Anthrax, Then and Now (cont.)

What is anthrax?

Anthrax is a disease caused by a type of bacteria, or germ, (bacillus anthracis) that was discovered in 1850. Notably, it is actually the first bacterium to be shown to cause a disease. In fact, it was the well-known German physician Robert Koch who discovered this. He grew the anthrax bacteria in culture plates, injected them into animals, and thereby demonstrated that the bacteria produced the disease. Then, the famous French scientist Louis Pasteur (known for pasteurizing milk) used anthrax bacteria that he damaged to develop a vaccine for anthrax. His idea was that the damaged bacteria would not cause the disease but would still protect (produce immunity) against anthrax. Indeed, he showed that this vaccine protected animals from getting the disease when they were subsequently injected with healthy, virulent (disease-causing) anthrax bacteria.

Anthrax differs from most bacteria in that they exist in an inactive (dormant) state called spores. The spores are found in soil, animal carcasses and feces (including sheep, goats, cattle, bison, horses, and deer), and animal products (for example, hides and wool). Some animals (cats, dogs, rats, and swine) are very resistant to anthrax. Remarkably, anthrax spores can remain dormant in soil for many years, perhaps decades. Likened somewhat to eggs that have the ability to hatch, spores can transform (germinate) into active bacteria under appropriate conditions. The spores themselves do not cause any significant damage to tissue. However, they can lead to disease by (1) entering broken skin (cutaneous anthrax), (2) being inhaled (inhalation anthrax), or (3) being eaten (gastrointestinal anthrax). Once in the body, the spores germinate to form the virulent (disease-causing) bacteria.

What symptoms does anthrax cause?

Cutaneous anthrax results in a large, relatively painless, ugly skin sore referred to as a malignant pustule. Death is rare with treatment; and 80% of untreated patients survive as well. In the other 20%, death occurs because the infection spreads to other parts of the body or the patients succumb to a poison (toxin) that the bacteria produce.

Gastrointestinal anthrax is rare and appears to follow ingestion of contaminated raw meat containing the spores. Symptoms caused by this type of anthrax can include nausea, vomiting, abdominal pain, and diarrhea. As with cutaneous anthrax, most people having gastrointestinal anthrax survive, with or without antibiotic treatment.

The most dangerous form of anthrax, and the greatest bioterrorism threat, is inhalation anthrax. It has also been called wool sorter's disease because it is an occupational hazard for people who sort wool. Inhaling spore-bearing dust is the usual way that inhalation anthrax is contracted. To cause the disease, spores must be inhaled and transported through the air passages into the tiny air sacs (alveoli) in the lungs. The spores are then picked up by scavenger cells (macrophages) in the lungs and are transported through small vessels (lymphatics) to the glands (lymph nodes) in the central chest cavity (mediastinum). In the glands, the spores transform (germinate) into active, multiplying (reproducing) bacteria. Damage to the central chest cavity and lungs can cause chest pain and difficulty breathing.