Tetanus, Blackleg and the other Clostridial Diseases

Diseases caused by the family of bacteria known as the Clostridia are among some of the most devastating illnesses found in both domestic livestock and man. Some of those diseases include tetanus, botulism, and gas gangrene; equally serious in man or the animals that are susceptible to them. There are however, several close relatives of these well-known conditions that are commonplace, easy to prevent, and incredibly difficult to treat and not nearly as infamous. In the livestock world, sudden death without premonitory signs are the hallmark of these conditions.

The Clostridia are a family of relatively large, anaerobic (grow only in the absence of oxygen) spore-forming organisms. The ability to form spores enables these bacteria to survive for long periods of time outside of an animals body and exposed to air (and therefore oxygen). Once relocated in an environment devoid of oxygen, either by accidental ingestion or contaminated injury, the bacteria start to grow and produce toxins (poisons) that are some of the most powerful in nature.

Members of this family cause not only tetanus, botulism, and gas gangrene, but also infectious necrotic hepatitis,(Black disease) bacillary hemoglobinuria (redwater), enterotoxemia types B, C, (purple gut in calves) and D (overeating disease also known as pulpy kidney disease, which incidentally is not the same condition as grain overload). Two other very important diseases found in livestock discussed here are Blackleg and Malignant edema.

The Clostridia normally are found in the intestinal tracts of animals and man, and the spores are found in the soil. Pathogenic strains may be acquired by either ingestion of spores or wound contamination. Clostridial diseases are considered infectious, but not contagious. Cattle that become infected will not directly transmit the disease to other cattle. However, the carcass of an animal that dies of these diseases becomes a source of the spores that will remain infective for years. Any animal that dies of a clostridial disease should be buried very deep preferably where it dies, or at least without dragging the carcass all over creation depositing spores as you go.

Blackleg is an acute disease in cattle and sheep caused by Clostridium chauvoei (feseri) and in characterized by emphysematous swelling (the production of gas in the animal’s tissues), usually in the heavy muscle groups of the rump and loin. The disease is found worldwide. C. chauvoei is naturally found in the intestinal tract of animals. As a spore-former, it can remain viable in the ground soil for years, although it does not multiply there. Clostridial spores are resistant to heat, cold, drought, uv radiation and chemical disinfectants. Contaminated pastures appear to be the source of the organisms. Sometimes outbreaks of blackleg can occur following recent excavations, suggesting exposure of a once hidden pocket of spores.

 Once a premise is contaminated with heavy populations of the organism, it is likely that cases of Blackleg will occur in subsequent years. The spores are ingested, but from that point, the pathogenesis of Blackleg is not certain. It is believed that the actual spores are absorbed into the bloodstream and from there are deposited into muscle tissue throughout the body, including the diaphragm and heart. The spores remain dormant at that location until some event precipitates the rapid growth of the organism. It is theorized that any thing that causes even simple bruising of muscles may decrease the oxygen content of those muscles enough to allow the Clostridia to grow. This bruising can be caused by handling, transport, injections or just rough pasture activity as commonly seen with cattle. With the rapid multiplication of bacterial numbers, toxin is produced that causes rapid tissue necrosis (rotting) in the muscles. There is a production of gas (essentially gas gangrene) in the tissues and running a hand over the affected area may give a crackling feeling under the skin, which is a characteristic of blackleg.

Typically, blackleg affects well nourished young cattle, 6 months to 2 years in age. Older cattle seem immune. If you are lucky enough to discover an animal before the disease kills it, the signs may include acute lameness and marked depression. Fever is common very early on, but typically the disease progresses so fast that if alive, often the animal will have either a normal or subnormal temperature. Edematous (fluid) and crepitous (air) swelling occurs in the hip, shoulder, loin, neck or elsewhere. If the primary muscle group involved happens to be the diaphragm or heart, there will be no localizing feature of the disease to aid in diagnosis prior to death.

