Rats can be really interesting pets. They can be quite social and are interesting to watch. Being larger than hamsters and gerbils, they can also be more easily and safely handled. They can still bite, however, particularly if they are not properly socialized and/or they are handled by people who don’t know how to do it properly. Even though rats have tiny teeth, bites can still cause problems. One concern is rat bite fever. This disease is actually caused by two completely separate bacteria. Streptobacillus moniliformis is the most common cause in North America and Europe, while Spirillum minus is the main cause in Asia.

I’ll focus on Streptobacillus moniliformis today. This bacterium is very commonly found in the mouths of healthy rats. Up to 100% of rats can be carriers. It doesn’t cause disease in the rats, but it can be transmitted to people by bites or scratches. It can also be spread simply by handling rats (especially if a person has any cuts or broken skin), and through close contact with rats’ mouth, such as kissing and sharing food (yes, some people do).

In most people, rat bite fever causes a high fever, headache, chills, vomiting, joint and muscle pain and a rash, most commonly over the soles of the feet, palms of the hands and the extremities. While the disease will resolve on its own in many cases, treatment with antibiotics is indicated because severe complications such as inflammation of the heart, pneumonia and meningitis can also develop.

Common sense can help reduce the risk of rat bite fever.

  • Assume all rats are carrying S. moniliformis in their mouths.
  • Only handle rats if you know how to do so properly, and if you know the rat is amenable to being handled. Avoid contact with the rat’s mouth (e.g. kissing).
  • If you have open sores or cuts on your hands, avoid handling rats or wear gloves.
  • Always wash your hands thoroughly after handling a rat or cleaning its cage.
  • Thoroughly clean any bites from any rodent immediately with lots of soap and water.
  • If you develop signs consistent with rat bite fever after being bitten, consult your physician as soon as possible, and be sure to let your physician know about the bite.

More information about the care of bites can be found in our bites archives and on the Cat Bites information sheet on the  Worms&Germs Resources page.

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  • Judy

    I have two pet rats and am concerned about this illness. Can my rats be tested for the bacteria, and if so what should I ask my vet to test for? So far most of the vets in the Maryland area have never heard of this and are quite shocked!

  • Scott Weese

    Testing isn’t useful because the bacteria are very common and a negative test certainly doesn’t mean a rat is not (or will not be) a carrier. The key is prevention of bites and appropriate care of bites.

  • Dylan

    Hello. I have been a rat owner for about two years now. I contracted this illness in December of 2008. I was hospitalized for four days with severe knee and ankle pain in my right leg, headache, fever, and a rash on my hands, feet, and a couple of spots on my stomach. The only spots that turned to papules were on my hands and legs. Considering that by the time I went to the emergency room, I could barely walk from the pain, I ended up needing about three days of intravenous penicillin, followed by a 15-day supply of oral doxycycline once I was released.

    I seriously recommend doing everything in your power to stay safe and sanitary by washing your hands after contact and limiting or preventing face-to-mouth contact with your rats (NO MORE KISSES!).

    If you are afraid that you have caught this, please make sure to bring this CDC article with you to your health care provider. It’s remarkably rare and my mother was actually the one to find this disease online. Having this information will potentially make your treatment, and therefore stay, shorter and easier.