What type of bacteria is associated with cat scratches?

Bacteria Associated with Cat Scratches

Cat scratch disease is primarily caused by Bartonella henselae, a gram-negative bacillus that is transmitted through cat scratches, with cats being the main reservoir for this bacterium. 1

Epidemiology and Transmission

• Bartonella henselae is the most common Bartonella species worldwide and is the primary causative agent of cat scratch disease 2
• Transmission occurs through:
  • Cat scratches (most common route to humans)
  • Cat fleas (Ctenocephalides felis felis) serve as the vector between cats
  • Flea feces can also transmit the bacteria 1, 2
• A high percentage of young cats carry B. henselae, with prevalence approaching 50% in some areas of the United States 3
• Blood transfusion also represents a potential risk for transmission 2

Clinical Manifestations

Cat scratch disease typically presents as:

• Regional lymphadenopathy that develops approximately 3 weeks after inoculation
• Lymphadenopathy usually resolves within 1-6 months
• Suppuration occurs in about 10% of cases 1

In immunocompetent hosts, cat scratch disease is usually self-limited, but can occasionally present with atypical manifestations:

• Parinaud oculoglandular syndrome
• Stellate neuroretinitis
• Persistent fever without localizing signs
• Hepatosplenic infection
• Encephalopathy
• Osteomyelitis
• Endocarditis 4

In immunocompromised individuals, especially those with HIV and CD4+ counts <100 cells/μL, B. henselae can cause more severe manifestations:

• Bacillary angiomatosis (BA)
• Bacillary peliosis hepatis
• Relapsing bacteremia with fever syndrome 3, 1

Diagnosis

Diagnosis of cat scratch disease can be confirmed through:

1. Serology: Primary diagnostic method, though antibodies may not be detectable for up to 6 weeks after infection 1

   • In immunocompromised patients with advanced HIV, up to 25% of culture-positive patients might never develop antibodies 3

2. Histopathology: Using Warthin-Starry silver stain of infected tissue shows characteristic bacilli 1

   • BA lesions are characterized by vascular proliferation
   • Tissue Gram staining and acid-fast staining are negative 3

3. PCR: Available for identification and speciation but not widely accessible 1

4. Culture: Difficult due to the fastidious nature of the organism; blood should be collected in EDTA tubes 1

Prevention

To prevent cat scratch disease:

• Wash cat scratches promptly with soap and water
• Implement flea control for cats (crucial prevention strategy)
• Avoid rough play with cats
• Keep cats' nails trimmed
• Do not allow cats to lick open wounds or cuts
• If acquiring a cat, choose one >1 year old and in good health 1
• Immunocompromised individuals should consider the risks of cat ownership 1

Important Considerations

• While B. henselae is the most common species associated with cat scratches, B. quintana can also cause infections in humans (particularly in homeless populations with body louse infestation) 3
• Most cats naturally infected by B. henselae do not show clinical signs but may occasionally develop cardiac (endocarditis, myocarditis) or ocular (uveitis) manifestations 2
• B. vinsonii subspecies berkhoffii has been reported to cause lameness in cats with recurrent osteomyelitis and polyarthritis 2

Cat scratch disease should be included in the differential diagnosis when regional lymphadenopathy develops suddenly in a previously healthy patient who owns a cat, particularly when neurologic symptoms are present 5.