There are three types of human illness caused by anthrax:
- Cutaneous (skin) anthrax:
This is the most common form, causing 95 percent of human cases in North America.
Skin anthrax is usually contracted when a person with a pre-existing break in their skin (such as a cut or abrasion) comes into direct contact with anthrax spores. An itchy bump appears 1 to 12 days later, followed by a blister and a skin ulcer with a black centre in the next 24-36 hours. The lesion resolves in about 6 weeks in most people.
Some people may also develop headaches, muscle aches, fever and vomiting.
- Gastrointestinal anthrax:
People get this form of anthrax by eating contaminated food, primarily uncooked or undercooked meat from an infected animal.
The initial symptoms are nausea and vomiting but can worsen to include severe abdominal pain, vomiting of blood and bloody diarrhea.
Gastrointestinal anthrax is up to 200 times less common than skin anthrax.
- Inhalation or pulmonary anthrax:
This is the more rare form of human anthrax but it is the most dangerous.
The first symptoms of pulmonary anthrax are similar to those of a common cold, but this can rapidly progress to severe breathing difficulties and shock.
People acquire pulmonary anthrax when breathing in a large number of anthrax spores present in the air. This type of exposure happens in occupational settings where people work with contaminated skins or wool. It has also been reported in bioterrorist events.
It is estimated that a person would have to inhale 8,000 -10,000 spores to develop the pulmonary disease, which is likely why the disease is not common in people during agricultural outbreaks in animals. Fresh open carcasses have fewer spores than decaying carcasses.
The risk of pulmonary anthrax in agricultural settings is extremely low. There is virtually no risk of pulmonary anthrax from working with infected animals even during autopsy.