FORT COLLINS, Colo. (AP) — The Centers for Disease Control and Prevention is trying to determine how prevalent the plague is in northern Colorado after a 16-year-old boy died of the disease, which was possibly spread by fleas on his family’s rural property.

Taylor Gaes (Gays) died June 8 after coming down with what he thought was a bad case of the flu, but tests confirmed it was a rare form of the plague.

The most common type of plague, bubonic, affects the body’s lymphatic system. But Gaes is believed to have had septicemic plague, which spreads directly through the bloodstream.

Cases of plague are rare, with an average of seven human cases nationally a year.

County health officials are working with the CDC to test animals on the family’s property near Fort Collins for the plague.