Spores of the potentially fatal Bacillus anthracis bacterium—which causes the disease anthrax—sit in a lung.
Once inhaled, spores may germinate and release toxic substances that have been known to cause internal bleeding, swelling, and tissue death. The disease can also enter the bloodstream when spores are ingested or make contact with an open wound.
Anthrax outbreaks this summer have killed more than a hundred farm animals on ranches in Colorado and Texas, with some experts pointing to drought as a culprit. The extended warmth, they say, could expedite the production of more spores and help them survive for years in the soil. Livestock may also be forced to root around more for food in dry conditions, unsettling soil and releasing spores.
But the primary concern about drought is the stress it inflicts on animals, weakening their immune systems, said Martin Hugh-Jones, professor emeritus of epidemiology at Louisiana State University and coordinator of the World Health Organization's Working Group on Anthrax Research and Control.
"The animals are less efficient in hot weather when dealing with an infection, and therefore a smaller dose [of the pathogen] can result in a deadly case," said Hugh-Jones, who has investigated many outbreaks.
Despite the numbers, Hugh-Jones said it actually has been a "mellow" year for anthrax. "There have been very few outbreaks so far this summer, but the ones that have happened have been severe."
Once a member of a herd is infected, it is easy for the disease to spread if animals are corralled together or carcasses and blood are left out in the open. A wet spring can also bring swarms of biting flies that help to transmit anthrax.
"This season's outbreaks have more to do with management than ecology," Hugh-Jones added. "If you control [anthrax] correctly, you also eradicate it."
Livestock can be vaccinated for the infectious disease. Humans contract anthrax most commonly through contact with infected animals and can usually be treated with antibiotics.