Diphtheria - Causes of diphtheria

Two types of bacteria can cause diphtheria.

They are:

• Corynebacterium diphtheriae
• Corynebacterium ulcerans

The bacteria spread when an infected person coughs or sneezes and droplets of their saliva enter another person's mouth or nose. Less commonly, the bacteria that cause diphtheria can be transferred by an infected person onto household items, such as glasses, towels or eating utensils.

Diphtheria is usually caught after being in close or prolonged contact with someone who has the condition or is carrying the infection. For example, you may catch diphtheria from someone you live with.

In countries where standards of hygiene are poor, diphtheria can often affect the skin (cutaneous diphtheria). In these cases, the bacterial infection is spread through contact with the infected wound rather than by breathing in infected droplets.

Infection from animals

You can become infected with Corynebacterium ulcerans after coming into close contact with cattle, because they carry the bacteria in their nose and throat.

You can also become infected with the bacteria after drinking unpasteurised milk or eating food made with unpasteurised milk.

How the condition develops

Once a person is infected, the bacteria quickly multiply and spread through the inside surface of the mouth, throat and nose.

The bacteria produce a toxin (poison) that begins to kill the cells in the throat. The dead cells rapidly build up and form a grey-white membrane in the throat (see symptoms of diphtheria).

The toxin can also spread through the blood and damage the heart and nervous system.