Bordetella bronchiseptica infection in cats

 

Updated June 2022

 

These Guidelines were first published by Herman Egberink et al. in Journal of Feline Medicine and Surgery 11 (7), 2009, 610-614. This update has been compiled by Herman Egberink.

 

Key points

 

  • Bordetella bronchiseptica (Bb) is a primary pathogen of cats.
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  • The bacterium is shed in oral and nasal secretions of infected cats.
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  • The bacterium is susceptible to common disinfectants.
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  • Cats can catch Bb infection from dogs with kennel cough.
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  • Bb colonises the ciliated epithelium of the respiratory tract of the host.
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  • A wide range of respiratory signs has been associated with Bb infection, from mild upper respiratory signs to those of severe pneumonia with dyspnoea, cyanosis and potentially death, especially in young kittens.
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  • When sensitivity data are unavailable, tetracycline antibiotics are recommended, since most feline Bb isolates are susceptible.
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  • In some European countries an intranasal modified live vaccine is available.
  •  

  • Zoonotic infections have been incidentally recorded in the literature.

 

Agent properties

 

Bordetella bronchiseptica (Bb) is a primary respiratory pathogen of cats, particularly in high population density conditions such as rescue shelters and multicat households.

 

Bordetella (B.) pertussis, B. 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 a human lineage of B. parapertussis. Being the least host-restricted member of this taxonomic cluster, Bb can cause chronic respiratory infections in cats, dogs, rabbits, pigs and rarely 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 could be related to loss of regulatory or control functions (Parkhill et al., 2003).

 

Epidemiology

 

Prevalence

 

Infection with Bb is widespread in the cat population as evidenced by the high level of seroprevalence and isolation rates from cats with and without respiratory disease (Gaskell et al., 2011). The larger the group of cats is, the higher is the prevalence of Bb infections.

 

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 signs of respiratory disease and in 1.3 % of households in which no cat showed respiratory disease (Helps et al., 2005). The larger the group, the more likely a cat was to be found infected. PCR will have underestimated the true prevalence since in this study it was found to be less sensitive than bacterial culture. In a cross-sectional survey of a convenience sample (740 cats), Bb was isolated in 19 % of cats in rescue catteries, in 13.5 % in research colonies and not at all in household pets (Binns et al., 1999). In a study of clinical field cases of cats with upper respiratory tract disease (URTD) Bb was isolated from only 0.4% of 460 samples (Adler et al., 2007). In another survey, only 3/52 cats with acute respiratory signs living in a shelter were shown to be Bb-culture positive (Veir et al., 2008). A similar low prevalence was determined in a more recent study in a shelter in which 4/82 cats with upper respiratory tract clinical signs were shown to be Bb culture positive (Walter et al., 2020).

 

Antibody prevalence was 61 % and 41 % in household with versus without respiratory signs, respectively. Poor hygiene in rescue shelters was associated with higher antibody prevalence (Helps et al., 2005). In another antibody prevalence study in multicat households, a significant difference was found in antibody prevalence between cats with and without clinical signs of URTD. Also, especially in animal shelters, the risk of being seropositive was shown to be high (Gaston et al., 2005).

 

Transmission

 

The bacterium is shed in oral and nasal secretions of infected cats (Speakman et al., 1999). After experimental infection, the organism was isolated in some cases for at least 19 weeks (Coutts et al., 1996).

 

Direct and indirect contacts with such secretions are probably mainly responsible for Bb transmission, although this has not been experimentally confirmed. As with other respiratory pathogens, such as feline calicivirus (FCV) and feline herpesvirus (FHV), overcrowding and poor management predispose to infection and disease.

 

Dogs with respiratory disease are a risk factor for cats; dog-to-cat transmission of Bb has been confirmed by molecular data (Dawson et al., 2000).

 

Bb was also cultured from post-parturient queens that had been culture-negative previously. Under these conditions, the kittens remained Bb antibody-negative (Coutts et al, 1996).

 

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 and Ewald, 2004). The bacterium is susceptible to common disinfectants.

 

Pathogenesis

 

Bb is a primary pathogen for cats. Respiratory disease has been reproduced in specific pathogen-free cats after aerosol and nasal challenge (Willoughby et al., 1991; Jacobs et al., 1993; Coutts et al., 1996; Welsh, 1996). Infections occur frequently in the field, but several factors are involved in disease development, including environmental conditions leading to stress (e.g. overcrowding) and/ or pre-existing viral infections.

 

Little information exists about the true pathogenicity of Bb as a single infection 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 (Gaskell et al., 2011).

 

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 Bb infection (Mattoo et al., 2000). Once attached, toxins and Bb-specific secreted proteins result in ciliostasis and destruction of the cilia.

