Washington Animal Disease Diagnostic Lab

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 reasonably well.

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 week’s run.
Culture: 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 pathogen-free.

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