Dog Infected Owner with Pneumonia - What You Need To Know

A dog has been identified as the cause of infecting humans with the pneumonic plague for the first time in the United States, the U.S. Centers for Disease Control and Prevention said Thursday.

The U.S. Centers for Disease Control and Prevention published a report on a plague outbreak in rural Colorado that began last June.  The outbreak took place in the rural Eastern Plains of Colorado, and centered around a 2-year-old pit bull terrier. The dog had to be put to sleep in June 2014 after developing a mysterious illness that caused bloody mucous.

The dog's owner was hospitalized four days later with a fever and bloody cough, and was eventually diagnosed with the pneumonic plague. Meanwhile, a friend of the owner and two workers at the veterinarian's office also became sick, according to the report.

"The fact that a dog could get fatally ill and transmit a (plague) infection to humans was really a big wake-up call," said Dr. John Douglas, executive director of the Tri-County Health Department in Colorado and one of the report's co-authors. "Plague is rare but pneumonic plague is really rare and we haven't had an outbreak since 1924."

Plague is caused by a bacterium called Yersinia pestis and is largely transmitted by infected fleas. In the 14th century, it caused the "Black Death" pandemic, which killed an estimated 50 million people in Europe.

"For pneumonic plague a more likely scenario would be you have a cat [play] with prairie dogs and infected fleas get on the cat," study author Janine Runfola of the Tri-County Health Department in Colorado told ABC News. "The cat gets sick and sneezes and coughs on its owner."

The CDC said about seven people in the United States become sick with the plague each year.