Bordetella () is a genus of small (0.2 – 0.7 µm), Gram-negative, coccobacilli bacteria of the phylum Pseudomonadota. Bordetella species, with the exception of B. petrii, are obligate aerobes, as well as highly fastidious, or difficult to culture. All species can infect humans. The first three species to be described (B. pertussis, B. parapertussis, B. bronchiseptica); are sometimes referred to as the 'classical species'. Two of these (B. pertussis and B. bronchiseptica) are also motile. B. pertussis and occasionally B. parapertussis cause pertussis (whooping cough) in humans, and some B. parapertussis strains can colonise sheep. B. bronchiseptica rarely infects healthy humans, though disease in immunocompromised patients has been reported. B. bronchiseptica causes several diseases in other mammals, including kennel cough in dogs and atrophic rhinitis in pigs. Other members of the genus cause similar diseases in other mammals, and in birds (B. hinzii, B. avium). The genus Bordetella is named after Jules Bordet. Pathogenesis The three most common species of Bordetella are B. pertussis, B. parapertussis and B. bronchiseptica. These species are known to accumulate in the respiratory tracts of mammals. This is most commonly seen in human infants as a product of an illness known as whooping cough. The particular species responsible for this illness is B. pertussis, and can only be found in humans. Even with extensive vaccination research on B. pertussis, whooping cough is still considered endemic in many countries. Due to the fact B. pertussis is only found in humans and shows little genetic variation from the other Bordetella species, it is thought that it was derived from a common ancestor in recent years. B. parapertussis can affect both humans and other mammals, primarily sheep. Similar to B. pertussis, it causes whooping cough in babies. Yet, when strains found in sheep are isolated there is a strong distinction between those found in humans. This suggests that the varying strains of this species evolved independently of one another, the one found in humans and the one found in sheep. With this particular distinction it means that there is little to no transmission between the two reservoirs. The species B. bronchiseptica however has a broader host range, causing similar symptoms in a wide range of animals, while only occasionally affecting humans. These symptoms often manifest as chronic and asymptomatic respiratory infections. B. bronchiseptica is a small, coccoid shape sized at approximately 0.5 µm. It has peritrichous flagella that