Bartonella henselae

Background

• Species of Gram-negative intracellular bacteria within the genus Bartonella
• Causes cat-scratch disease

Epidemiology

• Present worldwide
• Main reservoir is cats, and especially kittens
• Infections are more common in children, likely due to increased exposure to kittens
• Transmitted to humans by inoculation of cat flea (Ctenocephalides felis) feces into a cat scratch or bite

Clinical Manifestations

Cat Scratch Disease

• Typical cat-scratch disease is a self-limited febrile illness with regional lymphadenopathy
  • Following an incubation period of 3 to 10 days, and initial pustule develops at site of inoculation which may last for up to 3 weeks
  • Usually a history of cat exposure (adult or kitten), but 5-10% have no known exposure
  • This is followed in 1 to 7 weeks by ipsilateral lymphadenopathy (usually the head or neck)
    • May involve one or more lymph nodes
    • May drain pus
    • Will eventually resolve, over months or longer
  • There may be a concurrent low-grade fever for several days, with malaise or fatigue
  • May have headache, sore throat, transient rash, or, rarely, erythema nodosum
  • May have mild leukocytosis (neutrophils or eosinophils), mildly elevated C-reactive protein or ESR
• CSD may be complicated by encephalopathy in 2 to 4% of cases
  • Headache is common, and they may develop seizures and neurologic deficits
  • Resolves over weeks to months (to as long as a year)
  • CSF is usually normal, although lymphocytic pleiocytosis and elevated protein are seen in one third
  • MRI brain is almost always normal
  • EEG is nonspecific
  • Proportionally less common in children

Other Syndromes

• Other syndromes include:
  • Parinaud oculoglandular syndrome, with granulomatous conjunctivitis and ipsilateral (usually preauricular) lymphadenopathy
  • Neuroretinitis and other ophthalmic complications
  • Fever of unknown origin, in children
  • Culture-negative endocarditis in patients with existing valve abnormalities
  • Chronic endocarditis, with vasculitis and glomerulonephritis
• Disseminated disease is possible in immunocompromised patients, including bacteremia, disseminated skin lesions, and hepatosplenic lesions (see also bacillary angiomatosis)

Diagnosis

• Histopathology of node aspirate shows nonspecific inflammation, with granulomas and stellate necrosis
  • Microabscesses are classic finding
  • Bacilli may be seen with Warthin-Starry staining
• Culture
  • Fastidious organism which may not be detected by automated blood culture systems
  • If suspected, cultures should be held for 21 days
• Molecular
  • PCR of node aspirate (or blood) is the best and most sensitive test
• Serology
  • 1:64 is suggestive, 1:256 is strongly suggestive, and a four-fold rise from acute to convalescent titres is diagnostic
  • Cross-reacts with other Bartonella species, but possibly also with Chlamydia and Coxiella burnetii

Management

Cat-Scratch Disease

• Disease is usually self-limited in immunocompetent patients
• May wish to treat if extensive lymphadenitis
• First-line: azithromycin 500 mg po on day 1 followed by 250 mg po daily for 4 more days (10 mg/kg and 5 mg/kg for children)
• Hepatosplenic CSD in children may respond to combination azithromycin ± rifampin for 14 days

Endocarditis

• Doxycycline and gentamicin for 14 days followed by doxycycline alone for three months, or until 6 weeks after valve replacement (if done)