After 20 years without any reports of plague in cats, Wyoming public health officials have found a fourth case this year, causing mounting concerns over human exposure. An infected cat might bring infected fleas into a home; it might also infect people by biting, scratching or coughing.

Gus Lopez, director of the Cheyenne-Laramie County Health Department, said the latest case occurred west of the city, in the same general area where two other cats contracted the disease. A fourth cat, in neighboring Albany County, also was diagnosed with plague.

"Getting four of them in southern Wyoming in a short period of time is unusual," said Ken Gage of the Centers for Disease Control and Prevention in Fort Collins, Colo. "It's not cause for panic, or anything, but it is cause for some concern."

Tip of the Iceberg?

In many parts of the West, plague is endemic in the fleas infesting rodent populations. The disease can jump to other animals, including humans, if they come into contact with infected fleas. Researchers speculate that the infected cats probably caught or ate infected rodents.

Human cases remain extremely rare. A southwest Colorado woman who caught plague from infected fleas is the region's only human case this year. Wyoming has had just five human cases since 1978.

But state health officials also point out that they hadn't recorded any feline cases in more than 20 years.

"I think this is just going to be the tip of the iceberg," Lopez said. "And what really concerns me is these cases with cats right now really increase the risk of human exposure."

That's because handling infected animals is much riskier than simply being exposed to infected fleas. In the five recorded human cases since 1978 in Wyoming, each had handled an infected animal, Gage said.

An infected cat might bring infected fleas into a home; it might also infect people by biting, scratching or coughing.

"That's very, very dangerous, because the disease progresses very rapidly in that situation," Gage said.

Immediate Medical Attention

Dr. Tracy Murphy, Wyoming's state epidemiologist, said rodent populations appeared to be up in Wyoming and much of the West this year, in part because of increased rain and snow during winter and spring. As rodent populations increase, so does the chance that rodents will infect each other, spreading plague.

Health officials are warning people to avoid contact with rodents or with any sick or dead animals.

If such contact is unavoidable, people should wear gloves and insect repellant. Pets or people showing plague symptoms -- swollen glands, fever, chills, pain and extreme exhaustion -- should get immediate medical attention.