Bordetella bronchiseptica (Bb) has long been recognized as an important agent in Canine Infectious Respiratory Disease Complex (CIRDC) but only in recent years has its role in the development of Upper Respiratory Tract Disease (URTD) of cats been recognised. The clinical signs of Bb infection are very similar to those of viral upper respiratory tract disease and there is mounting evidence that infection is widespread. Stress predisposes cats to the development of disease associated with Bb and this is most common in multicat households and catteries. The disease is most severe in kittens (where fatal bronchopneumonia has been reported). Transmission of Bordetella bronchiseptica between dogs and cats has been reported.
Etiology and Pathogenesis
B. bronchiseptica bacteria are small (0.2 mm X 0.7 mm), aerobic, motile, Gram negative coccobacilli which occur singly, in pairs, or in small clumps.
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.
B. bronchiseptica colonizes the ciliated respiratory mucosa, a surface designed to eliminate foreign particles, thereby making the adherence and persistence mechanisms of these bacteria crucial. The release of toxins following colonisation is responsible for local and systemic inflammatory damage for the first 3-5 days after infection. Damage and loss of tracheal epithelial cells containing adherent bacteria contributes to respiratory disease and ciliostasis, destruction of the cilia and failure of the mucociliary clearance mechanism together facilitate further colonisation, persistence, and transmission of bacteria.
After onset of the local immune response the bacteria are gradually eliminated. In cats most illness appears self-limiting with spontaneous resolution occurring after about 10-14 days. However, severe bronchopneumonia associated with B. bronchiseptica may occur, particularly in kittens, and can be lethal.
Studies have shown that B. bronchiseptica is able to induce respiratory disease in the absence of other pathogens. However, although B. bronchiseptica can act as a primary pathogen and cause URTD in cats it is highly likely that in many circumstances other factors are involved including stress and concurrent infection with respiratory viruses. B. bronchiseptica may also act as a secondary pathogen, particularly in cases of URTD which progress to more lethal bronchopneumonia.
Clinical and Pathological Findings
B. bronchiseptica associated URTD is a complex disease. There is a considerable overlap between the clinical signs seen with other agents that can cause URTD including FCV and FHV-1. In studies in cats in which B. bronchiseptica is known to be the only causative agent, clinical signs have include fever, sneezing, nasal discharge, submandibular lymphadenopathy, coughing and, pulmonary rales. In most cats the disease is usually mild and signs normally disappear after about 10 days. However, in some cats, particularly younger animals, it can develop into bronchopneumonia and be life-threatening. Some cats may become long-term carriers and recovered cats have been shown to shed Bb for at least 19 weeks after initial exposure.
The presence of Bb can be confirmed by either isolation and culture or PCR on oropharyngeal or nasal swabs . For bacterial isolation and culture, swabs should be placed into bacterial transport medium and cultured on a selective medium such as charcoal/cephalexin agar, which reduces overgrowth by other respiratory flora.
Sensitive real-time PCR methods are capable of detecting the presence of low numbers of organisms. Some laboratories have developed multiplex assays that allow the simultaneous detection of all common feline respiratory pathogens.
Serology is of limited diagnostic use due to the high seroprevalence in the general cat population.