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Pit Bull Spreads Plague to Four People

Image: A bubonic plague smear

A bubonic plague smear, prepared from a lymph removed from an adenopathic lymph node, or bubo, of a plague patient, demonstrates the presence of the Yersinia pestis bacteria that causes the plague in this undated photo. Centers for Disease Control and Prevention / Getty Images file

An outbreak of plague that affected four people and a dog in Colorado might be the first instance of person-to-person transmission of plague in the United States in 90 years, officials said Thursday.

It started with a sick pit bull, and its owner, two vet techs and a close personal contact of the dog’s owner all ended up infected. The dog died but all four people were treated with antibiotics and are okay.

And while the Yersinia pestis bacteria that causes plague is usually passed along in flea bites, the pneumonic form that infects the lungs can be transmitted by little droplets in a cough or through other close contact.

“We know that he got it from the dog."

“Although human plague is rare in North America, it remains a public health concern in the western United States where Y. pestis circulates among wild rodent populations,” the researchers wrote in a report circulated by the Centers for Disease Control and Prevention.

The dog got sick last summer, and was euthanized at a veterinary office after it coughed up blood and became very weak. No one suspected plague until its owner got sick too. He was initially diagnosed with another bacterial infection, but later tests showed he was infected by Yersinia pestis -– the same bacteria that wiped out 25 million people in the year 541 and tens of millions more throughout the Middle Ages.

It’s still seen from time to time around the world and in Western states –- about eight human cases a year, on average. “Plague is virtually always confined in this day and age to rural regions in the West,” Dr. John Douglas, director of Colorado’s Tri-County Health Department, told NBC News. “That is because the vector of plague is typically the prairie dog although there are other rodents that can transmit as well.”

The last documented case of human-to-human transmission of plague in the U.S. was during an outbreak in Los Angeles in 1924.

When the Colorado health officials got the report of plague, they started investigating. The first human patient was very ill, in the hospital and intubated, so he couldn’t talk. But officials learned the dog had been sick. They tested tissue samples at the vet’s and found plague.

“We know that he got it from the dog,” Tri-County’s Janine Runfola said. “He was coughing up blood. That is likely when some of the cases got infected, including the index patient.” When patients with pneumonic plague cough, particles of infected blood and mucus spread and other people and animals nearby can breathe them in and become infected.

It’s the most dangerous form of plague because it can spread this way, and it’s the only way plague is transmitted from human to human.

7-year-old plague victim heads home

Separately, two veterinary technicians who treated the dog got respiratory infections. They treated themselves with antibiotics. After the dog owner was diagnosed with plague, they were checked and put on extra intravenous antibiotics to be certain they were cured of the infection.

But the two technicians never became seriously ill -– something else that’s new and good to know, said Douglas. Doctors usually assumed that pneumonic plague patients become very seriously ill. That could suggest that sometimes people get infected and don’t know it, Douglas said.

But the most troubling case is the fourth one, a close female contact of the dog owner. Health officials are trying hard not to identify any of the people involved to protect their privacy.

“She also had contact with the dog and also had more intensive contact with the patient when he got sick,” Douglas said. Both the man and the dog were coughing up blood, so either could have infected her. But the timeline makes it look more likely that the man infected her.

“There’s no way to be sure that she also didn’t get it from the dog,” Douglas notes.

“Don’t let your dog run around where the prairie dogs are."

Either way, the case is unusual and serves as a warning to doctors and vets alike to be on the lookout for plague when animals or people have unusual respiratory symptoms and have been in possible contact with rodents such as prairie dogs or squirrels.

In 2012, a 7-year-old Denver girl caught bubonic plague from a dead squirrel.

The good news is that all forms of plague can be treated with antibiotics. But it must be diagnosed properly.

“If you live in the West and you live in places where there are rodents or you are hiking … you need to be generally aware,” Douglas said. Pets should get flea treatments and be kept away from wild animals.

“Don’t let your dog run around where the prairie dogs are. Wear insect repellant and socks,” he advised.