Rat-bite fever (RBF) is an acute, febrile human illness caused by bacteria transmitted by rodents, in most cases, which is passed from rodent to human by the rodent's urine or mucous secretions. Alternative names for rat-bite fever include streptobacillary fever, streptobacillosis, spirillary fever, bogger, and epidemic arthritic erythema. It is a rare disease spread by infected rodents and caused by two specific types of bacteria:
Streptobacillus moniliformis, the only reported bacteria that causes RBF in North America (streptobacillary RBF) Spirillum minus, common in Asia (spirillary RBF, also known as sodoku). Most cases occur in Japan, but specific strains of the disease are present in the United States, Europe, Australia, and Africa. Some cases are diagnosed after patients were exposed to the urine or bodily secretions of an infected animal. These secretions can come from the mouth, nose, or eyes of the rodent. The majority of cases are due to the animal's bite. It can also be transmitted through food or water contaminated with rat feces or urine. Other animals can be infected with this disease, including weasels, gerbils, and squirrels. Household pets such as dogs or cats exposed to these animals can also carry the disease and infect humans. If a person is bitten by a rodent, it is important to quickly wash and cleanse the wound area thoroughly with antiseptic solution to reduce the risk of infection.
Symptoms and signs Symptoms are different depending on the type of rat-bite fever with which the person is infected. Both spirillary and streptobacillary rat-bite fever have a few individual symptoms, although most symptoms are shared. Streptobacillosis is most commonly found in the United States and spirillary rat-bite fever is generally diagnosed in Africa. Rat-bite symptoms are visually seen in most cases and include inflammation around the open sore. A rash can also spread around the area and appear red or purple. Other symptoms associated with streptobacillary rat-bite fever include chills, fever, vomiting, headaches, and muscle aches. Joints can also become painfully swollen and pain can be experienced in the back. Skin irritations such as ulcers or inflammation can develop on the hands and feet. Wounds heal slowly, so symptoms possibly come and go over the course of a few months. Symptoms associated with spirillary rat-bite fever include issues with the lymph nodes, which often swell or become inflamed as a reaction to the infection. The most common locations of lymph node swelling are in the neck, groin, and underarm. Symptoms generally appear within two to ten days of exposure to the infected animal. It begins with the fever and progresses to the rash on the hands and feet within two to four days. The rash appears all over the body with this form but rarely causes joint pain.
Causes Two types of Gram-negative, facultatively anaerobic bacteria can cause the infection.
Spirillosis
Rat-bite fever transmitted by the Gram-negative coiled rod Spirillum minus (also known as Spirillum minor) is rarer, 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. Rectal pain and gastrointestinal symptoms are less severe or are absent. Penicillin is the most common treatment.
Streptobacillosis
The streptobacillosis form of rat-bite fever is known by the alternative 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 an incubation period of 2–10 days, Haverhill fever begins with high prostrating fevers, rigors (shivering), headache, and polyarthralgia (joint pain). Soon, an exanthem (widespread rash) appears, either maculopapular (flat red with bumps) or petechial (red or purple spots) and arthritis of large joints can be seen. The organism can be cultivated in blood or articular fluid. The disease can be fatal if untreated in 20% of cases due to malignant endocarditis, meningoencephalitis, or septic shock. Treatment is with penicillin, tetracycline, or doxycycline.
Diagnosis This condition is diagnosed by detecting the bacteria in skin, blood, joint fluid, or lymph nodes. Blood antibody tests may also be used. To get a proper diagnosis for rat-bite fever, different tests are run depending on the symptoms being experienced. To diagnosis streptobacillary rat-bite fever, blood or joint fluid is extracted and the organisms living in it are cultured. Diagnosis for spirillary rat bite fever is by direct visualization or culture of spirilla from blood smears or tissue from lesions or lymph nodes.
Prevention Eliminating exposure is very important when it comes to disease prevention. When handling rodents or cleaning areas where rodents have been, contact between hand and mouth should be avoided. Hands and face should be washed after contact and any scratches both cleaned and antiseptics applied. The effect of chemoprophylaxis following rodent bites or scratches on the disease is unknown. No vaccines are available for these diseases. Improved conditions to minimize rodent contact with humans are the best preventive measures. Animal handlers, laboratory workers, and sanitation and sewer workers must take special precautions against exposure. Wild rodents, dead or alive, should not be touched and pets must not be allowed to ingest rodents. Those living in the inner cities where overcrowding and poor sanitation cause rodent problems are at risk from the disease. Half of all cases reported are children under 12 living in these conditions.
Treatment Treatment should begin with assessment and management of the bite wound. The wound should be well irrigated. Although rats and small rodents are rarely infected with rabies, the individual must seek medical attention for possible tetanus or rabies post-exposure prophylaxis. Antibiotic therapy should be started immediately as laboratory confirmation may take a few days. Once results are obtained, therapy can be adjusted according to the antimicrobial susceptibility. Lack of treatment is highly associated with an increased risk of death.
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