Anthrax is a bacterial disease caused by Bacillus anthracis. The bacteria forms spores that are resistant to poor environmental conditions and can survive for years on dried or processed hides and soil.
Anthrax is primarily a disease of herbivores (i.e. cattle, sheep, goats, horses), which are exposed to the spores while grazing. Outbreaks typically occur in these areas when heavy rainfall is followed by a drought.
Animal cases pose minimal risk to humans. People can get infected through direct contact with sick animals or carcasses.
1. Anthrax and human health
The human health risk from anthrax is limited to people who have direct contact with sick animals or carcasses.
Infection most commonly occurs when broken skin comes into direct contact with anthrax spores. The infection starts with a small bump on the skin that develops into a blister and then a skin ulcer with a black centre.
Individuals with these types of skin lesions should see a physician urgently.
2. How people become infected with anthrax
People are exposed to naturally-occurring anthrax through:
- Contact with infected animals when farming; or
- Contact with infected animal products through occupation (people working with infected animal hides, wool or yarns and laboratory workers).
3. Types of human anthrax illness
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.
Anthrax is treated with antibiotics.
Skin anthrax responds very well to antibiotic treatment. The current practice in Saskatchewan is to give a 14 day treatment course of antibiotics if skin lesions develop.
Sometimes a preventive 10- to 14-day course of antibiotics may be prescribed to people who had direct, unprotected contact with infected animals or carcasses, and have broken skin.
For inhalation exposures only, the official recommendation used during the U.S. bioterrorism events of 2001 was to use preventive antibiotics for 60 days.
Mortality is less than one percent with antibiotic treatments. Although treatment doesn't shorten the evolution of skin lesions, it does prevent development of a more serious form of anthrax.
5. The risk of getting anthrax
The risk of getting anthrax is very low, even to agricultural workers caring for sick animals. They typically get the skin form of disease, which is easily treated with antibiotics.
Anthrax is not transmitted from person to person.
Inhalation anthrax can only be contracted by directly inhaling anthrax spores. Gastrointestinal anthrax is acquired by eating uncooked, contaminated food.
There is a very small risk of infection with skin anthrax from direct contact with the lesions on another person's body before antibiotic treatment begins. This risk can be prevented through routine infection control practices.
People cannot get anthrax from swimming in water that is used by cattle or drained from areas with cattle.
6. How to reduce your risk of exposure to anthrax
- Get educated about the disease, how it is transmitted, signs, and symptoms.
- Use proper personal protective equipment (like gloves, overalls, etc.) while caring for sick animals.
- Wash your hands after working outside in the fields or touching animals. Teach your children to use these hygienic practices as well.
- Change your clothing and wash your hands after working with sick animals.
- Clean or dispose of equipment used on sick animals and clothing worn when in contact with them.
- Change clothing and wash hands before any contact with people or healthy animals after working with sick animals.
- Clean skin abrasions with soap and water as soon as possible.
- Wash your hands after going to the toilet and before eating.
- Follow safe food practices, thoroughly cook meat and other products, and properly wash raw vegetables and fruits from farms before eating them.
7. Vaccination against anthrax
There is a human vaccine against anthrax, but it is not approved for widespread use because it hasn't been comprehensively tested in human trials. The vaccine is sometimes given to people likely to be exposed to anthrax through their occupation, such as tannery workers or military personnel. It's not widely available and it's not recommended for mass immunization.
There is a vaccine used for animals which is made with a non-pathogenic form of anthrax. If you get an accidental needle poke with this vaccine, you do not need to take any special measures or get treatment – you can clean the wound with soap and water.
You should also make sure your tetanus shots are up to date (every 10 years).
8. Risk to animal health
Although all mammals are susceptible to anthrax, it is primarily a disease of herbivores. Cattle, bison, sheep, goats and horses are highly susceptible. Omnivores, like pigs, and carnivores, such as dogs and cats, are less susceptible and can sometimes be exposed to the bacterium repeatedly before becoming infected. Birds and wildlife also appear to be at a lower risk for anthrax.
For more information:
Contact the Chief Veterinary Officer, Saskatchewan Ministry of Agriculture, Livestock Branch at 306-787-5547; or
Visit the Canadian Food Inspection Agency and click on Animals/Reportable Diseases/Anthrax.