Pertussis - what is it? plus Aetiology

Pertussis, also known as whooping cough, is a highly contagious disease caused by the bacterium Bordetella pertussis; it derived its name from the characteristic severe hacking cough followed by intake of breath that sounds like 'whoop'; a similar, milder disease is caused by B. parapertussis. Although many medical sources describe the whoop as "high-pitched," this is generally the case with infected babies and children only, not adults.

Characterization

After a two day incubation period, 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 an increase 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 and dehydration. 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. Other complications of the disease include pneumonia, encephalitis, pulmonary hypertension, and secondary bacterial superinfection.

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, who are at greatest risk of severe complications from pertussis.