Cause
Pertussis is caused by the bacterium Bordetella pertussis. It is an airborne disease (through droplets) that spreads easily through the coughs and sneezes of an infected person. Spread from animals
Uncertainties have existed of B. pertussis and whooping cough as a zoonotic disease since around 1910, but in the 1930s knowledge was gained that the bacteria lost their virulent power when repeatedly spread on agar media. This explained the difficulties to reproduce results from different studies as the pre-inoculating handlings of the bacteria were not standardized among scientists.Today it is established that at least some primate species are highly susceptible to B. pertussis and develop clinical whooping cough in high incidence when exposed to low inoculation doses. The bacteria may be present in wild animal populations, but this is not confirmed by laboratory diagnosis, although whooping cough is known among wild gorillas. Several zoos also have a long-standing custom of vaccinating their primates against whooping cough. Mechanism
After the bacteria are inhaled, they initially adhere to the ciliated epithelium in the nasopharynx. Surface proteins of B. pertussis, including filamentous hemaglutinin and pertactin, mediate attachment to the epithelium. The bacteria then multiply. In infants, who experience more severe disease, the bacteria spread down to the lungs.The bacteria secretes a number of toxins. Tracheal cytotoxin, a fragment of peptidoglycan, kills ciliated epithelial cells and thereby inhibits the mucociliary elevator by which mucus and debris are removed. TCT may contribute to the cough characteristic of pertussis. The cough may also be caused by a yet-to-be identified "cough toxin".
Another estimated 195,000 child deaths yearly from the disease worldwide. This is despite generally high coverage with the DTP and DTaP vaccines. Pertussis is one of the leading causes of vaccine-preventable deaths worldwide. About 90% of all cases occur in developing countries.Before vaccines, an average of 178,171 cases was reported in the U.S., with peaks reported every two to five years; more than 93% of reported cases occurred in children under 10 years of age. The actual incidence was likely much higher. After vaccinations were introduced in the 1940s, pertussis incidence fell dramatically to approximately 1,000 by 1976. Incidence rates have increased since 1980. In 2015, 20,762 people were reported to have been infected in the United States.Pertussis is the only vaccine-preventable disease that is associated with increasing deaths in the U.S. The number of deaths increased from four in 1996 to 17 in 2001, almost all of which were infants under one year. In Canada, the number of pertussis infections has varied between 2,000 and 10,000 reported cases each year over the last ten years, and it is the most common vaccine-preventable illness in Toronto.In 2009 Australia reported an average of 10,000 cases a year, and the number of cases had increased. In the U.S. pertussis in adults has increased significantly since about 2004.In 2017, India had a reported 23,766 reported pertussis cases, making it one of the highest reported number of cases of the year.