Causative agent: Clostridium chauvei
There are other bacteria in this family that cause disease in cattle but C. chauvei is the only one that has been reported in bison (8). C. chauvei is a soil borne bacterium and can survive in the soil for many years. The bacterium enters the body through consumption of contaminated grass or hay. The disease is usually seen in the late summer when pasture is low, or bacteria can be picked up in hay swaths and cause disease during the winter when the hay is fed.
These bacteria may be found in the spleen, liver and intestinal tract of normal animals. However, disease occurs when bacterial spores that are lodged in normal tissue, usually muscle, proliferate. This usually occurs secondary to bruising of the tissue. As the bacteria proliferate they produce toxins that kill tissue and bring about toxemia.
Clinical signs:
The clinical signs of blackleg in bison have not yet been described (8), probably because of its rapid onset and quick progression to death. The following are some clinical signs that occur in cattle (9):
- the most common finding is sudden death.
- animals found alive will be depressed, anorexic, have a high heart rate and high body temperature.
- swellings may be seen in localized areas. Characteristically, they show crepitus or the feel of gas under the skin.
Postmortem Findings:
Pathological changes associated with blackleg have not yet been described for bison (8). The following are some pathological changes associated with blackleg in cattle (9):
- the carcass bloats and putrefies quickly after death.
- body cavities often contain excess fluid, often reddish in color.
- infected muscle masses are swollen, discolored and have a foul odor.
- in some cases a small muscle mass will be affected and lesions may be hard to find.
Diagnosis:
The diagnosis of blackleg is most commonly made on postmortem examination. Affected tissue may be submitted to a diagnostic pathology laboratory for bacterial culture and identification.
Treatment:
There have been no treatment protocols established for bison (8). Treatment protocols that have been used for bison are similar to those described for cattle (9). The response to treatment is often poor and usually the animal is found dead, or too sick to consider treating. C. chauvei is susceptible to most antibiotics commonly used in cattle. Procaine penicillin G is often used. Vaccinate all animals in the face of an outbreak and treat all at risk animals with long acting antibiotic preparations to provide protection until immunity develops.
Control:
There have been no control protocols established for bison (8). Programs for controlling blackleg in bison are similar to those used in cattle (9). The clostridial vaccines commercially available in Canada have not been approved for use in bison. Studies on the effectiveness of these vaccines for the prevention of clostridial diseases in bison have not been reported. However, all bison should be immunized against blackleg. Bison that are properly vaccinated should not develop the disease. Commercially available vaccines are inexpensive, therefore costs should not be prohibitive. A multivalent 8-way vaccine should be used. Though C.chauveii is the only member of the clostridial family of bacteria actually reported to have caused disease in bison, it is quite likely that bison are susceptible to disease caused by other bacteria in this family. There are anecdotal (word-of-mouth”) reports of Cl. haemoliticum infection causing acute and severe “redwater” or bacillary hemoglobinuria disease in bison. Many bison ranchers vaccinate all of their bison with a clostridial vaccine on a yearly basis.