Cat Scratch Disease
A bacterial infection spread by cat scratches, causing a bump at the scratch site followed by swollen, painful lymph nodes.
Emergency Management: Severe disseminated bacillary angiomatosis or peliosis hepatis in an HIV patient requires hospital admission and prolonged IV Doxycycline (or Erythromycin) therapy.
An infectious disease caused by the intracellular bacterium Bartonella henselae, typically transmitted via scratches or bites from infected cats, particularly kittens. It is the most common cause of chronic regional lymphadenopathy in children and young adults.
Detailed Overview
B. henselae is carried by cat fleas and transmitted to cats (who remain asymptomatic). Humans are infected when contaminated flea feces are inoculated into the skin via a scratch. The disease typically features an initial skin lesion followed a few weeks later by tender, markedly enlarged lymph nodes draining the site. In immunocompetent hosts, it is usually self-limiting; in immunocompromised hosts (e.g., HIV), it can cause severe disseminated diseases like bacillary angiomatosis.
Epidemiology & Demographics
Incidence is roughly 9 per 100,000 persons per year. Approximately 80% of cases occur in children and young adults under 21 years old. Peak incidence in temperate climates is during fall and winter.
Etiological Mechanism
Bartonella henselae, a fastidious, slow-growing, Gram-negative rod.
Primary Causes
["Inoculation of Bartonella henselae via a cat scratch, bite, or saliva touching broken skin", "Exposure to kitten fleas (Ctenocephalides felis)"]
After skin inoculation, the bacteria multiply locally, causing a primary papule. They are then transported by macrophages to regional lymph nodes, leading to a vigorous Th1-mediated immune response. This causes profound follicular hyperplasia, microabscesses, and granuloma formation with central necrosis in the node. In immunocompromised patients, B. henselae drives intense vascular proliferation leading to angiomatous lesions (bacillary angiomatosis).
Diagnostic Criteria & Guidelines
Clinical diagnosis supported by history of cat contact and typical regional lymphadenopathy. Confirmed primarily by serology (IFA).
For mild to moderate lymphadenopathy in immunocompetent patients: Azithromycin (Adults: 500 mg Day 1, then 250 mg Days 2-5; Children: 10 mg/kg Day 1, then 5 mg/kg Days 2-5) accelerates node resolution. Many cases resolve spontaneously without antibiotics within 2-4 months. Analgesics and warm compresses for pain.
Second-Line & Adjunctive Therapy
For adults, oral Doxycycline 100 mg BID for 10-14 days. Rifampin or Ciprofloxacin are alternatives.
Surgical & Procedural Management
Needle aspiration of a fluctuant, suppurative lymph node provides pain relief. Incision and drainage (I&D) is generally avoided as it can lead to chronic sinus tract formation.
Patient Counseling & Advice
Reassure parents that the massive swelling looks alarming but is typically a benign, self-resolving infection. Explain that the node may take several months to completely disappear even after antibiotics.
Follow-Up & Monitoring Schedule
Re-examine in 2-3 weeks to ensure the node is not enlarging further or becoming suppurative.
Preventive Strategies
Avoid rough play with kittens. Do not allow cats to lick open wounds. Aggressive flea control for all household pets.
Excellent for immunocompetent hosts. Complete resolution is expected, though lymphadenopathy may persist for 2-6 months. Lifelong immunity usually follows.