Clostridium tetani

Barry Whitworth, DVM

Area Food/Animal Quality and

Health Specialist for Eastern Oklahoma

Tetanus or “Lockjaw” is a condition caused by a neurotoxin produced by the bacteria Clostridium tetani.  The neurotoxin is very potent.  Most animals are susceptible to the toxin, but some species are more sensitive than others.  Birds seem to be very resistant, but horses and sheep seem very sensitive.  The disease is usually fatal.  The characteristics of the disease include increase sensitivity to stimulation, contracting muscles, and convulsions.

C. tetani form spores may persist in the soil for many years. The bacteria may also be found in fecal material of many animals. The spores are very resistant to many disinfectants.  They are also resistant to high temperatures but can be destroyed by extremely high temperatures (2390 F for 20 minutes).

C. tetani usually enters the animal by a deep puncture wound. The bacteria may enter the reproductive tract following uterine infections. Other ways to introduce the pathogen are through farm procedures such as castration, dehorning, shearing, and tail docking.

Once the bacteria enter the body of an animal, they will only proliferate under the right situations.  The most important condition is low tissue oxygen levels.  This may take one to three weeks or may take several months.  Many times, the original wound has healed long before clinical signs of tetanus are seen.

The organism produces three toxins.  The most important is a neurotoxin called tetanospasmin.  This toxin reaches the central nervous system by passing up the peripheral nerves.  The toxin prevents the inhibition of contraction of muscles which results in muscle spasms.  The second toxin produced is called tetanolysin, which is thought to cause tissue necrosis.  This creates a good environment for the proliferation of the organism.  The third toxin is also a neurotoxin.

The initial clinical signs of the disease are muscle stiffness and muscle tremors.  One of the first signs seen is the prolapsing of the third eyelid.  The third eyelid can be induced to prolapse by tapping between the eyes or raising the head.  This is followed by generalized stiffness, problems walking, restriction of jaw movement (lockjaw), raised tail (pump-handle), erect ears, nostrils dilated and exaggerated response to stimuli.  Constipation, failure to urinate, and bloat may also be seen.  As the disease progresses, the muscle constriction intensifies, and animals may have a “saw-horse” stance.  Animals usually fall to the ground when attempting to walk.  Animals will convulse when stimulated, but eventually the convulsion become spontaneous.  Severely affected animals are recumbent with the neck and legs extended.  Animals die due to asphyxiation due to respiratory failure.

If a veterinarian finds the original site of the infection, he/she may attempt to culture the organism to confirm the diagnosis.  However, culturing the bacteria is difficult.  Most veterinarians make a diagnosis of tetanus based on clinical signs.

Learn more about the treatment of tetanus in the December issue of Oklahoma Farm & Ranch.