TAILIEUCHUNG - Chapter 139. Haemophilus Infections (Kỳ 2)

Pathogenesis Hib strains cause systemic disease by invasion and hematogenous spread from the respiratory tract to distant sites such as the meninges, bones, and joints. The type b polysaccharide capsule is an important virulence factor affecting the bacterium's ability to avoid opsonization and cause systemic disease. Nontypable strains cause disease by local invasion of mucosal surfaces. Otitis media results when bacteria reach the middle ear by way of the eustachian tube. Adults with chronic bronchitis experience recurrent lower respiratory tract infection due to nontypable strains. In addition, persistent nontypable H. influenzae colonization of the lower airways of adults with chronic obstructive pulmonary. | Chapter 139. Haemophilus Infections Kỳ 2 Pathogenesis Hib strains cause systemic disease by invasion and hematogenous spread from the respiratory tract to distant sites such as the meninges bones and joints. The type b polysaccharide capsule is an important virulence factor affecting the bacterium s ability to avoid opsonization and cause systemic disease. Nontypable strains cause disease by local invasion of mucosal surfaces. Otitis media results when bacteria reach the middle ear by way of the eustachian tube. Adults with chronic bronchitis experience recurrent lower respiratory tract infection due to nontypable strains. In addition persistent nontypable H. influenzae colonization of the lower airways of adults with chronic obstructive pulmonary disease COPD contributes to the airway inflammation that is a hallmark of the disease. The incidence of invasive disease caused by nontypable strains is low. Immune Response Antibody to the capsule is important in protection from infection by Hib strains. The level of maternally acquired serum antibody to the capsular polysaccharide which is a polymer of polyribitol ribose phosphate PRP declines from birth to 6 months of age and in the absence of vaccination remains low until 2 or 3 years of age. The age at the antibody nadir correlates with that of the peak incidence of type b disease. Antibody to PRP then appears partly as a result of exposure to Hib or cross-reacting antigens. Systemic Hib disease is unusual after the age of 6 years because of the presence of protective antibody. Vaccines in which PRP is conjugated to protein carrier molecules have been developed and are now used widely. These vaccines generate an antibody response to PRP in infants and effectively prevent invasive infections in infants and children. Since nontypable strains lack a capsule the immune response to infection is directed at noncapsular antigens. These antigens have generated considerable interest as immune targets and potential vaccine .

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