Caseous Lymphadenitis of Sheep and Goats
Testing for Caseous Lymphadenitis (CL) is recommended as part of the small ruminant herd biosecurity screen offered through the Washington State University-Washington Animal Disease Diagnostic Laboratory (WSU-WADDL). This infection is a potential health threat to a sheep or goat herd. WSU-WADDL receives numerous inquiries about CL, how to test for it, and most importantly, how to take steps to control the infection in herds and flocks. We have taken some of the most frequently asked questions and presented them along with some short answers. If you have further questions, please call the main WADDL office at 509-595-9696 and ask to speak with the consulting microbiologist.
Click on a question or
Corynebacterium pseudotuberculosis, the bacterium that causes the
disease CL, is spread from animal to animal primarily through contact with
material from subcutaneous abscesses (pus) or fomites (inanimate objects)
contaminated with abscess material. The organism can survive several months in
the soil and environment, remaining a source of infection. Though much less
common than visible subcutaneous abscesses, abscesses may also form in the lungs
and abdominal organs as a result of spread of the organism within the animal via
blood or lymph. When abscesses are present in the lungs, the organism may be
transmitted through respiratory secretions (nasal discharge or coughing). In
rare cases, C. pseudotuberculosis may be present in the milk. Although
CL is not sexually transmitted, it is recommended to avoid natural breeding of
animals with abscesses.
There are two testing methods for CL offered at WSU-WADDL: bacterial culture
to detect the bacterial organism in abscess material, and serology to detect
C. pseudotuberculosis-specific antibodies in sheep and goat blood samples.
For animals with visible subcutaneous abscesses, it is best to submit abscess
material for culture since this is the most direct and definitive method to
diagnose CL in an individual animal. It is recommended that all abscesses be
cultured regardless of serology test results.
The serological test is the best
method of “herd-level diagnosis” (screening herds). WSU-WADDL runs the
Synergistic Hemolysin Inhibition (SHI) test, which measures the antibody
response to an exotoxin produced by the organism. No CL serological test is
sufficiently reliable to confidently detect infection in individual sheep or
goats, therefore the serology results for an individual animal test should be
interpreted with caution. The SHI test specificity and sensitivity for
individual animals may not be high in some herds, however, the prevalence of
positive tests within a herd usually reflects the herd prevalence of infection
We recommend working with your veterinarian to obtain appropriate samples. Send sample(s) to the lab by overnight mail (FedEx (choose "Standard Overnight" for quickest delivery), UPS, or USPS).
For bacterial culture, collect abscess material in a sterile container (red top tube, for example) or with a bacterial culture swab. If an abscess is lanced, be sure not to contaminate the environment (see #4 for more information). Please include ice packs with samples intended for culture.
For serology, blood should be collected into a five or ten ml. "red-top" clot tube or serum separator tube. Leave the blood at room temperature for at least 1 hour to allow clot formation. We do not recommend separating the serum from the clot prior to shipment. Ice packs are not required for shipping blood samples.
Until proven negative by culture, all abscesses should be treated as if they
were CL. Bacterial culture is the most reliable test for determining the CL
status of an animal with abscesses. It is possible for infected animals with
active abscesses to test negative on serology due to a delay in antibody
production. Many environmental bacteria can cause abscesses via traumatic
wounds, but unlike CL these are sporadic and not readily transmitted from animal
to animal. Animals with CL abscesses should be quarantined until the abscess has
completely healed or be culled. If an abscess is lanced, it should be over a
hard surface that can be disinfected (concrete) or thrown away (tarp). If an
abscess ruptures in a pasture, the organic material (soil, grass) is
contaminated, and the pasture should be rested for at least one month.
Serology: CL serum (SHI) tests are generally run once a
week. Samples must arrive by Tuesday afternoon for results to be reported on
Friday. If samples arrive Wednesday-Friday, they will be held until the next
Bacterial cultures for CL are set up on the day received in the lab, and results
are typically available within a week.
The serology test is best used as a screen to find out if a herd or flock has
been infected, rather than to diagnose an individual animal with CL. An
individual animal positive CL serology test does not necessarily mean an animal
is infected with C. pseudotuberculosis or has CL. Furthermore, the test
cannot distinguish between natural exposure and vaccination, therefore
vaccinated herds may test positive. Nonetheless, herds with a high proportion of
animals with positive SHI tests are very likely to contain C.
pseudotuberculosis infected animals, whereas herds with few or no SHI
positive animals may represent little risk of CL introduction. Animals within a
positive herd are at risk for developing abscesses, and the herd should be
monitored for visible subcutaneous abscesses. Titers in an individual animal do
not correlate well with risk of abscess development. A negative serologic result
on an individual animal does not definitively rule out infection by C.
pseudotuberculosis. The confidence in a negative result is enhanced if most
or all herd mates also test negative.
