Introduction

Tetanus is a severe and often life-threatening bacterial infection caused by the bacterium Clostridium tetani. The condition is characterised by muscle contractions which typically begin at the jaw and neck muscles. This is how tetanus also gets its other name, “lockjaw”.¹

The World Health Organisation (WHO) defines (non-neonatal) tetanus as the presence of at least one of the following signs:²

• Sustained spasm of muscles of face – patient appears to grin
• Painful muscular contractions

What is tetanus?

Tetanus is supposed to have been derived from the Greek word “tetanos”, which means “tension”, or “to stretch”.³ It is a potentially fatal condition that is identified by increased rigidity and convulsive spasms of muscles.

The tetanus toxin was first isolated from free-living anaerobic bacteria in the soil by Arthur Nicolaier, and C. tetani was first isolated from a human by Kitasato Shibasaburō in 1891.³

Tetanus should not be confused with tetany which refers to the involuntary contraction of muscles due to over-stimulated nerves. Tetany is usually caused by an electrolyte imbalance in the blood (typically low blood calcium ion level), in contrast, tetanus occurs when spores of Clostridium tetani enter the body through breaks in the skin and germinate, ultimately releasing tetanospasmin, a potent neurotoxin.⁴

Tetanus is a global occurrence, but it is most commonly observed in densely populated areas with a tropical (hot and damp) climate.⁵ According to data from the United States, mortality due to tetanus has seen a decline since 1900, and new cases have declined since the 1940s (reporting of new cases began during this time). In 2017, a total of 33 cases and 2 deaths were reported from tetanus in the United States, and all tetanus-related deaths were reported among people more than 55 years of age.⁴

The bacterium: Clostridium tetani

Physical characteristics

C. tetani can be classified as a spore-producing, motile, gram-positive bacillus (rod-shaped bacteria). They measure about 2 to 2.5 microns in length and 0.3 to 0.5 microns in width, and they are motile due to the presence of some projections on the cell surface called peritrichous flagella. These flagella are lost during the spore stage, where it take on a drumstick appearance.⁶ 

C. tetani is classified as a strict anaerobe (grows in the absence of air), and the ideal temperature for its growth is 33-37 °C. The spores of C. tetani are very robust. They may persist in soil for several months to years and are resistant to boiling and common disinfectants, inactivation of spores often requires chemical mixtures such as a solution of formalin, phenol and chloramine; or advanced sterilisation techniques such as autoclaving.⁶

C. tetani reservoirs

The largest environmental reservoir of C. tetani bacilli and its spores is the soil. Studies indicate that viable spores are more commonly distributed in nutrient-rich soil and have an alkaline pH, in warm moist climates. Other reservoirs include surfaces of rusty tools such as rusted needles, nails, barbed wire, etc.²

C. tetani are also found in animals. Herbivores and omnivores may host the bacteria and spores in their intestines and spread them through their faeces. Among humans, people living in rural areas were reported to have higher rates of C. tetani in their intestines, compared to people residing in urban areas.⁶

Modes of transmission

Tetanus is spread by the direct transmission of C. tetani spores from a reservoir to the body through opening/breakage in the skin. This usually occurs in cases of wounds such as:

• Puncture wounds from rusty instruments such as pins, nails
• Lacerations/cuts from sharp tools
• Animal bites and scratches, especially if the animal lives close to the soil
• Burns
• Intravenously(through the veins) if non-sterile, rusted needles are used
• Other skin injuries such as abrasions, ulcers, etc., through which spores may enter
• Neonatal tetanus may occur if the umbilical cord is cut using non-sterile/rusted instruments

Mechanism of action

Once the spores enter the body, there is minimal contact with air, allowing spores to germinate and grow. The following events occur after:⁷

• As spores germinate, they release toxins tetanolysin and tetanospasmin. Out of these, tetanospasmin is responsible for the symptoms of tetanus. Tetanospasmin is one of the most potent known toxins, with a dose of about 2.5 nanograms per kg body weight estimated to be lethal.
• Tetanospasmin spreads via the bloodstream and lymphatic system, from where it enters the nervous system.
• Within the nervous system, tetanospasmin blocks the release of inhibitory neurotransmitters (which deactivate neurons), which leads to widespread, continuous activation of motor neurons(nerves supplying muscles) and muscle spasming.
• Spasms generally begin at the top of the body and move down, and it occur generally between 3 to 21 (average 8) days after exposure to C. tetani.

Signs and symptoms

The most common primary symptom of tetanus is a spasm of the jaw muscle – also known as “lockjaw”. Other possible symptoms include:^1,8

• Muscle spasms in other parts of the body including extremities, back and abdomen.
• Difficulty in swallowing
• Painful stiffness in the entire body
• Seizures
• Headaches
• Fluctuations in heart rate and blood pressure

Complications

Often life-threatening, potential complications of tetanus include:

• Spasms of muscles of breathing (laryngospasm) which may lead to difficulty breathing
• Fractures of long bones due to sustained contractions of muscles
• Abnormal heart rhythm
• Hypertension
• Pulmonary embolism(blood clots in the lungs) 
• Nosocomial infections (infections contracted in hospitals) as tetanus patients tend to be hospitalised over long periods.

Diagnosis

Diagnosis is usually based on clinical examination and injury and vaccination history. Laboratory tests are not usually recommended as C. tetani is recovered from wounds of patients in about 30% of cases, and can also be extracted from individuals not suffering from tetanus.⁵

Management

Due to the absence of a specific treatment, this condition is managed to reduce and control symptoms. Common steps involve:⁵

• Clean all wounds properly
• Administer tetanus immune globulin (TIG) to patients suffering from tetanus. It is important to note that TIG can only remove free tetanus toxin from the blood, not the toxin that is attached to nerve endings
• Tetanus toxoid vaccine is also suggested in some cases to improve protective levels of antitoxin
• For severe spasms, drugs that reduce spasms are prescribed
• Additional supportive care and maintenance of adequate airway

Prevention

Immunisation plays the most important role in tetanus prevention.⁵ The World Health Organization(WHO) recommends every individual to receive 6 doses in total (3 primary plus 3 booster doses) of tetanus-toxoid-containing vaccines (TTCVs). These TTCVs are often included in routine immunisation programs globally.

A 3-primary dose series usually begins at 6 weeks of age, with subsequent doses at a minimum of week intervals. 3 booster doses should ideally be given during the second year of life (12 to 23 months), 4 to 7 and 9 to 15 years of age. It is recommended to have at least 4 years between booster doses.

Summary

Tetanus is a potentially life-threatening infection that occurs when spores of C. tetani enter the body through wounds and other surfaces. Upon injury, individuals should clean the wound area with antiseptic solutions, and consult with a medical professional who can recommend further steps (such as tetanus immune globulin administration) based on the nature of the injury, cause and medical history of the patient.

Although there is no treatment for tetanus, it is highly preventable through proper immunisation, thus highlighting the importance and necessity of proper vaccination.