ReviewMeningitis caused by Capnocytophaga canimorsus: When to expect the unexpected
Introduction
Bacterial meningitis in adults is most often caused by Streptococcus pneumonia or Neisseria meningiditis, other bacteria account for less than 20% of cases [1]. Although rare, meningitis due to infection with Capnocytophaga canimorsus, formerly known as dysgonic fermenter-2 (DF-2), should be suspected when signs and symptoms of meningitis coincides with a history of a recent dog or cat bite. This fastidious, capnophilic, slow growing Gram-negative bacillus is considered part of the bacterial flora in the mouth of domestic canine and feline species. It is unclear under which circumstances C. canimorsus may cause sepsis or meningitis in humans. Splenectomy, alcohol abuse and use of immune suppressive drugs have been associated with increased susceptibility [2]. Although septic shock attributable to infection with C. canimorsus has frequently been described, the occurrence of meningitis seems rare. In this article we describe two illustrative cases presenting with C. canimorsus meningitis and review the literature with the focus on associated factors to contribute to a better understanding and increased recognition of this uncommon clinical entity. In addition an overview of microbiological aspects and management issues in case the diagnosis is suspected, is presented.
Section snippets
Historical perspective
In 1976 Bobo and Newton described a patient who developed meningitis and sepsis, caused by a yet unidentified Gram-negative bacillus, after recent dog bites [3]. In this report the cellular and colony morphology as well as the biochemical characteristics of a member of Capnocytophaga spp., probably C. canimorsus – at that time nominated dysgonic fermenter 2 (DF-2) – are first described. A year later, in 1977 Butler et al. described a series of of 17 cases, the majority of which presented with
Case reports
Patient A, a 69-year-old male with a history of chronic obstructive pulmonary disease, presented to the emergency department because of the sudden onset of fever and cold chills. Over the last 2 h he had become increasingly disorientated and confused. His medication included bronchodilators and prednisone 5 mg once daily. In the recent past he had received multiple courses of prednisone because of exacerbations of his pulmonary disease. Physical examination revealed a temperature of 39.5 °C and a
Clinical characteristics of C. canimorsus meningitis
Interestingly, both cases differ on several major aspects regarding their clinical presentation. Patient A became acutely ill and developed a diminished consciousness 4 days after he was bitten by his dog, whereas in patient B disease developed more gradually. Only patient A was bitten by a dog prior to his illness. The use of low dose steroids by patient A was the single observed predisposition. C. canimorsus meningitis can not be suspected based on signs and symptoms alone; i.e. the clinical
Microbiological aspects
C. canimorsus is a fastidious, capnophilic, slow growing Gram-negative bacillus that belongs to the DF-2 group of Capnocytophaga spp. DF-2 strains are oxidase- and katalase-positive and have been isolated from dogs, cats, and from patients after dog or cat bites. DF-1 strains, in contrast, originate from the human oral cavity and are oxidase- and katalase-negative and can only cause disseminated infections in severely immunocompromised patients. Among the DF-2 strains, two species have been
Management issues
In case the diagnosis is suspected, the microbiology department should be informed to ensure the application of appropriate culture methods and determination techniques (see previous paragraph). Due to the fact that it concerns a slow growing micro-organism, the cultures should be incubated for more than 1 week. Because confirmation of the diagnosis may take more than 7 days, the patient's history combined with the morphology of the bacteria in the Gram stain of the CSF are most helpful to
Conclusions
C. canimorsus meningitis is rare but prone to be underreported due to unawareness of physicians, slow growth in culture media and to susceptibility of C. canimorsus to a broad spectrum of antibiotics. Adequate history taking, revealing recent exposure to a dog or cat, is critical and should draw the attention of the attending physician to the possibility of the diagnosis. The clinical presentation can range from acute to subacute meningitis. Apart from a possible bite wound found at physical
Acknowledgements
Identification of C. canimorsus of cases A and B was performed by the laboratory of the ‘Rijks Instituut voor Volksgezondheid en Milieu’ (RIVM), Bilthoven, The Netherlands.
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