What is anthrax infection?
Anthrax is an infection caused by a bacteria called Bacillus Anthracis. The name anthrax comes from the Greek word "anthrakas" which means "coal" reflecting the black rash caused by infection of the skin by this bacterium. The bacteria is naturally found in soil and can infect livestock. Most of the animal infections occur in South and Central America. There have been outbreaks of human anthrax as well. In the USA there were about 130 cases/year of human anthrax in the early 1900's. Between 1993-2000 there were no reported human anthrax cases in the USA. It is not surprising that most physicians in North America have never seen a case of anthrax during the course of their practice.
How is anthrax spread to humans?
Anthrax is usually found in sheep, cattle and other animals. The infection however is not considered contagious; in other words it cannot be transmitted from one infected person to another. The anthrax bacterium is a type that can make spores. By enclosing itself in a microscopic wall, almost like a cocoon, the spore form of the bacteria can last a long time(years) outside of a living body. Once the spores get inside a body they start to multiply and cause an infection. Most of the human infections, which are very rare, to begin with, result from contact with infected animals or animal parts such as sheepskin.
What is the difference between contact with the spore and actually getting anthrax?
This is a very important point. Just because a person comes into contact with anthrax spores does not mean that he or she will develop the infection. The spores have to be a certain size and enter the body in large numbers(up to 50,000) in order to cause an infection. Just because a person touches or comes into contact with a spores does not automatically mean that infection will occur.
What type of infection does anthrax cause?
The anthrax bacteria can cause 3 types if infection in humans depending on the way the spores enter the body.
- Skin: a skin infection can result if the bacterium gets in through a cut or tear on the skin. Once it causes an infection, a rash is formed and the bacterium can possibly enter the blood stream This type of infection has a mortality rate of about 20% if untreated.
- Gastro-intestinal: the spores enter the body through the stomach and intestines of after eating meet infected with anthrax. The mortality rate in untreated cases is thought to be between 25-60%. This is very rare in North America where meat is stringently controlled for infection.
- Inhalation: the spores(in sufficient numbers and size) get into the lungs causing symptoms of a chest infection including, cough, difficulty breathing and fever. The anthrax bacterium can then get into the blood and dangerously infect the covering of the brain, causing meningitis. This form of anthrax is considered very deadly with a mortality rate of over 90% if untreated.
How is anthrax infection confirmed?
Specimens taken by swab either from the nose or the skin are sent to a Microbiology laboratory where they look for the anthrax bacteria. This process takes at least several days. Today there exist more sophisticated portable equipment that can actually screen for and detect the bacteria within minutes.
Why and when are antibiotics prescribed?
In the recent cases of contact with anthrax most people did not develop any serious infection. These people came into contact with the anthrax spores(in other words the bacterium was found on their skin or nasal passages). Only these people were given antibiotics. It is important to note that most of these people were otherwise well and antibiotics were given as a precautionary step. Obviously if there is an active infection antibiotics are also necessary. Additionally if public health authorities suspect that certain groups of people(such as postal workers etc) where possibly exposed to anthrax spores they may recommend antibiotics as a precaution, even without testing.
Is there a vaccine against anthrax?
Animal vaccines exist that protect animals form anthrax. There is also a vaccine for humans that has been used mostly to protect high risk individuals such as livestock farmers(working in areas where there is a high rate of anthrax spores present), laboratory workers and more recently, because of the fear of bio-terrorism or biological warfare, army troops. In order to be effective, multiple doses need to be given to an individual over a prolonged period of time. After the initial shots, a booster vaccine is given annually. The human anthrax vaccine, considered to be 93% effective be has not been used in people less than 18 years or older than 65 years.
What can people do to prevent exposure to anthrax?
According to security authorities it is essential not touch or open any suspicious or unexpected pieces of mail. Taking antibiotics just in case is not recommended. Over-use of antibiotics can cause more problems than it solves. Only persons who have had proven contact(by laboratory tests)need to take antibiotics. Also, certain groups of people who work where anthrax bacteria spores were found may need to take antibiotics. This decision is made, based on the individual situation, by public health officials.
It is important to keep in mind that:
- Contact with the anthrax spores does not necessarily mean an infection
- A very large number of anthrax spores must enter the body to cause an infection
- It is very difficult to make spores small enough and in enough quantity to deliberately cause infection
- Antibiotics are prescribed to prevent an anthrax infection in proven contacts with the bacteria, whether they have an active infection or not
- Antibiotics may also be prescribed to certain groups of people(i.e. postal workers) working in a area where anthrax spores were found
- Anthrax is not contagious: in other words cannot spread form an infected person to another
- Antibiotics taken just in case without proven or suspected contact are not necessary