Tetanus

Researched by Honeyle Stinson BSN Student

Compiled and Summarized by Anthony
Tetanus is a medical condition that is characterized by a prolonged contraction of skeletal muscle fibers. The primary symptoms are caused by tetanospasmin, a neurotoxin produced by the Gram-positive, obligate anaerobic bacterium Clostridium tetani. Infection generally occurs through wound contamination, and often involves a cut or deep puncture wound. As the infection progresses, muscle spasms in the jaw develop hence the common name, lockjaw. This is followed by difficulty swallowing and general muscle stiffness and spasms in other parts of the body.

The clinical manifestations of tetanus are caused when tetanus toxin blocks inhibitory nerve impulses, by interfering with the release of neurotransmitters. This leads to unopposed muscle contraction and spasm. Seizures may occur, and the autonomic nervous system may also be affected.

Tetanus can be either mild or severe. The severe type requires admission to an intensive care.

Tetanus is a global health problem since C. tetani and Geravium tetani spores are ubiquitous. The disease occurs almost exclusively in persons who are unvaccinated or inadequately immunized. Tetanus occurs worldwide but is more common in hot, damp climates with soil rich in organic matter. This is particularly true with manure-treated soils, the spores are widely distributed in the intestines and feces of many non-human animals such as horses, sheep, cattle, dogs, cats, rats, guinea pigs, and chickens. In agricultural areas, a significant number of human adults may harbor the organism. The spores can also be found on skin surfaces and in contaminated heroin.

Tetanus is not contagious from person to person and is the only vaccine-preventable disease that is infectious but is not contagious.

Signs and Symptoms

Local tetanus is an uncommon form of the disease, in which patients have persistent contraction of muscles in the same anatomic area as the injury. The contractions may persist for many weeks before gradually subsiding. Local tetanus is generally milder; only about 1% of cases are fatal, but it may precede the onset of generalized tetanus.

Cephalic tetanus is a rare form of the disease, occasionally occurring with otitis media (ear infections) in which C. tetani is present in the flora of the middle ear, or following injuries to the head. There is involvement of the cranial nerves, especially in the facial area.

Generalized tetanus is the most common type of tetanus, representing about 80% of cases. The generalized form usually presents with a descending pattern. The first sign is trismus or lockjaw, followed by stiffness of the neck, difficulty in swallowing, and rigidity of pectoral and calf muscles. Other symptoms include elevated temperature, sweating, elevated blood pressure, and episodic rapid heart rate. Spasms may occur frequently and last for several minutes. Spasms continue for 3–4 weeks and complete recovery may take months.

Neonatal tetanus is a form of generalized tetanus that occurs in newborn infants. It occurs in infants who have not acquired passive immunity because the mother has never been immunized. It usually occurs through infection of the unhealed umbilical stump, particularly when the stump is cut with a non-sterile instrument. It has the characteristics similar to a Generalized tetanus.

Causative Agent

Clostridium tetani

Mode of Transmission

Tetanus is not directly transmitted from person to person.

Spores may be introduced through contaminated puncture wounds, lacerations, burns or contaminated injected ‘street drugs’. Tetanus can result from minor wounds considered too trivial for medical consultation.

The presence of necrotic tissue or foreign bodies encourages the growth of anaerobic organism such as C. tetani. Tetanus rarely follows surgical procedures today.

Diagnosis

There are no laboratory findings characteristic of tetanus. The diagnosis is entirely clinical and does not depend upon bacteriologic confirmation. C. tetani is recovered from the wound in only 30% of cases, and not infrequently it is isolated from patients who do not have tetanus.

Incubation Period

The incubation period is usually 3 to 21 days although it may range from one day to several months depending upon the nature of exposure. Most cases occur within14 days.

Cases with shorter incubation periods tend to have more severe disease and thereby a greater risk of death.

Pathogenesis

The organism is found in soil, animal feces and, occasionally, human feces. Spores are often deposited in dead (oxygen-free) tissue through a wound, burn, or ulcer. The lesion of infection often goes unnoticed allowing spores to germinate and spread long before treatment can be obtained. By secreting a powerful neurotoxin, tetanospasmin, C. tetani blocks the release of neurotransmitters from the presynaptic membranes of inhibitory nerve synapses. The toxin can be up to 10% of the bacterial weight.

Pathophysiology

Most cases of tetanus are caused by direct contamination of wounds with clostridial spores. Wounds with low oxidation-reduction potential, such as those with dead or devitalized tissue, a foreign body, or active infection, are ideal for germination of the spores and release of toxin. Infection by C. tetani results in a benign appearance at the portal of entry because of its inability to evoke an inflammatory reaction (unless co-infection with other organisms develops).

