Capnocytophaga species are gram-negative bacteria from the Bacteroidetes group. Species of these bacteria are isolated from the oral cavity and often cause periodontitis. Several species such as Capnocytophaga gingivalis, Capnocytophaga ochracea, and Capnocytophaga sputigena are human hosted while Capnocytophaga canimorsus and Capnocytophaga cynodegmi live in the mouth of dogs and cats. Capnocytophaga canimorsus represents one more example illustrating that the distinction between commensals and pathogens is illusive. Commensalism (relationship between two organisms when one benefits from the other without affecting it) and pathogenesis are two faces of the same coin.
Although Capnocytophaga canimorsus has not been reported to cause infections in dogs, it causes rare but severe infections in humans who are in contact with their pet dogs. The usual syndrome is blood poisoning, gangrene or meningitis with mortality in the range of 50%. Patients are generally older than 40 years old, and roughly half of them have had their spleen removed or liver damage as a result of alcohol abuse. However, the other half have had no medical history. Bites or simple licks are sufficient to transmit the disease and, yet, the disease is rare.
Rash caused by Capnocytophaga canimorsus
as a result of dog bite (Source: JAAD Case Rep. 2016 Mar; 2(2): 98–101)
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Capnocytophaga canimorsus robust growth in human blood is possible because it resists engulfing and killing by macrophages and also feeds on them. Using highly sophisticated mechanisms, the bacterium also blocks the immune system response to enterobacteria.
Recently two additional Capnocytophaga species were identified as part of the oral flora of healthy dogs and was given the name C. canis and Capnocytophaga stomatis. Both species can be transmitted from cats and dogs to humans.3
- Glycan-Foraging Systems Reveal the Adaptation of Capnocytophaga canimorsus to the Dog Mouth. Francesco Renzi et al.
- Capnocytophaga canimorsus: A Human Pathogen Feeding at the Surface of Epithelial Cells and Phagocytes. Manuela Mally et al.
- Whole genome sequencing identifies a novel species of the genus Capnocytophaga isolated from dog and cat bite wounds in humans. Salah Zangenah, Nasir Abbasi, Anders F. Andersson, and Peter Bergmanb. 2016
- Urticarial exanthem associated with Capnocytophaga canimorsus bacteremia after a dog bite. Christian S. Jordan, PhD,a Una Miniter, MD,b Kevin Yarbrough, MD,b,c and Stephanie J. Mengden, MDb,∗