CL Can Be Nasty and Persistent in Flock, Goat Herd

By Jane Fyksen Crops Editor
Thursday, December 11, 2008 8:28 AM CST

Caseous lymphadenitis is its technical name, but this chronic, recurring sheep and goat disease has all sorts of “handles,” as nasty as the disease itself, from contagious abscesses, “cheesy gland” and “boils” to the more palatable CLA or CL.

CL occurs throughout the world and cuts into meat yield through carcass condemnation, hinders reproductive efficiency, damages pelts with abscess scars and may even cause death in severely infected sheep and goats.

CL is caused by the bacterium Corynebacterium pseudotuberculosis. This “bug” can survive in the environment several months n or longer. Infection usually occurs through skin abrasions or wounds caused by shearing, barbwire fence or exposed nails, but it can also result from “aerosol infection” of the lungs, say North Dakota Sheep Specialist Justin Luther and NSDU Veterinarian Charlie Stoltenow.

CL in confinement sheep and goats typically shows as abscesses around the head and neck following infection from contaminated feeders and panels, or jostling with infected animals in the flock or herd. In pasture situations, abscesses are generally limited to the shoulders and neck because of limited contact with feeding facilities and flock or herdmates.

One to three months after infection, localized abscesses develop at the point of entry into the skin or in the regional lymph node. They gradually get bigger n in size and number n eventually rupturing and discharging infectious pus. That’s the external form of this disease. CL can also manifest internally, spreading through the blood or lymphatic system and cause abscesses on organs (mostly to the liver, lung, kidney and spinal column) or internal lymph nodes.

Secondary complications include breathing difficulties due to abscesses in the neck region, pneumonia, arthritis, mastitis and male infertility (because of scrotal abscesses). Severe internal “abscessation” can cause extreme weight loss, abortion, paralysis and death, say the NDSU sheep experts.

Ohio State University Veterinarian Bill Shulaw says shepherds and goat raisers are apt to see individual animals now and then with an abscess n due to a puncture wound or injury (and caused by a variety of bacteria common in all environments, like streptococci and staphylococci. However, CL-infected flocks, it’s common for many animals to develop this highly contagious disease.

“The superficial form affects the lymph nodes that are close to the surface of the skin and results in swollen nodes commonly seen under or at the rear of the jaw, in front of the shoulder, in front of the hind leg, or above the udder or scrotum,” says Shulaw. “In the superficial form, the abscess causes the lymph node to swell up and, usually, to eventually rupture releasing thick, cheesy pus. Reoccurrence is common after the abscess appears to heal. If the abscess involves a solitary node and doesn’t interfere with the animal’s eating or movement, it may not appear to be ill.”

“If an internal organ is infected, you can’t usually tell that it is infected until function of the organ is affected or until enlargement of the abscess causes systemic signs of weight loss and unthriftiness,” Shulaw continues, noting that CL is considered part of the “thin ewe syndrome” because of this characteristic. Some Australian studies show that a majority of the abscesses are internal, he adds.

“Sheep are often infected during shearing when the skin is broken or cut by contaminated shearing equipment,” notes Shulaw, highlighting the importance of shearing equipment hygiene to prevent flock-to-flock and within-flock CL spread. Sometimes internal lymph node abscesses are cut open during shearing.

CL is usually diagnosed based on flock or herd history, and clinical signs mentioned above. Pus can also be collected from an intact abscess using a syringe and needle and submitted to a veterinary diagnostic.

Luther and Stoltenow say chronic cases characterized by walled-off abscesses will result in false negative results, and the vaccine for this disease will induce false positive results.

Using dirty needles when vaccinating sheep or goats can also cause injection site abscesses, that shouldn’t be confused with CL.

This NDSU pair says eradicating CL “is very difficult.”

“Because the bacteria are protected in the abscesses, they cannot be reached effectively by injectable antibiotics. Emaciated animals and those with recurring abscesses should be culled,” they say. “When an infected sheep or goat is too valuable to cull, external abscesses can be lanced, drained and cleaned with iodine after separation from other animals.” Wear surgical gloves. It’s helpful to flush the lanced abscess area with hydrogen peroxide first, and then apply iodine.

“Since the disease primarily is spread through shearing in sheep, younger animals always should be shorn first,” they continue. “If a sheep is diagnosed during shearing, equipment should be disinfected before continuing with the next animal. Furthermore, shearing equipment always should be cleaned and disinfected between flocks.”

Don’t buy replacements from flocks or goat herds infected with CLA. All purchased animals should always be isolated for at least one month, and two newly purchased flocks should never be immediately co-mingled.

Luther and Stoltenow say the Case-Bac vaccine from Colorado Serum Co. provides protection in sheep, and it’s been demonstrated that primary vaccination with a booster at four weeks significantly reduces the incidence of CL external and internal abscesses. Sheep also were challenged eight months post-vaccination, and the vaccinated group showed 90 percent protection against the internal form of CL and 58 percent protection against the external form. Non-vaccinated controls showed 100 percent infection with both forms, they detail.

Repeating vaccination at least annually will help reduce disease prevalence, they say. Vaccinating sheep with high exposure (i.e. infected farm flocks) every four to six months may be most beneficial. While vaccination against CL is “clearly beneficial,” only 3.1 percent of U.S. sheep flocks received the vaccine in 2000, according to USDA.

As noted, the vaccine doesn’t prevent all new infections, nor does it “cure” animals already infected with the bacteria. It’s generally not recommended pregnant ewes or lambs eight weeks of age be vaccinated. Even though the vaccine is a killed bacterin, it will cause a relatively large percentage of animals to develop a secondary lameness since it is administered in the front flank. Also, many animals will develop a transient fever and become lethargic for a day or two after vaccination. Stress resulting from the latter conditions could result in cortisol release by the dam resulting in premature labor or abortion, the NDSU experts report.

Although the vaccine is not labeled for use in goats, positive results have been reported by producers using the vaccine, Luther and Stoltenow report. Goats do tend to be more susceptible to the adverse reactions above, they warn. CL vaccine usage in goats is off-label and needs to be done under a vet’s oversight.

Shulaw, too, says vaccination won’t cure abscesses or make them go away. “Vaccination will not prevent all new abscesses in exposed animals, but it has been shown to reduce the number of new abscesses substantially,” says this Ohio State vet, noting adult sheep need two doses four weeks apart and annual booster vaccinations.

Colorado Serum also has a Caseous D-T vaccine that is also only licensed for use in sheep. It also contains tetanus toxoid and Clostridium perfringens type D.

Shulaw suggests isolating an infected animal before its abscess ruptures, and cull it. Disinfect any areas that might be contaminated by discharges from a ruptured abscess. Remove sharp objects on feeders, sharp corners and protruding wires from animals’ environment that may become contaminated and serve to inoculate the skin of other animals.

“Provide your own shearing surface for sheep shearers to avoid possible contamination of your sheep with some other flock’s bacteria,” he recommends. “Disinfect all shearing gear before starting to shear. Four ounces of bleach in a gallon of water with a two-minute contact time should be adequate on smooth clean surfaces. Shear affected animals last and shear from youngest to oldest if possible to reduce the risk of opening an abscess in the process of shearing.”

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