A man is critically ill in a hospital in Oregon with suspected plague, the disease that caused the Black Death, which wiped out 25 million people in 14th-century Europe.

The unidentified man, who is in his 50s, was reported to have been bitten on the hand while trying to save a mouse caught by a stray cat. He fell ill with a fever several days later and was admitted to hospital where doctors said he had classic symptoms of the disease. Laboratory tests are being carried out.

Without treatment, plague kills two-thirds of its victims within days. But modern drugs can cure the infection, if they are given soon enough. "This can be a serious illness," said Emilio DeBess, Oregon's public health veterinarian. "But it is treatable with antibiotics, and it's also preventable."

The man initially showed the classic signs of bubonic plague – swollen lymph nodes ("buboes") in the groin and armpits. But according to doctors, he subsequently developed symptoms of septicaemic plague, resulting in abdominal pain and bleeding. A third type, pneumonic plague, affects the lungs.

It is unclear whether it was the cat or the mouse that bit him but the bacterium that causes plague, Yersinia pestis, is known to be carried by rodents, cats and other carnivores. The infection is usually passed to humans via the bite of a flea that has fed on an infected animal.

In this case, it appears the man may have contracted the disease directly. Reports said the stray cat, which has since died and had its body sent for analysis, had made its home in his neighbourhood six years ago and the man and his family had "had a lot of contact with it".

"Taking a mouse out of a cat's mouth is probably not a good idea," Dr DeBess said.

There have been repeated outbreaks of plague around the world over the centuries. Although the disease no longer causes devastation on the scale of the Black Death, the bacterium that causes it has never disappeared and human cases still appear in rural parts of the US as well as Africa, Asia and South America.