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Shigellosis (bacterial dysentery)

The disease is an acute inflammatory process in the gastrointestinal tract, caused by bacteria from the genus Shigella and characterized by fever, cramping abdominal pain and diarrhea mixed with mucus, pus and blood in the stools. Sometimes the disease proceeds as normal diarrhea.

Etiology. Shigella - short fixed Gram-negative rods, the biochemical feature of which is the absence or very slow fermentation of lactose. Other biochemical features help to distinguish Shigella from E. coli, which also do not ferment lactose and do not emit gas. The Shigella genus is divided into four groups (A, B, C, and D), depending on their biochemical properties and antigenic composition. Group A includes 10 serotypes, of which Shigella disenteriae is the most important. Group B includes 6 serotypes, of which Shigella flexneri is the most common. Of the serotypes of group C, S. boydii is found, and group D includes only one pathogen, most often S. sonnei, which accounts for half of the cases of the disease.

Epidemiology. Shigella is common throughout the world. Most often, children get sick at the age of 1-4 years. The maximum incidence is observed at the end of the summer, but the seasonality is not as pronounced as with salmonellosis.

Man serves as the main reservoir of infection. Infection occurs through the direct infection of the feces of patients with water or food. Ways of infection: contact-household, food, water. Flies are active carriers of the disease.

Pathogenesis. For the development of the disease is enough infection with a small number of Shigella (less than 200). The pathogens remain viable in the acidic environment of the gastric contents for 4 hours. The infection develops only when the pathogen penetrates the intestinal epithelial cells. Reproduction of the pathogen can occur simultaneously in the epithelial cells, the submucosal layer lamina propria. At the same time, epithelial cells are destroyed, edema, local inflammation and hyperemia develop. Damage is superficial, and therefore intestinal perforation does not occur, and bacteremia is very rare. Gastroenterocolitis phenomena are usually resolved spontaneously in 4–7 days. S. disenteriae produce enterotoxin, but their role in the pathogenesis of the disease is not entirely clear. Toxigenic, but minimally invasive forms of shigella do not cause disease. At the same time, non-toxic, but highly invasive strains cause severe dysentery. Virulent strains of S. flexneri and S. sonnei are distinguished by the presence of a plasmid that encodes the J antigen belonging to the side chain of O-polysaccharides of Shigella.

Clinical manifestations. The incubation period depends on the route of infection and the dose of the pathogen and usually ranges from 6-8 hours to 7 days, most often 36-72 hours, during which the shigella reach the large intestine. Initially, patients complain of fever and cramping abdominal pain. The body temperature can reach 40 ° С, the phenomena of general intoxication intensify. 48 hours after the onset of the disease, diarrhea appears, feces with blood and mucus occur up to 20 times a day. In the following days of the disease, bloody diarrhea may persist against the background of normalized body temperature or the absence of abdominal pain. When examining a child there is a slight tenderness of the abdomen on palpation without clear localization.

At high temperatures and cramps, shigellosis may be accompanied by symptoms of a lesion of the nervous system, resembling meningitis, encephalitis. A significant loss of fluid and electrolytes can lead to dehydration, acidosis, and electrolyte imbalance. Children can have tenesmus. In severe forms of dysentery, especially in debilitated, dystrophic children, prolapse of the rectum may develop.

When eyes are contaminated with fingers or other objects, conjunctivitis develops. Bacteremia develops extremely rarely, so local foci of infection outside the intestine usually do not occur. A common infection with the development of pneumonia, meningitis, osteomyelitis and arthritis can occur only in young children with significant eating disorders. In such cases, there is severe dehydration, sometimes leading to hemolytic-uremic syndrome and renal failure.
Suppurative arthritis and Reiter’s syndrome on the basis of dysenteric infection are usually associated with the presence of HLA B27 antigen. Mortality in bacteremia on the basis of shigellosis reaches 50%, this complication usually occurs during dehydration in non-temperate children with prolonged diarrhea and eating disorders.

Diagnosis. Dysentery should be suspected in all patients with diarrhea, accompanied by fever. The diagnosis of shigellosis is made on the basis of clinical and epidemiological data, with mandatory laboratory confirmation.

For final diagnosis use:

1) the bacteriological method with the greatest value. Is carried out before the appointment of antibiotic therapy. For the study of material choose particles of feces with pathological impurities, except for blood. Sowing material produced on selective medium. A negative result is given on days 3–51, and a positive result is given on days 5–7 after the material is delivered to the laboratory;

2) serological methods used in doubtful cases and with negative results of bacteriological examination of feces. Conducted in two directions: the determination of the titer of specific antibodies in the serum of the patient and the antigen in the feces. In the presence of typical clinical symptoms and detection of a diagnostic titer of specific antibodies (1: 200 and higher) or an increase in their titer in the dynamics of the disease, the clinical diagnosis of a shigella infection is considered established even in the absence of seeding shigella from the patient’s stool;

3) rapid diagnostic methods based on the detection of a Shigella antigen in feces using the direct method of luminescent antibodies or the immunoadsorption method;

4) rectoromanoscopic method used to diagnose erased forms of the disease and to determine the cause of long-term bacterial excretion of shigella;

5) scatological method used as an aid in the diagnosis of shigellosis in the presence of colitis. In patients with shigellosis, along with inflammatory changes, signs of impaired enzymatic and absorption functions of the intestine are determined;

6) peripheral blood examination. With all shigellosis, moderate leukocytosis, neutrophilic and stab-shift blood formula, accelerated by ESR are noted. Differential diagnosis. Bacterial dysentery must be differentiated from other forms of enterocolitis, caused by enterotoxigenic intestinal sticks, Salmonella, campylobacter, amoebic dysentery, viral infections, acute appendicitis, intestinal invagination and mesenteric lymphadenitis.

Treatment. With antibiotic treatment, the duration of the disease and the timing of the release of shigella are significantly reduced. The choice of antibiotic depends on the drug susceptibility of pathogens that persist among members of this team. Antibiotics usually allow shigella to clear the gastrointestinal tract. Prolonged bacterial carriage develops very rarely. In such cases, the temporary effect causes lactulose, a derivative of lactose. In acute forms of dysentery, lactulose is ineffective. Peristalsis-reducing drugs are contraindicated in bacterial dysentery. The need for the introduction of fluid and electrolytes is determined by the hydration status of the patient.

Prognosis and prevention. In most previously healthy children, shigellosis occurs favorably and is prone to spontaneous cure. Pathogens continue to stand out for about 3 months after an acute illness. High levels of morbidity and mortality from bacterial dysentery are observed in closed collectives in developing countries in which children often suffer from dystrophy.

Strict personal hygiene and sanitary measures are the basis for the prevention of shigellosis. Thorough and systematic hand washing should be the law for all persons caring for patients with bacterial dysentery. In hospitals it is necessary to strictly comply with all requirements for isolation of patients. There is no effective and affordable vaccine.

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Shigellosis (bacterial dysentery)

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