Amber Hunt, File, Associated Press
This Sept. 23, 2012 file photo shows bison in a state park in South Dakota. The year’s first case of animal anthrax in South Dakota has been confirmed in a bison herd in the state, home to the second-most cattle ranches in the country. But experts say there is little need to be alarmed because most livestock is vaccinated and the threat to humans is minimal in the U.S. thanks to meat-quality inspections and ranchers adept at dealing with the bacteria.

PIERRE, S.D. — The year's first case of animal anthrax in South Dakota has been confirmed in a bison herd in the northern part of the state, which is home to the most domesticated bison on ranches in the country. But experts say there is little need to be alarmed because the threat to humans is minimal in the U.S. and most livestock are vaccinated.

Anthrax is found throughout the world, but it is rare in the U.S., according to the Centers for Disease Control and Prevention. In the Dakotas, where ranching is common, ranchers see a few cases each year in unvaccinated herds of cattle or other animals. The disease causes death in livestock quickly and without warning.

Here are some questions and answers about the illness:

Q: What is anthrax and how does it make its way to livestock?

A: Anthrax is an infectious disease caused by Bacillus anthracis, bacteria whose spores lie dormant in soil and become active under extreme weather conditions such as drought or flooding, according to South Dakota's state veterinarian, Dustin Oedekoven.

Livestock grazing in areas where spores are present can get infected by consuming or breathing in the spores. Affected animals are often found dead with no prior illness outwardly detected, Oedekoven said. It can kill an affected animal in a matter of days, sometimes within 24 hours.

Veterinarians recommend quarantining unaffected animals and disposing of affected animals as quickly as possible to avoid spreading the disease to other animals. In South Dakota, carcasses of infected animals must be burned and buried at least 4 feet below the ground within 36 hours of death, and any livestock near an outbreak is quarantined for 30 days.

Q: What happened in South Dakota?

A: State examiners found a herd of unvaccinated bison to be infected on July 31, after ranchers in Dewey County in the north-central part of the state found six dead bison at the same time, Oedekoven said. Although only a handful of cases are usually found each year, sometimes it can be more widespread. North Dakota saw an outbreak in 2005 that killed more than 1,000 animals, though the state's first and only case this year was detected about a month ago in a beef cow.

Q: Can it be passed to humans or affect meat processed for human consumption?

A: Typically, the only risk for humans from the disease in the U.S. comes from indirectly handling carcasses or fluids from affected livestock without protective clothing, which can result in a skin infection, Oedekoven said. Anthrax can be consumed through infected meat, but veterinarians say that isn't a concern in the U.S. and other developed nations where meat undergoes vigorous safety inspections. A gastrointestinal infection is more common in developing countries that have fewer food-safety regulations.

The CDC notes on its website that humans can become infected by breathing in spores, or eating food or drinking water that has been contaminated, but that it's very uncommon in the U.S.

Anthrax has been weaponized in a form where the spore has been processed and ground up so it can be used as a biological weapon. However, naturally occurring anthrax is not found in this form.

Q: Is the vaccination widely used?

A: An effective anthrax vaccine is readily available through licensed veterinarians, but it takes about a week for immunity to take hold. State veterinarians encourage all ranchers — especially those in areas with a history of the disease — to vaccinate their livestock.

Oedekoven said most producers and ranchers employ the vaccine, but some often choose not to if several years have passed without an outbreak or if new ranchers are unfamiliar with the need to vaccinate.

The vaccine is inexpensive and highly effective, he said.