Vet´s Perspective

News
Aug 30, 2013
by WLJ

Blackleg

Blackleg is just one of the diseases caused by the Clostridium group of bacteria species. Other common illnesses include tetanus, enterotoxemia, and malignant edema. Blackleg is specifically caused by Clostridium chauvoei.

Bacteria are found in the environment, primarily soil, as well as the intestinal tract of healthy and ill animals. They have increased infectivity due to environmental adaptation by producing endospores; these structures allow bacterium to be very resistant to heat, drought, UV radiation, and many chemical disinfectants. Once the endospore is introduced into an animal, it has the capability to grow and cause disease by releasing toxins into the affected body. Toxins cross over the gastrointestinal tract and enter the bloodstream. These types of diseases are highly infectious in a herd.

Clostridium becomes activated in anaerobic, or oxygen deficient, environments. Devitalized and bruised tissues are an opportune environment for this type of infection to occur; the compromised blood flow means that less oxygen is travelling to the damaged tissue. Disease has been known to occur in animals without signs of external wounds.

Cattle that are most often affected by C. chauvoei tend to be over six months and under two years of age, and those with rapid growth rates. Infections occur most often in the summer and early fall. Animals succumb rapidly (even between 12 to 48 hours after contracting disease) and many times will not exhibit signs of illness. Early clinical signs that may be noted are lameness, fever, lethargy, and going off feed. Appropriate dosages of penicillin have been most helpful in saving affected animals.

Ranchers may note more infections in areas where soil has been recently tilled, or in environments which have suffered flooding or drought—in these cases, the spores are close to the top of soil and are easily ingested by unsuspecting grazers.

Lesions that may be identified on necropsy include muscle swelling due to fluid and gas accumulation caused by the bacterium. A ‘crackling’ noise can be heard when touching affected tissues. The muscle also becomes dark red to black in color and takes on a rancid odor.

Prevention of disease is primarily through vaccination. Recommendations center on vaccinating calves at three to four months of age and continuing boosters through the weaning period if necessary according to manufacturer labels for individual products; vaccination is annual thereafter.

Vaccines are given under the skin in the neck region. During an outbreak, your veterinarian may advice vaccinating all healthy animals at risk and potentially boostering these injections as well. Contact your veterinarian regarding proper disposal of carcasses, and make attempts not to drag a carcass and further contaminate the local environment.

About Anthrax…

Anthrax is a highly infectious and fatal disease caused by a spore forming bacterium named Bacillus anthracis. The bacterium has been identified upon every continent on the globe. Bacillus sp. Can be found in the soil and form deadly spores upon contact with oxygen. The spores release toxins that account for the high mortality rates associated with exposure.

Animals are most often infected by ingesting contaminated soil or feed.

Spores within the soil are very resistant for several years after an outbreak; these spores may be released during rainy seasons or deep tilling of the ground.

The main clinical sign of infection is an otherwise healthy animal that is suddenly found dead; animals are often noted to die within two hours of exposure to the bacteria. If caught early enough, animals may be seen to have difficulty breathing, suffer convulsions, muscle tremors, and exhibit a high fever. Most often, animals are found dead with bloody discharge from their nose, mouth, and rectum.

Many times diagnoses of animals infected by Anthrax are diagnosed based off of history, environment, and clinical signs. Blood smears from affected animals may show rod shaped bacteria with a thick capsule. This capsule is the mechanism that allows the bacteria to survive in very dry, hot, and cold environments. Necropsies are NOT advised in animals that are suspected to have been affected by Anthrax, so as to avoid releasing harmful spores that may infect people and other animals within the surrounding area.

Unfortunately, the disease ensues so rapidly that treatment is futile in most cases. Very high dosages of penicillin may have been helpful in late stages of disease outbreaks, according to some reported cases.

Some endemic areas may consider vaccinating cattle to prevent further spread of disease, especially during an outbreak scenario.

Anthrax vaccine is created from an attenuated strain of B. anthracis.

Carcasses must not be opened (the exposure to oxygen causes release of infective spores from their vegetative, growing state) and health department officials should be notified as this is considered a reportable disease by the World Health Organization. Premises will be considered quarantined until disposal is addressed.

Dr. Genevieve JM. Grammer (Dr. Genevieve JM. Grammer is a veterinarian working out of the Pikes Peak region. Please address correspondence to drgigi19@ gmail.com.)

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