The first indication of a problem, may be the discovery of one or two dead animals in the pasture. Animals dying from blackleg bloat very rapidly and are usually found with extremely distended abdomen and the legs rigidly extended. If the animal found dead was alive 12 to 24 hours before, and its body is so swollen that all four legs are lifted up off the ground, be suspicious of blackleg. All dead animals will bloat, but the bloat seen in animals dead of these clostridial diseases is substantially greater, and even animals recently dead may have skin that is separated from the underlying tissues by a layer of gas, and thus will be literally as tight as a drum (not just over the abdomen, but possibly between the legs, over the neck or over the rump; not typically areas of normal postmortem bloat.) On cut surface the affected muscle will be very dark red to black, dry and spongy. The muscle may have a sweetish or a rancid butter odor and may be covered with small bubbles, but edema (excess fluid) in the muscles themselves is usually not seen.

Treatment of blackleg is unlikely because of the rapid death. Massive doses of intravenous crystalline penicillin and aqueous procaine penicillin G in the muscle may result in a cure. All Clostridia are sensitive to the penicillins but the likelihood of getting the medication into the animal in time to help is unlikely.

Prevention of blackleg is the only practical approach, and is fortunately very effective. There are a variety of bacterins or bacterin/toxoid combinations that will induce immunity to the various clostridial diseases. They are generally given to animals at 6months of age and older, with a booster dose usually required in 2 -8 weeks. In the event of an outbreak of blackleg, it is possible to administer injections of penicillin and vaccinate. Covering exposed cattle with penicillin may prevent rapid growth of the causative organism for a long enough period of time that the bacterin will have a chance to stimulate natural immunity to the disease. Estimates suggest it takes about 10 days for adequate immunity from an initial vaccination.

 Malignant edema is another clostridial disease that is also sometimes called false blackleg because the postmortem lesions and rapid deterioration of the animal once infected resemble blackleg. Laboratory testing is the only means to differentiate the two. Malignant edema can affect cattle, sheep, pigs and horses, where blackleg is a disease of cattle and sheep.

Malignant edema is caused by Clostridium septicum, often accompanied by other clostridial species, and occurs worldwide. The organism is found in soil and the intestinal tracts of animals and man. Infection usually occurs through contamination of wounds containing devitalized tissue, actual soil or some other tissue irritant (such as some injectable medications.) Wounds caused by accidents, castration, tail docking , dirty needles and parturition may become infected.

The organism causing malignant edema is not endogenous (already present) in the animal, as in blackleg, but is introduced through some external means. Signs of infection develop within a few hours or days after the predisposing injury. The local lesions are soft swellings that pit on pressure and spread rapidly because of the production of large amounts of exudate (pus and serum) that infiltrate the subcutaneous and intramuscular connective tissue of the affected area.  The muscle in the involved area will be dark red to black, thus the name false blackleg. It is reported that accumulations of gas is uncommon, but definitely can occur in an identical fashion to blackleg. Laboratory tests can confirm the present of C septicum in a wound, however, it is a rapid postmortem invader, and specimens taken more than 24 hours after death may not be significant.  Malignant edema is not contagious, and requires introduction of the organism through some sort of trauma.  Certain soils may in fact have higher levels of the spores present, but these have to be introduced into the body; they are not ingested as is the case for blackleg. Treatment can be attempted with high doses of penicillin which may be curative if caught early enough. Injection of penicillin around the periphery of the lesion may prevent the rapid spread of infection, although if this approach works, the affected area may still slough.    

Prevention is highly effective with the use of bacterins or a bacterin/toxoid combination. Malignant edema can affect any age cattle, and vaccinations can begin as early as 2 months of age with booster doses as appropriate. In high risk areas, yearly vaccinations are recommended for the entire cow herd.

Bacterins for blackleg and malignant edema are often found in combination with bacterins for a number of clostridial diseases, and sometimes tetanus toxoid. The bacterins can cause a pretty dramatic swelling that will eventually disappear over weeks and sometimes months. It is possible that these swellings will occasionally develop into sterile abscesses and either break open and drain spontaneously, or require intervention to induce drainage. There are newer vaccines available that are lower dose and less likely to cause large blemishes. While the lumps are unsightly and the abscesses inconvenient, vaccination is the only method to prevent these diseases and treatment is for the most part worthless unless caught very early.

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