- Bordetella bronchiseptica infection in cats
- Bacterial properties
- Epidemiology: the larger the group, the higher the prevalence
- Passive immunity
- Active immune response
- Clinical signs: a range of respiratory signs
- Bacterial culture
- Disease management
- General recommendations on vaccination: only if a history of disease
- Primary vaccination course
- Booster vaccinations
- Disease control in specific situations
- Breeding catteries
- Vaccination of immunocompromised cats
Bordetella bronchiseptica infection in cats
Edited October 8, 2015
• Bordetella bronchiseptica (Bb) is a primary pathogen of domestic cats,
• Zoonotic infections have been incidentally recorded in the literature.
• The bacterium is shed in oral and nasal secretions of infected cats.
• The bacterium is susceptible to common disinfectants.
• Dogs with respiratory disease are a risk for cats.
• Bb colonises the ciliated epithelium of the respiratory tract of the host.
• A wide range of respiratory signs has been associated with Bb infection, from a mild
one to severe pneumonia with dyspnoea, cyanosis and death.
• Where sensitivity data are unavailable, tetracyclines are recommended, since most
feline Bb isolates have been found susceptible.
• In some European countries an intranasal modified live vaccine is available.
Bordetella bronchiseptica (Bb) is a primary pathogen of domestic cats, particularly in high population density conditions such as rescue shelters and multicat households.
Bordetella pertussis, Bordetella parapertussis and Bb are closely-related Gram-negative coccobacilli that colonise the respiratory tracts of mammals. B. pertussis is a strictly human pathogen and the primary aetiologic agent of whooping cough, which can also be caused by B. parapertussis. Being the least host-restricted member of this taxonomic cluster, Bb causes chronic respiratory infections in cats, dogs, rabbits, pigs and humans. Sequence analysis has shown that B. parapertussis and B. pertussis are independent derivatives of Bb-like ancestors.
During their evolution, there was large-scale gene loss and inactivation; host adaptation seems to be a consequence of loss, not gain, of function, and differences in virulence may be related to loss of regulatory or control functions(Parkhill et al., 2003).
Because of its role as a human pathogen, Bb is becoming more and more important (Woolfrey & Moody, 1991; Bauwens et al., 1992). Most cases occur in immunocompromised patients, without clear evidence for exposure to animals. Zoonotic infections have been incidentally recorded in the literature: a possible human infection from a rabbit, infections in paediatric lung transplant recipients, where dogs had been suspected as the origin of infection, and cases in immune compromised humans were cats were suspected as source of the infection (Gueirard et al., 1995; Ner et al., 2003; Redelman-Sidi et al., 2011; Wernli et al. 20011). It is sensible therefore to consider Bb as a rare potential cause of zoonotic infections.
Epidemiology: the larger the group, the higher the prevalence
The bacterium is shed in oral and nasal secretions of infected cats (Speakman et al., 1999).
Direct and indirect contacts with such discharges are probably responsible for Bb transmission, although this has not been experimentally confirmed. As with feline calicivirus (FCV) and feline herpesvirus (FHV), overcrowding and poor management predispose to infection and disease.
The physicochemical stability of Bb is unknown. The mean environmental persistence of B. pertussis is longer than 10 days, and Bb probably is equally hardy, so indirect transmission must be assumed (Walther & Ewald, 2004). The bacterium is susceptible to common disinfectants.
In a large survey of pathogens associated with respiratory disease in multicat (≥5) households in nine European countries, Bb was detected by PCR in 5 % of cats from households with disease and in 1.3 % without disease. The larger the group, the more likely a cat was to be found positive. PCR will have underestimated the true prevalence since it was found to be less sensitive than bacterial culture. Seroprevalence was 61 % and 41 %, respectively, and the poor hygiene in rescue shelters was also associated with higher seroprevalence (Helps et al., 2005).
