Bordetella pertussis
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Pertussis Microchapters |
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Bordetella pertussis On the Web |
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American Roentgen Ray Society Images of Bordetella pertussis |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]
Overview
Bordetella pertussis is a Gram-negative, aerobic coccobacillus capsulate of the genus Bordetella, and the causative agent of pertussis or whooping cough. Unlike B. bronchiseptica, B. pertussis is not motile. Its virulence factors include pertussis toxin, filamentous hæmagglutinin, pertactin, fimbria, and tracheal cytotoxin. A zoonotic reservoir for B. pertussis does not appear to exist; humans are its only known host, which means universal vaccination could potentially eradicate the disease.[citation needed] The bacterium is spread by airborne droplets; its incubation period is 7 to 14 days.
Pertussis
Pertussis (or whooping cough) is an infection of the respiratory system characterized by a “whooping” sound when the person breathes in. In the US, it killed between 10,000 and 20,000 people per year before a vaccine was available. Vaccination has transformed this; between 1985 and 1988, fewer than 100 children died from pertussis. Worldwide in 2000, according to the WHO, around 39 million people were infected annually and about 297,000 died. A graph is available showing the dramatic effect of introducing vaccination in England.[1] B. pertussis infects its host by colonizing lung epithelial cells. The bacterium contains a surface protein, filamentous haemagglutinin adhesin, which binds to the sulfatides found on cilia of epithelial cells. Once anchored, the bacterium produces tracheal cytotoxin, which stops the cilia from beating. This prevents the cilia from clearing debris from the lungs, so the body responds by sending the host into a coughing fit. These coughs expel some bacteria into the air, which are free to infect other hosts.
B. pertussis has the ability to inhibit the function of the host's immune system. The toxin, known as pertussis toxin (or PTx), inhibits G protein coupling that regulates an adenylate cyclase-mediated conversion of ATP to cyclic AMP. The end result is phagocytes convert too much ATP to cyclic AMP, which can cause disturbances in cellular signaling mechanisms, and prevent phagocytes from correctly responding to an infection. PTx, formerly known as lymphocytosis-promoting factor, causes a decrease in the entry of lymphocytes into lymph nodes, which can lead to a condition known as lymphocytosis, with a complete lymphocyte count of over 4000/μl in adults or over 8000/μl in children.
The infection occurs mostly in children under the age of one when they are unimmunized, or children with faded immunity, normally around the ages 11 through 18. The signs and symptoms are similar to a common cold: runny nose, sneezing, mild cough, and low-grade fever. The patient becomes most contagious during the catarrhal stage of infection, normally two weeks after the coughing begins. It may become airborne when the person coughs, sneezes, or laughs. Pertussis vaccine is part of the diphtheria, tetanus, and acellular pertussis (DTaP) immunization. The paroxysmal cough precedes a crowing inspiratory sound characteristic of pertussis. After a spell, the patient might make a “whooping” sound when breathing in, or may vomit. Adults have milder symptoms, such as prolonged coughing without the “whoop”. Infants less than six months also may not have the typical whoop. A coughing spell may last a minute or more, producing cyanosis, apnoea, and seizures. However, when not in a coughing fit, the patient does not experience trouble breathing. This is because B. pertussis inhibits the immune response, so very little mucus is generated in the lungs. A prolonged cough may be irritating and sometimes a disabling cough may go undiagnosed in adults for many months.
References
- ↑ "Whooping Cough (Pertussis)". HPA. Retrieved 2009-04-12.
- Ray, C.G., ed. (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9.
- Todar, K. (2008). "Bordetella pertussis and Whooping Cough". Online Textbook of Bacteriology. Retrieved December 11, 2009.