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Bordetella
ORGANISM:
- Genus: Bordetella
- Species: pertussis, parapertussis, bronchiseptica
GENERAL CONCEPTS:
- The genus Bordetella is responsible for respiratory disease in humans and animals. B. pertussis, in particular, is the etiologic agent of pertussis, more commonly known as whooping cough. B. parapertussis causes a milder form of pertussis, while B. bronchiseptica mostly affects animals but occasionally humans.
- Bordetella cause disease by producing toxins that impair ciliary function in the respiratory tract.
DISTINCTIVE PROPERTIES:
- Bordetella are Gram negative coccobacilli. They produce a capsule and are strict aerobes. Only B. bronchiseptica is motile.
- Bordetella possess the heat stable endotoxin LPS and produce several exotoxins. These include:
- Pertussigen: A 120 kD protein exhibiting the A-B model for toxin activity. Pertussigen is an ADP-ribosyl-transferase that interferes with the transfer of signals from cell surface receptors. Pertussigen is also involved in mediating attachment to respiratory epithelia.
- Adenylate cyclase toxin: this toxin increases cAMP levels, inhibiting immune effector cell functions.
- Tracheal cytotoxin: This toxin causes ciliostasis and extrusion of ciliated epithelia.
- Dermonecrotic toxin: This heat labile substance causes tissue destruction.
- Filamentous hemagglutinin: This is involved in attachment to host cells.
PATHOGENESIS:
- Whooping cough results from colonization and multiplication of Bordetella pertussis on the mucus membranes of the respiratory tract, in particular, the ciliated epithelial cells.
- Production of toxins irritates cells causing ciliostasis and leukocytosis.
- The hallmark of pertussis is the spasmatic cough that may last 6 weeks. Occasional secondary complications include encephalopathy, seizures and pneumonia.
HOST DEFENSES:
- Antibody against the pertussigen exotoxin affords immunity.
EPIDEMIOLOGY:
- The mucus membranes of the respiratory tract are the organism's natural habitat.
- Disease generally follows direct contact with an infected person.
- Pertussis is generally a disease of infants (50% of cases occur in children less than 1 year old).
- The disease is highly contagious.
DIAGNOSIS:
- Clinical: Whooping cough requires a 7-14 day asymptomatic incubation period. This is followed by the catarrhal stage, which lasts 1-2 weeks. Symptoms include fever, rhinorrhea and a highly infectious cough. The next 2-4 weeks define the paroxysmal phase, during which the spasmatic ("whooping") cough is observed. Vomiting and leukocytosis (> 100,000 lymphocytes/mm3) are also evident. Finally, the convalescent phase marks the end of disease and may last 3-4 weeks or longer. During this period, secondary complications may occur.
- Laboratory: The organisms can be grown on Bordet-Gengou agar media after 3-4 days incubation. Immunological techniques may also be employed.
CONTROL:
- Sanitary: This very contagious disease requires quarantine for a period of 4-6 weeks.
- Immunological: Pertussis vaccine is a part of the required "DPT" schedule.
- Chemotherapeutic: Antibiotic prophylaxis (erythromycin) may be used for contacts. Treatment of disease with antibiotics does not affect its course.
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