When a man in Colorado contracted the plague from his two-year-old pit bull terrier and spread it to four other people last summer, the resulting outbreak was the largest in 88 years – and the first known dog-to-human transmission of the disease, according to a new study released by the US Centers for Disease Control and Prevention.
The first patient to be identified with plague, described as a previously healthy middle-aged man, was first wrongly diagnosed with pneumonia. It wasn’t until 10 days later, after the man’s condition had precipitously worsened, that doctors realized he had contracted pneumonic plague. The disease, which attacks the lungs, is caused by the same bacterium that causes the more common bubonic plague and is typically passed to humans through flea bites.
Researchers later tracked the man’s exposure to his dog, which had recently died after coughing up blood. The transmission from dog to human is the first known case in the US. Three more patients were also sickened with plague, including two veterinary workers and one of the man’s close associates.
The man recovered after 23 days in the hospital in July 2014, after he received doses of broad-spectrum antibiotics. The three other patients also recovered after being contacted by health officials and dosed with antibiotics.
In total, researchers notified 114 people who had been in contact with the four, advising them to monitor themselves for signs of fever.
“Frankly, one of the biggest surprises of this outbreak is the source,” said John Douglas of Tri-County Health Department in Colorado, one of the study authors, told the Associated Press. “Primarily … dogs don’t get sick at all or they get a minor illness” when infected with the plague.
Plague is endemic to the western United States, particularly Arizona, California, Colorado and New Mexico, according to the study. Transmission between dogs and humans was not previously documented. In western states, it’s more common for people to contract the disease through contact with prairie dog fleas.
The outbreak also represents “the largest outbreak and first instance of possible human-to-human transmission since an outbreak in Los Angeles in 1924”. Primary pneumonic plague, a subset of plague that causes a pneumonia, is rare in the US. Only 74 cases have been reported between 1900 and 2012. Each year, about eight cases of all kinds of plague are reported.
