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Lecture notes, cheat sheets
Детские инфекционные заболевания. Пневмококковые инфекции (конспект лекций)
Directory / Lecture notes, cheat sheets Table of contents (expand) Lecture number 3. Pneumococcal infections Pneumococci (Streptococcus pneumoniae) are common inhabitants of the human upper respiratory tract, but under certain conditions they can become pathogens of infectious diseases that are clinically manifested by purulent-inflammatory changes in various organs and systems, more often in the lungs - by the type of croupous pneumonia and in the central nervous system - by type of purulent meningitis. Etiology. Pneumococci are gram-positive, lanceolate, capsule-forming diplococci that can be found in the form of individual cocci or chains. Due to differences in the composition of the capsular polysaccharide, more than 80 different serotypes of the microorganism are distinguished. Only smooth capsular strains of pneumococci are pathogenic for humans. Somatic antigens of pneumococcus have been isolated, antibodies to which determine an insignificant part of immunity. Antibodies to capsular antigens are of primary importance in protective reactions. Pneumococci produce hemolytic toxin, pneumolysin and toxic neuraminidase. When the pathogen is destroyed, endotoxin is released, causing hemorrhages on the skin and mucous membranes of the rabbit. On solid nutrient media, pneumococci form non-pigmented, with impressions in the center of the colony, surrounded by a zone of incomplete hemolysis. The pneumococcal capsule can be seen when the microorganisms are treated with a type-specific antiserum mixed with the appropriate capsular polysaccharide. In this case, the pneumococcus capsule acquires the ability to refract light rays. Epidemiology. Many healthy individuals are carriers of pneumococci. Among the carriers, serovars that do not have pronounced virulent properties predominate. The development of the disease in these cases is possible with a sharp decrease in the immunological reactivity of the body. In epidemiological terms, clones of pneumococci with greater virulence, which are formed in weakened children, matter. The source of infection is a person - a patient or a carrier of pneumococci. The infection is transmitted by airborne droplets. Susceptibility has not been precisely established. Pneumococcal disease is usually sporadic, and its frequency and severity is greatest in patients with sickle cell anemia, asplenia, splenosis, humoral (B-lymphocyte) immunity deficiency, or complement deficiency. Pathogenesis and pathomorphology. Pneumococci must be considered as potential pathogens. Nonspecific mechanisms of local immunity, including the presence of other microorganisms in the nasopharynx, significantly limit the proliferation of pneumococcus. Pneumococcal diseases often develop after a viral infection of the respiratory tract, which affects the ciliated epithelium and reduces its activity, and also suppresses the activity of alveolar macrophages. Airway secretions may delay the process of phagocytosis. In the tissues, pneumococci begin to multiply and spread with the flow of lymph and blood or through contact from the site of infection. The severity of the disease is determined by the virulence of the pathogen, its quantity, especially in bacteremia, and the state of reactivity of the macroorganism. The most unfavorable prognosis is with massive bacteremia and a high concentration of capsular polysaccharide in the blood. A severe progressive form of the disease develops in most patients with antigenemia, despite ongoing intensive antibiotic therapy. Deficiency of the terminal complement component (C3-C9) is associated with a tendency to recurrent purulent infections, among which pneumococci also play a role. An increased tendency to pneumococcal infections in patients with a removed spleen or its congenital absence is associated with insufficient opsonization of pneumococci, the lack of a filtering function of the spleen during bacteremia. Pneumococcal infection is especially common in patients with sickle cell anemia and other forms of hemoglobinopathy due to the fact that patients lack the ability to activate C3 in other ways and fix this opsonin to the pneumococcal cell wall. The efficiency of phagocytosis decreases with a deficiency of T- and B-cell immunity due to the insufficiency of opsonin anticapsular antibodies and the inability to cause lysis and agglutination of bacteria. Pneumococcal disease develops in individuals with transient and pre-existing factor B suppression. The spread of infection in the tissues of patients is enhanced by the action of the antiphagocytic substance of the soluble pneumococcal capsular antigen. An important role is played by the factor contributing to the development of edema. Subsequently, the number of macrophages in the exudate increases, and the phagocytosis of pneumococci increases. Pneumonia resolution processes are completed in 7-10 days. The introduction of effective antibiotics and type-specific serum can accelerate the healing process. Clinical manifestations. The clinical symptoms of pneumococcal infection depend on the location of the main pathological process. Most often it involves the upper and deep parts of the respiratory tract, often accompanied by a viral infection. Pneumonia, otitis media, sinusitis and pharyngitis, laryngotracheobronchitis, peritonitis and bacteremia develop. Pneumococci remain the most common causative agents of otitis media in children over 1 month of age. The spread of infection can occur through contact, leading to the development of empyema, pericarditis, mastoiditis, epidural abscess and, in rare cases, meningitis. Bacteremia can cause meningitis, purulent arthritis, osteomyelitis, endocarditis and brain abscess. The development of pneumococcal epiglottitis has been described in children with impaired immunity. Subcutaneous abscesses rarely form in pneumococcal bacteremia. Kidney diseases such as glomerulonephritis and cortical arteriolar thrombosis are often associated with pneumococcal bacteremia. Localized gingivitis, gangrenous areas of the face or extremities, and disseminated intravascular coagulation of the blood may also represent pneumococcal bacteremia. Diagnosis. An accurate diagnosis of pneumococcal infection can be established based on the isolation of pneumococci from the site of inflammation or blood. At the same time, microorganisms found in the nasopharynx of patients with pneumonia, otitis media, septicemia or meningitis may not be the cause of the disease. Pneumococci are often found in urine cultures. In the early stages of pneumococcal meningitis, cocci may be found in the CSF. Quantitative immunoelectrophoresis of serum, CSF or urine using combined pneumococcal serum can be of great help in the diagnosis of pneumococcal meningitis or bacteremia. Pneumococcal antigens in blood and urine can also be detected in localized pneumococcal disease. Type-specific antiserum significantly improves the accuracy of serological diagnostic methods, and previous antibiotic therapy does not significantly affect their results. Differential diagnosis pneumococcal infections are carried out with staphylococcal, meningococcal, streptococcal, hemophilic and other bacterial infections. In many ways, it depends on the results of bacteriological and serological studies. Treatment. Penicillin is the drug of choice for pneumococcal infections. Doses and duration of treatment should vary depending on the location of the infection. It is advisable in all cases to determine the drug sensitivity of isolated pneumococci using the dilution method to correct treatment tactics. In case of resistance to penicillin, but sensitivity to chloramphenicol, treatment is carried out last. The inability to foresee or predict the drug resistance of the pathogen in advance creates the need to carry out in all cases an appropriate bacteriological study of all strains of pneumococci isolated from the blood and CSF. Erythromycin, cephalosporin, clindamycin and chloramphenicol, sulfadiazine and sulfazoxazole can be successfully used to treat patients intolerant to penicillin. Forecast. The outcome of the disease depends on the age of the patient, the state of his defenses, the virulence of the pathogen, the localization of the infection, and the adequacy of therapy. Prevention. The polyvalent pneumococcal vaccine "PNEUMO-23" is highly immunogenic and rarely causes adverse reactions; it is recommended for vaccination of children over 2 years of age from a high-risk group. Children with an immunodeficiency state who come into contact with a patient with pneumococcal infection can be given gammaglobulin. Author: Muradova E.O. << Back: Diseases caused by Neisseria (Meningococcal infections. Gonococcal infection) >> Forward: staph infection
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