Etiology and pathogenicity factors
The causative agents of the disease are bacteria of the genus Shigella. They are capable of prolonged persistence and accumulation in the external environment.
The development of the disease and the severity of clinical manifestations depend on the main pathogenicity factors of shigellae:
- Adhesiveness — the ability to attach to epithelial cells.
- Enteroinvasiveness — the ability to penetrate into the cells of the mucous membrane.
- Enterotoxigenicity and cytopathogenicity — factors causing cell damage and death, leading to inflammation and ulceration.
- Colicinogenicity — production of substances that suppress the normal intestinal microflora.
Epidemiology
Shigellosis is a strict anthroponosis — humans are the sole source of infection.
In the Russian Federation, the incidence rate is 30–50 cases per 100,000 population. The disease occurs both sporadically and in groups, with marked seasonality. There is a clear correlation between the virulence of specific Shigella species and their predominant transmission routes (the mechanism of infection, routes, and vehicles of transmission require detailed analysis during epidemiological investigation).
Pathogenesis and clinical presentation
The portal of entry for the infection is the gastrointestinal tract. The pathogen passes through the stomach and adheres to the epithelial cells of the small intestine and subsequently the colon. The cytopathic effect of shigellae, along with their invasive and toxigenic properties, causes pronounced pathomorphological changes in the mucous membrane, up to the formation of erosions and ulcers. Long-term persistence of the pathogen in the body is possible.
Clinically, shigellosis manifests with several leading syndromes:
- Intoxication syndrome.
- Colitic syndrome.
- Gastroenteritic syndrome.
- Gastroenterocolitic syndrome.
- Dehydration syndrome.
Example of a typical clinical course (colitic variant of acute shigellosis): The disease begins acutely with chills, headache, weakness, and fever (up to 38.0–38.9°C). Soon, pain in the lower abdomen joins. Gradually, the pain becomes cramping in nature. Stool becomes frequent (up to 14–16 times a day), loose, with abundant mucus and blood. Exhausting false urges to defecate — tenesmus — are characteristic. There is little fecal matter; the discharge consists predominantly of mucus with blood streaks. On examination, the abdomen is scaphoid, and in the left iliac region, a sharply tender, dense, and spastic sigmoid colon is palpated.
Diagnostics and differential diagnosis
The diagnostic algorithm begins with targeted identification of complaints, history taking, and, most importantly, epidemiological history (identifying contact with infectious patients). Physical examination and visual assessment of the nature of discharges are mandatory.
The plan for laboratory and instrumental examination includes:
- Complete blood count (CBC).
- Urinalysis.
- Stool bacteriological culture.
- Immunological methods.
- Sigmoidoscopy (assessment of the colonic mucosa state).
Differential diagnosis is primarily performed with acute foodborne toxic infections (FTI). A crucial criterion for ruling out FTI: toxic infections are characterized by a fulminant onset with acute gastroenteritis, whereas typical shigellosis is dominated by spastic hemocolitis.
Treatment and management
Treatment principles depend on the form of the disease. Uncomplicated forms of shigellosis can be treated either at home or in a hospital.
Critical conditions requiring emergency medical care demand special attention:
- Infectious-toxic shock.
- Dehydration shock.
Indications for hospitalization: A patient may be hospitalized not only due to the severity of the condition, but also based on strict epidemiological indications. For example, if the patient lives in the same apartment with young children (2–4 years old) attending preschool institutions, hospitalization in a specialized infectious disease ward is mandatory to prevent an outbreak.
At the pre-hospital stage, specific medical care is generally not required. However, the physician must work in the epidemic focus: explain the routes of transmission to family members and instruct them on strict personal prevention measures.
Briefly: answers to topical questions
Which Shigella species are the most significant causative agents of shigellosis in humans?
The main causative agents of human shigellosis are several species of bacteria of the genus Shigella, which differ in the severity of the disease they cause. These include:
- Shiga bacillus (Shigella dysenteriae) — causes the most severe forms of dysenteric colitis; children have a high risk of systemic generalization.
- Flexner bacillus (Shigella flexneri) — causes a moderate to severe course with pronounced distal colitis and a risk of hemorrhagic syndrome.
- Sonne dysentery (Shigella sonnei) — characterized by a milder course, often presenting as catarrhal gastroenterocolitis, predominantly seen in older children.
- Boyd bacillus (Shigella boydii) — runs a mild course with mildly expressed symptoms of intoxication.
- Newcastle bacillus (Shigella newcastle) — clinically similar to the course of Flexner shigellosis.
What are the epidemiological indications for mandatory hospitalization in shigellosis?
Epidemiological indications for mandatory hospitalization of patients with shigellosis are conditions that facilitate the spread of infection in society. Hospitalization is carried out in the following cases:
- the patient belongs to a decreed occupational group (e.g., food industry workers, water supply service personnel, and equivalent persons);
- lack of adequate living conditions to maintain the anti-epidemic regime (living in a dormitory, boarding school, hotel);
- cohabitation of a pathogen-shedding patient with children attending preschool institutions or with individuals of decreed professions.
What antibacterial drugs are used for etiotropic treatment of shigellosis?
Systemic antibacterial drugs are used for the etiotropic treatment of shigellosis, taking into account regional bacterial susceptibility profiles. The following drugs and regimens are used:
- Ciprofloxacin — prescribed at 500 mg twice daily; the course of therapy lasts from 5 to 14 days.
- Nalidixic acid — 500 mg 4 times daily for 7–10 days.
- Co-trimoxazole — used at a dose of 160/800 mg twice daily; the course duration is 10 days.
An important condition is that antibiotics are prescribed strictly after collecting stool samples for bacteriological examination.
What specific complications, in addition to shock states, can develop in severe shigellosis?
In severe shigellosis, a number of threatening systemic, intestinal, and local complications may develop. Specific complications include:
- Systemic — acute adrenal insufficiency, encephalic syndrome, and hemolytic-uremic syndrome (HUS).
- Intestinal — bowel perforation, peritonitis, intestinal bleeding, toxic megacolon, paresis, intussusception and intestinal obstruction, gangrene of the bowel wall.
- Local — rectal prolapse, paraproctitis, pericolitis, formation of intestinal and entero-vesical fistulas, anal fissures, and cicatricial stenosis of the bowel.
Reactive arthritis and Reiter's syndrome are also classified among rare complications.
The symptom complex of typical colitic shigellosis can be described by three "C"s: Cramping abdominal pain, Colitis mucus (and blood) in the stool, Sigmoid colon spasm.
Class and exam questions
Which disease is the onset of shigellosis most often confused with?
Differential diagnosis is primarily conducted with foodborne toxicoinfections (FTI). The main difference is that FTI presents with acute gastroenteritis rather than spastic colitis with tenesmus.
What changes are detected during abdominal palpation?
The abdomen is usually retracted. A spastic, indurated, and sharply tender sigmoid colon is palpated in the left iliac region.
Is hospitalization always mandatory for a patient with shigellosis?
No, treatment of uncomplicated forms is possible at home. However, hospitalization is mandatory if there are epidemiological indications (e.g., sharing a household with children attending nursery school) or if severe complications develop.
What else to study on this topic
- Mechanism of infection, routes and factors of transmission (correlation with species virulence)
- Pathomorphological changes of the intestinal mucosa depending on the form
- Susceptibility and immunity in shigellosis
- Classification of Shigella (species and serotypes)
- Emergency care algorithms for infectious-toxic and dehydration shock
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