In humans, typically a benign, subacute regional disease of the lymph nodes (lymphadenopathy) resulting from dermal inoculation of the causative agent, the bacterium Bartonella henselae. The domestic cat is the major reservoir of B. henselae, and the cat flea, Ctenocephalides felis, is the main vector of transmission from cat to cat. Bartonella clarridgeiae has been isolated from domestic cats. Recently, a new bacterium, B. koehlerae, has also been isolated from the blood of domestic cats. Cat scratch disease occurs in immunocompetent patients of all ages, with 55–80% being less than 20 years of age. More than 90% of cases have a history of contact with cats, and 57–83% recall being scratched by a cat. Incidence varies by season; most cases occur in the fall and winter. More cases are observed in males than females. In humans, 1–3 weeks may elapse between the scratch (or bite) and the appearance of clinical signs. In 50% of the cases, a small skin lesion, often resembling an insect bite, appears at the inoculation site (usually on the hand or forearm) and evolves from a pimple (papule) to a skin blister to partially healed ulcers. These lesions resolve within a few days to a few weeks. Inflammation of lymph nodes develops approximately 3 weeks after exposure. Swelling of the lymph node is usually painful and persists for several weeks or months. In 25% of the cases, a discharge of pus occurs. A large majority of the cases show signs of systemic infection, such as fever, chills, malaise, anorexia, or headaches. In general, the disease is benign and heals spontaneously without aftereffects. No major clinical signs of cat scratch disease have been reported in cats, although enlargement of the lymph nodes caused by a cat scratch disease–like organism has been reported. Most individuals with cat scratch disease experience mild illness and require minimal treatment. In severe forms, antibiotics such as ciprofloxacin, rifampin, or gentamicin have been recommended. Use of oral azithromycin for 5 days has shown significant clinical benefit in typical cat scratch disease. |