In a cross-sectional survey of a convenience sample (740 cats), Bb was isolated from 19 % of the cats in rescue catteries, from 13.5 % in research colonies and not at all from household pets (Binns et al., 1999). In a study of clinical field cases of cats with URTD Bb was isolated from only 0,4% of 460 samples (Adler 2007). In another survey 3 out of 52 cats with acute respiratory symptoms living in a shelter were shown to be Bb positive (Veir et al. 2008). Dogs with respiratory disease are a risk factor for cats; the suggestion of dog-to-cat transmission of Bb was supported by molecular data (Dawson et al., 2000).
After experimental infection, the organism has been isolated for 19 weeks. It was also cultured from post-parturient queens that had been negative previously. Under these conditions, the kittens remained Bb-negative and did not seroconvert (Coutts et al, 1996).
Bb is a primary pathogen for cats. Respiratory disease has been reproduced in specific pathogen free cats after aerosol and nasal challenge, and field cases associated with Bb have also been reported. (Figs. 1 and 2; Coutts et al., 1996; Jacobs et al., 1993; Willoughby et al., 1991; Welsh, 1996). However, in the field, additional factors may be involved in disease development, including environmental conditions leading to stress (e.g. overcrowding), or pre-existing viral
Little information exists about the pathogenicity of Bb in the cat, and much has to be inferred from infections in other species. Features responsible for Bb acting as a primary pathogen in the feline respiratory tract are its motility (propulsion by flagella), the presence of adhesins and toxin production.
This microorganism colonises the ciliated epithelium of the respiratory tract of the host, establishing chronic infections. Bordetellae have evolved mechanisms, some of them shared, that allow them to colonise this site, a surface designed to eliminate foreign particles (Mattoo et al., 2001). These include adhesins such as filamentous hemagglutinin, fimbriae and periactin. Fimbriae are required for efficient and persistent colonisation of the trachea. They also play an important role in the development of humoral immunity to Bordetella infection (Mattoo et al., 2000). Once attached, toxins and Bb-specific secreted proteins result in ciliostasis and destruction of the cilia.
Antibodies play an important role in the immune response to Bb and bacterial clearance.
Little information is available on the transmission of maternally derived antibodies (MDA) to kittens. In one study of kittens born to Bb positive queens, MDA remained low and were only detectable for 2 weeks (Coutts et al., 1996). In another study, low levels of MDA remained detectable for 8 weeks but were not assayed for longer (Jacobs et al., 1993).
Active immune response
After Bb infection, serum antibodies rise rapidly, but it is unknown for how long they persist (Coutts et al., 1996). Immunoglobulin A (IgA) is the main class in mucosal secretions.
Individuals deficient in IgA are more susceptible to certain sinopulmonary infections (Renegar et al., 2004). In mice it was shown that IgA is also essential for controlling Bb in the upper respiratory tract. Transfer of IgA-containing convalescent serum effectively reduced Bb numbers in the trachea; they cleared only Bb, not the human Bordetella pathogens (Wolfe et al., 2007).
Clinical signs: a range of respiratory signs
Experimental infection of specific pathogen free cats induced mild clinical signs consisting of fever, coughing, sneezing, ocular discharge and lymphadenopathy, which resolved after about 10 days (Coutts et al., 1996: Jacobs et al., 1993).
In the field, a wide range of respiratory signs has been associated with Bb infection, from the mild ones described above to severe pneumonia with dyspnoea, cyanosis and death (Speakman et al., 1999; Willoughby et al., 1991; Welsh, 1996). Pneumonia is usually seen in kittens of less than 10 weeks, but older cats can be affected as well (Fig. 3). Bb infection should be considered in coughing cats (acute and chronic).
Both bacterial culture (isolation) and PCR are available, but both methods suffer from a lack of sensitivity. Samples for isolation can be obtained from the oropharynx (swabs), nasal cavity or through transtracheal wash/broncheo-alveolar lavage. In one study nasal swabs were shown to more often positive then oropharyngeal swabs, suggesting that for Bb isolation a nasal swab is preferred. (Veir et al. 2008). Cytological analysis of tracheal washes demonstrate polymorphonuclear leucocytes, macrophages and bacteria (Welsh, 1996).