When acquiring new animals, testing the herd of origin (10 or more animals)
is the preferred approach to determining the status of the new additions. If
testing the herd of origin is impossible, new additions should be quarantined
and tested twice (30 days apart) before introduction into the negative herd.
Testing only the new additions provides less confidence in negative tests than
does testing the herd of origin. The frequency for testing an established herd
or flock should be based on previous test results, eradication strategies, and
the risk of exposure to other herds or flocks.
There is a vaccine available for use in sheep. Currently, there is
no licensed vaccine labeled for use in goats. Both the safety and
efficacy of CL vaccines have been unacceptable in goat trials. If a herd
or flock is vaccinated, then serologic screening is no longer a useful
method for detecting natural infection. Vaccinated herds may test
positive on the blood test (serology).
Because CL is a chronic infection, efforts should be directed toward
preventing spread to uninfected animals. The first step is to identify infected
animals within a herd or flock, which can be done through a combination of
palpation for external abscesses, with confirmation by bacterial culture (see
#3), and serological screening. Animals with CL abscesses should be quarantined
until the abscesses have completely healed or be culled. Serological screening
can assist in determining the prevalence of CL within a herd. Frequency of
screening should be based on the prevalence within the herd (from previous herd
tests) and the risk of outside exposure (level of biosecurity for new animals
entering the herd, and animals attending outside events). Animals with signs of
respiratory or wasting disease in a known CL positive herd or flock should also
be quarantined, as these may be signs of abscesses in the lungs or abdominal
organs. Any animals dying of respiratory or wasting disease should be necropsied
by a veterinarian, and any abscesses cultured, to identify the cause of death.
Flock owners should purchase and disinfect their own shearing equipment to
prevent introduction of CL from outside farms, and be sure to disinfect feed
bunks and stanchions, which may become contaminated by abscess material. Keep
new additions in a separate pen until either the herd of origin tests negative,
or the animals test negative on two tests 30 days apart. See #6 for more
information on testing new additions.
Human infections with this bacterium are rare, but when found are often
associated with occupational exposure to sheep and goats. Drinking raw
milk is a potential source of human infection. There are other more
serious zoonotic pathogens (infectious agents transmitted from animals
to humans) that are regularly transmitted to humans through raw milk.
Consult your veterinarian regarding the public health hazards of
consuming raw milk.
No. Pigeon Fever in horses is caused by a different biovar (strain) of C. pseudotuberculosis. There is no evidence that the biovar infecting horses can be
spread to goats or sheep, or that the biovar infecting goats and sheep can be
spread to horses.
We recommend the screen below for establishing the status of a herd, new
animals entering the herd and animals producing milk for human
consumption. This screen includes caprine arthritis and encephalitis
(CAE), Johne’s disease, caseous lymphadenitis and brucellosis. For
sheep, ovine progressive pneumonia (OPP) replaces the CAE test. Tests
are priced individually. Additionally, Q-Fever testing is recommended,
and may be required in your area, for animals producing raw milk for
human consumption. Please keep in mind that it is not possible to test
for every pathogen potentially transmitted to humans through raw milk,
and that negative tests do not guarantee raw milk is safe or
Baird, G J and M C Fontaine: Corynebacterium pseudotuberculosis
and its role in ovine caseous lymphadenitis. J. Comp Path 137:179-210,
Brown, Corrie C et al.: Serodiagnosis of inapparent caseous
lymphadenitis in goats and sheep, using the synergistic hemolysis-inhibition
test. Am J Vet Res 47:1461-1463, 1986.
Dorella, F A et al.: Corynebacterium pseudotuberculosis:
microbiology, biochemical properties, pathogenesis and molecular studies
of virulence. Vet Res 37:201-218, 2006.
Kaba, J et al.: Evaluation of the risk factors influencing the spread of
caseous lymphadenitis in goat herds. Polish J of Vet Sciences
Radostitts, O M et al.: Veterinary Medicine; A textbook of the diseases
of cattle, horses, sheep, pigs and goats. 10:795-798, 2007.
Schreuder, B E et al.: Corynebacterium pseudotuberculosis in
milk of CL affected goats. Vet Rec 127:387, 1990.
Williamson, Lisa H: Caseous lymphadenitis in small ruminants. Vet
Clinics No Amer: Food Animal Practice 17:359-371, 2001.
Windsor, P A: Control of caseous lymphadenitis. Vet Clin Food Anim
Dr. Kenitra Hammac, Dr. Jim Evermann, and Dr. Tom Besser