33       Bordetella species

 

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The genus Bordetella contains eight species, four of which, B. pertussis, B. parapertussis, B. bronchiseptica and B. avium, are significant human or animal pathogens. Bordetella pertussis, the type species, and B. parapertussis are human pathogens associated with whooping cough in children. Bordetella bronchiseptica infects a wide range of animal species, while B. avium is a pathogen of avian species. The bordetellae are occasional pathogens with an affinity for ciliated respiratory epithelium. Bordetella bronchiseptica and B. avium are small Gram-negative rods with a coccobacillary appearance. They are catalase-positive, oxidase-positive aerobes and are motile peritrichous bacteria. They derive their energy mainly from oxidation of amino acids. They are commensals on the mucous membranes of the upper respiratory tract of animals and their survival time in the environment is short.

Bordetellae can be identified by their growth characteristics, biochemical reactions and by their ability to agglutinate red blood cells (Table 33.1). Bordetella avium requires differentiation from Alcaligenes faecalis, which is non-pathogenic. Bordetellae exhibit phase changes, thought to be associated with loss of a capsule-like structure. These changes, which correlate with virulence, are identifiable by colonial appearance. Virulence is mediated by several factors including a filamentous haemagglutinin, pertactin and fimbriae which facilitate attachment to cilia of the upper respiratory tract. Bordetellae also produce a number of toxins, including an adenylate cyclase haemolysin with antiphagocytic activity, a tracheal cytotoxin and a dermonecrotic toxin responsible for nasal turbinate atrophy in infected pigs.

Table 33.1 Differentiating features of Bordetella bronchiseptica, B. avium and Alcaligenes faecalis.

Feature B. bronchiseptica B. avium Alcaligenes faecalisa
Colonial characteristics on:
 Sheep blood agar Haemolysis No haemolysis No haemolysis
 MacConkey agar Pale, pinkish hue Pale, pinkish hue Pale
Oxidase production + + +
Catalase production + + +
Urease production +
Utilization of carbon exclusively from:
 Citrate + + +
 Malonate +
Nitrate reduction +
Motility + + +
Haemagglutinating activity of virulent strains Agglutination of ovine and bovine red blood cells Agglutination of guinea-pig red blood cells

aNot of veterinary significance, but may require differentiation from bordetellae.

Clinical signs associated with bordetellae usually relate to upper respiratory tract infection. Young animals are more susceptible than adults and stress predisposes to outbreaks of disease. Canine infectious tracheobronchitis (kennel cough) is one of the most prevalent respiratory complexes of dogs. The microbial pathogens implicated in kennel cough include B. bronchiseptica, canine parainfluenzavirus 2 and canine adenovirus 2. Transmission occurs through respiratory secretions, either by direct contact or by aerosols. Indirect transmission via feed and water bowls can occur in kennels if hygiene is poor. Clinical signs, which include coughing, gagging or retching, develop within days of exposure. The disease, which may persist for up to 14 days, is usually self-limiting. Diagnosis is based on a history of recent exposure to carrier dogs and characteristic clinical signs. Detection of the associated pathogens can be performed by PCR-based techniques and, in the case of B. bronchiseptica, by culture. Selective media for the isolation of bordetellae have been developed. Carriage rates of B. bronchiseptica are high in healthy dogs and in the absence of clinical signs isolation of the organism may not be of diagnostic significance. Modified live vaccines decrease the severity of clinical signs but may not prevent infection.

In pigs, infection with B. bronchiseptica may facilitate colonization by toxigenic Pasteurella multocida type D, with the subsequent development of severe atrophic rhinitis and distortion of the snout. Infection is usually transmitted by direct contact, both from the sow to her piglets and through mixing of piglets at weaning. Overstocking and poor ventilation can contribute to the development of atrophic rhinitis. In addition to respiratory signs, growth rates are affected and economic losses may be significant. Vaccines containing B. bronchiseptica bacterin and P. multocida toxoid are available for prevention of the disease in pigs. Atrophic rhinitis-free herds can be set up by depopulating and restocking with specific pathogen-free animals.

Bordetella avium causes coryza, rhinotracheitis and sinusitis in young turkey poults. Morbidity may be high but mortality is usually low in the absence of secondary infection by opportunistic pathogens such as E. coli. Buildings which have housed infected turkeys should be thoroughly cleaned and disinfected following a disease outbreak. If there are recurring outbreaks of disease in a turkey flock, vaccination should be considered.