For isolation, swabs should be placed into charcoal (or regular) Amies transport medium. Bb should be cultured on a selective medium such as charcoal/cephalexin agar, which reduces overgrowth by other respiratory flora. The identification of Bb form bronchoalveolar lavage samples of cats with lower respiratory signs is considered to be diagnostic. The significance of Bordetella in oropharyngeal swabs from cats with predominantly upper respiratory clinical signs is less clear-cut, but will usually be considered as an indication for antibiotic treatment.
In cats from multicat households and other crowded environments, the prevalence of Bb infection is higher and the bacterium may simply be present co-incidentally; other causes for the presenting clinical signs must then be considered.
Sensitive real-time PCR methods are capable of discriminating between different Bordetellae and can detect less than 10 genome copies of Bb/µl (Koidl et al., 2007). Some laboratories have developed multiplex assays that allow the simultaneous detection of all common feline respiratory pathogens. Unfortunately, such assays are often less sensitive (Helps et al., 2005).
Serology is of limited diagnostic use due to the high seroprevalence in the general cat population.
Antibacterial therapy may be indicated, even when the signs are mild, because Bb might progress to colonize the lower respiratory tract. Therapy should be based on the results of antibiotic susceptibility testing. In a study with 42 canine/feline Bb strains, a considerable number of strains were shown to be resistant or exhibited high MIC values against a number of bacterial agents (Schwarz et al., 2007) Where sensitivity data are unavailable, tetracyclines are recommended, since most feline Bb isolates have been found susceptible. Doxycycline is the antimicrobial of choice. Feline Bb isolates are less susceptible to clavulanate-potentiated amoxycillin, and resistance has often been detected to ampicillin and trimethoprim (Speakman et al., 1997; EBM grade III). Whilst antimicrobial therapy should help to alleviate clinical signs, short courses of antibiotic treatment in recovered carrier cats has little effect on shedding (Coutts et al., 1996).
Cats severely affected by Bb require supportive therapy and intensive nursing care. The resolution of dehydration and restoration of electrolyte and acid-base disturbances preferably by intravenous fluid administration may be required.
General recommendations on vaccination: only if a history of disease
In some European countries an intranasal modified live vaccine is available. Bb vaccines containing viable bacteria should never be administered to kittens less than 4 weeks of age. In addition, they are ineffective in cats on, or due to receive, antibiotics. Cats receiving live vaccines will shed bacteria and must be avoided where an owner is known to be immunocompromised. As in dogs, these vaccines may occasionally induce mild clinical signs in cats.
Primary vaccination course
The ABCD does not recommend routine vaccination against Bb (non-core), since the infection generally causes only mild disease. Vaccination should be limited to cats living in or moving into high-density populations with a history of Bb disease and should be performed according to the manufacturer’s recommendations.
The modified live vaccine is licensed for use as a single vaccination with annual boosters. Duration of immunity of at least a year has been demonstrated (Williams et al., 2002).
Boosters should be continued as long as the cat remains in the high-risk situation.
Disease control in specific situations
Control of Bb in cat populations is aimed at minimising the exposure of naïve cats. Stocking densities may need to be reduced and the environment cleaned and disinfected to minimize the risk of transmission. Otherwise, the measures advocated for the control of other common respiratory pathogens such as FCV and FHV in groups of cats will help control infection and disease.
Random source populations with largely unknown vaccination histories, continuous resident turnover, and high risk for infectious disease characterize most shelters. In these, Bb vaccination is encouraged, particularly if there is a history of microbiologically confirmed disease.
The vaccination schedules used for privately owned cats are appropriate for most breeding catteries. Again, Bb vaccination should only be encouraged where this organism has been confirmed to be associated with disease.
Vaccination of immunocompromised cats
Vaccination of immunocompromised cats is not recommended.
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