The bacteria that cause deadly anthrax disease persist in the earth, a place their ancestors preferred over petri dishes and blood-filled tissues.
The bacteria that cause anthrax are called Bacillus anthracis. In the soil, they hang out and can form communities around plant roots. They also interact with neighboring organisms, though they’re an admittedly less-than-ideal neighbor to the soil-dwelling amoebae they infect and kill.
As a public health researcher, I am fascinated by how diseases move among people, animals and the environment. When I worked in a state health department, I was surprised to learn how the bacteria that cause anthrax cycle between land and the animals that rely on that land – including people.
Anthrax in the ecosystem
Give these bacteria alkaline-rich dirt, calcium and some nitrogen, and they happily subsist in the ground. If the temperature, humidity or acidity is not favorable, these bacteria can also slumber for decades in a spore form – underfoot and forgotten by nearly all except cattle.
Cattle, deer and other large herbivores disturb the abodes of bacteria. They sometimes unintentionally eat anthrax spores along with their food or are exposed to them through a cut. After anthrax spores enter the animal’s body, immune cells known as macrophages pick up these spores for removal. But instead of being destroyed like other intruding pathogens, the spores germinate and multiply.
Immune cells (yellow) engulfing anthrax bacteria (orange).
Volker Brinkmann/Wikimedia Commons, CC BY-SA
Once the spores take the form of bacteria, they can also mount an aggressive offensive. Anthrax bacteria can cleave vital proteins with toxins and wreak havoc on their cellular adversaries. Cattle succumb to the bacteria within days if left untreated – sometimes within 48 hours of infection.
Through the cattle’s death, the bacteria are brought back to the earth to vegetate or sporulate once more.
Humans seeding anthrax
People can get caught in the life cycle of Bacillus anthracis.
Throughout history, humans and animals have seeded new lands with Bacillus anthracis spores. The spores are hardy travelers: They can survive for over 50 years and are resilient to dehydration, radiation, toxic chemicals and enzymatic degradation.
Anthrax in early Egypt may have been one of the plagues described in the Bible. Animal husbandry texts in China have described anthrax for millennia. French explorers brought Bacillus anthracis spores to American soil in the early 1700s.
While people usually spread anthrax accidentally, there are infamous examples of anthrax spread on purpose.
In the 1930s and ’40s, Japanese military leaders released anthrax spores in Chinese villages, killing thousands of people. On Sept. 18, 2001, envelopes of spores were mailed to American media and congressional leaders, killing five people.
The weaponized use of Bacillus anthracis spores brings to mind white…
