Tetanus

Tetanus (from , and τείνειν teinein "to stretch") is a medical condition characterized by a prolonged contraction of skeletal muscle fibers. The primary symptoms are caused by tetanospasmin, a neurotoxin produced by the Gram-positive, spore forming, 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 develop in the jaw (thus the name "lockjaw") and elsewhere in the body. Infection can be prevented by proper immunization and by post-exposure prophylaxis.

Signs and symptoms

Tetanus affects skeletal muscle, a type of striated muscle used in voluntary movement. The other type of striated muscle, cardiac or heart muscle, cannot be tetanized because of its intrinsic electrical properties. Mortality rates reported vary from 48% to 73%. In recent years, approximately 11% of reported tetanus cases have been fatal. The highest mortality rates are in unvaccinated people and people over 60 years of age. In general, the further the injury site is from the central nervous system, the longer the incubation period. The shorter the incubation period, the more severe the symptoms. In neonatal tetanus, symptoms usually appear from 4 to 14 days after birth, averaging about 7 days. On the basis of clinical findings, four different forms of tetanus have been described.

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.

Cause

Tetanus is often associated with rust, especially rusty nails, but this concept is somewhat misleading. Objects that accumulate rust are often found outdoors, or in places that harbor anaerobic bacteria, but the rust itself does not cause tetanus nor does it contain more C. tetani bacteria. The rough surface of rusty metal merely provides a prime habitat for a C. tetani endospore to reside, and the nail affords a means to puncture skin and deliver endospore into the wound. An endospore is a non-metabolizing survival structure that begins to metabolize and cause infection once in an adequate environment. Because C. tetani is an anaerobic bacterium, it and its endospores survive well in an environment that lacks oxygen. Hence, stepping on a nail (rusty or not) may result in a tetanus infection, as the low-oxygen (anaerobic) environment is provided by the same object which causes a puncture wound, delivering endospores to a suitable environment for growth.

Pathophysiology

Tetanus begins when spores of Clostridium tetani enter damaged tissue. The spores transform into rod-shaped bacteria and produce the neurotoxin tetanospasmin (also known as tetanus toxin). This toxin is inactive inside the bacteria, but when the bacteria die, the toxin is released and activated by proteases. Active tetanospasmin is carried by retrograde axonal transport to the spinal cord and brain stem where it binds irreversibly to receptors at these sites. which in turn blocks neurotransmission. Ultimately, this produces the symptoms of the disease. Damaged upper motor neurons can no longer inhibit lower motor neurons (see Renshaw cells), plus they cannot control reflex responses to afferent sensory stimuli.

Prevention

Unlike many infectious diseases, recovery from naturally acquired tetanus does not usually result in immunity to tetanus. This is due to the extreme potency of the tetanospasmin toxin; even a lethal dose of tetanospasmin is insufficient to provoke an immune response.

Tetanus can be prevented by vaccination with tetanus toxoid. The CDC recommends that adults receive a booster vaccine every ten years, and standard care practice 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 he or she has had fewer than three lifetime doses of the vaccine. The booster may not prevent a potentially fatal case of tetanus from the current wound, however, 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/DTaP vaccine, 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.]]

Tetanus is an international health problem, as C. tetani spores are ubiquitous. The disease occurs almost exclusively in persons who are unvaccinated or inadequately immunized. In the United States, 50-100 people become infected with tetanus each year. In 1884, Arthur Nicolaier isolated the strychnine-like toxin of tetanus from free-living, anaerobic soil bacteria. The etiology of the disease was further elucidated in 1884 by Antonio Carle and Giorgio Rattone, who demonstrated the transmissibility of tetanus for the first time. They produced tetanus in rabbits by injecting pus from a patient with fatal tetanus into their sciatic nerves. In 1889, C. tetani was isolated from a human victim by Kitasato Shibasaburō, who later showed that the organism could produce disease when injected into animals, and that the toxin could be neutralized by specific antibodies. In 1897, Edmond Nocard showed that tetanus antitoxin induced passive immunity in humans, and could be used for prophylaxis and treatment. Alex Kolodziej also a contractor for the disease. Tetanus toxoid vaccine was developed by P. Descombey in 1924, and was widely used to prevent tetanus induced by battle wounds during World War II.

Notable victims

Tom Butler – English footballer; contracted after suffering a badly broken arm.

George Hogg – English adventurer who rescued war orphans in China; died in 1945 from an infection resulting from a foot injury.

Joe Hill Louis – Memphis blues musician; died in 1957 as a result of an infected wound to his thumb.

George Montagu – English ornithologist; contracted tetanus when he stepped on a nail.

Joe Powell – English footballer; contracted following amputation of a badly broken arm.

John A. Roebling – Civil Engineer and Architect famous for his bridge designs, particularly the Brooklyn Bridge; contracted tetanus following amputation of his foot due to an injury caused by a ferry when it crashed into a wharf.

George Crockett Strong – Union brigadier general in the American Civil War; from wounds sustained in the assault against Fort Wagner on Morris Island, South Carolina.

Fred Thomson – silent film actor; stepped on a nail.

John Thoreau (brother of Henry David Thoreau); nicked himself with a razor while shaving.

Johann Tserclaes, Count of Tilly; wounded by a cannon ball in the Battle of Rain.

Traveller – General Robert E. Lee's favorite horse; stepped on a nail.

See also

Tetanized state

Tetanospasmin

References

External links

Tetanus Symptoms

Tetanus Information from Medline Plus

Tetanus Surveillance -- United States, 1998-2000 (Data and Analysis)

Media

Video: Generalized tetanus in a 70-year-old woman (Neurology)

Video: Tetanus in dogs

Category:Bacterial diseases