common Barnyard
Fomites.” American Journal Veterinary Research 47:713-7
15, 1986.
Brown, C.C. and H.J. Olander. “Caseous Lymphadenitis of Goats and
Sheep: A Review.” Veterinary
Bulletin 57:1-12,
1987.
Ellis, J.A. “Ovine Caseous Lymphadenitis.” Comp. on Continuing
Education 5:504-510, 1983.
Goldberger et al. American
Journal of Clinical Pathology 76: 486-490, 1981.
Kimberling, C.V. Jensen
and Swift’s Diseases of Sheep. Third
ed. Lea and Febiger Publishing, 374-377, 1988.
Laak, E.A., J. Basch, and G.C. Bijl. “Double-Antibody Sandwich
Enzyme-Linked Immunosorbent Assay and Immunoblot Analysis Used to
Control Caseous Lymphadenitis in Goats and Sheep.” American
Journal of Veterinary Research 53 (7): 1125-1132, 1992.
Martin, W.B. and I.D. Aitken. Diseases of
Sheep. Second
ed. Blackwell Scientific Publications, 343-345, 1991.
Renshaw, H.W., V.P. Graff, and N.L. Gates. “Visceral Caseous
Lymphadenitis in Thin Ewe Syndrome: Isolation of Corynebacterium,
Staphylococcus, and Moraxella
spp.
from Internal Abscesses in Emaciated Ewes.” American
Journal of Veterinary Research 40:1110-1114, 1978.
Schreuder, B.E.C., E.A. ter Laak, and D.P. Derksen. “Eradication of
Caseous Lymphadenitis in Sheep with the Help of a Newly Developed ELISA
Technique.” Veterinary
Record 135:174-176,
1994.
Smith, B.P. Large
Animal Internal Medicine. Second
Ed. Mosby, St. Louis, 125 1-1257, 1996.
Stoops, S.G., H.W. Renshaw, and J.P. Thilsted. “Ovine Caseous
Lymphadenitis: Disease Prevalence, Lesion Distribution, and Thoracic
Manifestations in a Population of Mature Culled Sheep from Western
United States. American Journal of Veterinary Research
45:557-561, 1984.
|
