Four Colorado residents contracted the pneumonic plague from a local dog, according to the state Department of Public Health and Environment

The announcement came after an investigation of the death of a local dog, who died of the disease, officials said. All four of the Colorado individuals had contact with the animal and while three showed mild symptoms, one has been hospitalized. 

The pneumonic plague is rarer and more deadly than the bubonic plague and can spread through coughing and sneezing. This was the first infection of the disease reported in Colorado in the last decade. 

“We’ve had quite a number of cases this year,” Jennifer House, a spokeswoman for the Colorado Department of Public Health and Environment department, told Bloomberg. “We do believe the outbreak itself to be over.”

Those infected were treated with antibiotics and are believed to be no longer contagious. Officials think that the dog may have caught the illness through a flea bite. Rodents like prairie dogs and rabbits in Adams County, the area affected, have been known to carry fleas with plague infections.

Colorado has identified 60 cases of human plague since 1957, nine (15 percent) of which were fatal.