Pertussis, also known as whooping cough, is a highly contagious disease caused by the bacterium Bordetella pertussis; it derived its name from a characteristic of severe hacking cough followed by a high-pitched intake of breath that sounds like "whoop"; a similar, milder disease is caused by B. parapertussis. Worldwide, there are 30–50 million pertussis cases and about 300,000 deaths per year. Despite generally high coverage with the DTP (Diphtheria, Tetanus, and Pertussis) or the DTaP (Diphtheria, Tetanus, and Pertussis -acellular) vaccines, pertussis remains to be one of the leading causes of vaccine-preventable deaths world-wide. Most deaths occur in young infants who are either unvaccinated or incompletely vaccinated; three doses of the vaccine are necessary for complete protection against pertussis. Ninety percent of all cases occur in the developing world.Pertussis was recognizably described as early as 1578 by Guillaume de Baillou (1538-1616), but earlier reports date back at least to the 12th century. B. pertussis was isolated in pure culture in 1906 by Jules Bordet and Octave Gengou, who also developed the first serology and vaccine. The complete B. pertussis genome of 4,086,186 base pairs was sequenced in 2002.
Signs and Symptoms
Pertussis in infants and young children is characterized initially by mild respiratory infection symptoms such as cough, sneezing, and runny nose (catarrhal stage). After one to two weeks, the cough changes character, with paroxysms of coughing followed by an inspiratory "whooping" sound (paroxysmal stage). Coughing fits may be followed by vomiting due to the sheer violence of the fit. In severe cases, the vomiting induced by coughing fits can lead to malnutrition. The fits that do occur on their own can also be triggered by yawning, stretching, laughing, or yelling. Coughing fits gradually diminish over one to two months during the convalescent stage.
Because neither vaccination nor infection confers long-term immunity, infection of adolescents and adults is also common. Most adults and adolescents who become infected with Bordetella pertussis have been vaccinated or infected years previously. When there is residual immunity from previous infection or immunization, symptoms may be milder, such as a prolonged cough without the other classic symptoms of pertussis. Nevertheless, infected adults and adolescents can transmit the bacteria to susceptible individuals. Adults and adolescent family members are the major source of transmission of the bacteria to unimmunized or partially immunized infants.
Causative Agent
Bordetella pertussis
Mode of Transmission
Adults and adolescents are the primary reservoir for pertussis. Pertussis is spread by contact with airborne discharges from the mucous membranes of infected people, who are most contagious during the catarrhal stage.
Diagnosis
The symptoms during the catarrhal stage are nonspecific, pertussis is usually not diagnosed until the appearance of the characteristic cough of the paroxysmal stage. Methods used in laboratory diagnosis include culturing of nasopharyngeal swabs on Bordet-Gengou medium, polymerase chain reaction (PCR), immunofluorescence (DFA), and serological methods. The bacteria can be recovered from the patient only during the first three weeks of illness, rendering culturing and DFA useless after this period, although PCR may have some limited usefulness for an additional three weeks. For most adults and adolescents, who often do not seek medical care until several weeks into their illness, serology is often used to determine whether antibody against pertussis toxin or another component of B. pertussis is present at high levels in the blood of the patient.
Incubation Period
The incubation period of pertussis is commonly seven to 10 days, with a range of 5-21 days.
Pathogenesis
For a detailed explanation on the pathogenesis of the disease, click here.
Pathophysiology
Bordetella pertussis is an aerobic, nonmotile, gram-negative coccobacillus that attaches to and multiplies on the respiratory epithelium, starting in the nasopharynx and ending primarily in the bronchi and bronchioles. Transmission is only human to human by means of exposure to aerosol droplets. The disease is highly contagious. Approximately 80-90% of susceptible individuals who are exposed develop the disease. Most cases occur in the late summer and early fall.
A mucopurulosanguineous exudate forms in the respiratory tract. This exudate compromises the small airways (especially those of infants) and predisposes the affected individual to atelectasis, cough, cyanosis, and pneumonia. The lung parenchyma and blood stream are not invaded; therefore, blood cultures are negative.
Prevention
DtaP vaccine or pertussis immunization (vaccine) starting in infancy helps protect children against this disease. During epidemics, health care providers or others at risk may be advised to receive a booster dose of the vaccine.
During epidemics, unimmunized children under the age of seven should be excused from school and public gatherings for 14 days after the last reported exposure and isolated from anyone known or suspected to be infected.
Cases of the disease are reported to public health officials by health care providers so that health warning announcements and other preventative measures can be taken. Pertussis is now recognized more often in adolescents and adults.
Pertussis immunization is not 100% effective and it slowly becomes less effective over the years. Individuals who have been immunized in the past may still develop infection, but it is usually atypical or very mild. Therefore, during epidemics, adolescents in school, health care workers, or other adults with high exposure risk should consider a booster immunization.
Treatment
Infants under 18 months of age require constant supervision because breathing may temporarily stop during coughing spells. Infants with severe cases should be hospitalized.
An oxygen tent with high humidity may be used. Intravenous fluid may be indicated if coughing spells are severe enough to prevent adequate oral fluid intake. Sedatives may be prescribed for young children.
Treatment with an effective antibiotic (erythromycin or azithromycin) shortens the infectious period but does not generally alter the outcome of the disease; however, when treatment is initiated during the catarrhal stage, symptoms may be less severe. Three macrolides, erythromycin, azithromycin and clarithromycin are used in the U.S. for treatment of pertussis; trimethoprim-sulfamethoxazole is generally used when a macrolide is ineffective or is contraindicated. Click here for a complete detail on the drugs.
Cough mixtures or expectorants and cough suppressants are usually not helpful and should not be used.
Complication
Complications of the disease include pneumonia, encephalitis, pulmonary hypertension, and secondary bacterial superinfection.
References
http://www.wikipedia.org
Provided the baseline information
http://www.vaccineinformation.org
Provided additional information on the subject.
http://www.textbookofbacteriology.net
Provided information on the Pathogenesis of the disease.
http://health.allrefer.com
Provided additional information, and used as cross reference.
http://www.emedicine.com
Provided articles and drug information written by certified doctors.
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