Pet rats might seem like a different beast from those garbage-frolicking rats who live fast and loose on the city streets. However, as this grim medical case report details, pet rats are still capable of harboring and spreading some nasty diseases. 

A woman developed "rat bite fever," a serious and potentially fatal disease, after receiving a bite from her pet rat, a report in The New England Journal of Medicine reveals.

The 36-year-old woman was rushed to the infectious disease clinic at a hospital in the French city of Strasbourg with complaints of fever, aching muscles, and a splitting headache. On closer inspection, her doctors spotted a distinctive rash on her hands and feet, as well as swelling around her ankles and wrists.  

She hadn’t traveled recently and she hadn’t been with any new sexual partners, so the cause of the unusual infection initially remained unclear. However, the patient did recall that she had been bitten on her left hand by a pet rat around 10 days before the symptoms first arose. 

By no surprise, her blood tests later revealed the presence of Streptobacillus moniliformis. This bacteria lives in the mouths of rats and is responsible for the so-called “rat bite fever.” As the name makes pretty clear, the infection is transmitted to humans through a bite, although it can also spread via food or water contaminated with the pee and poop of rodents carrying the bacteria. The disease is not able to spread from person to person.

This woman was fortunate enough to catch the disease early. After taking a simple course of antibiotics, her symptoms resolved and she quickly returned to good health.

However, rat bite fever can be extremely unpleasant and even fatal. Around 1 in 10 people who have streptobacillary rat bite fever infections die, according to the Centers for Disease Control and Prevention (CDC). 

If left untreated, the infection can lead to a number of complications, including infections of the liver (hepatitis), kidneys (nephritis), lungs (pneumonia), brain (meningitis), and heart (endocarditis, myocarditis, or pericarditis). It can also cause abscesses of infected fluid to build up inside the belly. 

People who come into regular contact with rats are most at risk of the infection, such as pet-owners, people who work at animal research laboratories, pest control workers, and pet store workers. Kids under five, elderly people, and others with a weakened immune system are at higher risk of infection.

If you get bitten by a rat, you are advised to immediately clean the wound with soap and warm water. While that should slightly reduce the risk of infection, it’s also strongly recommended that you contact a health care provider and tell them about your recent injury.

While rats (and their fleas) are frequently blamed for the Black Death in the 14th century, one of the most devastating pandemics in human history, recent studies have suggested that there were perhaps a few other guilty parties involved too.