Bartonella Infections, Including Cat-Scratch Disease¶
Chapter 177 | Part 5: Infectious Diseases
KEY CLINICAL POINTS¶
- Bartonella species are fastidious, facultative intracellular bacteria causing a broad spectrum of diseases, including cat-scratch disease (CSD), endocarditis, and bacillary angiomatosis.
- Cat-scratch disease (CSD) is caused primarily by B. henselae, with typical presentation of regional lymphadenopathy and atypical manifestations like neuroretinitis or encephalitis.
- Diagnosis of Bartonella infections relies on PCR, serology, and imaging, with PCR being most sensitive for seronegative patients.
- Treatment varies by infection type: doxycycline/azithromycin for CSD, combination therapy (gentamicin + doxycycline) for endocarditis, and prolonged macrolides/doxycycline for bacillary angiomatosis/peliosis.
- Prevention focuses on flea control, avoiding cat scratches, and managing immunocompromised patients to reduce transmission risks.
1. DEFINITION & OVERVIEW¶
Bartonella species are fastidious, facultative intracellular, slow-growing, gram-negative bacteria that cause a broad spectrum of diseases in humans. This genus includes >40 species, with B. bacilliformis, B. quintana, and B. henselae being the most clinically significant. Bartonella species have adapted to survive in specific domestic or wild mammals, creating reservoirs for human infections. Chronic bacteremia and immune evasion mechanisms contribute to persistent infections.
Table 177-1 Bartonella Species Known or Suspected to Be Human Pathogens¶
| BARTONELLA SPECIESa | DISEASE(S)b | RESERVOIR HOST(S)c | ARTHROPOD VECTOR |
|---|---|---|---|
| B. alsatica | Endocarditis, lymphadenitis, vascular graft infection | Rabbits | Fleas |
| B. bacilliformis | Carrión’s disease | Humans | Sandflies (Lutzomyia verrucarum) |
| B. henselae | Cat-scratch disease, bacillary angiomatosis, endocarditis | Cats, other felines | Cat fleas (Ctenocephalides felis) |
| B. quintana | Trench fever, chronic bacteremia, bacillary angiomatosis, endocarditis | Humans | Human body lice (Pediculus humanus corporis) |
| B. vinsonii subsp. berkhoffii | Endocarditis | Domestic dogs, coyotes, gray foxes | Ticks |
| BARTONELLA SPECIESa | DISEASE(S)b | RESERVOIR HOST(S)c | ARTHROPOD VECTOR |
|---|---|---|---|
| B. henselae | Bacillary peliosis, bacteremia | Cats | Unknown |
1.1 Clinical Spectrum¶
Bartonella infections range from self-limiting illnesses like CSD to severe conditions such as endocarditis and bacillary angiomatosis. Immunosuppressed patients are at higher risk for disseminated infections, including bacillary peliosis and endocarditis. Transmission occurs via arthropod vectors (fleas, lice) or direct contact with infected animals.
2. EPIDEMIOLOGY¶
CSD occurs globally, with higher incidence in warm, humid climates. In the U.S., 4–9 outpatient cases per 100,000 population annually, with higher rates in southern states and children 5–9 years old. Bartonella endocarditis is more common in homeless individuals, alcoholics, and those with body louse infestations. B. quintana endocarditis is associated with homelessness, while B. henselae endocarditis is linked to cat exposure.
2.1 Risk Factors¶
Risk factors include cat contact (especially kittens), flea infestations, homelessness, alcoholism, body louse infestation, and immunosuppression. B. quintana is prevalent in low-income populations, while B. hens,elae is associated with cat exposure.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Bartonella species evade host immunity via antigenic variation, intracellular survival, and immune suppression. B. henselae causes CSD via cat flea vectors, while B. quintana spreads through body lice. Bartonella adhesin A and outer-membrane proteins mediate adherence to endothelial cells. Chronic bacteremia and immune evasion contribute to persistent infections, particularly in immunocompromised hosts.
3.1 Immune Evasion¶
Bartonella modifies virulence factors (e.g., lipopolysaccharides, flagella) and attenuates immune responses. Intracellular survival within endothelial cells and erythrocytes protects against innate and adaptive immunity. Arthropod vectors facilitate transmission, with some species (e.g., B. quintana) persisting in human hosts without vector involvement.
4. CLINICAL FEATURES¶
CSD typically presents with subacute regional lymphadenopathy, often following cat scratches. Atypical forms include neuroretinitis, encephalitis, and hepatosplenic disease. Bartonella endocarditis presents with fever, heart murmurs, and embolic events. Bacillary angiomatosis manifests as cutaneous lesions, while bacillary peliosis involves hepatic and splenic lesions. Severe cases may mimic malignancies or autoimmune disorders.
