Before that they emerged from small-scale farming. “Whooping cough comes from pigs as does flu as well as from birds; our friend the cow alone is responsible for measles, tuberculosis and smallpox” [1]. Proximity, to humans and animals, drives disease.
B. pertussis “evolved from Bordetella bronchiseptica or a B. bronchiseptica-like ancestor… B. bronchiseptica infects a broad range of mammals, including humans, and although it can cause overt disease such as kennel cough in dogs and atrophic rhinitis in pig” [1].
The San Francisco Chronicle, December 17, 1979, p. 5 reported a claim by the Church of Scientology that the CIA conducted an open-air biological warfare experiment in 1955 near Tampa, Florida, and elsewhere in Florida with whooping cough bacteria. It was alleged that the experiment tripled the whooping cough infections in Florida to over one-thousand cases and caused whooping cough deaths in the state to increase from one to 12 over the previous year. This claim has been cited in a number of later sources, although these added no further supporting evidence.[52][53]