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Rat Bite Fever: General Information

  • Synopsis: Published: 2015-06-10 - Information regarding Rat Bite Fever, a condition sometimes transmitted to humans in around 10% of rat bites. For further information pertaining to this article contact: Disabled World at Disabled World.
Rat Bite Fever

Rat-bite fever is an acute, febrile human illness caused by bacteria transmitted by rodents, rats or mice in most cases, which is passed from rodent to human via the rodent's urine or mucous secretions. Alternative names for rat bite fever include streptobacillary fever, streptobacillosis, spirillary fever, sodoku, and epidemic arthritic erythema. Most cases occur in Japan, but specific strains of the disease are present in the United States, Europe, Australia, and Africa.

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Quote: "A person's main wound from a rat bite commonly heals quickly, yet after an incubation period of 1-22 days (often times less than 10 days) a viral-like syndrome develops rapidly causing fever, chills, headache, vomiting and joint and back pains."

Rat bite fever (RBF) is caused by either Spirillum minus or Streptobacillus moniliformis. The symptoms of the streptobacillary form include a rash, a fever and arthralgias. The spirillary form causes rash, relapsing fever and regional lymphadenitis. Diagnosis is clinical and confirmed by culture and at times rising antibody titers. RBF is treated with doxycycline or penicillin.

Rat bite fever is transmitted to people in around 10% of rat bites. There may also; however, be no history of rat bite. Rat bite fever (RBF) is most commonly caused by rat bites, yet may be caused by the bite of any rodent or of a carnivore that preys on rodents. Both the spirillary and streptobacillary forms affect mainly people who live in cities in crowded conditions, as well as biomedical laboratory personnel. In America and Europe, rat bite fever is usually due to streptobacillus moniliformus, while in Asia it is usually due to spirillary minus.

Rat Bite Fever, Streptobacillary Form

The streptobacillary form of rat bite fever is caused by the pleomorphic gram-negative bacillus streptobacillary moniliformis, which is an organism present in the oropharnyx of rats that are healthy. Epidemics have been associated with ingestion of unpasteurized milk contaminated by streptobacillary moniliformis or, 'Haverhill fever,' although infection is usually caused by the bite of a wild mouse or rat. Other kinds of rodents, as well as weasels, have also been implicated.

A person's main wound from a rat bite commonly heals quickly, yet after an incubation period of 1-22 days (often times less than 10 days) a viral-like syndrome develops rapidly causing fever, chills, headache, vomiting and joint and back pains. The majority of people affected by RBF develop a petechial, morbilliform, or vesicular rash on their feet and hands around three days later. Polyarthralgia or arthritis, commonly affecting the large joints asymmetrically, develops in many people within a week and if it is left untreated, might persist for several days or even months.

The fever associated with RBF might return, happening irregularly over a period of weeks to months. Bacterial endocarditis and abscesses in the person's brain or other tissues are serious, yet rare. Some people have infected pericardial effusion and infected amniotic fluid. Haverhill fever resembles percutaneously acquired rat bite fever, although with more prominent vomiting and pharyngitis.

A diagnosis is confirmed by culturing the organism from the person's joint fluid or blood. Measurable agglutinins develop during the second or third week and are important from a diagnostic perspective if the titer increases. Enzyme-linked immunosorbent assay (ELISA) tests or PCR may be helpful. The person's white blood cell count ranges between 6,000-30,000 uL. Syphilis serologic tests might return as false-positive. The streptobacillary form of rat bite fever can usually be differentiated clinically from the spirillary form.

Treatment of this form of rat bite fever involves administration of amoxicillin 1 g per oral, procaine penicillin G 600,000 units IM every 12 hours, or penicillin V 500 milligrams per oral for 7 to 10 days. Erythromycin 500 milligrams might be administered to people who are allergic to penicillin. Doxycycline 100 milligrams every 12 hours for 14 days is an alternative form of treatment.

Rat Bite Fever, Spirillary Form

An S. minus infection is acquired through a rat bite, or on occasion - a mouse bite. Ingestion of the organism does not cause disease. The person's wound usually heals quickly, although inflammation recurs at the site of the bite after 4-28 days (often less than ten), accompanied by regional lymphadenitis and relapsing fever. A roseolar-urticarial rash at times develops but is less prominent than the streptobacillary rash. Systemic symptoms usually accompany the person's fever, although arthritis is rare. In people who have not received treatment, 2-4 day cycles of fever commonly recur for 4-8 weeks, yet febrile episodes rarely recur for less than a year.

A diagnosis is achieved through direct visualization or a culture of spirillum from blood smears, or tissue from the person's lymph nodes or lesions, or by Giemsa stain or darkfield examination of the blood from mice who have been inoculated. The white blood cell count ranges between 5,000-30,000 uL. The Venereal Disease Research Laboratory (VDRL) results are false-positive in around 50% of those affected. The disease might easily be confused with Borrelia recurrentis infection or malaria - both are characterized by relapsing fever.

Risk Factors for Rat Bite Fever

The fact of the matter is, anyone who is exposed to the bacteria that causes rat bite fever is at risk for getting the disease. There are some people who might be at increased risk. These people include those who:

  • Live in rat-infested buildings
  • Have pet rats living in their home
  • Work with rats in laboratories or in pet stores

Preventing Rat Bite Fever

There are some different things people can do to prevent rat bite fever. A person can protect themselves from RBF by:

  • Drinking water and pasteurized milk from sources that are safe
  • Avoiding contact with rodents, or places where rodents might be present
  • Avoiding drinking water or milk that might have come in contact with rodents

People who clean rodent cages or handle rodents should wear protective gloves, avoid touching their mouths with their hands, and practice regular hand washing.

Occurrence of Rat Bite Fever

In the United States of America, rat bite fever is rare. Accurate data concerning the rate of incidence is not available because the disease may not be reportable to state health departments. Since rat bite fever is not a nationally notifiable disease, trends in disease incidence in America are not available. Recent incidence reports have highlighted the potential risk for rat bite fever among people who have contact with rodents at work or in their own homes.

Learn More About Rat Bite Fever

  • ATSU - Rat Bite Fever
    www.atsu.edu/faculty/chamberlain/website/lectures/lecture/ratfever.htm
  • Patient - Rat Bite Fever
    patient.info/doctor/rat-bite-fever-pro
  • HealthyChildren.org - Rat Bite Fever
    https://www.healthychildren.org/English/health-issues/conditions/from-insects-animals/Pages/Rat-Bite-Fever.aspx

Facts: Rat Bite Fever

  • Rats are usually the source of the infection. Other animals that may cause this infection include: Gerbils, Squirrels, Mice, Cats and Weasels.
  • Most people get rat-bite fever through contact with urine or fluids from the mouth, eye, or nose of an infected animal. This most commonly occurs through a bite, yet some cases may occur simply through contact with these fluids.
  • After the onset of fever, a red, bumpy rash may appear on the hands and feet. Joints can become swollen, red and painful.


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