Illustration of whooping cough bacteria (yellow rods) and mucus in a lung. Whooping cough, also known as pertussis or the 100-day cough, is a highly contagious disease caused by the bacterium Bordetella pertussis. Once anchored, the bacterium releases a cytotoxin that paralyses the cilia (hair-like), stopping them from beating properly to clear mucus and debris. The body reacts to the build-up of mucus and debris by inducing violent coughing, which expels the bacteria into the air, heightening the chance of infecting others.