ISOLATION OF BORDETELLA BRONCHISEPTICA IN CATS: CLINICAL AND EPIDEMIOLOGICAL EVALUATION

Pennisi M.G., Fera M.T.*, Masucci M., De Majo M., Carbone M.*

Department of Veterinary Medicine and Pharmacology, University of Messina, Italy.
*Institute of Microbiology, Faculty of Medicine and Surgery, University of Messina, Italy.

I.A.I.E.V. National Meeting, Palermo (Italy)

INTRODUCTION

Bordetella bronchiseptica, a Gram-negative, aerobic coccobacillus, has long been considered responsible for respiratory disease in many animal species: dogs (kennel cough), pigs (atrophic rhinitis), rabbits, rodents and primates.
Even though in the past the bacterium has been isolated both from healthy cats and from those with respiratory disease (Switzer et al., 1966; Fisk et al., 1973; Synder et al., 1973; Willoughby et al., 1991), it is not yet clear if it simply behaves like an opportunistic germ or if it can also act like a primary pathogen. Only in the last few years, through studies on experimental infection in pathogen free cats (free from feline Herpesvirus, Calicivirus and Clamydia psittaci), has it been possible to demonstrate the role of Bordetella bronchiseptica as a primary pathogen in the respiratory tract of cats (Jacobs et al., 1993; Coutts et al., 1996; Hoskins et al., 1998).
These findings have stimulated numerous studies in cats from which it has emerged that exposure to the bacterium is very common in these animals (McArdle et al., 1994 Hoskins et al., 1998 Jensen et al., 1998) and that the infection may proceed in an asymptomatic manner or may determine upper respiratory tract infections that are particularly severe in kittens, where frequently lethal pneumonia may occur (Willoughby et al., 1991; Jacobs et al., 1993, McArdle et al., 1994; Coutts et al., 1996; Welsh et al., 1996; Hoskins et al., 1998). Vaccination against Bordetella bronchiseptica, achieved using fimbrial antigens of the bacterium, seems to reduce the severity of the clinical symptoms and the duration of infection (Jacobs et al., 1993).
It is probable that an interspecies transmission of Bordetella bronchiseptica may occur from dogs to cats (Binns et al., 1999, Speakman et al., 1999). The risk of transmission to man has also been hypothesised, even though the majority of human infections has been associated with immunodeficiency and not consequent to documented contacts with animals (Speakman et al., 1999).
The results of an epidemiological study regarding the presence of Bordetella bronchiseptica in cats bred in Sicily (Pennisi et al., 1998) are reported in this paper in order to evaluate the existence of risk factors for infection.

MATERIALS AND METHODS

During the period October 1996 - October 1999, 162 cats bred in the provinces of Messina and Catania were tested: 66 males and 96 females; 42 aged < 1 year (range 1-10 months), 117 aged > 1 year (range 1-17 years), 3 of unknown age; 53 were pure-bred (51 Persian, 1 Norwegian Forest, 1 Russian Blue), and 109 were crossbreeds (89 unselected domestic cats, 13 Siamese crosses, 6 Persian crosses, 1 Persian crossed with Siamese).
Of the 162 cats examined, 137 belonged to 27 different groups while 25 were bred singularly. Of the 137 animals living in groups, 36 came from small catteries, (2-5 cats), 62 from medium catteries (6-20 cats) and 39 from large catteries (>20 cats).
While 116 cats were permanently house bound, 46 had free outdoor access.
Both the group of cats coming from catteries and that of cats bred individually had a heterogeneous state of health. Of animals bred in catteries, 61 had respiratory symptoms, 36 presented other non-respiratory symptoms, and 40 were asymptomatic. Of cats bred singularly, 10 had respiratory symptoms, 5 presented other non-respiratory symptoms, and 10 were asymptomatic. Acute or chronic respiratory symptoms were reported in 16 of the 27 catteries examined.
Medical history revealed past respiratory tract disease in 68 of the 162 cats examined, no respiratory tract disease in 67 cats, while in 27 subjects no relevant medical condition in the past was reported.
A pharyngeal swab was performed in all the cats examined which was then transported by Transystem/Amies and thus inoculated within two hours onto a selective medium (charcoal agar supplemented with 10% defibrinated horse blood and cefalexin at a concentration of 40 mg/ml). After 48 h of incubation at 37°C, the isolated bacteria were tested for oxidase production and those found positive were identified with the API 20 NE (Bio Merieux) system.
The data obtained were statistically analysed using the c2 test and by calculation of the linear correlation coefficient.

