Whooping cough (pertussis) was originally an infection of ducks that only passed to humans after these birds were domesticated many thousands of years ago. It is now a preventable bacterial infection of the respiratory tract that may be very serious in children.
A much milder form of the disease (parapertussis) is also known, against which the pertussis vaccine gives no protection. The cause is the bacterium Bordetella pertussis, which is widespread in the community.
In adults an infection merely has the symptoms of a cold, but in young children the disease is more severe, and spreads from person to person in the microscopic droplets exhaled or coughed out in the breath of a patient, so an adult with minimal symptoms may carry the disease from one infant to another.
The incubation period is one to two weeks. It starts in a child as a cold that lasts a week or two, but then the cough becomes steadily more severe and occurs in increasingly distressing spasms, characterised by a sudden intake of breath before each cough. Coughing spasms may last up to 30 minutes, and leave the child exhausted, then another spasm starts after only a few minutes.
As the infection worsens, the child may become blue, lose consciousness, and thick stringy mucus is coughed up and vomited. The patient has no appetite and rapidly loses weight. Severe coughing may cause bleeding in the lungs, throat and nose, that may be severe enough to cause suffocation.
If the child survives, the spasms start to ease after a few weeks, but mild recurrences may occur for months. Permanent lung damage is also possible.