Tetanus is caused by the toxin of Clostridium Tetani. Clostridia are gram positive bacilli. They are strictly anaerobic and can protect themselves in spores. They are found in soil and manure, they may be found in the gastrointestinal tract of man. Under the microscope they appear as gram positive bacilli with or without terminal spores (drumstick appearance). Following innoculation into a wound the bacteria proliferate and produce exotoxins. The best wounds for growing Clostridia are those with extensive necrosis and devitalised tissue. However, in most patients with tetanus the wound usually does not show signs of major inflammation, it may even be un apparant. The toxin which is responsible for most of the trouble is a neurotoxin that is taken up by nerve endings and transported to the anterior horns of the spinal column. There it will result in overactivity of motor nerves. At first there may be local tetanus and subsequently generalised tetanus.
Local tetanus is an early sign and the muscles in the area of the wound are affected. The patient may have increased tone and find it difficult to relax the injured part.
Generalised tetanus occurs later, the marked increase in neuromuscular activity results in inability to open the mouth (trismus) which is one of the first signs. The facial muscles go into spasm and the patient exhibits a sardonic smile (risus sardonicus). There is generalised muscular rigidity which is tonic and persists through out the illness. As the disease becomes more severe there are severe generalised spasms where all the muscles painfully contract. These spasms may be percipitated by loud noise, light or knocking the patients bed. The patient may become so rigid that only the head and the feet are on the bed (opisthotonos). Death follows from spasm of the respiratory muscles and cardiovascular complications.