Tetanospasmin, a zinc metalloprotease, is released in the wound and binds to the peripheral motor neuron terminal, enters the axon, and, via retrograde intraneuronal transport, reaches the nerve cell body in the brainstem and spinal cord. The toxin migrates across the synapse to presynaptic terminals where it blocks the release of the inhibitory neurotransmitters glycine and gamma-aminobutyric acid (GABA) by cleaving proteins crucial for the proper functioning of the synaptic vesicle release apparatus. One of these important proteins is synaptobrevin. This diminished inhibition results in an increase in the resting firing rate of the motor neuron, which is responsible for the observed muscle rigidity.

The lessened activity of reflexes limits the polysynaptic spread of impulses (a glycinergic activity). Agonists and antagonists may be recruited rather than inhibited, with consequent production of spasms. Loss of inhibition may also affect preganglionic sympathetic neurons in the lateral gray matter of the spinal cord and produce sympathetic hyperactivity and high levels of circulating catecholamines. Finally, tetanospasmin can block neurotransmitter release at the neuromuscular junction, causing weakness and paralysis.

Localized tetanus develops when only the nerves supplying the affected muscle are involved. Generalized tetanus develops when the toxin released at the wound spreads through the lymphatics and blood to multiple nerve terminals. The blood-brain barrier prevents direct entry of toxin to the CNS.

Prevention

Tetanus can be prevented by vaccination. The CDC recommends that adults receive a booster vaccine every ten years, and standard care in many places is to give the booster to any patient with a puncture wound who is uncertain of when he or she was last vaccinated, or if the patient has had fewer than 3 lifetime doses of the vaccine. The booster cannot prevent a potentially fatal case of tetanus from the current wound, as it can take up to two weeks for tetanus antibodies to form. In children under the age of seven, the tetanus vaccine is often administered as a combined vaccine, DPT vaccine or DTaP, which also includes vaccines against diphtheria and pertussis. For adults and children over seven, the Td vaccine (tetanus and diphtheria) or Tdap (tetanus, diphtheria, and acellular pertussis) is commonly used.

Treatment

The wound must be cleaned. Dead and infected tissue should be removed by surgical debridement. Metronidazole treatment decreases the number of bacteria but has no effect on the bacterial toxin. Penicillin was once used to treat tetanus, but is no longer the treatment of choice because of a theoretical risk of increased spasms. It should still be used if metronidazole is not available. Passive immunization with human anti-tetanospasmin immunoglobulin or tetanus immune globulin is crucial. If specific anti-tetanospasmin immunoglobulin is not available, then normal human immunoglobulin may be given instead. All tetanus victims should be vaccinated against the disease or offered a booster shot.

Mild tetanus

Mild cases of tetanus can be treated with:

• Tetanus immune globulin IV or IM
• Metronidazole IV for 10 days
• Diazepam
• Tetanus vaccination
  

Severe tetanus

Severe cases will require admission to intensive care. In addition to the measures listed above for mild tetanus:

• Human tetanus immunoglobulin injected intrathecally (increases clinical improvement from 4% to 35%)
• Tracheostomy and mechanical ventilation for 3 to 4 weeks,
• Magnesium, as an intravenous (IV) infusion, to prevent muscle spasm,
• Diazepam (known under the common name Valium) as a continuous IV infusion,
• The autonomic effects of tetanus can be difficult to manage (alternating hyper- and hypotension, hyperpyrexia/hypothermia) and may require IV labetalol, magnesium, clonidine, or nifedipine.
  

Drugs such as chlorpromazine or diazepam, or other muscle relaxants can be given to control the muscle spasms. In extreme cases it may be necessary to chemically paralyze the patient with curare-like drugs and use a mechanical ventilator.

In order to survive a tetanus infection, the maintenance of an airway and proper nutrition are required. An intake of 3500-4000 Calories, and at least 150g of protein, is often given in liquid form through a tube directly into the stomach, or through a drip into a vein. This high-caloric diet maintenance is required due to the increased metabolic strain brought on by the increased muscle activity.

See Emedicine for information on drugs.

Complications

• Airway obstruction is common.
• Urinary retention and constipation may develop because of sphincter spasm.
• Respiratory failure and cardiac failure are late life-threatening events.
• Fractures may result from sustained spasms.
• Seizures can occur.
• Pulmonary emboli may develop.
• Bacterial superinfections are possible complications.
• Dehydration can develop.
  

References

http://www.wikipedia.org
Provided the main article.

http://www.health.vic.gov.au
Provided extra information.

http://sprojects.mmi.mcgill.ca
Source for Diagnosis.

http://microbes.historique.net
Provided information on C. tetani's Pathogenesis

http://www.emedicine.com
Provided the complete information on Tetanus.

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