Rat-bite fever

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Rat-bite fever is an acute, febrile human illness caused by bacteria transmitted by rodents, rats in most cases. Two types of gram-negative facultatively anaerobic bacteria can cause the infection, which is passed from rodent to human via the rodent’s urine or mucous secretions.Rat-bite fever (RBF) is an infectious disease caused by two different organisms, Streptobacillus moniliformis and Spirillum minus. In the United States, Rat-bite fever is primarily due to infection with S. moniliformis. Spirillum minus causes Rat-bite fever cases in countries such as Asia and Africa. S. moniliformis and S. minus are part of the normal respiratory flora of rats. Both organisms may be transmitted to humans through rat bites or scratches. Infection can also result from handling an infected rat, with no reported bite or scratch. Infection with S. moniliformis can also occur through ingestion of food or drink contaminated with rat excrement (Haverhill fever). Other rodents (e.g. mice, gerbils) may also be reservoirs. Person-to-person transmission has not been reported.

Rat-bite fever transmitted by the gram-negative spirochaete Spirillum minus is more rare, and is found most often in Asia. In Japan the disease is called Sodoku. Symptoms do not manifest for two to four weeks after exposure to the organism, and the wound through which it entered exhibits slow healing and marked inflammation. The fever lasts longer and is recurring, for months in some cases. Joint pain and gastrointestinal symptoms are less severe or are absent. Penicillin is the most common treatment.

The Streptobacillosis form of rat-bite fever is known by the alternate names Haverhill Fever and epidemic arthritic erythema. It is a severe disease caused by Streptobacillus moniliformis , transmitted either by rat bite or ingestion of contaminated products ( Haverhill fever). After a incubation period of around 10 days, Haverhill fever begins with high prostrating fevers, rigors, headache and polyarthralgia. Soon a exanthem appears, either maculopapular or petechial and arthritis of large joints can be seen. The organism can be cultivated in blood or articular fluid. The disease can be fatal if untreataed in 10% of cases due to malignant endocarditis, meningoencephalitis or septic shock. The treatment is with penicillin or tetracycline.

The initial scratch or wound caused by bite from a carrier rodent will result in mild inflammatory reactions and ulcerations. The wounds may heal initially, but reappears with the onset of symptoms. The incubation period is 4 to 28 days.

Persons who are at risk for infection include those who work with animals in labs or pet stores and persons living in dwellings infested with wild rats. People who have pet rats may also be at risk for infection.

Initial symptoms are non-specific and include fever, chills, myalgias, arthralgias, headache, vomiting. Patients may develop a maculopapular rash on the extremities or septic arthritis 2-4 days after fever onset. The incubation period typically ranges from 2-10 days. If not appropriately treated, severe manifestations may include endocarditis, myocarditis, meningitis, pneumonia and sepsis. In rare cases, death occurs.

The findings of rash, fever, and arthritis in individuals with a history of rat exposure suggest the diagnosis of Rat-bite fever.

The findings of rash, fever, and arthritis in individuals with a history of rat exposure suggest the diagnosis of Rat-bite fever.

Responds to penicillin antibiotics. In cases allergic to penicillin, erythromycin or tetracyclines can be used for respectively streptobacillary or spirillary infections.

Preventable by staying away from rodents, washing hands and face thoroughly after contact and cleaning and applying antiseptics to any scratches.

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In the U.S., rat bite fever is primarily caused by transmission of S. moniliformis from the bite of a rat.^[1] However, approximately 30% of patients diagnosed with rat bite fever do not recall being scratched or bitten by an infected animal.^[2][3] Transmission of the bacterium is also known to occur via consumption of infected water, close contact with, or handling of rats.^[1][4] Haverhill fever, named after the 1926 outbreak of the disease in Haverhill, Massachusetts, is a form of rat bite fever that can result from ingesting food contaminated with S. moniliformis.^[5] In 1986 at a boarding school in the United Kingdom, another outbreak of Haverhill fever was reported. Some 304 people were reported to have been afflicted.^[6] Infection was suspected to have resulted from the consumption of either unpasteurized milk or water contaminated with rat feces.^[7] Infected individuals described symptoms including a sudden development of vomiting, severe headache, and cold sweats with a high fever.^[7] Parker and Hudson first isolated the cause of this outbreak, which they named Haverhilia multiformis.^[3] This organism was later matched to S. moniliformis after further research.^[8]

Symptoms of rate bite fever include the abrupt onset of fever ranging from 38.0 °C to 41 °C.^[5] Approximately 75% of infected individuals develop a rash in addition to hemorrhaging vesicles.^[1] Both the rash and vesicles are usually located on the hands and feet, although the rash has been known to spread to other parts of the body.^[9]

The microaerophilic nature of S. moniliformis makes identification difficult.^[5] PCR testing is being utilized more for its identification.^[8] However, there is still a 13% mortality rate for untreated cases.^[4] Immunocompromised individuals, such as HIV-positive individuals, are more at risk of death from this disease.^[10] Lab personnel and pet store workers, who work closely with animals on a daily basis, also have an increased risk of infection.^[5]

Although S. moniliformis is believed to be part of the commensal bacteria of the respiratory tract of rats,^[11] rats have occasionally shown signs of the disease.^[5] Antibiotics used to treat infection may cause the formation of the L-form, which persists in the body although this form is not pathogenic.^[5]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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The initial scratch or wound caused by bite from a carrier rodent will result in mild inflammatory reactions and ulcerations. The wounds may heal initially, but reappears with the onset of symptoms. The incubation period is 4 to 28 days.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Rat-bite fever is rare in the United States. However, since RBF is not a notifiable disease, exact numbers of cases are not known.

Rat-bite fever is not a reportable disease in any state. However, unexplained deaths or critical illnesses or rare diseases of public health importance may be reportable in certain states. If RBF is suspected in a severe illness or death but a diagnosis has not been made, physicians can consider reporting the case to their state or local health department.

Since Rat-bite fever is not a reportable disease, trends in disease incidence are not available. However, recent reports have highlighted the potential risk for RBF among persons having contact with rats at home or in the workplace.

The disease has been seen in

• Africa

• Australia

• Europe

• Japan

• North and South America

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Persons who are at risk for infection include those who work with animals in labs or pet stores and persons living in dwellings infested with wild rats. People who have pet rats may also be at risk for infection.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Rat-bite fever can be caused by the two different bacteria, Streptobacillus moniliformis or Spirillum minus, both of which are found in the mouths of rodents.

Most people get rat-bite fever through contact with urine or secretions from the mouth, eye, or nose of an infected animal. This most commonly occurs though a bite, yet some cases may occur simply through contact with these secretions.

The source of the infection is usually a rat. It can occur as nosocomial infections (ie, acquired from hospitals), or due to exposure or close associations with animals predating rats, mice, squirrels etc. Other animals that may cause infection include squirrels, weasels, and gerbils.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]

Rat-bite fever must be differentiated from other diseases that cause fever and maculopapular rash on the extremities, including chickenpox, herpes zoster and erythema multiforme, among others.

Different rash-like conditions can be confused with rat-bite fever and are thus included in its differential diagnosis. The various conditions that should be differentiated from rat-bite fever include:^{[1][2][3][4][5][6][7]}

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Severe complications such as endocarditis, myocarditis, pericarditis, pneumonia, meningitis, and focal organ abscesses may occur.

Rapidly fatal cases have been reported. Untreated RBF is associated with a mortality of 7%-10%. With appropriate antimicrobial therapy, the clinical course may be shortened and severe complications may be prevented. The outlook is excellent with early treatment. Untreated, the death rate can be as high as 25%.

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