4.1 Cat-Scratch Disease¶
Typical CSD: 85–90% of cases present with painless papules/pustules at the inoculation site, followed by tender lymphadenopathy. Atypical CSD includes Parinaud’s oculoglandular syndrome, neuroretinitis, and systemic manifestations like fever of unknown origin (FUO).
5. DIFFERENTIAL DIAGNOSIS¶
CSD must be differentiated from syphilis, brucellosis, toxoplasmosis, and other bacterial infections. Bartonella endocarditis overlaps with other culture-negative endocarditis pathogens (e.g., HACEK group). Bacillary angiomatosis mimics Kaposi’s sarcoma, pyogenic granulomas, and verruga peruana. Neuroretinitis may resemble posterior uveitis or optic neuritis.
6. INVESTIGATIONS & DIAGNOSIS¶
PCR of lymph node aspirates or biopsy is most sensitive for diagnosing Bartonella infections. Serology (IgG detection) is less reliable due to cross-reactivity. Blood cultures are positive in ~25% of cases, with B. quintana more frequently isolated. Imaging (CT, MRI) detects hepatic/splenic lesions in bacillary peliosis. Echocardiography identifies vegetations in endocarditis.
6.1 Diagnostic Algorithms¶
For seronegative CSD: PCR of lymph node aspirate or biopsy. For endocarditis: Blood cultures + PCR of valve tissue. For bacillary angiomatosis: Histopathology with Warthin-Starry staining. For neuroretinitis: Ophthalmologic imaging and serology.
7. MANAGEMENT & TREATMENT¶
Treatment varies by infection type: azithromycin/doxycycline for CSD, gentamicin + doxycycline for endocarditis, and prolonged macrolides/doxycycline for bacillary angiomatosis/peliosis. Surgical valve replacement may be required for severe endocarditis. Prevention includes flea control, avoiding cat scratches, and managing immunocompromised patients.
Table 177-2 Antimicrobial Therapy for Bartonella Infections in Adults¶
| DISEASE | ANTIMICROBIAL THERAPY |
|---|---|
| Typical cat-scratch disease | Azithromycin (500 mg PO day 1, 250 mg PO daily x4 days) |
| Bacillary angiomatosis/peliosis | Doxycycline (100 mg bid x6 weeks) or macrolides (500 mg qid x3–4 months) |
| Bartonella endocarditis | Gentamicin (3 mg/kg IV daily) + doxycycline (100 mg bid) x6 weeks |
| Trench fever | Doxycycline (100 mg bid x14 days) + gentamicin (3 mg/kg IV daily) |
| Carrión’s disease | Chloramphenicol (500 mg qid x14 days) + b-lactam |
7.1 Antimicrobial Therapy¶
Table 177-2 outlines regimens: Doxycycline (100 mg bid) for CSD, gentamicin + doxycycline for endocarditis, and macrolides (erythromycin/azithromycin) for bacillary angiomatosis. For immunocompromised patients, prolonged therapy (3–6 months) may be needed.
8. PROGNOSIS & COMPLICATIONS¶
CSD typically resolves without treatment, but severe complications (e.g., neuroretinitis) may require prolonged therapy. Bartonella endocarditis has high morbidity/mortality without valve replacement. Bacillary angiomatosis/peliosis can progress to liver failure or disseminated infection in immunocompromised patients. Early diagnosis and treatment improve outcomes.
8.1 Complications¶
Chronic bacteremia, embolic events, endocardial vegetations, and multiorgan involvement (hepatosplenic, osteomyelitic) are common. Severe cases may mimic malignancies or autoimmune disorders, leading to delayed diagnosis.
9. SPECIAL CONSIDERATIONS¶
Immunocompromised patients (e.g., HIV, transplant recipients) are at higher risk for disseminated Bartonella infections. Prevention includes flea control, avoiding cat scratches, and managing cat-to-human transmission. Antiretroviral therapy and rifabutin/macrolides reduce Mycobacterium avium complex risk in HIV patients.
9.1 Pregnancy & Pediatrics¶
Bartonella infections are generally safe in pregnancy, but maternal transmission is rare. In children, CSD is common, with atypical presentations requiring prompt diagnosis to prevent chronic complications.
10. KEY POINTS & CLINICAL PEARLS¶
- PCR is the most sensitive diagnostic tool for Bartonella infections, especially in seronegative patients.
- Doxycycline/azithromycin are first-line treatments for CSD and bacillary angiomatosis.
- Bartonella endocarditis requires combination therapy (gentamicin + doxycycline) and valve replacement in severe cases.
- Atypical CSD (e.g., neuroretinitis) may require prolonged antibiotic therapy and surgical drainage.
- Prevention focuses on flea control, avoiding cat scratches, and managing immunocompromised patients.