 

Immunity

 

Antibodies play an important role in the immune response to Bb and bacterial clearance. Cats vaccinated with modified live intranasal FHV and FCV vaccines showed reduced clinical signs during the first ten days after Bb challenge infection. One study showed that a specific innate immunity could also be beneficial for short term protection (Bradley et al., 2012).

 

Passive immunity

 

Little information is available on the transmission of maternally derived antibodies (MDA) to kittens. In one study of kittens born to Bb antibody-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 infections of the paranasal sinuses and airways of the lung (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, but not human Bordetella pathogens (Wolfe et al., 2007).

 

Clinical 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 (Jacobs et al., 1993; Coutts et al., 1996).

 

In the field, a wide range of respiratory signs has been associated with Bb infection, from mild clinical signs, such as coughing, sneezing, ocular discharge, fever, and lymphadenopathy to severe pneumonia with dyspnoea, cyanosis and potentially death (Willoughby et al., 1991; Welsh, 1996; Speakman et al., 1999). Pneumonia is usually seen in kittens of less than 12 weeks, but older cats can be affected as well (Figs. 1, 2 and 3). Bb infection should be considered  as a differential in cats with acute and chronic cough.

 

Fig. 3. Bordetella bronchiseptica infection can sometimes lead to bronchopneumonia as a complication. Courtesy of Andy Sparkes, UK

Fig. 1. Pneumonia caused by Bordetella bronchiseptica infection. Courtesy of Andy Sparkes, UK

 

Fig. 1. Lungs of a kitten that had died of pneumonia. Bordetella bronchiseptica was isolated from the organ. Courtesy of Maria Grazia Pennisi, University of Messina, Italy

Fig. 2. Lungs of a kitten that had died of pneumonia. Bordetella bronchiseptica was isolated from the organ. Courtesy of Maria Grazia Pennisi, University of Messina, Italy

 

Fig. 2. Lungs section from a kitten that had died of pneumonia. Bordetella bronchiseptica was isolated from the organ. Courtesy of The Feline Centre, University of Bristol, UK

Fig. 3. Lungs section from a kitten that had died of pneumonia. Bordetella bronchiseptica was isolated from the organ. Courtesy of The Feline Centre, University of Bristol, UK

 

Diagnosis

 

In cats infected with Bb, cytological analysis of tracheal washes can demonstrate polymorphonuclear leucocytes, macrophages and bacteria (Welsh, 1996).

 

Direct detection of the infectious agent

 

For direct detection of the bacterium or bacterial DNA, both bacterial culture (isolation) and PCR are available. Samples for culture can be obtained from oropharyngeal swabs, nasal cavity swabs or broncheo-alveolar lavage samples. Transtracheal washes as a source for culture are also described in one study (Welsh, 1996). In one study, nasal swabs were shown to be more often culture-positive than oropharyngeal swabs, suggesting that for Bb isolation nasal swab is preferred over an oropharyngeal swab (Veir et al. 2008). However, the significance of Bb in nasal, oropharyngeal, or nasopharyngeal swabs is questionable as it may not represent a primary pathogen but rather be opportunistic here instead.

 

Bacterial culture

For bacterial culture (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 bacteria. If Bb is identified from bronchoalveolar lavage samples of cats with lower respiratory signs an etiological role is assumed. The significance of Bordetella in oropharyngeal swabs from cats with predominantly upper respiratory clinical signs is less clear, as outlined above; it may be that antibiotic treatment is indicated if no other underlying causes are found.

 

In cats from multicat households and other crowded environments, the prevalence of Bb infection is higher than in other conditions and the bacterium is often present co-incidentally in the upper respiratory tract (Gaskell et al., 2011); other causes for the presenting clinical signs must then be considered (Gaston et al., 2005).

 

PCR

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 several common feline respiratory pathogens. In one study, Bb (and FHV and Mycoplasma felis) was found more frequently using real-time PCR than bacterial culture (Litster et al., 2015), although differences were not significant due to the low number of samples included.

 

Indirect detection of the infectious agent

 

Antibody detection is of limited diagnostic use due to the high antibody prevalence in the general cat population (Gaskell et al., 2011).

 

Treatment

 

Antimicrobial treatment

 

Antibacterial therapy is indicated if Bb infection is considered the cause of clinical signs, even when the signs are mild, because Bb might progress to colonise the lower respiratory tract. Therapy should be based on the results of antibiotic susceptibility testing. In a study with 42 canine or feline Bb strains, a considerable number of strains were shown to be resistant or exhibited high minimum inhibitory concentration (MIC) values against a number of antibacterial agents (Schwarz et al., 2007). Where sensitivity data are unavailable, doxycycline is recommended as the antimicrobial of choice, since most feline Bb isolates are susceptible. Oral doxycycline (5 mg/kg q12h or 10 mg/kg q 24h) for 7-10 days is recommended as a first line treatment in the ISCAID guidelines (Lappin et al., 2017). Different formulations of doxycycline exist but it should be noted that doxycycline hydrate tablets can cause oesophagitis if incompletely swallowed, so dosing of this formulation, if used, should be followed by food and/or water to encourage complete swallowing and passage of the tablet into the stomach.

