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Epidemiology and Pathology

Clostridium tetani is an actively motile anaerobic, noncapsulated gram-positive bacillus in the range of 3-8 by 2-5 µm, sometimes having a swollen end resembling a drum stick because of a retained spore. Staining characteristics of the bacillus may alter from the normal gram-positive state to gram-variable or even gram-negative. The bacillus is found in soil and in the feces of domestic and wild animals, as well as in human feces. Spores can be recovered from house dust, clothing, and air. Many studies have shown spores to be present in hospital wards in many parts of the world. The spores are capable of lying dormant for weeks or even months under adverse conditions, unless exposed to sunlight. They will only germinate and multiply if there is also low oxygen tension. Tetanus can therefore only develop where there is trauma with devitalised tissue necrosis, or where there are foreign bodies in the wound. Earth or calcium salts in the tissues and contamination with aerobic bacteria such as Staphylococcus are contributory factors. Only a very small anaerobic area is necessary to produce enough tetanus toxin to be fatal. The incubation period may be as short as 2 days or as long as 30 days or more: the average is 6-12 days, and the site and nature of the wound are significant factors in the incubation period.

The bacilli produce a highly potent neurotoxin (tetanospasmin), which is active in very small amounts. It affects the myoneural junction by inhibiting the release of acetycholine. The clinical symptoms are the result of the action of the toxin on the brain and spinal cord. There are two other toxins: tetanolysin, which probably has little clinical significance but can cause hemolysis, and a factor with peripheral action on motor nerve end plates, the significance of which is debatable. There are more than ten antigen strains of Cl. tetani, but fortunately the neurotoxins are very similar antigenically, so that the antigens are multiactive and also contain some antitetanolysin activity.

The most common cause of tetanus is a perforating or puncture wound contaminated by soil, street dust, dirty splinters or nails, etc. A further source of infection is inadequate sterilization: tetanus has followed injections or vaccinations. Bites from animals, particularly those which are carrion-eaters, may result in tetanus: human bites carry a lesser, but still significant risk. Other causes in tropical countries include insect bites and jigger wounds, male and female circumcision, tribal scarification, uvulectomy, and the variety of dirty materials used to dress open wounds.
Tetanus may follow contamination of a tropical ulcer or even chronic middle ear disease. In Dakar, it was noted in 1967 that 34% of all cases of tetanus in females were the result of ear-piercing, but fortunately this carried a low mortality.

The elimination of unskilled midwifery is of vital importance in the elimination of tetanus. This was demonstrated as long ago as the late eighteenth century in Scotland, where tetanus neonatum caused 30% of all neonatal deaths. Fifty years later it had virtually disappeared, along with the self-taught midwife. In developing countries, traditional midwifery is still a major cause of tetanus, due to the use of dirty scissors or razor blades to cut the umbilical cord, and the custom of treating the cord with cow dung, vegetable material, or a soiled dressing of leaves, which inevitably leads to infection. In some countries, similar applications are used postpartum to the vagina and are potent sources of infection.
Almost everywhere tetanus occurs more commonly in males than in females with a ratio of 2:1-3:1. This is in part due to the increased masculine liability to injury, but this does not explain the difference completely because there is the same tilted ratio in tetanus neonatum.


Laboratory Diagnosis

The bacilli may be identified in pus from a wound or cultured, but there are no other laboratory tests which are of help in the diagnosis of tetanus; most often the condition must be recognized on clinical grounds.

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Copyright: Palmer and Reeder