American Fancy Rat & Mouse Association

This article is from the WSSF 2009 AFRMA Rat & Mouse Tales news-magazine.

Medical - Rat Bite Fever

By Carmen Jane Booth, D.V.M., Ph.D.

Amy, e-mail
I just wanted to pass on the story of my 7-year-old daughter who had a pet rat and came down with rat bite fever. We had never heard of this disease, and didn’t know it was a risk with rats. This is a rare disease in the US, but is still a risk. My daughter was never bitten or scratched by her rat, it was just from contact. The bacteria (Streptobacillus moniliformis) that causes rat bite fever is normal in rat urine, feces, and saliva (other rodents also, but usually not in as high concentrations). This was not a sick rat. From what we were told some rats can have higher concentrations than others. She was hospitalized for 8 days with rash, high fevers, sepsis, and hip infection. She now has a PICC line at home and is getting continuous IV penicillin for the next 3 weeks. She has never been sick, does not have a compromised immune system, and has been around numerous different animals since birth as we live on a farm. So she had nothing that put her at high risk to get an infection. Rat owners should know that this is a risk, especially with children who are not as good at hand washing after contact. They should also know the symptoms of rat bite fever in case they come down with it. Again this is a rare disease, but it can happen. Also because it is rare it is harder to diagnose. I agree rats make wonderful pets, but it would have been nice to know about this disease before we owned one.

Reply by Carmen Jane Booth, D.V.M., Ph.D.

Rat Bite Fever (RBF)

Information summarized from the Center for Disease Control and Prevention website:


The agent responsible for the clinical disease referred to as “Rat Bite Fever” depends upon where you live in the world. In the United States the primary etiology (cause) is the bacterium, Streptobacillus moniliformis. In Africa and Asia the primary etiology is the bacterium, Spirillum minus. These bacteria are Gram-negative. RBF is very uncommon in the US and not a reportable disease. That means that physicians are not required to report human cases to the CDC.


RBF is transmitted from infected rodents to humans by a bite, scratch, or from ingestion of food or water contaminated by rodent droppings. The disease is called Haverhill fever when contracted through ingestion of contaminated food or water. In addition to rats, infected mice and gerbils can transmit the disease. RBF is not transmitted through contact with infected humans. Although not common in the pet rats, there have been recent reports of humans infected from pet rats.

Clinical Symptoms

The clinical symptoms are similar for other systemic bacterial infections caused by Streptobacillus sp. infections spread after a wound. Symptoms usually occur 2–10 days after exposure to an infected animal. Common symptoms include an abrupt onset of chills and fever, vomiting, pain in the back and joints, headache and muscle pain. By this time, the wound itself has usually already healed. Within 2–4 days after the onset of fever, a rash appears on the hands and feet. One or more large joints may then become swollen, red, and painful.


As with other disease caused by bacteria, antibiotic treatment is usually curative. Without treatment, the disease course can be fatal.


Avoid contact with rats or rat-contaminated dwellings. In addition to Rat Bite Fever, contact with rodents, rodent droppings, and dead rodents may result in other infectious diseases. If you cannot avoid contact with rats, wear protective gloves, practice regular hand washing, and avoid hand-to-mouth contact when handling rats or cleaning rat cages. Because you can also get infected with Rat Bite Fever after drinking contaminated milk or water, drink pasteurized milk and water from safe sources.


I did a search for human reports of RBF on PubMed ( and found a few reports of human cases in children who had exposure to pet rats. The true incidence of Strep. monliformis in wild and pet rats is unknown. Some papers suggest the incidence is 50–100%. I would suspect that the incidence is higher in wild rodents than pet rats from reputable sources when one considers the large number of humans who have pet rats and the very low number who get a bacterial infection from their rats. Perhaps the AFRMA should poll their members and look at the number of people who have pet rats and mice and the number who have become ill from their rats and mice. One has to remember that bacteria are everywhere and a bite or scratch from any animal (including humans) has the potential to cause infection. Therefore, any pet animal has the potential to carry a bacteria zoonotic to humans. Should people be alarmed and not have pet rats? My answer would be, no. Rats make wonderful pets; however, the risk of zoonosis is not zero as with any pet animal. Each person has to make their own choice of the risk benefit before adding a pet to share their home. Most pet rats from reputable sources will die from old age from cancer or from respiratory disease secondary to Mycoplasmosis. If a younger rat became ill and died from unknown causes, I would suggest handling the rat with care, using gloves, and frequent hand washing, and having a necropsy performed to determine cause of death. Any person with a bite or scratch from any animal should clean the area and seek further medical attention as directed by their health care provider. Any person who develops a skin rash and fever regardless of direct exposure to rodents should seek medical attention from their health care provider.

Ed. Note 2014: There is an article by the HPA (part of Public Health England) “Reducing the risk of human infection from pet rodents.” (PDF file; and in a PDF brochure) that goes into detail on caring for pet rodents that may be suspect to harboring disease such as leptospirosis, hantavirus, rat bite fever, or lymphocytic choriomeningitis (LCMV).

For more on possible diseases, see:
“Contagious Rat Diseases?; Zoonotic Diseases”
“Leptospirosis in Pet Rats?”
“Illness in Rat Bites and Feces?”
“Papilloma Wart Virus or Rat Pox Virus”
and for more on zoonotic diseases see "Zoonotic Diseases" from the UC Santa Barbara Office of Research web site (archived page)
“Ringworm & Rats”
“Ringworm on Mice”

Rat Bite Fever from The Center for Food Security & Public Health with section on Infections in Animals and treatment. New!

Update on My Rat Project: Blue Rat Bleeding Disorders/Blue Rats With Hemophilia; Russian Blue Bleeding Problem

A few years ago, I was asked to answer a question about bleeding problems in Blue rats and wrote an article for the AFRMA (“Blue Rat Bleeding Disorders/Blue Rats With Hemophilia” WSSF 2006, online at; see also the “Russian Blue Bleeding Problem” topic A few months later, a research rat with a massive hematoma (bruise) was sent to the diagnostic service where I work at Yale University. I worked up this case as a coagulation defect from the onset in part because of the AFRMA article I had recently written. There are no reports of spontaneous rat models with hemophilia or other bleeding defects. We determined that this colony of rats had a spontaneous coagulopathy (bleeding) problem and have been working to elucidate the specific disease and genetic defect. The first paper describing the coagulopathy will be published in January in the journal, Comparative Medicine. [Ed. Note 4-19-2020: published in the Volume 60, Number 1, February 2010 Comparative Medicine, Spontaneous Coagulopathy in Inbred WAG/RijYcb Rats]. I don’t know if there are any remaining Blue rats with the bleeding problems, but if there are, I would be interested in finding out and getting an oral swab DNA sample. Once I have formally published the information in a scientific journal, I can write about what we think the disease is and the defect for AFRMA.

I wanted to thank Karen for requesting articles and the AFRMA members for sending in their questions to Karen. It is because of my interest in and love of rats and mice that has been the foundation for my career. Best, Carmen. *

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Updated July 13, 2021