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Anthrax in humans
- Anthrax is a highly infectious disease of animals, particularly cows and sheep, which is transmitted to man by contact with infected animals or their products.
- It is caused by bacillus anthracis.
- Spores can live in contaminated soil and animal products for decades.
- The skin is the usual method of infection in humans but it can occur through eating contaminated meat.
- There are three main forms affecting the skin (cutaneous), chest (pulmonary) and gut (gastrointestinal).
- The antibiotics penicillin, streptomycin, tetracycline and erythromycin can all be used in treatment.
- The cutaneous form is rarely fatal, but the pulmonary form usually results in death.
- The disease is prevented by good husbandry and abattoir controls.
What causes anthrax
Anthrax is caused by the bacterium bacillus anthracis. This bacterium can live in tissues that contain little or no oxygen. Its spores are very resistant to destruction, so can survive in contaminated soil and animal products for decades.
Humans are usually infected through the skin, but people have become infected after eating contaminated meat. Inhaling spores when there is a respiratory infection present can result in pulmonary (chest) anthrax, called woolsorter’s disease, which is often fatal.
Symptoms and signs of anthrax
The incubation period varies from 12 hours to five days, and is usually three to five days.
There are three main forms, affecting the skin (cutaneous), the chest (pulmonary) and the gut (gastrointestinal).
Cutaneous form
This begins as a red-brown papule on the skin that enlarges and is surrounded by an inflamed, red area. The central area of the papule then ulcerates and clear fluid leaks from it, eventually forming a characteristic black eschar.
There may be swollen glands in the area of the sore, and some people experience malaise, muscle aches and pains, headache, fever, nausea and vomiting.
Pulmonary anthrax
This form of the illness occurs if spores are inhaled. The spores then multiply rapidly in the lymph nodes in the centre of the chest. These lymph nodes start to bleed and their tissue breaks down and the infection spreads within the chest. This caused a build up of fluid within the lungs.
The initial symptoms are insidious and similar to flu. The fever rises and within a few days the person suffers severe respiratory distress, shock, lack of oxygen to the tissues (cyanosis) and coma. There may also be a form of inflammation of the brain with bleeding and inflammation of the membranes and brain tissue – called haemorrhagic meningoencephalitis.
Unless this form of the disease is treated early with specific and supportive measures, the person usually dies.
Gastrointestinal anthrax
This is very unusual. This form of the disease follows ingestion of contaminated meat when the person has a break in the lining of the oesophagus or gut, which allows the anthrax bacterium to infiltrate the wall of the gut.
The toxin which the bacterium releases causes bleeding and breakdown of the gut wall which then extends to the lymph nodes which drain the gut. Eventually the person becomes septicaemic and can die.
How is anthrax treated?
The cutaneous form is treated with intravenous penicillin initially and then oral penicillin for seven to ten days, which prevents spread and induces gradual resolution of the skin pustule. Tetracycline or erythromycin taken orally can also be used, particularly in children.
Pulmonary anthrax is treated with an early and continuous intravenous infusion of penicillin, sometimes in combination with streptomycin. A similar regime is used to treat gastrointestinal anthrax and anthrax meningitis.
What is the outcome of the disease?
Deaths from cutaneous anthrax are very unusual with the appropriate treatment, and the mortality rate is between 10 and 20% if it is not treated. However, pulmonary anthrax carries a mortality of nearly 100% even when treated. Gastrointestinal anthrax has a mortality of 50% and anthrax meningitis is usually fatal.
Can anthrax be prevented?
Anthrax is now almost unknown in the western world, other than in stockpiles of spores which could potentially be used for biological warfare.
Pulmonary anthrax was virtually eliminated in Britain before 1940 by developing methods to decontaminate wool and goat hair and by improving working conditions for those handling animal products.
Good livestock and abattoir control usually means that the disease is seldom seen.
There is a vaccine for humans available in the USA, but apparently no stocks are kept in South Africa.
