Pneumococcal infection is one of the major causes of death in children in developing countries.  More than 1.2 million deaths are the result of infection by S. Pneumoniae, a gram-positive bacteria that colonizes in the nasopharynx areas of humans.   Worldwide, Pneumococcal infection is the major cause of mortality in children under 5, and accounts for 10-20% of all deaths in this age group.(1)  Infection by this bacterium is a major cause of both, pneumonia and meningitis.

Doctor examining child in
Vietnamese hospital (2)

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Disease
Pathogen
Pneumococcus is caused by the bacterium Streptococcus pneumoniae which colonizes in the nasopharynx area, specifically the nose and throat.  These gram positive bacteria are anaerobic organisms and typically are observed in pairs or in short chains.  The bacterial polysaccharide capsules are antigenic and induce a type specific antibody response which is protective.  These antibodies interact with complement components to opsonize pneumococci, which facilitates phagocytosis and clearance of the organism.(3)

An individual can carry the infection without showing any signs or symptoms of disease.  Pneumococci are common inhabitants of the respiratory tract and may be isolated from 5% to 70% of normal adults.  The immunologic mechanism that allows disease to occur in carriers is also not clearly understood; often, however, disease occurs when a predisposing condition or immunocompromised state exists.(3)

Transmission occurs from person to person through sneezing, coughing, or speaking closely.
 
 

Gram stain of the sputum: The lancet-shaped cocci exists in pairs, and short chains that stain Gram positive (violet) are characteristic of Streptococcus pneumoniae. (4) http://www.vh.org/Providers/TeachingFiles/PulmonaryCoreCurric /InvasivePneumonia/GramStain1.html

Symptoms
Symptoms of infection include fever, chills, headache, ear pain, cough, chest pain, disorientation, shortness of breath, stiff neck.  Infection by this pathogen can cause pneumonia, meningitis, ear infections, or bactermia (blood stream infection).(5)
 

Diagnosing
Currently no rapid, specific, or sensitive tool exists to diagnose infection, and this has made diagnosis difficult.  Children may carry the bacteria colonized without any signs and still be able to transmit it.   A definitive diagnosis of infection generally relies on isolation of the organism from blood or other normally sterile body fluids.  (6)

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Vaccines

Treatment
In developed countries, Pneumococcus infection can often be treated with antibiotics; however, increasingly resistant strains are emerging, including bacteria resistance to penicillin, cephalosporin, erythromycin, azithromycin, sulfama, and or bactrim.

Vaccines
Two major types of vaccines are currently available or under study.

Unconjugated Pneumococcal polysaccharide vaccines have been available for two decades.  However, their use has been limited, especially in developing countries, because these vaccines are not effective in children under 2 years of age.  Polysaccharide capsular antigens induce type-specific antibodies that enhance opsonization, phagocytosis, and the killing of pneumococci by leukocytes and other phagocytic cells.  After vaccination, an antigen specific antibody develops within 2-3 weeks, conferring protection to infection.  Bacterial capsular polysaccharides induce antibodies primarily by T cell independent mechanisms; therefore antibody response to most pneumococcoal capsular types is generally poor or inconsistent in children under age 2 whose immune systems are immature. Levels of Ab remain elevated for at least 5 years in healthy adults.(6)

The problem of poor immunogenicity in children under the age of 2 seems to have been solved by conjugating the polysaccharide to a protein antigen, which increases the antibody response and ensures an anamnestic response to subsequent exposure to the polysaccharide.  Several varieties of conjugated Pneumococcal vaccines are now in preclinicial, clinical, and efficacy studies.  These vaccines show high immunogenicity in children under 2 as well as in adults.  Several positive aspects of these new vaccines include: a three dose schedule (2, 4, 6 months) that is well tolerated, and a possible reduction in Pneumococcal colonization, which suggests that conjugate vaccines might induce herd immunity in unvaccinated children. (6)

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Issues

*Antibiotic Resistance
New strains are continually emerging in the developing world that are resistant to the available antibiotics.
*Administration
New vaccine is a three dose schedule
*Cost Effectiveness
New vaccine will be expensive for developing countries

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Additional Links

Bacterial Meningitis--Bio 160 Project
http://www.childrensvaccine.com/html/v_pnuemo_links.htm

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