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Rat-bite Fever (RBF)
Rat-bite fever (RBF) is an infectious disease that can be caused by two different bacteria. Streptobacillary RBF is caused by Streptobacillus moniliformis in North America while spirillary RBF or sodoku is caused by Spirillum minus and occurs mostly in Asia. People usually get the disease from infected rodents or consumption of contaminated food or water. When the latter occurs, the disease is often known as Haverhill fever. If not treated, RBF can be a serious or even fatal disease.
Information for Health Care Workers
Transmission
There are several ways people can get RBF. The most common include:
- Bites or scratches from infected rodents (such as rats, mice, and gerbils)
- Handling rodents with the disease (even without a bite or scratch)
- Consuming food or drink contaminated with the bacteria
RBF is not spread from one person to another.
Symptoms and Signs
Symptoms are often different for the two types of RBF: streptobacillary RBF and spirillary RBF.
Symptoms and signs of streptobacillary RBF include:
- Fever
- Vomiting
- Headache
- Muscle pain
- Joint pain
- Rash
Symptoms usually occur 3-10 days after exposure to an infected rodent, but can be delayed as long as 3 weeks. By this time, any associated bite or scratch wound has usually healed.
Within 2-4 days after fever onset, a maculopapular rash may appear on the hands and feet. This rash is identified by flat, reddened areas with small bumps. One or more joints may then become swollen, red, or painful.
Symptoms and signs of spirillary RBF (also known as sodoku) can vary and often include:
- Fever (that may occur repeatedly)
- Development of an ulcer at the bite wound (when applicable)
- Swelling near the wound
- Swollen lymph nodes
- Rash (occurs following partial healing of the wound)
These symptoms usually occur 7-21 days after exposure to an infected rodent.
The symptoms associated with Haverhill fever (RBF you can get from consuming contaminated food or water) can differ from those that occur when you get the disease through bites and/or scratches. The most notable differences may include more severe vomiting and sore throat.
Risk Factors
Any person who is exposed to the bacteria that cause RBF is at risk for getting the disease.
Some people who may be at increased risk include those who:
- Live in rat-infested buildings
- Have pet rats at their home
- Work with rats in laboratories or pet stores
Treatment
If you have any symptoms of rat-bite fever after exposure to rats or other rodents, please immediately contact your health care provider. Be sure to tell your provider of your exposure to rodents.
If you have RBF, your doctor can give you antibiotics that are highly effective at curing the disease. Penicillin is the antibiotic most often used. If you are allergic to penicillin, your doctor can give you other antibiotics.
Without treatment, RBF can be serious or potentially fatal. Severe illnesses can include:
- Infections involving the heart (endocarditis, myocarditis, or pericarditis)
- Infections involving the brain (meningitis)
- Infections involving the lungs (pneumonia)
- Abscesses in internal organs
While death from RBF is rare, it can occur if it goes untreated.
Prevention
You can protect yourself from RBF by:
- Avoiding contact with rodents or places where rodents may be present
- Avoiding drinking milk or water that may have come in contact with rodents
- Drinking pasteurized milk and water from safe sources
If you handle rats or clean their cages:
- Wear protective gloves
- Practice regular handwashing
- Avoid touching your mouth with your hands
In addition to RBF, contact with rodents may result in other illnesses. For more information on rodent control, see: Prevent rodent infestations.
Information for Health Care Workers
Etiologic Agent
In North America, rat-bite fever (RBF) is caused primarily by Streptobacillus moniliformis, a fastidious, non-motile, gram-negative microaerophilic bacillus. Spirillum minus, a short, thick, motile spirochete, has been reported to cause RBF predominately in Asia.
Transmission
S. moniliformis and S. minus are part of the normal respiratory flora of rodents. Either organism may be transmitted to humans through bites or scratches. Infection can also result from handling an infected rodent (even with no reported bite or scratch), or ingestion of food or drink contaminated with these bacteria (Haverhill fever). Rats are considered the natural reservoir of RBF, but the bacterium has also been found in other rodent species such as, mice and gerbils. Person-to-person transmission has not been reported.
Clinical Features
Initial symptoms of S. moniliformis are non-specific and include fever, chills, myalgia, headache, and vomiting. Patients may develop a maculopapular rash on the extremities 2-4 days after fever onset, followed by polyarthritis in approximately 50% of patients. The incubation period typically ranges from 3-10 days. The symptoms and signs of Haverhill fever differ slightly from those of RBF acquired through bites and/or scratches. Haverhill fever can be associated with more severe nausea/vomiting and pharyngitis.
Symptoms due to Spirillum minus usually occur 7-21 days after exposure to an infected animal and the patient is likely to have a history of travel outside of the U.S. Following partial healing of the rat bite, common symptoms and signs include fever, ulceration at the site, lymphangitis, lymphadenopathy, and a distinct rash of purple or red plaques.
If not appropriately treated, infection may result in as endocarditis, myocarditis, meningitis, pneumonia or sepsis. The mortality rate for untreated RBF is between 7%-13%.
Diagnosis
RBF should be suspected in people with rash, fever, and arthritis and a known or suspected history of rodent exposure. S. moniliformis is difficult to grow in culture and requires specific media and incubation conditions. RBF is diagnosed by isolating S. moniliformis from blood, synovial fluid, or other body fluids. In the absence of a positive culture, identification of pleomorphic gram-negative bacilli in appropriate specimens supports a preliminary diagnosis. S. minus does not grow in artificial media. For this reason, diagnosis is made by identifying characteristic spirochetes in appropriate specimens using darkfield microscopy or differential stains. If RBF is suspected in a severe illness or death, but a diagnosis has not been made, physicians can consider requesting diagnosis assistance from their state public health laboratories.
Occurence
RBF is rare in the United States. Accurate data about incidence rates are unavailable because the disease may not be reportable to state health departments. Since RBF is not a nationally notifiable disease, trends in disease incidence in the U.S. are not available. Recent case reports have highlighted the potential risk for RBF among persons having contact with rodents at home or in the workplace.
THANKS TO
http://www.cdc.gov/rat-bite-fever/index.html
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A.M.Abdul Malick
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