Tetanus in Bovines

Also known as

Lockjaw

Description

Tetanus is a highly fatal disease caused by toxins produced by the bacterium Clostridium tetani. This bacterium is found in the soil and the guts of animals and humans. The disease starts when the organism gets into wounded or damaged tissue as a result of contamination. In the absence of oxygen the bacteria multiply and produce a local infection.

C tetani, is an anaerobe with terminal, spherical spores, is found in soil, especially cultivated soil, and intestinal tracts. In most cases, it is introduced into the tissues through wounds, particularly deep puncture wounds, that provide a suitable anaerobic environment. Sometimes, the point of entry cannot be found because the wound itself may be minor or healed.

As they grow, the bacteria produce poisons (toxins), which spread along the nerves to the brain and cause the clinical signs of tetanus.

Signs

• Stiffness and reluctance to move
• Twitching and tremors of the muscles
• Lockjaw
• Prominent protruding third eyelid
• Unsteady gait with stiff held out tail
• Affected cattle are usually anxious and easily excited by sudden movements or handling
• Bloat is common because the rumen stops working
• Collapse, lying on side with legs held stiffly out, spasm and dea

Cause

Tetanus is a highly fatal disease caused by toxins produced by the bacterium Clostridium tetani. This bacterium is found in the soil and the guts of animals and humans. The disease starts when the organism gets into wounded or damaged tissue as a result of contamination. In the absence of oxygen the bacteria multiply and produce a local infection.

The spores of C tetani are unable to grow in normal tissue or even in wounds if the tissue remains at the normal oxidation-reduction potential of the circulating blood. Suitable conditions for multiplication occur when a small amount of soil or a foreign object causes tissue necrosis.

The bacteria remain localized in the necrotic tissue at the original site of infection and multiply. As bacterial cells undergo autolysis, the potent neurotoxin is released. The neurotoxin is a zinc-binding protease that cleaves synaptobrevin, a vesicle-associated membrane protein.

Usually, toxin is absorbed by the motor nerves in the area and travels retrograde up the nerve tract to the spinal cord, where it causes ascending tetanus.

The toxin causes spasmodic, tonic contractions of the voluntary muscles by interfering with the release of inhibitory neurotransmitters from presynaptic nerve endings. If more toxin is released at the site of the infection than the surrounding nerves can take up, the excess is carried off by the lymph to the bloodstream and thus to the CNS, where it causes descending tetanus.

Even minor stimulation of the affected animal may trigger the characteristic tetanic muscular spasms. The spasms may be severe enough to cause bone fractures.

Spasms affecting the larynx, diaphragm, and intercostal muscles lead to respiratory failure. Involvement of the autonomic nervous system results in cardiac arrhythmias, tachycardia, and hypertension.

Calving and castration seem to be the most common procedures linked to the development of tetanus.

Prevention

Tetanus can be easily prevented through the use of an effective vaccination program. For previously unvaccinated cattle, the primary course consists of 2 doses ideally given 4-6 weeks apart in cattle. This should be followed by a booster dose 12 months later. Annual boosters should be done about a month before calving so that passive immunity is transferred from dam to offspring. This will protect them in the first vulnerable period of life prior to them receiving their first vaccination at marking time.

Undertaking surgical procedures (such as castration) properly, in a clean environment, with disinfected instruments and surgical area, will significantly reduce the risk of tetanus.

Any calf castrated with an elastrator band should be given tetanus prevention in the form of either tetanus toxoid (two doses required with the 2nd given two weeks prior to castration), tetanus antitoxin (given the day of banding) or, in some cases, both are used concurrently or sequentially.

In dealing with calving, be as clean as possible and minimise contamination. Antitoxin can be useful as a short-acting (up to 21 days) preventative if used at high risk times, however on such farms vaccination may be better as a three dose course of vaccination can result in protection for over three years.

Treatment

The time between infection and disease can be very short (two or three days) or quite long (four weeks or more), depending on how long it takes for the contaminated area to develop a low level of oxygen (such as by a wound healing over sealing off the tissue from the outside).

Cattle with early tetanus probably respond to treatment better than most other livestock. In very early cases very high doses of penicillin may be helpful, particularly if combined with local treatment of the infected site. In some cases sedatives and relaxants can aid recovery

Good nursing is important. Treated animals need dark quiet surroundings with lots of space and plentiful bedding

It is not worth treating cattle with fully developed tetanus