Microbiology
Pathogens
A mother brings her child to ED with a dirty wound sustained at a playground. The patient is due a tetanus booster and you decide to give it in the department. The mother wants to know how the vaccine works. You explain that vaccination results in the production of antibodies that prevent disease. By what mechanism do these protective antibodies prevent tetanus:
Answer:
C. tetani produces the exotoxin tetanospasmin which is responsible for the neurotoxic effects of tetanus. The tetanus vaccine contains inactivated tetanus toxoid which stimulates the body to create protective antibodies which act to neutralise tetanus toxin.Clostridium Tetani
Microbiology / Pathogens / Clostridial Infection
Last Updated: 18th June 2019
| Microorganism | Clostridium Tetani |
|---|---|
| Gram stain | Gram positive |
| Shape | Rod |
| Oxygen requirements | Obligate anaerobe |
| Additional features | Spore-forming, Produces tetanospasmin |
| Reservoir | Soil, dust & intestinal flora |
| Diseases | Tetanus |
Clostridium tetani is the causative agent of tetanus.
Transmission
Clostridium tetani is found in the human intestinal flora, but infection seems to be predominantly derived from animal faeces and soil.
Transmission occurs from spores contaminating open wounds. Germination of clostridial spores and their outgrowth depend upon reduced oxygen tension in devitalised tissue and non-viable material in a wound.
Pathogenesis
C. tetani produces the exotoxins tetanolysin and tetanospasmin. Tetanospasmin impairs the membrane of synaptic vesicles, preventing the release of the inhibitory neurotransmitter GABA at the presynaptic membrane; motor neurons are left under no inhibitory control and undergo sustained excitatory discharge, causing the characteristic spasms and spastic paralysis of tetanus. The toxin acts on the spinal cord, the brainstem, the peripheral nerves, the neuromuscular junction and directly on muscles.
Clinical Disease
The period between injury and the first signs is usually about 3 - 21 days (average 10 days).
The onset of signs and symptoms following a prodromal fever, malaise and headache, is typically gradual and descending, usually starting with some stiffness or pain near a recent wound.
Pain, stiffness and muscle spasm in the face, jaw (lockjaw), neck, back and abdomen may follow; perioral muscle spasm causes risus sardonicus (a grin-like expression), and spasms of the back muscles can produce arching of the back with an extended neck (opisthotonus).
Complications include:
- swallowing difficulties
- aspiration pneumonia
- laryngospasm
- respiratory failure
- autonomic dysfunction
![By Charles Bell [Public domain], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2016/12/Tetanus-300x174.jpg)
Opisthotonus. (Image by Charles Bell [Public domain], via Wikimedia Commons)
Treatment
- Management of infection
- Wound debridement (removes spores and necrotic tissue, eradicating the anaerobic conditions that facilitate clostridial growth)
- Antibiotic therapy (metronidazole is the antibiotic of choice)
- Intravenous human tetanus immunoglobulin (neutralises unbound toxin, reducing the duration and severity of tetanus)
- Tetanus toxoid immunisation (stimulates long-term humoral and cellular immunity)
- Control of muscle spasm
- Benzodiazepines and other sedatives
- Non-depolarising neuromuscular blocking agents
- Baclofen
- Supportive care
- Airway support with prevention of aspiration
- Mechanical ventilation
- Nutritional support
- VTE prophylaxis
- Physiotherapy
- Ulcer prevention
Immunisation Schedule
Tetanus Routine Childhood Immunisation Schedule:
| Dose | Time | Vaccination type |
|---|---|---|
| 1st dose | 2 months | As DTaP/IPV/Hib |
| 2nd dose | 3 months | As DTaP/IPV/Hib |
| 3rd dose | 4 months | As DTaP/IPV/Hib |
| 4th dose (1st booster) | 3.5 - 5 years (preschool) | As DTaP/IPV |
| 5th dose (2nd booster) | 13 - 18 years | As Td/IPV |
If the primary course is interrupted it should be resumed but not repeated, allowing an interval of one month between the remaining doses.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
