An outbreak of pneumonic plague, caused by the Yersinia pestis bacteria (pictured above) has been traced to a pit bull terrier who spread the disease to its owner

A 2014 outbreak of pneumonic plague, caused by the Yersinia pestis bacteria (pictured above), has been traced to a pit bull terrier who spread the disease to its owner and sparked the largest U.S. outbreak of the deadly infection in 90 years.

The largest outbreak of pneumonic plague in the U.S. in 90 years started with an infected pit bull in rural Colorado, according to a new report from the Centers for Disease Control and Prevention. The agency says this is first ever incidence of a human contracting the disease from a dog in the U.S., and it may be the first case of human-to-human plague transmission in the country in almost a century.