What are the reservoirs and modes of transmission of Bartonella, and what are its common clinical manifestations?

Bartonella: Reservoirs, Transmission, and Clinical Manifestations

Reservoirs and Transmission

The two clinically significant Bartonella species in humans—B. henselae and B. quintana—have distinct reservoirs and transmission routes that directly inform prevention strategies. 1

B. henselae Transmission

• Cats are the primary reservoir, with bacteremia prevalence approaching 50% in some U.S. regions 1
• Cat fleas (Ctenocephalides felis) serve as the vector among cats, with transmission occurring through infected flea feces 1
• Cat scratches are the most common mode of human transmission, likely when claws become contaminated with flea feces containing B. henselae 1
• Cat bites can also transmit infection 1
• Young cats (<1 year old) and feral cats pose higher transmission risk 2
• Blood transfusion represents an additional transmission route 3

B. quintana Transmission

• Body lice serve as the vector for human-to-human transmission 1
• Homelessness and body louse infestation are the primary risk factors for B. quintana infection 1
• This species does not involve animal reservoirs in the same manner as B. henselae 1

Geographic and Environmental Factors

• Prevalence is highest in warm, humid climates optimal for flea survival 4
• B. henselae genotype distribution varies globally: Houston I predominates in the Far East, while Marseille genotype dominates in western Europe, Australia, and western United States 4

Clinical Manifestations

Bartonella presents with dramatically different clinical pictures depending on immune status, with immunocompromised patients at risk for severe, life-threatening manifestations.

In Immunocompetent Patients (Cat Scratch Disease)

• A papule or pustule develops 3-30 days after inoculation at the scratch or bite site 2
• Regional lymphadenopathy occurs approximately 3 weeks after inoculation, representing the hallmark finding 2
• Lymphadenopathy typically resolves within 1-6 months, with suppuration occurring in ~10% of cases 2
• Extranodal disease develops in ≤2% of cases, including encephalopathy (almost exclusively in children and young adults) 1, 2

In Immunocompromised Patients (Particularly HIV/AIDS)

Bartonella infection in severely immunocompromised patients (CD4+ <100 cells/μL) causes distinct, severe manifestations requiring aggressive treatment. 5

Bacillary Angiomatosis (BA)

• Cutaneous lesions are the most readily identified manifestation, appearing as vascular proliferative lesions 1
• BA lesions can be clinically indistinguishable from Kaposi's sarcoma, necessitating biopsy for differentiation 1, 2
• Subcutaneous nodules may also occur 1
• BA can affect nearly every organ system despite cutaneous presentation 1

Systemic Manifestations

• Fever, night sweats, and weight loss commonly accompany BA, reflecting hematogenous dissemination 1
• Bartonella is a major cause of unexplained fever in late-stage AIDS patients with CD4+ <100 cells/μL 1, 5
• Bacillary peliosis hepatis occurs only with B. henselae infection 1
• Osteomyelitis is usually caused by B. quintana 1
• Endocarditis, relapsing bacteremia, and CNS involvement can occur 1

Chronic Course

• In HIV-infected patients, bartonellosis is often chronic, lasting months to years with intermittent bacteremia 1, 5
• Most cases occur with median CD4+ counts <50 cells/μL 1

Other Clinical Presentations

• Trench fever (B. quintana): prominent myalgias, headache, pharyngitis, and respiratory symptoms 1
• Cardiac manifestations: endocarditis and myocarditis (rare in cats, more common in humans) 3
• Ocular manifestations: uveitis 3
• Neurological signs including encephalopathy, seizures, hemiparesis, and cranial nerve palsies 1

Critical Clinical Pitfalls

Consider Bartonella in any HIV patient with unexplained fever and CD4+ <100 cells/μL, as this is a major diagnostic consideration that can be fatal if missed 1, 2

Up to 25% of culture-positive patients with advanced HIV may never develop antibodies, making serologic testing unreliable in this population 1, 2

Always biopsy suspicious cutaneous lesions in immunocompromised patients to distinguish BA from Kaposi's sarcoma, as they are clinically indistinguishable 1, 2