The 63-year-old man showed up in the hospital with a burning sensation in his left leg and muscle pain in both. His flu-like symptoms were severe, with laboured breathing for three days. He had petechiae, or rounds spots on the skin that look like rashes as a result of bleeding capillaries, which made his legs look discoloured.

The patient's heartbeat was stable, doctors said, even though he was running a temperature of 38.8 degrees. His laboured breathing caused an inadequate supply of oxygen to his tissue. His failing kidneys were not producing urine, researchers wrote.

The man was infected with a type of bacteria found in the saliva of healthy dogs and cats. Credit:iStock

But doctors had no idea what was wrong with him. He had not recently been in the hospital. They suspected some kind of bacteria, but he didn't have any open wounds and he didn't have meningitis.

It wasn't until his fourth day in the hospital that a blood test revealed that the man had a type of bacteria found in the saliva of healthy dogs and cats. It's a kind of bacteria that's usually only transmitted to humans if they are bitten.