Rat-Bite Fever

Rat-Bite Fever

Brain & Nerve
Digestive Health
Contributed byKrish Tangella MD, MBAJan 10, 2019

What are the other Names for this Condition? (Also known as/Synonyms)

  • Epidemic Arthritic Erythema
  • Spirillary Rat-Bite Fever
  • Streptobacillosis causing Rat-Bite Fever

What is Rat-Bite Fever? (Definition/Background Information)

  • Rat-Bite Fever (RBF) is a rare, zoonotic disease caused by two different bacteria, namely Streptobacillus moniliformis and Spirillum minus. The disease is transmitted through rodents, such as rats, mice, and gerbils, and mammals, such as weasels
  • The disease spreads from rodents to humans through animal bites and scratches, handling infected animals, ingesting food, milk, or water contaminated with animal excreta (such as rat urine)
  • RBF is characterized by relapsing fever, rashes, rigors and aches, and pain affecting the joints. It could lead to complications such as brain and soft tissue abscesses, inflammation of the heart lining, heart valve, parotid gland, and liver
  • Rat-Bite Fever is treated with antibiotics and the prognosis is excellent with early treatment

Who gets Rat-Bite Fever? (Age and Sex Distribution)

  • All individuals irrespective of age, gender, race, or ethnicity are likely to affected by Rat-Bite Fever
  • RBF is an infectious disease that is common in Asia, Europe, and North America

What are the Risk Factors for Rat-Bite Fever? (Predisposing Factors)

The following individuals are at risk for Rat-Bite Fever:

  • Animal handlers
  • Laboratory technicians (who handle rats or other such animals)
  • Poor people living in overcrowded areas with poor sanitation and garbage disposal facility
  • People having rodent pets at home; children who play with pet mice, gerbils, and rats
  • Pet shop employees
  • People who live in rat-infested dwellings

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Rat-Bite Fever? (Etiology)

Rat-Bite Fever (RBF) is caused by two different types of gram negative anaerobic bacteria, which include:

  • Streptobacillus moniliformis
  • Spirillum minus

Rats are usually the source of infection, because human interactions with rats are generally at a higher incidence. Other animals that may cause RBF may include:

  • Gerbils
  • Squirrels
  • Weasels

The disease is transmitted from rats (and other animals) to humans by:

  • Bites or scratches of the infected rodents
  • Handling infected rodents
  • Consuming food or drink contaminated with rat urine
  • Contact with urine or secretions from the mouth, eye, or nose of an infected animal

What are the Signs and Symptoms of Rat-Bite Fever?

The clinical manifestation differs for both Streptobacillary Rat-Bite Fever and Spirillary Rat-Bite Fever.

  • The signs and symptoms of Streptobacillary RBF include:
    • Fever
    • Muscle pain
    • Vomiting
    • Joint pain, redness, or swelling (several joints may be affected)
    • Headache
    • Skin rashes
  • The signs and symptoms of Spirillary RBF include:
    • Recurrent fever
    • Development of ulcers at the bite wound area
    • Swelling near the wound
    • Swollen lymph nodes
    • Rashes           

How is Rat-Bite Fever Diagnosed?

The diagnosis of Rat-Bite Fever may involve:

  • Complete evaluation of medical history along with a thorough physical exam
  • Detecting the bacteria in skin, blood, joint fluid, or lymph nodes
  • Streptobacillary Rat Bite Fever is diagnosed by:
    • Culturing the blood and joint fluid
    • Blood antibody titers against the bacteria
  • Spirillary Rat Bite Fever is diagnosed by the following methods:
    • Direct visualization of blood smear under the microscope
    • Culture of spirillum from blood, tissues from lesions and lymph nodes             

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Rat-Bite Fever?

Rat-Bite Fever can affect many organs and body systems if the condition is severe or the treatment is delayed. The possible complications associated with Rat-Bite Fever could include:

Brain-related complications:

  • Abscesses of the brain - collection of pus in the brain
  • Meningitis - bacterial infection of the membrane covering the brain and spinal cord
  • Encephalitis - irritation and swelling of the brain

Heart-related complications:

  • Endocarditis - infection of the heart valves
  • Pericarditis - inflammation of the sac-like covering around the heart
  • Myocarditis - inflammation of the heart muscle
  • Systemic vasculitis - inflammation of the blood vessels

Lung-related complications:

  • Pneumonia - inflammation in the lungs
  • Bronchitis - inflammation and swelling of the bronchial tubes (airway)

Blood-related complications:

  • Anemia - reduced number of red blood cells
  • Septicemia - presence of bacteria in blood

Complications affecting other parts of the body may include:

  • Abscesses of the soft tissues - collection of pus in the soft tissues
  • Parotitis - inflammation of the parotid glands
  • Tenosynovitis - inflammation of the tendons
  • Destructive joint disease
  • Pain in the muscle situated at the back of the neck
  • Pancreatitis - inflammation of the pancreas
  • Hepatitis - swelling and inflammation of the liver
  • Amnionitis - inflammation of the uterus and amniotic sac affecting the fetus

How is Rat-Bite Fever Treated?

Antibiotics are the mainstay of treatment of Rat-Bite Fever. The following measures may be employed:

  • Intravenous penicillin is given for 7-10 days; this is followed by oral penicillin for 7 days
  • Alternatively, tetracycline may also be used
  • For penicillin-allergic patients, streptomycin and tetracycline are used
  • For patients with moniliformis endocarditis, dual therapy with high dose of penicillin G along with streptomycin or gentamicin is administered

How can Rat-Bite Fever be Prevented?

Currently, there are no vaccines available for the prevention of Rat-Bite Fever. The following precautions should be adopted to reduce the incidence of RBF:

  • The wound caused by a rodent bite should be immediately cleaned with soap and water. Medical care should be taken immediately after being bitten by a rodent
  • Contact with rats and living in rat-contaminated dwellings should be avoided
  • Animal handlers, lab workers, sanitation and sewerage workers should take special precautions against exposure to RBF. Such precaution may include:
    • Wearing gloves while handling animals
    • Avoid touching wild rodents either alive or dead             
  • House pets should not be allowed to catch rodents and eat them
  • Sanitation facilities should be improved to prevent RBF
  • Avoid overcrowding in an area, as it easily leads to the spread of diseases such as RBF

What is the Prognosis of Rat-Bite Fever? (Outcomes/Resolutions)

  • The prognosis of Rat-Bite Fever is excellent with suitable early treatment
  • If left untreated, it could lead to several complications; the death rate is as high as 25% for untreated cases of RBF

Additional and Relevant Useful Information for Rat-Bite Fever:

  • Rat-Bite Fever is also known as Haverhill Fever, if the source of infection is contaminated food or water
  • A blood culture is a laboratory test to check for bacteria, fungi, or virus, in a blood sample

The following article link will help you understand blood culture:


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Krish Tangella MD, MBA

Pathology, Medical Editorial Board, DoveMed Team


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