Some infectious diseases are as common as dirt and, under the right circumstances, about as harmless. It's only when they encounter a suitable environment -- or when humans weaponize them -- that they become a threat.
Take Bacillus anthracis, the rod-shaped bacteria found in soil all over the world. Its spores remain dormant until they enter the body, where they propagate and churn out harmful toxic byproducts. Domestic herds and wild animals can breathe in or consume spores in contaminated soil, plants or water. Although rare, humans can get it too, usually through encounters with infected animals or contaminated animal products.
Anthrax enters humans via four main routes:
- Cutaneous, from cuts or scrapes that occur while handling affected animals
- Gastrointestinal, from eating or drinking contaminated products
- Injection, mostly limited to northern Europeans heroin users
- Inhalation, from weaponized anthrax or from bacteria kicked up while handling contaminated hair, hides or wool.
Each kind has its own symptoms, which can take one day to two-plus months to appear [source: CDC]. Inhalation and gastrointestinal anthrax hit like a terrible flu, but gastrointestinal adds swollen glands and potentially bloody diarrhea or vomiting. The cutaneous kind involves blisters and ulcers, as does injection anthrax, which spreads faster and throws in fever and chills.
If not treated in time, anthrax can kill, but all types can be avoided and remedied using precautions and antibiotics. A vaccine exists, but is only meant for particularly at-risk adults. Some countries, including the U.S., have veterinary public health programs that vaccinate animals against anthrax.