Immunisation is to the toxin rather than the bacterium. It is produced by a phage infecting the bacterium rather than encoded on bacterial DNA
- Corynebacterium diphtheria and occasionally C. ulcerans.
- Fatality rates between 5% and 10%
- Releases an exotoxin that blocks protein synthesis
- Toxin gene is encoded by a bacteriophage
- Mild cases can go undiagnosed
- Gram positive, club-shaped, non-motile rods
- They grow at angles forming V,L,W shapes "Chinese letter shapes"
- Grows best with oxygen at 37 degrees
- Exotoxin only produced by those with the relevant phage
- Exotoxin has two components A and B as described below
- Toxin acts as an RNA translational inhibitor
- 535 residues, 58 kDa exotoxin whose active form consists of two
polypeptide chains linked by a disulphide bond
- Causes local tissue necrosis
- Toxaemia and paralysis due to demyelinating peripheral neuritis
- Cardiac failure due to myocarditis.
- Those bacteria infected with the corynephage beta produces an A-B toxin
- The A component is an ADP ribosyl transferase that binds to eukaryotic elongation factor 2 blocking protein synthesis
- The B component directs the toxin to the oropharynx, heart and nerve cells
- Spread by direct physical contact
- Breathing aerosolized secretion from an infected person
Clinical (IP is 2-4 days)
- Pharyngitis - grey dirty pseudomembrane is visibly composed of fibrin and dead cells and there is associated lymphadenopathy producing a "bull neck"
- Nasal, laryngeal and pharyngeal mucosa affected
- Can lead to airway obstruction and stridor
- Sore throat, fever, malaise
- Heart failure, heart block and arrhythmias
- Cranial nerve palsies: diplopia, dysarthria, dysphagia
- Myocarditis and cardiac dysfunction - bradycardia, chest pain
- Laryngeal nerve palsy - hoarseness
- Grows on Hoyle's media (Blood tellurite) producing black colonies reducing tellurite to tellurium. An alternative is the Tinsdales medium with added horse serum.
- There are 3 types - gravis (worst), intermedius, mitis (best) which suggest the severity of disease caused and can be separated by haemolysis and appearance
- Biochemical testing for catalase, urease, nitrate, pyranzinamidase, cystinase
- Test for toxin production using Elek test using antitoxin
- Serotyping and bacteriophage typing
- Culture of swabs from larynx/pharynx
- ECG/Monitor - heart block and arrhythmias
- Echocardiogram to assess LV function
Diphtheria was eradicated from much of the developed world by mass vaccination in the mid-20th century
- ABCs. Bed rest. Telemetry. Isolation and treatment of the index case
- Diphtheria antitoxin produced from hyperimmune horse serum:
neutralises any toxin not fixed to tissue but can cause anaphylaxis
- Give Amoxicillin or Erythromycin for two weeks and treat contacts
- Remove membrane by laryngoscopy or bronchoscopy to prevent airways obstruction.
- All contacts should also be immunised or given a booster dose of toxoid. Booster doses are required every 10 yrs to maintain immunity