PATHOGENESIS OF PNEUMOCOCCAL INFECTION

Name : lavina loungani 2006M015

PATHOGENESIS OF PNEUMOCOCCAL INFECTION

Types of pneumococci

In adults, types 1-8 are responsible for about 75% of cases of pneumococcal pneumonia and for more than half of all fatalities in pneumococcal bacteremia; in children, types 6, 14, 19 and 23 are frequent.

Production of disease

Pneumococci produce disease through their ability to multiply in the tissues. They produce no toxins of significance. The virulence of the organism is a function of its capsule, which prevents or delays ingestion by phagocytes. A serum that contains antibodies against the type-specific polysaccharide protects against infection. If such a serum is absorbed it loses its protective power.

Animals or humans immunized with a given type of pneumococcal polysaccharide are subsequently immune to that type of pneumococcus and possess precipitating and opsonization antibodies for that type of polysaccharide.

Loss of natural resistance

Since 40%-70% of humans are at sometime carriers of virulent pneumococci, the normal respiratory mucosa must possess great natural resistance to the pneumococcus.
Among the factors that probably lower this resistance and thus predispose to pneumococcal infection are the following:

a) Viral and other respiratory tract infections that damage surface cells; abnormal accumulations of mucus (e.g. allergy), which protect pneumococci from phagocytosis; bronchial obstruction (e.g. atelectasis); and respiratory tract injury due to irritants disturbing its mucociliary function.
b) Alcohol or drug intoxication, which depresses phagocytic activity, depresses the cough reflex, and facilitates aspiration of foreign material.
c) Abnormal circulatory dynamics (e.g. pulmonary congestion, heart failure).
d) Other mechanisms, e.g., malnutrition, general debility, sickle cell anemia, hyposlpenism, nephrosis, or complement deficiency.