Thought the plague was a relic of the Middle Ages? Think again.

A man in Oregon is in critical condition after contracting the illness long known as Black Death.

The man, in his 50s, is thought to have picked up the deadly infection earlier this month while trying to remove a dead mouse from the mouth of a stray cat.

Within a couple of days, the man developed a high fever and nausea and headed to hospital. Doctors there diagnosed him with septicemic plague — the kind of plague that spreads in the blood.

He was last reported to be in critical condition.

While many of us think the plague was eradicated centuries ago, in fact, the bacteria that causes it, Yersinia pestis, still circulates among the fleas that live on rodents.

Oregon has about one human case a year, while the U.S. as a whole records an average of 11 cases a year, mostly in the South.

Human cases of plague are very rare in Canada, the Public Health Agency fo Canada says. The last case was reported in 1939.

The plague can develop into three forms: bubonic plague, which swells lymph nodes across the body; septicemic plague; and pneumonic plague, which affects the lungs.

The illness is treatable with antibiotics, but only if treatment is given quickly. The longer patients wait for treatment after symptoms begin, the worse their outcome.

It’s not clear whether the cat or the mouse in this incident was infected.

While rodents are usually thought to be the carriers, the stray cat later become ill and died. Its body has been sent to the U.S. Centers for Disease Control and Prevention for testing.

A plague vaccine exists but is no longer sold to the public. It’s typically offered to military personnel or animal handlers working in areas where the plague is more common.