Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Tetanus and tetanus immunization

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TTetanus and tetanus immunizationETANUS AND TETANUS IMMUNIZATION

Tetanus is a bacterial disease that affects the nervous system in

humans. The disease is caused by the bacteriaClostridium

tetani. This organism, which is a common inhabitant of soil,

dust, and manure, can contaminate an abrasion in the skin.

Small cuts and pinpoint wounds can be contaminated. Because

the organism can survive and grow in the absence of oxygen,

deep wounds, such as those caused by puncture with a nail or

a deep cut by a knife, are especially susceptible to infections

with Clostridium tetani. The disease cannot be transmitted

from one person to another.

In addition to being able to grow in oxygen-free envi-

ronments, such as is found in a deep wound, Clostridium

tetaniis able to hibernate in environments such as the soil.

This is because the bacteria can convert from an actively

growing and dividing state, when conditions are favorable for

growth, to a dormant state, when growth conditions are more

hostile. Dormancy is achieved by the conversion of the so-

called vegetative cell to an endospore. Essentially, an

endospore is an armored ball in which the genetic material of

the organism can be stored, in a form that resists heat, dryness,

and lack of nutrients. When conditions once again become

favorable, such as in the nutrient-rich and warm environment

of a wound, the dormant bacteria revive and begin to grow and

divide once more.

Tetanus is also commonly known as lockjaw, in recog-

nition of the stiffening of the jaw that occurs because of the

severe muscle spasms triggered by the infecting bacteria. The

muscle paralysis restricts swallowing, and may even lead to

death by suffocation. The muscular stiffening of the jaw, along

with a headache, are usually the first symptoms of infection.

These typically begin about a week after infection has begun.

Some people experience symptoms as early as three days or as

late as three weeks following the start of an infection.

Following the early symptoms, swallowing becomes difficult.

Other symptoms include the stiffening of the abdominal mus-

cles, muscle spasms, sweating, and fever.

The muscle contractions can be so severe that, in some

cases, they have actually broken bones with which they are

associated. Treatment can include drugs to stimulate muscle

relaxation, neutralize toxin that has not yet had a chance to

react with the nervous system, and the administration of

antibioticsto fight the bacterial infection. In spite of these

efforts, three of every 10 people who contract tetanus will die

from the effects of the disease. As of 2001, 50–100 cases of

tetanus occur each year, usually involving people who either

have never taken protective measures against the disease or

who have let this protection lapse. In the absence of the pro-

tective measures such as vaccination, many more people

would develop tetanus.

Interestingly, another group who are susceptible to

tetanus are heroin addicts who inject themselves with a com-

pound called quinine. This compound is used to dilute the

heroin. Available evidence indicates that quinine may actually

promote the growth of Clostridium tetani, by an as yet

unknown mechanism.

For those who survive tetanus, recovery can take

months and is not an easy process. Muscle stiffness and weak-

ness may persist.

The molecular basis of the effects of infection by

Clostridium tetani is a very potent toxin produced and

excreted from the bacteria. The toxin is a neurotoxin. That is,

the toxin affects neurons that are involved in transmitting sig-

nals to and from the brain in order to make possible the myr-

iad of functions of the body. Specifically, in tetanus the

neurotoxin blocks the release of neurotransmitters.

Clostridium tetani neurotoxin is composed of two

chains of protein that are linked together. An enzyme present

in the microorganism cuts these chains apart, which makes the

toxin capable of the neurotransmitter inhibitory activity. One

of the chains is called tetanospasmin. It binds to the ends of

neurons and blocks the transmission of impulses. This block-

age results in the characteristic spasms of the infection. The

other toxin chain is known as tetanolysin. This chain has a

structure that allows it to insert itself into the membrane sur-

rounding the neuron. The inserted protein actually forms a

pore, or hole, through the membrane. Molecules can move

freely back and forth through the hole, which disrupts the

functioning of the membrane.

The devastating effects of tetanus are entirely preventa-

ble. Vaccination in childhood, and even in adulthood, can pre-

vent an infection from developing if Clostridium tetanishould

subsequently gain entry to a wound. Indeed, in the United

States, laws requiring children to be immunized against

tetanus now exist in most states, and all states require children

in day care facilities to be immunized against tetanus.

Tetanus vaccination involves the administration of what

is called tetanus toxoid. In use since the 1920s, tetanus toxoid

is inactivated tetanus toxin. Injection of the toxoid stimulates

the production of antibodies that will act to neutralize the

active toxin. The toxoid can be given on its own. But typically,

the toxoid is administered in combination with vaccines

against diphtheriaand pertussis(diphtheria toxoid pertussis,

or DTP, vaccine). The DTP vaccine is given to children sev-

eral times (two months after birth, four months, six months, 15

months, and between four and six years of age). Thereafter, a

booster injection should be given every 10 years to maintain

the immunityto tetanus. A lapse in the 10-year cycle of vacci-

nation can leave a person susceptible to infection.

Tetanus toxoid will not provide protection to some-

one who has already been wounded. There is a substance

called tetanus immune globulin that can provide immediate

immunity.

The tetanus vaccination can produce side effects, rang-

ing from slight fever and crankiness to severe, but non-lethal

convulsions. Very rarely, brain damage has resulted from vac-

cination. Even though the possibility of the serious side effects

is far outweighed by the health risks of foregoing vaccination,

controversy exists over the wisdom of tetanus vaccination.

Available evidence indicates that tetanus immunizationis a

wise measure.

See alsoAnaerobes and anaerobic infections

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