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The Toxin and the Toxoid

Tetanus is caused by the neurotoxin, tetanospasmin, also called tetanus toxin.  This is a very poisonous substance – the lethal dose is estimated to be one millionth of a milligram per kilogram of body weight.  Among the known poisons, only the botulinum toxin is more poisonous.  

The tetanus toxin is stored inside the bacteria, and is released on death of the bacteria.  It attaches to the distal nerve endings near the injury site, and travels up the nerve to the spinal cord.  

Tetanus immune globulin binds to this toxin and neutralizes it in the blood and tissues before it binds to the nerves.  Once tetanospasmin binds to the nerves, nothing can be done.  

The toxoid is a preparation of the toxin that has been modified by heating or chemical treatment.  This toxoid cannot cause disease, but stimulates the immune system of the recipient to produce antibodies against tetanospasmin.  

A person who has received the tetanus vaccination can get Clostridium tetani infection.  However, the toxin produced will be neutralized by the antibodies, and the person will not suffer tetanus.
 

 

Tetanus in Children

This article written by:
Dr. Parang Mehta
About Dr Parang

The disease is caused by bacteria named Clostridium tetani which enter the body usually by way of contaminated wounds.  Babies can also get it if the umbilical cord is cut with unsterile instruments at the time of birth, especially if their mothers have not received the tetanus toxoid vaccine during pregnancy.  

The bacteria are not invasive, and multiply only locally at their site of egress.  The bacteria do not cause much local problem, and the injury is often forgotten.  However, they produce a powerful toxin, tetanospasmin, which migrates to the nervous system and attaches to the nerves. The symptoms of tetanus usually occur 2-14 days later, but may be delayed for several months.

Signs of Tetanus

The toxin causes intense stimulation of the nervous system, causing the unfortunate patient to have painful spasms of the muscles.  The first sign is often "lockjaw", caused by a spasm of the masseter muscle. Other early signs are headache, difficulty swallowing, neck stiffness, irritability, and restlessness.

Spasms gradually increase to involve the entire body.   In severe spasm, the patient's body may be bent like a bow, with only the heels and back of the head touching the bed.  Spasms can be triggered by light, sound, or touch, and are intensely painful.  The patient is unfortunately fully conscious, in agony, and in terrified apprehension of the next spasm.  Once the toxin has reached the nerves, the binding is irreversible, and tetanus before the advent of modern intensive care was usually fatal.

Treatment of Tetanus

The treatment of tetanus is difficult.  Removal of infected tissue, antibiotics to kill the Clostridium tetani, and tetanus immune globulin, are initial measures.  Muscle relaxants and paralytic agents, with artificial (mechanical) respiration are essential components of successful therapy.

Prevention of Tetanus

Tetanus can be prevented by the tetanus toxoid.  For children this is available as the DTP vaccine, which is started at the age of 6 weeks.  Before the practice of vaccinating pregnant women with tetanus toxoid was adopted, tetanus of the newborn (tetanus neonatorum) was a major cause of neonatal deaths.

Last revision: July 15, 2007

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