thesis
Host-pathogen interaction during Streptococcus pneumoniae colonization and infection
- Publication date
- 2 June 2004
- Publisher
- __Abstract__
Streptococcus pneumoniae was discovered by Sternberg and Pasteur in 1880. It took
another six years to discover that this microorganism, called the pneumococcus, was the
actual cause of bacterial pneumonia . Subsequently, this bacterium has been shown to
provoke an impressive number of diseases, which can be roughly classified in respiratory
and invasive. Respiratory diseases by S. pneumoniae are sinusitis, otitis media, bronchitis
and pneumonia, of which the latter one may be complicated by septicemia . Disseminated
invasive infections caused by the pneumococcus include sepsis, meningitis, endocarditis
and arthritis. Morbidity and mortality are high both in the developing and the developed
world: annually 3 million people die worldwide of pneumococcal infections. Approximately 1
million are children under the age of five years . Risk groups for pneumococcal disease are
children younger than 2 years, elderly people and immunocompromised patients . In
children, the increased risk for pneumococcal infections is mainly due to a relatively
immature immune response to type II T-cell independent (TI-2) antigens such as capsular
polysaccharides . In the elderly, the ability of both the innate as well as the adaptive
immunity to respond to pneumococcal infection are thought to decline . In addition, higher
rates of pneumococcal invasive diseases have been observed among populations such as
Alaskan Natives, American Indians and African Americans . Patient groups who are at risk
for particular variants of pneumococcal diseases are well defined. For example functional
asplenia as in sickle cell disease as well as anatomic asplenia are serious risk factors for
pneumococcal sepsis. This is due to the absence or dysfunction of the spleen, which is
involved in systemic clearance of S. pneumoniae. In addition, complement deficiency and
lower levels of circulating antibodies are thought to contribute to the increased susceptibility
to pneumococcal infections in patients with sickle cell disease and other
haemoglobinopathies . A relatively new risk group for pneumococcal meningitis are children
with a cochlear implantation . Disease in these patients is thought to occur by the presence
of a continuum between the outer ear and the inner skull. In general, patients with
cerebrospinal fluid leakage, immunodeficiencies, chronic cardiovascular and pulmonary
disease, HIV infections and diabetes mellitus are considered at risk for pneumococcal
invasive disease.