In an incident that caused considerable anxiety and chaos, 116 employees and students in a veterinary teaching hospital were exposed to pneumonic plague by a dog with unrecognized infection, investigators report.1

The scourge of the Middle Ages in outbreaks that killed millions, Yersinia pestis is now treatable by antibiotics — but the prognosis diminishes if drug therapy is not given promptly.

Clinicians missed the initial diagnosis of the infected dog, which then exposed a lot of the hospital staff in transport throughout the facility, says Paula Schaffer, DVM, lead author of the report and a pathologist/assistant professor at Colorado State University Veterinary Teaching Hospital in Fort Collins.

A scramble began when the dog’s plague infection was belatedly recognized, and many staff members contacted for post-exposure prophylaxis were frustrated and concerned about the delay.

“Misdiagnosis in the canine patient exposed a lot of people to a serious disease. This was the biggest concern,” Schaffer says.

“Plague is treatable with antibiotics in animals and people when the diagnosis is made early. However, once the disease progresses, it can be very hard to treat successfully. This was very concerning for our staff. Fortunately, we had no reports of illness related to exposure.”

While test results for the dog were pending, paper sheets were circulated to personnel to record contact with the dog. After the positive test result, emails were sent to those who signed, followed by an email to all personnel.

“The delay between suspicion and diagnosis of Y. pestis resulted in word of mouth traveling faster than official communication, which caused anxiety among personnel,” Schaffer and colleagues reported. “Many expressed frustration that suspicion and diagnosis of plague did not occur earlier. Two hospitalwide meetings were held for questions, discussion, and feedback.”

The communication process for zoonotic exposures at the hospital was set up to handle small-scale events and was found lacking in this case, according to investigators. The facility is now frequently updating email and phone lists and using a computerized log to document staff contacts that may be zoonotic exposures.

Employee fears were well-founded based on information from the World Health Organization (WHO), which still sees bubonic and pneumonic plague appearing in some human populations.

“Pneumonic plague, or lung-based plague, is the most virulent form of plague,” the WHO reports.2 “Incubation can be as short as 24 hours. Any person with pneumonic plague may transmit the disease via droplets to other humans. Untreated pneumonic plague, if not diagnosed and treated early, can be fatal.”

Plague has a horrific history, killing some 50 million people in 14th century Europe, when it was known as the “Black Death.”

Those exposed in Colorado included 64 hospital employees, 35 veterinary students, and 17 other employees and students in laboratory roles, Schaffer says.

Treatment recommendations included antimicrobial prophylaxis for those with highest concern for exposure (59% of total cases). Overall, one-third of the 116 people also were under fever and symptom watch.

There were several confounding factors about the case, one being that pneumonic plague is far more common in cats than dogs and is rarely seen in mid-winter, when the animal was brought in. The dog was seen near a dead prairie dog — an animal reservoir of the pathogen via fleas — but did not have classic signs of the infection (enlarged lymph nodes).

“Our protocols have been updated to stress that dogs can get pneumonic plague, that it may not present with typical enlarged lymph nodes, and that plague may present out of season,” Schaffer says.

Plague is still present in the world and warrants caution with animals under treatment or brought in facilities as service animals or therapy pets, she emphasizes.

“Veterinary workers are at increased risk for infection with zoonotic diseases, and exposure to infectious agents is an occupational stressor with potential emotional toll,” Schaffer and colleagues concluded.


  1. Schaffer PA, Brault SA, Hershkowitz C, et al. Pneumonic Plague in a Dog and Widespread Potential Human Exposure in a Veterinary Hospital, United States. Emerging Infectious Diseases. 2019;25(4):800-803. doi:10.3201/eid2504.181195.
  2. World Health Organization. Plague fact sheet. Available at: