Rat bite fever is a disease of the spirochetosis group that develops when bitten by mouse–like rodents, occurring with recurrent fever and skin manifestations. Symptoms include primary affect (infiltrate with an expression at the bite site, lymphangitis), as well as recurrent attacks of fever, polymorphic rash, regional lymphadenitis. The methods of specific diagnosis are microscopy of a thick drop of blood and a smear from the primary affect, bacteriological seeding, serological reactions, biological test. The causative agent is sensitive to the appointment of penicillins, tetracyclines, cephalosporins, macrolides.
Rat bite fever is a bacterial anthropozoonosis that occurs with febrile attacks, local inflammatory changes, lymphadenitis and polymorphic skin rashes. The name of the disease comes from the Japanese words “so” – rat and “doku” – poison. For the first time, Rat bite fever disease was registered in the Asian region (Japan, China, India), but currently cases of the disease are known in all countries of the world. To date, over 500 episodes of rat bite fever have been described in the medical literature, 55 of them on the territory of the former USSR. In North America, a disease close to sodoc in clinical and epidemiological terms is common – Haverhill (Haverhill) fever or streptobacillosis.
Rat bite fever disease is caused by a small spirilla from the family of spirochaetes (Spirillum minus Carter, syn. – Spirochaeta morsus muris, Spirochaeta, Treponema japonicum). Spirilla is a short, thin, spiral gram-negative bacterium with 2-3 corkscrew-like curls. The length of spirillae is from 3-5 microns (sometimes up to 15 microns), the width is 0.2 microns. Thanks to the terminal flagella, the spirilla is mobile and moves by rotating around its axis. The causative agent is sensitive to environmental factors; it quickly dies under the influence of high temperatures and disinfectants.
The reservoir and source of the causative agent of rat bite fever are mainly rats, whose infection with Carter’s spirilli can reach 10-25%. In rats, the disease occurs in the form of conjunctivitis and keratitis. Less often, other small rodents (mice, ferrets), cats, and dogs act as carriers of infection. In animals, spirilli are found in saliva, blood, tissues and organs. The saliva of infected animals is a factor of transmission of infection, and a person becomes infected with rat bite fever as a result of animal bites, mainly rats. There are cases of infection of laboratory staff, as well as infection when animal secretions get on damaged skin or mucous membranes, the use of contaminated food, milk.
According to literature data, about a quarter of the cases of rat bite fever are children aged 1 to 14 years, mostly boys. The wide geography of rat bite fever is associated with the ubiquity of rodents. The disease is more often registered in countries with a low level of sanitary culture of the population and places with a large concentration of rodents.
In the area of the entrance gate (skin wounds), spirilli cause a local inflammatory reaction – a primary affect characterized by hyperemia, cellular infiltration, and fibrin loss. Further spread of the pathogen occurs lymphogenically, which is accompanied by hyperplasia of the lymphatic apparatus. This is followed by a phase of hematogenic dissemination, leading to the spread of spirochetes throughout the body with blood flow. Thus, spirilli penetrate into organs (liver, spleen, kidneys), where they are fixed, from time to time causing repeated generalization of infection – recurrent temperature rises and skin manifestations.
From the moment of infection to the development of the clinical stage of infection, an average of 10-14 days pass (sometimes up to 4 weeks). By this time, the wound formed at the site of the bite of an infected rodent, as a rule, is already scarred, however, due to the manifestation of the disease, painful infiltration, hyperemia and swelling of soft tissues reappear at the entrance gate site. In the future, necrotic ulceration of the infiltrate occurs, regional lymphadenitis and lymphangitis occur. Together, all these manifestations constitute the primary affect in rat bite fever.
Generalized manifestations of rat bite fever develop acutely: a fever of up to 39-40 ° C suddenly occurs, accompanied by chills, bruising, myalgia, headaches, arthralgias. The high temperature is maintained for 4-6 days, then critically decreases with profuse sweating. A second attack occurs after 4-9 days and lasts 3-4 days. Relapses of fever, interspersed with afebrile periods, can be repeated from 4-5 to 20 times. Gradually, the fever weakens, and the apyrexic intervals lengthen, but the rat bite fever disease can be delayed for several months.
On the 2-3 day of the onset of a febrile attack, an urticar, maculo-papular or maculo-erythematous rash appears on the skin, which spreads from the place of primary affect to the entire body and limbs. Subsequent relapses of fever are accompanied by a new wave of polymorphic rashes. At the height of the temperature rise, the rash becomes brighter and more abundant, with a decrease it turns pale or disappears altogether. The phenomenon of “theatrical makeup” is characteristic – limited hyperemia of the eyelids on a pale face. Synchronously with the attacks of fever, there is an increase in the liver and spleen.
Patients with rat bite fever may develop polyarthritis, myositis, conjunctivitis. Less often, complications of rat bite fever are anemia, bronchopneumonia, glomerulonephritis, myocarditis, endocarditis, decreased vision, hearing loss, mental disorders, paralysis. In childhood, depending on the predominance of certain symptoms of rat bite fever, the following clinical forms of infection are distinguished:
- typical (primary affect, intermittent fever, skin rash)
- meningoencephalitic (strabismus, convulsions, tension of the fontanel)
- rheumatoid (arthralgia, swelling of the joints)
- gastrointestinal (nausea, vomiting, anorexia, abdominal pain, loose stools with mucus, dystrophy).
Diagnosis and treatment
The basis of clinical and epidemiological diagnosis of rat bite fever is anamnestic and clinical data: previous contact with rodents or rat bite, recurrent fever, synchronicity of exacerbation of primary affect and rash with febrile attacks, etc. The preliminary diagnosis of rat bite fever is confirmed in the laboratory by detecting spirillae in a thick drop of blood and a smear from the primary affect. Bacteriological sowing of blood and pus on nutrient media is also used. To identify specific antibodies, serological studies are carried out from the 8th to 10th day of the disease: agglutination reaction (RA), immunofluorescence (RIF), complement binding reaction (RSC).
It is not uncommon for a positive Wasserman reaction to occur with rat bite fever (a false positive test for syphilis). The biological test consists in intraperitoneal infection of guinea pigs; after a few days, spirilli are detected in the exudate of the abdominal cavity, and inguinal lymphadenitis and orchitis develop in animals. In order to avoid diagnostic errors, malaria, rheumatoid arthritis, recurrent typhus, leptospirosis, tularemia, brucellosis, cat scratch disease, rickettsiosis, meningococcal infection should be excluded.
The bite site is subject to primary surgical treatment. As etiotropic drugs for rat bite fever, penicillin antibiotics are used for a course of 7-10 days. When the pathogen is resistant to penicillin, tetracycline antibiotics, streptomycin, cephalosporins, macrolides, intravenous administration of novarsenol are used. Patients are subject to hospitalization until full recovery.
Without treatment, rat bite fever disease proceeds for a long time, up to 4-6 months, leading to exhaustion of patients and death in about 10% of cases. In order to prevent it, it is necessary to carry out deratization measures (extermination of rats), protecting people from contact with rodents, preventive tetracycline intake in case of rat bite. Methods of immunoprophylaxis of Sodoku have not been developed.