 

Feline Bb isolates have low susceptibility to clavulanate-potentiated amoxycillin, and resistance has often been detected to ampicillin and trimethoprim (Speakman et al., 1997). Whilst antimicrobial therapy should help to alleviate clinical signs, antibiotic treatment in recovered carrier cats has little effect on shedding (Coutts et al., 1996).

 

Symptomatic treatment

 

Cats severely affected by Bb infection require additional supportive therapy and intensive nursing care. The resolution of dehydration and restoration of electrolyte and acid-base disturbances preferably by intravenous fluid administration can be needed for cats with severe clinical signs. With severe lower respiratory disease and dyspnoea, oxygen therapy should be considered.

 

If the cats do not eat, appetite stimulants (e.g. mirtazapine; 1.88-2 mg/cat PO, q24h if renal and hepatic function is not compromised) can be indicated. Alternatively, commercial fluid high-energy diets can be used for hand feeding. If the cat is not eating for more than three days, placement of a feeding tube and enteral nutrition is indicated.

 

In cats with pneumonia, nebulization can help to rehydrate the upper respiratory tract, loosen secretions, reduce congestion and increase comfort. Cheap small nebulisers can be purchased for use in the veterinary clinic (or loaned to owners to use at home) for regular nebulization therapy with saline (q 4-6 hours if possible for 15 mins at a time). In the hospital setting this can be applied close to the cat’s face by placing the cat in an igloo and covering the exit and nebulizing inside the igloo. If a nebuliser is not available, an alternative is to provide steam therapy. Owners can do this at home by sitting with their cat with care in a bathroom with hot running water/shower. Drugs with mucolytic effects (e.g. bromhexine) may be helpful.

 

Vaccination

 

General recommendations on vaccination

 

In some European countries an intranasal modified live vaccine is available. 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 infections and should be performed according to the manufacturer’s recommendations.

 

Bb vaccines containing viable bacteria should never be administered to kittens less than 4 weeks of age as recommended by the manufacturer. In addition, they are ineffective in cats on, or due to receive, antibiotics. Cats receiving live vaccines will shed bacteria, and these vaccines must be avoided where an owner is known to be immunocompromised (Moore et al., 2021). These vaccines can occasionally induce mild clinical signs.

 

Since the Bb vaccine contains live bacteria there is a potential risk of infection during administration of the vaccine or indirectly through contact with a vaccinated cat during the post vaccination shedding period (Moore et al., 2021). As stated in the SPC, the shedding period can last up to one year. Therefore, the SPC includes the following precaution: “although the risk of immunocompromised humans becoming infected with Bb is extremely low, it is advised that cats, which are in close contact with immunocompromised humans are not vaccinated with this vaccine.”

 

Primary vaccination course

 

The modified live vaccine is licensed for use as a single vaccination with annual boosters.

 

Booster vaccinations

 

Annual boosters are recommended if protection should be maintained. Duration of immunity of at least a year has been demonstrated (Williams et al., 2002). Boosters are preferably given prior to going into a boarding or rescue cattery which has a history of Bb infections or before going to a cat show. 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 needs 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 also help control Bb infection and disease.

 

Shelters

 

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 confirmed Bb-associated disease.

 

Breeding catteries

 

The vaccination schedules used for privately owned cats are appropriate for most breeding catteries. Bb vaccination is rarely indicated in breeding catteries.

 

See also the ABCD Tool “Vaccine recommendations for cats according to their lifestyle”.

 

Vaccination of immunocompromised cats

 

Vaccination of immunocompromised cats is not recommended. See also the ABCD guidelines on vaccination of immunocompromised cats.

 

Zoonotic risk

 

Because of its role as a potential human pathogen, Bb is important (Woolfrey and Moody, 1991; Bauwens et al., 1992) although most cases in humans  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 where cats were suspected as source of the infection (Gueirard et al., 1995; Ner et al., 2003; Redelman-Sidi et al., 2011; Wernli et al. 2011). It is sensible therefore to consider Bb as a rare potential cause of zoonotic infections.

 

Acknowledgement

 

ABCD Europe gratefully acknowledges the support of Boehringer Ingelheim (the founding sponsor of the ABCD), Virbac and IDEXX GmbH.

 

References

 

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Bradley A, et al (2012): Efficacy of Intranasal Administration of a Modified Live Feline Herpesvirus 1 and Feline Calicivirus Vaccine against Disease Caused by Bordetella bronchiseptica after Experimental Challenge. J Vet Intern Med 26(5), 1121-1125.

 

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