Bordetella is shed in oral and nasal secretions of infected cats [Speakmann et al 1999]. It is therefore likely that direct or indirect contact with such discharges is the main route of transmission, although no detailed studies have been carried out to confirm this. Some cats may shed higher levels of the Bb and therefore be more likely to transmit it to other animals. As with the FCV and FHV, overcrowding and poor management may predispose to infection and disease.
Environmental persistence of B. bronchiseptica is unknown. However, the mean environmental persistence of B. pertussis is greater than 10 days [Weather & Ewald, 2004], so it would seem likely that B. bronchiseptica would be equally hardy, therefore we presume that indirect transmission is possible. However, it is susceptible to common disinfectants.
In a large survey of pathogens associated with respiratory disease in 1724 cats from 218 multicat (five or more cats) households in nine European countries, Bb was detected by PCR in 5% of cats from households with disease and 1.3% of cats from households without disease [Helps et al 2005]. The larger the group of cats the more likely a cat was to be positive. The PCR used in this study will underestimate true prevalence since it was shown to be less sensitive than bacterial isolation [Helps et al 2005]. Seroprevalence rates in 1463 cats from the same study for which blood samples were also available were 61% and 41% respectively with rescue shelters and poor hygiene also being associated with increased seroprevalence.
In a convenience study using isolation from 740 cats, Bb was isolated from 19% of cats in rescue catteries, 13.5% of those in research colonies and 0% of household pets. There was also evidence for dogs with respiratory disease being a risk factor for feline infection and suggesting dog to cat transmission, a possibility supported by molecular data in one case study [Dawson et al 2000].
In experimental infections the organism has been isolated for 19 weeks post infection and also from post-parturient queens that were negative before parturition perhaps suggesting that the physiological stress of giving birth may reactivate a previously undetectable infection [Coutts et al 1996]. However, under these experimental conditions, kittens remained Bb-negative suggesting transmission from mother to kitten does not always occur.