Case Report: Sometimes a Dog Can be Too Friendly
SPECIAL REPORT
A 56-year old woman had the abrupt onset of fever and malaise, followed by cough. A chest x-ray demonstrated evidence of pneumonia and she was treated with clarithromycin. However, her fever persisted and she developed worsening lower extremity pain.
The patient was receiving 5 mg prednisone daily because of a poorly defined vasculitis resembling polyarteritis nodosa, which had been in remission. Because of the fever and leg pain, her prednisone dose was increased to 60 mg daily. This led to only transient improvement and, with worsening of symptoms once again, she was hospitalized.
There had been no recent travel; her only animal exposure was to a pet dog, who was suffering from a persistent cough. The dog frequently licked the patient's face. The patient's husband also had a persistent cough.
On physical examination, she was febrile and coughed infrequently. Effusions were present in both knees and in both ankles, all of which were tender. Her WBC was 15,300/mm3 with 82% PMNs and 6% bands. Chest x-ray demonstrated that the previously identified right lower lobe pneumonia was resolving.
Cefazolin was administered, but fever persisted and the joint effusions worsened. Arthrocenteses were performed on both ankles: synovial fluid WBCs were 18,000 and 23,000/mm3 with 97% PMNs. Although plain films were normal, MRI revealed evidence of distal left tibial osteomyelitis. Blood cultures grew an aerobic gram-negative coccobacillus, subsequently identified as Bordetella bronchiseptica, susceptible to amikacin, ciprofloxacin, gentamicin, imipenem, tobramycin and trimethoprim/sulfamethoxazole, and resistant to all beta-lactams tested, as well as to erythromycin and tetracycline. The patient responded to treatment with ciprofloxacin.
A specimen obtained by tracheal aspiration from the pet dog failed to yield B. bronchiseptica; no culture was obtained from the patient's husband.
COMMENT BY ROBERT ARMSTRONG, MD
B. bronchiseptica is one of four species of Bordetella, tiny gram-negative coccobacilli which occur singly or in pairs and grow slowly in the laboratory. B. pertussis and B. parapertussis cause whooping cough syndromes in humans. B. avium, a cause of coryza in turkeys, is not known to infect humans, while B. bronchoseptica, which does, causes atrophic rhinitis in piglets, snuffles in rabbits, pneumonia in koalas, and kennel cough in dogs. B. bronchoseptica accounted for 12.1% of bacterial isolates from tracheal aspirates of dogs with lower respiratory tract disease.1 B. bronchiseptica is also, however, a rare cause of bronchitis, whooping cough syndrome and pneumonia in immunocompromised (and, even more rarely, immunocompetent) humans.2
B. bronchiseptica has been demonstrated by multiple methods to be closely related to the etiologic agent of whooping cough in humans, B. pertussis. B. bronchiseptica is capable of synthesis of all the virulence factors found in B. pertussis, with the exception of pertussis toxin itself.2 B. parapertussis does, however, contain pertussis toxin genes, but they are transcriptionally silent as the result of mutations in their promoter region.2 Recently, variant strains of B. bronchiseptica capable of producing pertussis toxin in vitro have been isolated from immunocompetent infants with episodic coughing.3
Treatment of B. bronchiseptica infection should probably last several weeks, particularly in the immunocompromised host, because of the ability of the organism to persist intracellularly. The organism can survive within both epithelial cells and professional phagocytes and it may persist in vivo as well as in vitro.4 It may, in fact, persist over several months, as evidenced by the case of a woman who had recurrent symptoms over a prolonged period of time despite antibiotic therapy.5
The diagnosis of this infection is unlikely to be suspected and the microbiology laboratory may have difficulty isolating and identifying the organism. Serological tests are not available. It has been reported that infection of B. bronchiseptica may cause a false positive serological test for Legionella.6
Whether, in the case described here, the history of chronic cough in the patient's pet dog is relevant can only be suspected, but transmission from dog to man has previously been demonstrated. (Robert Armstrong is Clinical Professor of Medicine, Division of Infectious Disease and Geographic Medicine, Stanford University. Consultant, Santa Clara Valley Medical Center.)
References
1. Angus JC, et al. Microbiological study of transtracheal aspirates from dogs with suspected lower respiratory tract disease: 264 cases (1989-1995). J Am Vet Med Assoc 1997;210:55-58.
2. Gomez L, et al. Bacterial pneumonia due to Bordetella bronchiseptica in a patient with acute leukemia. Clin Infect Dis 1998;4:1002-1003.
3. Arico B, Rappuoli R. Bordetella parapertussis and Bortedella bronchiseptica contain transcriptionally silent pertussis toxin genes. J Bacteriol 1987;169: 2847-2853.
4. Stefanelli P, et al. Molecular characterization of two Bordetella bronchiseptica strains isolated from children with coughs. J Clin Microbiol 1997;35: 1550-1556.
5. Banemann A, Gross R. Phase variation affects long-term survival of Bordetella bronchiseptica in professional phagocytes. Infect Immun 1997;65:3469-3473.
6. Gueirrard P, et al. Human Bortedella bronchiseptica infection related to contact with infected animals: Persistence of bacteria in host. J Clin Microbiol 1995; 33:2002-2006.
7. Jimenez-Lucho V, et al. Bordetella bronchiseptica in an AIDS patient cross-reacts with Legionella antisera. J Clin Microbiol 1994;32:3095-3096.
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