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Clostridium
chauvoei (Blackleg)
Randall J Berrier ,DVM
Staff Veterinarian
Technical Service
The Clostridium spp. of bacteria
are of major concern in livestock as primary causes of
disease. The clostridia are all gram positive, anaerobic
(don't require oxygen) and all have the ability to produce
endospores. The Clostridium spp. are potent producers
of exotoxins - which is the primary component of their
pathogenicity. For example, the exotoxin from Clostridium
tetani causes tetanus (lockjaw). The exotoxin in Clostridium
botulinum causes botulism (flaccid paralysis).
In this month's Vet's. Corner we will be
discussing a clostridial that causes a disease syndrome called
blackleg: Clostridium chauvoei.
Blackleg is usually acute. The disease is
infectious and causes severe inflammation of skeletal and
cardiac muscle, severe systemic toxicity and, not
surprisingly, a high mortality. It is most commonly seen in
cattle, but can occasionally be seen in other species. In
sheep it's almost always secondary to a skin wound. Other
species of clostridial bacteria can cause similar symptoms.
Clostridium septicum and Clostridium
novyi can cause 'false blackleg' which is more accurately
diagnosed as malignant edema. For this reason it is best to
use a multivalent vaccine containing antigens of Clostridium
chauvoei, Clostridium novyi and Clostridium
septicum when protecting cattle against blackleg.
Most cases of blackleg occur in the warm
months of the year. Outbreaks can occur following excavation
of soil, which can expose and activate latent spores. Also the
disease is enzootic in areas with a history of flooding. It is
common for a number of animals to be affected within a small
time frame. In cattle the disease is mostly confined to
animals that are rapidly growing and on a high nutritional
plane.
It is assumed that the route of infection
in cattle is through the intestinal mucosa following ingestion
of the soil borne spores. Blackleg develops when the spores
locate in normal skeletal and/or cardiac muscle and then
proliferate after localized trauma or anoxia. Toxin is then
released resulting in a necrotizing myostitis and systemic
toxemia.
In cattle observed prior to death, there
will be severe lameness and swelling in affected tissues. They
will run a high fever, be off feed and be very depressed. In
many cases cattle will be found dead in the pasture without
any prior symptoms. For this reason, lightning strike is a
common rule out.
Post mortem findings in cattle with
blackleg include dark, discolored, swollen and rancid muscle
upon incision of the affected area. The affected muscle will
have excess fluid and bubbles of gas. Body cavities will
contain excess fluid and overall decomposition of tissues is
rapid. In cardiac myositis there is usually a large
accumulation of fluid around the heart with large amounts of
fibrin. Quick post mortem examination and submission of
samples to the lab by your veterinarian is essential to
confirm a diagnosis of blackleg. Carcasses of animals with
blackleg infection should be burned or buried deep with quick
lime to limit contamination of the soil.
Treatment of cattle suspected of being
infected with blackleg results in only average success and
only if they are treated early in the course of the disease.
High doses of penicillin are the treatment
of choice.
Prevention in the form of routine
vaccination with multivalent bacterins containing Clostridium
chauvoei, Clostridium septicum (Colorado Serum Company's Essential
2 and Essential
2+P), and in some cases also Clostridium novyi
(Colorado Serum's Essential
4) has proven to be very effective. Vaccinating calves at
2 to 3 months old should be followed by a booster at 4 to 6
months of age. In endemic areas with a high incidence of
disease vaccinating calves as early as 3 weeks has been
recommended, followed by boosters at 2 months and 4 months of
age. Annual revaccination of adult cattle in the spring prior
to warm weather is also recommended. Killed bacterin is o.k.
to give to pregnant animals. In an outbreak all unaffected
cattle should be vaccinated immediately and given penicillin
for one to two weeks, as it will take about 2 weeks for
immunity to develop.
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