tetanus

Tetanus 

 Brief history of disease

 5^th century BC: Hippocrates first described the disease

 1884: Carle and Rattone discovered the etiology (cause/origin of disease)

p  Produced tetanus by injecting pus from a fatal human case

p  Nicolaier was able to do the same by injecting soil samples into animals

 1889: Kitasato isolated the organism from human victim, showed that it could produce disease when injected into animals. Reported that toxin could be neutralized by specific antibodies.

 1897: Nocard demonstrated the protective effect of passively transferred antitoxin à used in WWI

 1924: Descombey developed tetanus toxoid for active immunization à used in WWII

 Causative agent

Clostridium tetani

 

Morphology & Physiology

               Relatively large, Gram-positive, rod-shaped bacteria

Spore-forming, anaerobic.

Found in soil, especially heavily-manured soils, and in the intestinal tracts and feces of various animals.

Strictly fermentative mode of metabolism. 

 Virulence & Pathogenicity 

Not pathogenic to humans and animals by invasive infection but by the production of a potent protein toxin

tetanus toxin or tetanospasmin

The second exotoxin produced is tetanolysin—function not known.

                           Tetanus toxin

Produced when spores germinate and vegetative cells grow after gaining access to wounds. The organism multiplies locally and symptoms appear remote from the infection site.

One of the three most poisonous substances known on a weight basis, the other two being the toxins of botulism and diphtheria.

n  Tetanus toxin is produced in vitro in amounts up to 5 to 10% of the bacterial weight.

n  Estimated lethal human dose of Tetanospamin = 2.5 nanograms/kg body

  Because the toxin has a specific affinity for nervous tissue, it is referred to as a neurotoxin. The toxin has no known useful function to C. tetani. 

  Initially binds to peripheral nerve terminals

Transported within the axon and across synaptic junctions until it reaches the central nervous system. 

  Becomes rapidly fixed to gangliosides at the presynaptic inhibitory motor nerve endings, then taken up into the axon by endocytosis. 

Methods of transmission

C. tetani can live for years as spores in animal feces and soil. As soon as it enters the human body through a major or minor wound and the conditions are anaerobic, the spores germinate and release the toxins.

Tetanus may follow burns, deep puncture wounds, ear or dental infections, animal bites, abortion.

Only the growing bacteria can produce the toxin.

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

Symptoms

  Tetanic seizures (painful, powerful bursts of muscle contraction)

  if the muscle spasms affect the larynx or chest wall, they may cause asphyxiation

  stiffness of jaw (also called lockjaw)

  stiffness of abdominal and back muscles

  contraction of facial muscles

  fast pulse

 fever

sweating

Types of tetanus:  local, cephalic, generalized, neonatal

  Incubation period: 3-21 days, average 8 days.

Uncommon types:

  Local tetanus: persistent muscle contractions in the same anatomic area as the injury, which will however subside after many weeks; very rarely fatal; milder than generalized tetanus, although it could precede it.

  Cephalic tetanus: occurs with ear infections or following injuries of the head; facial muscles contractions. 

  Most common types:

Generalized tetanus

-          descending pattern: lockjaw à stiffness of neck à difficulty swallowing à rigidity of abdominal and back muscles.

-          Spasms continue for 3-4 weeks, and recovery can last for months

-          Death occurs when spasms interfere with respiration.

Neonatal tetanus:

-          Form of generalized tetanus that occurs in newborn infants born without protective passive immunity because the mother is not immune.

-        Usually occurs through infection of the unhealed umbilical stump, particularly when the stump is cut with an unsterile instrument.

 Methods of diagnosis

  Based on the patient’s account and physical findings that are characteristic of the disease.

  Diagnostic studies generally are of little value, as cultures of the wound site are negative for C. tetani two-thirds of the time.

n  When the culture is positive, it confirms the diagnosis of tetanus

  Tests that may be performed include the following:

n  Culture of the wound site (may be negative even if tetanus is present)

n  Tetanus antibody  test

n  Other tests may be used to rule out meningitis, rabies, strychnine poisoning, or other diseases with similar symptoms.

 Clinical treatment

 If treatment is not sought early, the disease is often fatal.

 The bacteria are killed with antibiotics, such as penicillin or tetracycline; further toxin production is thus prevented.

  The toxin is neutralized with shots of tetanus immune globulin, TIG.

  Other drugs may be given to provide sedation, relax the muscles and relieve pain.

 Due to the extreme potency of the toxin, immunity does not result after the disease.

 Method of prevention - immunization

  A person recovering from tetanus should begin active immunization with tetanus toxoid (Td) during convalescence.

  The tetanus toxoid is a formalin-inactivated toxin, with an efficiency of approx. 100%.

  The DTaP vaccine includes tetanus, diphteria and pertussis toxoids; it is routinely given in the US during childhood. After 7 years of age, only Td needs to be administered.

  Because the antitoxin levels decrease over time, booster immunization shots are needed every 10 years.

What else can be done?

  Remove and destroy the source of the toxin through surgical exploration and cleaning of the wound (debridement).

  Bedrest with a nonstimulating environment (dim light, reduced noise, and stable temperature) may be recommended.

  Sedation may be necessary to keep the affected person calm.

  Respiratory support with oxygen, endotracheal tube, and mechanical ventilation may be necessary.