Cat-scratch disease, also known as cat scratch fever or inoculation lymphoreticulosis, is a benign and self-limited bacterial infection of Bartonella henselae transmitted by the cat flea Ctenocephalides felis. The disease distribution is worldwide. It is more common in children and young adults. There is no sex predilection.

Cat-scratch disease is characterized in most cases by a primary papule, papulopustule, or nodule and enlarged localized lymph nodes with a history of cat scratch (less likely cat bite) distal to the involved node. Inoculation from canine or rodent scratches has also been reported. In rare cases, the primary inoculation may occur via the eye or mucosal membrane, presenting as conjunctivitis or mucosal ulcers. Fatigue, malaise, pharyngitis, conjunctivitis, headache, and low-grade fever may be present. 

Following inoculation, a papule, papulopustule, or nodule develops at the site of the bite within days. In two-thirds of patients, the inoculation site reaction lasts for less than a month. It may persist for 2 months or more in some cases. It typically heals without scarring.

Lymphadenopathy begins within weeks. Enlarged lymph nodes may be tender, and associated overlying erythema may be present. In immunocompetent patients, the disease is usually benign and self-limited, and most patients recover without sequelae. Around half of patients develop systemic symptoms and signs including fever, night sweats, headache, sore throat, malaise, nausea, and anorexia. Atypical presentations include stellate neuroretinitis, hepatosplenomegaly, encephalopathy, persistent fever, osteomyelitis, endocarditis, parotitis, and the oculoglandular syndrome of Parinaud (granulomatous conjunctivitis and preauricular lymphadenopathy). Encephalitis may occur in 1%-7% of cases, typically appearing 2-6 weeks after classic cat-scratch disease. Patients may present with associated seizures or status epilepticus.

Rarely, an associated widespread morbilliform eruption, erythema nodosum (warm, erythematous, and painful nodules in lower extremities), erythema multiforme, and/or thrombocytopenic purpura are seen.

In the immunocompromised host, infection with B henselae can manifest in numerous ways, from classic cat-scratch disease to bacillary angiomatosis, peliosis, or sepsis. Encephalitis is not uncommon and typically appears 2-6 weeks after classic cat-scratch disease. Patients may present with associated seizures or status epilepticus. Cystic hepatitis (peliosis), granulomatous conjunctivitis, culture-negative endocarditis, neuroretinitis, optic neuritis, and other neuropsychiatric disorders are less rare complications in immunocompromised patients.