| Epidemiology of Bordetella bronchiseptica infection in the cat |
 Summary of epidemiological findings:
Transmission of infection occurs between in-contact animals directly via intimate contact or by droplet infection. The organism does not survive for long periods outside the host and is readily killed by many common disinfectants and extremes of pH and temperature. However, in a heavily contaminated environment, particularly within infected mucus, survival may be long enough for indirect transmission to occur. |
| Large scale epidemiological studies |
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A large amount of information with regards to the epidemiology of the disease has emerged from surveys such as those of Binns et al (1999). In the breeding cattery animals there was a significant association of B. bronchiseptica infection with respiratory disease. McArdle et al (1994) showed similar results serologically in another Liverpool study. In this study the highest rates of exposure were seen in multi-cat households and rescue catteries (83-87%) whereas in private households containing 1-3 cats only 29% had been exposed at some time in the past. In a study of 162 cats in Italy Pennisi et al (1999) demonstrated an isolation rate of 38.5% in catteries with >20 cats, 24.8% in multi-cat households and 4% in single cat households. The findings of these studies and others (Pedersen 1988) suggest that feline B. bronchiseptica infection in the field can occur in all cats but is particularly associated with conditions of overcrowding and stress. |
| Studies on carrier cats and the effects of stress |
| Long-term asymptomatic carriage of B. bronchiseptica commonly occurs in cats (Coutts et al 1996) suggesting that it is an opportunistic pathogen as may be the case in other species. Disease is likely to be related to a variety of factors including stress caused by weaning, visiting catteries, travelling to cat exhibitions, overcrowding in catteries or poor hygiene. It may also be related to phase variation in virulence determinants seen in dogs and pigs. The importance of carrier cats is confirmed in experimental studies where recovered cats shed the organism for at least 19 weeks (Coutts et al 1996). In addition, the organism has been recovered post partum from clinically healthy, seropositive queens kept under barrier conditions that were not shedding before parturition suggesting that the stress of birth can induce shedding (Coutts et al 1996). Younger animals appear to be particularly vulnerable to the bacterium (Pennisi et al 1999), perhaps due to immuno-incompetence or due to the stress of weaning. Furthermore, infection seems more likely to predispose to more severe signs such as bronchopneumonia in these younger animals (Pedersen 1988). |
| Studies on transmission between cats and dogs |
 Another important finding from the Binns study (1999) was the strong positive association between the isolation of B. bronchiseptica from cats and the presence of dogs with recent respiratory tract disease in the same household. This suggests that the organism may be transmitted between dogs and cats. This hypothesis is supported by the finding that isolates from dogs and cats are either identical or similar (Binns et al 1998). Furthermore, Dawson et al (2000) reported an outbreak of coughing in two dogs in a private household, closely followed by similar signs in two in-contact cats. B. bronchiseptica isolates with similar PFGE profiles were obtained from all four animals, suggesting, first, that transmission had occurred between the species, and, second, that B. bronchiseptica was responsible for the respiratory signs seen in both species. |
| Summary of epidemiological findings |
| The implications of these epidemiological findings are as follows: B. bronchiseptica is widespread in the feline population but is probably usually carried asymptomatically. A variety of host and environmental factors, particularly involving stressful conditions and a young age, may result in opportunistic disease. Hence, disease is most frequently associated with cats kept in breeding catteries or research facilities but may also occur in household cats taken to cat exhibitions, boarded in catteries, living in multi-cat households or in the same household as a dog. During the stressful act of parturition, queens may pass B. bronchiseptica to their offspring, kittens obtained from breeding catteries and rescue shelters are, therefore, particularly at risk. This is particularly worrying given the increased likelihood of rapidly developing bronchopneumonia in kittens infected with B. bronchiseptica as compared to adults (Welsh 1996). |