Rat Bite Fever: Symptoms, Causes, and How to Stay Safe
While the thought of a rodent encounter might make your skin crawl, most people assume a quick nip is nothing more than a minor nuisance. However, rat bite fever (RBF) is a serious zoonotic disease that requires immediate medical attention. Though rare in the United Kingdom, it remains a significant health risk for those who handle rodents, whether they are beloved family pets or unwanted house guests.
In this guide, we will explore the symptoms to watch for, how the infection spreads, and the most effective ways to protect yourself and your family.
What exactly is rat bite fever?
Rat bite fever is a systemic bacterial illness transmitted to humans through contact with rodents carrying specific bacteria. It isn’t just limited to bites; even a scratch or contact with a rodent’s saliva or urine can trigger the infection. According to the Centers for Disease Control and Prevention, the disease is primarily caused by two different organisms: Streptobacillus moniliformis and Spirillum minus.
The streptobacillary form is the most common version found in North America and Europe, while the spirillary form, often called sodoku, is more frequently reported in Asia. Regardless of the strain, early diagnosis is vital to prevent severe complications.
Common causes and transmission
You don’t necessarily have to be bitten by a wild rat to contract this illness. Many cases involve pet rats or laboratory rats used in scientific research. The bacteria live naturally in the upper respiratory tracts and mouths of healthy rodents.
Humans can become infected through:
- Bites or scratches from an infected rodent (rats, mice, squirrels, or gerbils).
- Handling a rodent with the infection, even if no bite occurs.
- Consuming food or water contaminated with rodent excrement (this specific form is known as Haverhill fever).
- Touching surfaces that have come into contact with rodent exposure and then touching your mouth or eyes.
The NHS advises that any animal bite that breaks the skin should be cleaned thoroughly and assessed by a healthcare professional immediately.
Recognising the symptoms
The incubation period for rat bite fever varies depending on the type of bacteria involved. For the streptobacillary version, symptoms usually appear within 3 to 10 days of exposure. However, it can take up to three weeks for the first signs to emerge.
Early warning signs
Most patients will initially experience “flu-like” symptoms, which can make a diagnosis tricky. These include:
- Sudden high fever and chills.
- Severe headache.
- Muscle pain (myalgia).
- Vomiting and sore throat.
The RBF rash and joint pain
Within two to four days after the fever begins, a flat, red skin rash often appears on the hands and feet. This rash may look like small purple bumps or bruises. One of the most distinct symptoms of RBF is migratory polyarthritis, where joint swelling and pain move from one joint to another. This can be extremely debilitating and is often confused with other types of inflammatory arthritis.
Comparing the two types of Rat Bite Fever
To help you understand the differences, the following table breaks down the two primary forms of the systemic infection:
| Feature | Streptobacillary RBF | Spirillary RBF (Sodoku) |
|---|---|---|
| Causative Agent | Streptobacillus moniliformis | Spirillum minus |
| Incubation Period | 3–10 days | 7–21 days |
| Wound Healing | Usually heals before symptoms start | Wound may reopen or ulcerate |
| Common Symptoms | Fever, rash, joint pain | Fever, swollen lymph nodes, ulcer |
Diagnosis and antibiotic treatment
If you suspect you have rat bite fever, your doctor will likely perform a physical exam and order blood or joint fluid cultures to identify the presence of Streptobacillus moniliformis or Spirillum minus. Because the bacteria can be difficult to grow in a lab, molecular testing like PCR (polymerase chain reaction) is often utilised for a faster result.
The gold standard for antibiotic treatment is penicillin G, which is usually highly effective. For those with a penicillin allergy, doctors may prescribe tetracyclines such as doxycycline. According to research published in The Lancet, early intervention with antibiotics significantly reduces the risk of mortality, which can be as high as 10% in untreated cases.
If the infection has progressed, hospitalisation for intravenous (IV) antibiotics may be required to prevent complications like endocarditis (infection of the heart valves) or meningitis.
How to prevent Rat Bite Fever
Prevention is always better than cure. Whether you work in a lab or have a “fancy rat” as a companion, following these safety protocols from Mayo Clinic and Johns Hopkins Medicine can keep you safe:
- Hand Hygiene: Always wash your hands with warm soap and water after touching rodents or their bedding.
- Wear Protection: Use gloves when cleaning cages or handling wild rodents.
- Avoid Face Contact: Do not kiss your pet rats or hold them near your face.
- Seal Your Home: Prevent wild rodent exposure by sealing holes and keeping food in airtight containers.
- Clean Wounds Immediately: If bitten, wash the area vigorously with soap and water and seek medical advice from Public Health England guidelines or your GP.
The bottom line
While rat bite fever is uncommon, it is a reminder that even small animals can carry significant health risks. By practising good hygiene and seeking prompt medical attention for animal bites, you can enjoy your pets or manage your environment safely. If you experience a sudden fever and joint pain after being near a rodent, don’t wait—consult a professional immediately.
For more information on zoonotic risks, you can visit the World Health Organization or read the latest clinical updates on The New England Journal of Medicine and Nature.
Frequently Asked Questions (FAQs)
Can rat bite fever be cured?
Yes, RBF is highly treatable with the right antibiotic treatment. Most patients recover fully within 7 to 14 days of starting medication like penicillin G. However, without treatment, the infection can become chronic or lead to life-threatening complications.
Is rat bite fever contagious between humans?
No, rat bite fever is not known to spread from person to person. You can only contract it through direct contact with an infected animal, its waste, or contaminated food and water.
What happens if RBF is left untreated?
Untreated rat bite fever can lead to serious health issues, including abscesses in internal organs, pneumonia, hepatitis, and inflammation of the heart. Research shared by Oxford Academic and the British Medical Journal highlights that the mortality rate drops significantly with prompt medical care.
Can children catch RBF from pet rats?
Yes, children are particularly susceptible because they may handle pets more intimately or forget to wash their hands. The American Academy of Pediatrics suggests supervising children during pet interactions to ensure they follow hygiene rules and avoid being bitten.
