Story highlights

A man got sick last summer after his pit bull became infected with the plague

Four people who got sick with the plague from contact with the dog recovered

On average there are eight cases of plague in the U.S. annually, most cases are in Colorado, Arizona, New Mexico, and California

CNN —  

A pit bull was at the heart of a rare plague outbreak in Colorado that left four people sick last year. That’s what a Centers for Disease Control and Prevention investigation found in a new report released April 30.

The CDC says on average about eight people get the plague every year in the United States. While it still can be life threatening, with modern medicine it is not the death sentence it was back in the Middle Ages when millions died. Antibiotics and antimicrobials can clear it up.

In last summer’s incident, what stands out is the possible human-to-human transmission, according to the investigation. That hasn’t happened in the United States since 1924. Earlier studies have shown that pneumonic plague, even its most severe form, can be transmitted person-to-person, but it is rare. And the dog-to-human transmission was unexpected according to the local health department. The team that investigated the case said that they could only find one other case of dog to human transmission in the medical literature. That was a 2009 case in China.

Related: Hundreds of skeletons found under Paris supermarket

“There is no evidence this is a mutated strain or anything,” said Dr. John Douglas, director of Colorado’s Tri-County Health Department. “It is rare, and we don’t know if it has simply been missed before or if it something about this particular breed of dog. We haven’t been able to determine that.”

Douglas did add they were not trying to malign a particular breed of dog. People with pets who live in parts of the country where plague is present in wild animals do need to make sure that they keep their pets far away.

In this instance, in at least three of the four cases, people got sick after being exposed to the infected dog. With the fourth patient it is “less certain” if her exposure came from the dog or the person.

Related: Plague blame game, Gerbils replace rats as prime suspects

The Colorado Department of Public Health and Environment first learned about the plague after lab samples showed the presence of Yersinia pestis the bacterium that causes the plague in blood taken from a middle-aged man hospitalized with pneumonia.

The man, who remains unnamed in the report, checked himself into the hospital after coughing up blood. The hospital initially diagnosed him with a different bacterial infection. An automated lab had misdiagnosed it. After six days in the hospital, the man’s symptoms got worse, so they transferred him to another facility and ran further tests. It was only then that the lab figured out that he had the plague. He eventually recovered, but was hospitalized for 23 days.

When it was correctly identified, experts from the Tri-County Health Department looked into the case. What they found was that the patient’s dog had recently been euthanized. The vet diagnosed the 2-year-old pit bull with hemoptysis, a condition where the dog would have been spitting up blood. The dog also had a fever and a rigid jaw. Only after additional tests did health care workers lea