RESULTS

Bordetella bronchiseptica was isolated in 35 of the 162 samples examined, with an overall prevalence of 21.6%. Positive samples were found in 12 of the 26 catteries examined (46.2%).
No significant differences in the prevalence of the infection were observed between males (13/66=19.7%) and females (22/96=22.9%), while subjects aged less than 1 year, had a significantly higher prevalence (17/42=40.5%) with respect to those older than 1 year (18/117=15.4%) (c2=9.920; P=0.002). Even though pure-bred cats had a higher prevalence (27/109=24.8%) than crossbreeds (8/53=15.1%), the difference was not statistically significant.
Bordetella bronchiseptica was isolated in 34 (24.8%) of the 137 cats bred in catteries and only in 1 of the cats bred individually (4%), the difference was statistically significant (c2=4.250; P=0.039). The prevalence was directly correlated with the size of the group (r=0.87; P=0): 11.1% (4/36) in small catteries, 24.2% (15/62) in medium catteries, 38.5% (15/39) in large catteries. Significant differences were observed among the prevalences found in the three groups (c2= 7.529; P=0.023) and in particular between the small and the large catteries (c2=6.028; P=0.014).
No statistical differences were observed between the prevalence of house bound cats (26/116=22.4%) and that of cats with liberal outdoor access (9/37=24.3%).
Cats with respiratory symptoms had a prevalence of 25.3% (18/71), those with symptoms not pertaining to the respiratory tract had a prevalence of 24.4% (10/41), and asymptomatic cats had a 14.0% (7/50) rate of Bordetella isolation. Even though the highest prevalence was observed in cats with respiratory symptoms and the lowest in asymptomatic cats, there were no statistically significant differences among the three groups.
Isolation of Bordetella bronchiseptica was achieved in 22 (23.3%) of the 68 subjects with past respiratory disease and in only 9 (13.4%) of the 67 subjects without a history of respiratory disease. Between the two groups a significant statistical difference was observed (c2=5.802, P=0.016).
The prevalence of infection among cats coming from catteries in which respiratory problems had been reported was significantly higher (36/111=32.4%) than that found in cats belonging to catteries in which no such problems had been notified (1/17=5.9%) (c2= 3.847; P=0.05).

COMMENTS AND CONCLUSIONS

The results of this study confirm the diffusion of Bordetella bronchiseptica infection in cats bred in Italy with a prevalence (21.6% in individuals and 46.2% in catteries) higher than that reported in Great Britain (5-11% in individuals, 20% in catteries ) (Mc Ardle et al., 1994; Binns et al., 1999), Austria (21% of subjects living in large sized catteries) (Kosztolich et al., 1999) and in the United States (3.1% in individuals) (Hoskins et al., 1998).
The analysis of the data confirm (Binns et al.,1999) that the principal risk factors for infection are: young age of the cats (40.5% of positive subjects were aged less than 1 year old), community living (24.8% of positive subjects lived in catteries) and cramped conditions (38.5% of positive subjects came from large sized catteries). Cohabitation with a high number of subjects, apart from increasing the probability of horizontal contagion, is frequently associated with the presence of predisposing conditions (stress, inadequate hygienic conditions, insufficient ventilation etc.) and, according to Binns et al. (1999), makes possible an increase in virulence of the microorganism due to repeated passages in the host animal. In consideration of the validated role of Bordetella bronchiseptica as a primary pathogen of the respiratory tract in cats (Jacobs et al., 1993, Coutts et al., 1996, Bergman et al., 1997; Hoskins et al., 1998), it is not surprising that the animals with respiratory symptoms, and more so those with past history of respiratory disease, had a higher prevalence when compared to those clinically well and to those without any history of respiratory tract infections respectively. This latter finding underlines the risk that animals who have recovered from infection can act as healthy carriers, particularly important in the case of subjects living in groups or in reproductive females. In fact, the mother can become the principal source of infection for her kittens, also because of the fact that giving birth is stressful and can reactivate the elimination of the microorganism (Coutts et al., 1995). This study confirms that in young subjects there is a higher prevalence with respect to adults. The clinical implication of this behaviour is considerable because in the young respiratory infections are more severe and they are characterised by high a morbidity and mortality rate (Welsh et al., 1996).

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