Shinning a Light on Rat Bite Fever

By Eva Briggs, MD

One of my colleagues recently identified a patient sick with an unusual infectious disease. A disease that I’d learned about in medical school but long since forgotten. It’s one of those that could be easily missed with COVID-19 and other viral infections that cause fever running rampant through the community.

It’s called rat bite fever. The causative bacterium, Streptobacillus moniliformis, is spread by the bite or scratch of rodents. It can enter by a bite, by open skin or through mucus membranes such as the lining of the mouth, nose and eyes. 

Another name for this illness is sodoku — not to be confused with the popular game sudoku. The name sodoku is used mostly in Asia where a related bacterium Spirillum minus causes the same disease.

Perhaps rodent bite fever would be a better name because rats are not the only culprit. It’s been transmitted by mice, guinea pigs, gerbils and squirrels. It’s not just wild versions of these critters, but also pets. as well as feeder rats. 

People at risk include rodent pet owners, people who handle fresh or frozen feeder rats, workers in pet stores or laboratories, and people who live or spend time in rodent-infested areas. Those at increased risk of severe disease include children younger than 5, those older than 65, and people with weakened immune systems. The disease does not spread from person to person.

The bacteria can contaminate food or water and cause a similar illness termed Haverhill fever. The name comes from a 1926 outbreak caused by contaminated milk in Haverhill, Massachusetts.

The disease starts as soon as three days after exposure or as long as three weeks later. It’s possible for any bite to be healed and perhaps forgotten by the time symptoms start. The initial symptom is fever. Two to four days later a rash consisting of flat, reddened bumps may appear on the hands and feet. 75% of patients develop a rash. One or more joints may become red, painful and swollen. 50% of people develop joint symptoms. Rash on the hands and feet can happen with hand-foot-mouth disease and painful joints occur in Lyme disease. Both of these are much more common than rat bite fever. So, kudos to my colleague who identified the infection after learning that the patient had been bitten by a mouse. Other symptoms include headache, swollen glands, vomiting and muscle aches.

Untreated, the infection can spread to the liver, lung, brain or heart. It can cause internal abscesses. And 10% of people die.

Because bacteria cause rat bite fever, it responds to antibiotic treatment with penicillin and several other antibiotics.

How common is rat bite fever? It’s not a reportable disease so data is hard to come by. Probably at least several hundred cases occur in the U.S. every year.

Prevention boils down to good hygiene: protective gear like gloves and masks for pet store and laboratory workers and good hand washing with soap and water after handling rodents or cleaning their cages. There is no laboratory test to tell whether your pet is carrying this organism and no indication that treating your pet with antibiotics will decrease the chance they spread this disease to you.  If you are bitten, wash immediately with soap and water. If you develop any symptoms of rat bite fever, seek immediate medical care and be sure to tell the treating provider about your rodent bite

Eva Briggs is a retired medical doctor who practiced in Central New York for several decades. She lives in Marcellus.