Plague may have killed La Plata County man, possibly making him the first Colorado resident felled by the disease in six years, officials said.

San Juan Basin Public Health was notified of the potential plague case on Wednesday, according to a press release. The Colorado Department of Public Health and Environment is now leading an investigation and conducting additional tests to confirm what killed the man, whose identity hasn’t been revealed by authorities.

The plague is a bacteria-caused disease that is usually transferred to humans by flea bites, according to the Centers for Disease Control and Prevention. It is often found in rock squirrels, prairie dogs, wood rats and other species of ground squirrels, state health officials said.

Plague can be treated with antibiotics. In the absence of prompt treatment, infections can cause serious illness or death, officials.

The plague last killed Colorado residents in 2015 when a Pueblo County adult and a teenager in Larimer County succumbed to the disease. Those Coloradans accounted for half of all plague deaths in the U.S. in 2015 — the deadliest plague year in recent decades, according to federal health officials.

West Nile virus found in northern Colorado

The plague is most common in the western part of the U.S. and La Plata County has had the highest number of plague cases in Colorado, accounting for 9 out of 22 total human cases between 2005 and 2020, according to state health officials.

After four consecutive years of no human plague cases in Colorado, two people survived the disease in 2020 after exposure to infected animals.

State health officials warned of plague activity in the state back in May when a squirrel in El Paso County tested positive for the disease.

Plague symptoms include sudden fever, headache, chills and weakness. Residents can protect themselves from infection by keeping pets up-to-date on vaccinations and flea protections and by avoiding wild animals, officials said.