An extremely rare case of rat bite fever has been reported after a teenager contracted the disease from a pet rodent that lived in her bedroom. The 17-year-old was admitted to hospital with pain in her right hip and lower hip, doctors who treated her wrote in the online journal BMJ Case Reports.

Rat bite disease often goes undiagnosed and has only been reported 200 times in the US since 1839. It has been found in writings dating back 2,300 years and was regarded as a disease of the poor. More recently, it tends to affect people who work in laboratories or children with pet rats.

It is caused by a bacterium commonly found in the upper respiratory tract of rodents. It is transmitted by rat saliva and causes a fever, rash and arthritis in most patients. If left untreated, it has a mortality rate of around 13%.

The teenager was suffering from oligoarticular arthritis, fevers and a rash. The pain in her hip and back had left her immobile. Over the following two weeks, she had a fever, nausea, vomiting and a rash on her hands and feet. She had tenderness in a joint in her pelvis and pain in her right leg.

She had no medical history that could account for her symptoms, but doctors learned she lived with numerous pets, including three rats that lived in her bedroom. "One of these rats had died 3 weeks prior to onset of the patient's symptoms," they wrote.

A blood test came back positive for Streptobacillus moniliformis, which is the most common cause of rat bite fever in the western hemisphere. After four weeks on antibiotics she made a full recovery.

Researchers said the case shows the importance of taking a full history on admission into hospital. They concluded: "Owing to misdiagnosis and delayed therapy, mortality remains elevated. Appropriately treated patients generally experience full recovery, although some do have persistent fatigue and joint pain. Rat-bite fever is a treatable zoonosis with a confusing clinical presentation. Complete social history taking and a high clinical suspicion in patients with possible exposure is critical for appropriate and timely diagnosis."