Diphtheria is a rare disease, which is caused by the bacteria called Corynebacterium diphtheriae and Corynebacterium ulcerans. It may affect the throat or nose and sometimes the eyes or the skin. Some diphtheria bacteria are more dangerous than others and can cause serious illness. Only bacteria that produce diphtheria toxin (poison) cause the classical disease we call diphtheria. Non-toxigenic strains do not produce this toxin.
Diphtheria is contagious and can be passed from person to person through the tiny droplets in sneezes and coughs. It can be spread by close, prolonged contact (for example in the home) or by close face-to-face contact with an infected person.
Incubation period
The illness may develop up to seven days after contact with the bacteria.
Transmission
The C. diphtheriae bacteria are spread by being in very close contact over a period of time with someone who has the illness or is a carrier.
The C. ulcerans bacteria can be spread by being in very close contact over a period of time with animals that carry it in their nose or throat or by drinking unpasteurised milk or eating products made from unpasteurised milk.
Signs and symptoms
This depends on where the infection is. The most characteristic feature of diphtheria affecting the upper respiratory tract is a membranous pharyngitis (often referred to as a pseudo-membrane) with fever, enlarged anterior cervical lymph nodes and oedema of soft tissues giving a "bull neck" appearance. The pseudo-membrane may cause respiratory obstruction. The toxin also affects other parts of the body including the heart and nervous systems, causing paralysis and cardiac failure. Milder infections resemble streptococcal pharyngitis and the pseudo-membrane may not develop, particularly in vaccinated individuals. The bacteria can also be carried without any symptoms at all.
Cutaneous diphtheria usually appears on exposed parts, especially the legs. The lesions start as vesicles and quickly form small, clearly demarcated, and sometimes multiple ulcers. The lesions are usually difficult to treat and may take months or even years to heal.
Treatment
Patients with respiratory diphtheria require hospitalisation and treatment with diphtheria antitoxin. They will also be given appropriate antibiotics to eliminate the bacteria. When they have recovered they will be given a dose of diphtheria vaccine as having the disease does not necessarily protect against further infection.
In addition, people who have been in contact with a diphtheria patient will be assessed and may receive preventative antibiotic treatment and booster vaccination.
Treatment is always very urgent and should not be delayed. A person is no longer infectious after they have received a full course of treatment, which is usually given in hospital.
Prevention
The most important way to avoid the disease is vaccination. All children in Malta are routinely offered immunisation against diphtheria at two, three and four months old. Booster doses are given before starting school and then again between 16 and 18 years.
Diphtheria vaccine is given as part of a combined diphtheria, tetanus, pertussis, Hib (Haemophilus influenzae type b) and polio vaccine, and offers very effective protection against all these diseases.
Diphtheria is more common in some countries where vaccine uptake is poor, especially in Africa, South Asia and the former Soviet Union, so it is important to make sure your vaccinations are up to date before you travel to these areas.
The vaccine protects you against the diphtheria toxin. However, immunisation does not prevent you from carrying the bacteria.
Most cases occur in people who are unvaccinated or inadequately immunised.