Dog Scratch Fever Secondary to Capnocytophaga Species in a Patient Without Risk Factors

Capnocytophaga is a rare bacteria found in the saliva of canines. C. canimorsus is present in the oral cavity of 67-86% of dogs. In vitro growth requires specialized media. Patients who are immunocompromised are at greatest risk for infection. There are no clinical trials examining the duration of antibiotics.

Capnocytophaga species is a very rare fastidious, slow growing gram negative rod found in the saliva of canines and felines [ 1 ]. It belongs to the genus flavobacteriacea, a capnophilic facultative anaerobe [ 1 ]. In vitro growth requires a specialized media containing, high iron and carbon dioxide. The exact number of cases is unknown because this is not a reportable disease. In one study the incidence rate was estimated at 0.67 per million [ 2 ]. Humans contract the infection after receiving an animal bite, scratch, or an open wound being licked. Of the nine species within the genus C. canimorsus is the most common cause of infection in humans. In the Netherlands a retrospective study found 32 cases of C. canimorsus isolated over a three year period. Of those, 28 were diagnosed by blood culture [ 2 ]. This particular species is associated with a high morbidity and mortality. A large scale retrospective study from California reviewed 56 human isolates during a 32 year period with a 33% mortality rate [ 2 ]. One of the reasons for the high morbidity and mortality is because the bacteria contains lipo-proteins which inhibit hemolysis causing disseminated intravascular coagulation (DIC) [ 1 ]. Researchers have also discovered that C. canimorsus possesses a mechanism of passive evasion. The passive mechanism involves the escape of TLR4 detection through the unique LPS structure. Also, it has been discovered the bacteria does not activate signals leading to the release of proinflammatory cytokines, chemokines, and nitric oxide [ 3 ]. Patients who are immunocompromised, asplenic, alcoholic, or have cirrhosis are at the greatest risk for infection [ 2 ].