Case Report: Blackleg in Crossbred Beef Steers
Background: Blackleg is non-contagious disease of both cardiac and skeletal muscle caused by the bacterium Clostridium chauvoei. The organism is commonly found in the lower gastrointestinal track of cattle and the spores can remain viable in the soil for many years.1 The disease typically presents with low morbidity but very high mortality. Typically, cattle ingest the spores, and through an unknown mechanism, the organisms can then localize in muscle tissue.2 Wounds or bruising can activate the spores, but many times there is no known initiating cause. Blackleg is more typically observed in cattle under two years of age, but cases in older animals has been reported.
Figure 1. Thin layer of fibrin on the epicardial surface
History: A group of 250 steers from unknown sources were purchased through a Midwest salebarn and transported to Kansas and were housed in a single pen. Upon arrival, they were administered a commercial a 5-way respiratory vaccine and an oral parasiticide product. No Clostridial vaccine was administered.
Clinical signs: Approximately 5 weeks after arrival, and over the course of 3 days, 5 calves were found dead. None of the calves were reported to have been morbid in the previous days. Sudden death was reported as the only clinical sign.
Diagnostics: Two of the calves were presented for necropsy. Body condition was scored at 6 (scale 1-9). No external injuries or abnormalities were noted except subcutaneous emphysema was observed over the shoulders and hind quarters of both animals. Upon necropsy, areas of subcutaneous edema in the thoracic wall and brisket was noted. Fibrin and hemorrhage was observed over the costal pleura. The pericardial sacs contained approximately 1.5 liters and 0.5 liters of serosanguinous fluid, in each calf respectively. The epicardial surface of both hearts were covered with a thin layer of fibrin (Figure 1). The rear limb and cardiac muscles contained several areas of black colored muscle and a “rancid” odor was described (Figures 2 & 3).
Figure 2. Dark muscle tissue in the hind limb
Given the history and gross necropsy findings, Clostridium chauvoei was at the top of the rule-out list. Tissues were submitted to the KSVDL histopathology laboratory for fluorescent antibody (FA) testing. The appropriate tissues to submit for Clostridial diagnosis are fresh skeletal and cardiac muscle. The FA test is not specific for chauvoei and will be reported as positive if C. septicum, C. novyi, or C. sordelii are present. That this organism is common in the environment where cattle are raised, a positive anaerobic culture without associated histopathology lesions does not provide a definitive diagnosis.
Outcome: Positive Clostridial FA results were reported within 12 hours after submission (Figure 4). The referring veterinarian recommended that the client carefully process the calves and administer a 7-way Clostridial vaccine with the added recommendation to booster the same vaccine in 3 weeks. Another calf was found dead shortly after processing and the muscle tissues were consistent with C. chauvoei infection. No other deaths occurred; four weeks after processing.
|Figure 3. Dark cardiac muscle||Figure 4. Positive FA test for clostridium organisms|
Take home messages: The definitive diagnosis of this disease requires both histological lesions and a positive FA test on fresh skeletal and cardiac muscle. Although Blackleg is a sporadic disease, when it does occur it can be economically challenging. The number of published field trials proving the effectiveness of Clostridial vaccines are few.3 Even given the lack of scientific evidence, that these vaccines are inexpensive and other Clostridial prevention programs have not been devised, their use in high risk populations may be warranted.
1. Radostits M. Otto. Veterinary Medicine. A Textbook of the Diseases of Cattle, Sheep, Pigs, Goats, and Horses. W. B. Saunders 9th Edition, pages 761-767.
2. Useh N.M. et al. Pathogenesis and Pathology of Blackleg in Ruminants: The Role of Toxins and Neuraminidase. Veterinary Quarterly 25 (2003) pages 155-159.
3. Francisco A. Uzal. Evidence Based Medicine Concerning Efficacy of Vaccination against Clostridiumchauvoei Infection in Cattle. Veterinary Clinics of North America 28 (2012) pages 71-77.