It’s a cautionary tale about making assumptions.

When a three-year-old mixed-breed dog in Colorado developed a fever and began acting lethargic last December, his owner took him to a veterinarian, who treated him with antibiotics—specifically, amoxicillin/clavulanic acid, according to a new report to be published next month in Emerging Infectious Diseases, the journal of the Centers for Disease Control and Prevention.

When the dog started coughing up blood and the owner mentioned that the dog had been sniffing a dead prairie dog, who are known carriers of the plague bacteria Yersinia pestis, the veterinarian decided to test for it, however unlikely the diagnosis might seem—infections tend to occur between April and October, and cats tend to be more susceptible than dogs.

When the test came back positive for pneumonic plague (the most dangerous permutation of Y. pestis and easily transmissible to both people and animals through saliva) the veterinarian called in the big guns.

Enter the staff at Colorado State University’s (CSU) College of Veterinary Medicine and Biomedical Sciences.

The dog was put down the same day because doctors didn’t expect him to recover, but by that point 116 CSU veterinary staff had already been exposed.

“The dog had been transported throughout the hospital and housed in an oxygen cage vented to the room, potentially exposing personnel from multiple clinical services,” the authors write. “Those handling specimens in the diagnostic laboratory were also considered exposed to Y. pestis.”

In addition, 46 hospitalized animals cohoused in the same room as the infected dog were classified as potentially exposed.

Exposed, it turns out, but not infected: All who were exposed, both human and animal, were tested and found to be clean. However, the report warned that “Veterinary hospital administrations should educate staff about zoonotic [animal-borne] hazards, mitigate exposures, and communicate rapidly to personnel when potential exposures occur.”

Plague is a bacterial infection spread by fleas and infected rodents such as prairie dogs. Pneumonic plague is caused by the same bacteria as bubonic plague—the infamous Black Death that wiped out an estimated one-third of all Europeans during the Middle Ages—but it attacks the lungs.

Although rare today—around eight cases are reported in humans in the US each year—and treatable with antibiotics, plague is occasionally still deadly.

NEWStat reached out to the staff at CSU for comment. Stephanie Brault, DVM, PhD, DACVIM,  postdoctoral fellow in infection control and biosecurity, and one of report’s authors, provided the following insight into how CSU managed the case of plague documented in the report.

Brault wrote:

Essentially, the take-home message is that Occam’s razor is not always operative (i.e., the simplest explanation is not always the correct one). This particular case challenged several assumptions about Yersinia pestis infection and highlighted a few areas where veterinarians may need to alter their diagnostic prioritization approach:

Overall, this case was an excellent reminder that “common things are common,” except in situations when the diagnosis is rare.

Additionally, Brault offers this advice to veterinarians: “If you are evaluating patients where Yersinia pestis is a potential diagnosis, PCR testing (offered by the CSU Veterinary Diagnostic Laboratory) of the following sample types are recommended, in addition to traditional culture: 1) a respiratory sample (nasal swab, transtracheal wash, bronchoalveoloar lavage); 2) a lymph node aspirate; and 3) whole blood. Please use proper personal protective equipment when handling these patients (respiratory protection is recommended in pneumonic cases), and clearly mark the submission as suspect for Yersinia pestis.”

The last full-fledged pneumonic plague epidemic in the United States occurred in Los Angeles in 1924.

The largest outbreak since then took place five years ago. It happened, coincidently, in Colorado, and involved a two-year-old American pit bull terrier who’d also come into contact with a prairie dog. In that case, the dog and four people, including his owner and two veterinary staff, tested positive for Y. pestis.

All except the dog recovered.

The fate of the prairie dog remains unknown.

Photo credit: © iStock/Crisfotolux