People are likely to remember the letter-bound anthrax attacks of 2001, which ultimately killed five Americans and sickened 17 others. However, did you know that anthrax can naturally occur in Colorado’s soil?

Animals in at least two northeast Colorado cattle herds have succumbed to anthrax infections in recent days, with two people that were also exposed being put under close surveillance. While the risk to the public is believed to be low, digging into the topic reveals how recent weather conditions may be to blame for the appearance of the deadly infection.

For starters, anthrax is a non-contagious* infection caused by a bacteria called Bacillus anthracis. The infection occurs in four forms (skin, lung, intestinal, and injection), with infections among cattle typically occurring when the animals eat or breathe in spores while they’re grazing a field.

But how does anthrax end up in the soil in the first place?

The CDC says that the bacteria that causes anthrax occurs naturally in soil. At that point, an outbreak or infection may occur if a being comes in contact with the dangerous spores, which then activate once inside the body.

According to research published in an academic journal called Applied and Environmental Microbiology, “outbreaks of anthrax tend to occur in warm weather following rains that are believed to concentrate spores in low-lying areas where runoff collects.”

Once spores that cause anthrax develop, they can lay dormant for up to 50 years or for up to two centuries when found in the bones of an animal that succumbed to the infection.

These dormant spores in the soil can get pushed to the surface when the soil that contains them gets disturbed, including via flooding. Hot temperatures can make pools of stagnant water even more favorable for bacteria to fester. Oddly enough, outbreaks can also be spurred by dry spells and drought.

Given that disturbance effect, the long-present Colorado drought getting hit with big recent rain accompanied by extremely hot temperatures could be contributing factors in why this outbreak is happening now.

While the detection of the spores isn’t necessarily uncommon from a national standpoint, the last confirmed outbreak in Colorado took place in 2012, killing at least 75 animals – also in the northeast Colorado region.

Animals that become infected with anthrax can experience symptoms such as collapse, shortness of breath, and blood dripping from the nose.

According to the CDC, it is very uncommon for a human to be infected with anthrax in the United States, even when conditions may lead to cattle infection. The three main ways that humans can get anthrax are by breathing in spores, eating food or drinking water that is contaminated, or by getting spores in a wound.

*In terms of being contagious, there have been rare cases where person-to-person transmission has been reported with cutaneous anthrax with the infection being passed from discharges from skin lesions. However, the CDC still refers to anthrax as non-contagious.

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