DENVER (AP) — A cow that died in northeast Colorado's Logan County had anthrax, and about 50 other cattle that died at the same ranch in the last several days were likely exposed to the disease, the Colorado Department of Agriculture said Wednesday.

Seven people, including a veterinarian and ranch workers who had direct contact with the cattle, were potentially exposed and will be treated with antibiotics, health officials said. None has shown symptoms of infection so far, said Dr. Tony Cappello of the Northeast Colorado Health Department.

"Anthrax is not spread person to person, so there's no concern this will spread to the general population," Cappello said.

The ranch, which state agriculture officials would not identify, has been quarantined, and the remaining cows were being vaccinated. No cattle left the ranch before the quarantine, state veterinarian Keith Roehr said.

"None went to public exhibition or market or slaughter, so we know the food supply is safe," Roehr said.

He estimated the ranch has about 500 mother cows and an unknown number of calves. Test results this week confirmed one of the ranch's dead cows had anthrax, Roehr said.

Anthrax commonly affects hoofed animals and is caused by a bacterium that forms spores that can become active in drought or floods. People can be infected by ingesting or breathing in spores or by coming in contact with infected animals, soil or water. The disease can be treated with antibiotics if it is caught early.

Health officials were telling firefighters, state troopers and hazardous material teams in northeast Colorado how to protect themselves if they work near the affected ranch.

Roehr said the anthrax case is the first in Colorado in 31 years, but outbreaks have occasionally happened in the western U.S.

In 2001, a person who sent anthrax-laced letters to media and government offices infected five people who died and 17 others who were sickened.

Symptoms in humans vary depending on the type of anthrax, but people may develop small sores that turn into skin ulcers with a black center. Most people survive the most common cutaneous form of anthrax, according to health officials, but about half the cases of inhalation anthrax, whose symptoms are similar to those of the cold or flu, can end in death.