Rat-bite fever

Sodoku, also known as spirillosis and rat bite fever, is a bacterial zoonotic infection characterized by recurrent bouts of fever accompanied by exacerbation of inflammatory changes at the bite site rat, with lymphadenitis and with polymorphic eruptions.

The disease has been known since ancient times. Its causative agent was identified in 1887 and again in 1900 by two groups of Japanese scientists.


The cause of the disease is Spirilla minor, which is a thread and is able to move independently. The bacterium in the environment is unstable, it is quickly destroyed under the influence of disinfectants and high temperatures.


The main reservoir and source of infection in nature are gray and black rats and, in very rare cases, other rodents – mice, squirrels, ferrets, etc. and even less often cats and dogs infected with the causative agent of the infectious disease.

The mechanism of transmission of the infection is contact through the bite of a rat or other animal or when infected saliva falls on the surface of the human skin. The infection is not transmitted from person to person.

Under normal conditions, 10-20% of rats are infected, according to some researchers up to 50% of their population.

The disease is widespread in Japan, India and most of the port cities. In Bulgaria, only one case of spirillosis was registered and described in Varna. Among the risk groups are also workers in laboratories and vivariums, etc.


Entrance door for infection is the site of the rat bite, where a zone of hyperemia, infiltration and swelling develops.

After multiplying at the site of the bite of the bacteria causing the disease, the microorganisms enter the blood through the lymphatic vessels, causing lymphangitis and lymphadenitis.

As a result of bacteremia, the causative agent enters various organs, where it attaches to the elements of the mononuclear phagocytic system and accumulates in them.

Periodically, repeated bacteremia and new generalization of the infection occurs – clinically it manifests as a relapse of the disease.

The causative bacterium is found in organs rich in cells of the mononuclear phagocytic system – in the liver, spleen, lymph nodes, and also in the kidneys, adrenal glands, testicles, etc.

Clinical picture

The incubation period varies widely – from 3 days to 2 months, on average it lasts about 10-14 days. During this time, the bite wound heals.

The disease begins acutely, even suddenly, with chills and an increase in body temperature to 39-40 degrees Celsius and more. The patient feels weak and weak, has joint and muscle pains, and exhibits other symptoms of intoxication.

At the same time, a dense, painful and swollen infiltrate forms at the site of the bite. Sometimes necrosis develops on it or a blister forms with an exit, which is a deep ulcer with sharp edges.

All this, as well as lymphangitis, constitute the primary involvement, which, together with regional lymphadenitis, are very characteristic of spirillosis.

At the peak of these manifestations, a blood count reveals leukocytosis, neutrophilia, eosinophils are usually absent, the erythrocyte sedimentation rate (ESR) is increased. Proteins and erythrocytes appear in the urine, which is a sign of intoxication.

Treatment of rat bite fever

As with other spirochetoses, penicillins, tetracyclines, cephalosporins, macrolides are effective. Detoxification infusion therapy is also indicated.


Consists in deratization measures. For individual prevention when bitten by a rat or other animals – possible sources of the infectious microorganism, therapy with tetracycline 200-300 mg per day for 5 days or with another effective antibiotic is prescribed.

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