Americans are bitten by dogs annually. Cases of human infection following exposure to C. canimorsus have been observed worldwide. Cases have been reported in the United States, Canada, Europe, Australia and S. Africa. Symptoms may appear within 2–3 days after exposure, or up to 4 weeks later. Middle-aged and elderly persons are at greater risk for contraction of disease; more than 60% of sufferers are 50 years of age or older. In addition, individuals who spend a greater portion of their time with canines and felines are also at higher risk. This includes veterinarians, breeders, pet owners, and keepers. Having certain pre-existing medical conditions exacerbates the risk. Chance of infection by any bacterial species after dog bites varies between 3 and 20%; for cats, it may be as high as 50%. Morphology, culture, and isolation C. canimorsus is a fastidious, Gram-negative, fermentative, nonspore-forming rod. Bacilli are usually 1-3 μm in length. After growth on agar plates, longer rods tend to have a curved shape. The bacteria do not have flagella, but move with a gliding motion, although this can be difficult to see. C. canimorsus requires the right medium for growth. The bacterium cultures well on blood agar plates (heart infusion agar with 5% sheep or rabbit blood) and chocolate agar plates. Colonies may not be visible for up to 48 hours due to slow growth. At 18 hours, colonies are usually less than 0.5 mm in diameter, and are spotty and convex. At 24 hours, colonies may be up to 1 mm in diameter. After 48 hours, colonies are narrow, flat, and smooth, with spreading edges. At this time, colonies may appear to be purple, pink, or yellow, but once they are scraped from the agar plate, they are always yellow in appearance. Genome The genome of C. canimorsus strain Cc5 consists of a single circular chromosome of 2,571,406 bp with a G+C content of 36.11%, and it encodes 2,405 open reading frames. In animals Members of the genus Capnocytophaga are found in the oral cavities of humans and animals. Most of these species are not found in humans. C. canimorsus is a commensal bacterium found in dogs and cats; it is not a member of the normal microbiota of humans. About 26% of dogs carry these commensal bacteria in their mouths. C. canimorsus rarely causes disease symptoms in animals. One case of C. canimorsus isolated from a dog