NAVLE Multisystemic

Feline Bartonellosis Study Guide

📅 March 28, 2026 ⏱ 25 min read

Overview and Clinical Importance

Bartonellosis is an important emerging zoonotic infection caused by bacteria of the genus Bartonella. Cats serve as the primary reservoir host for Bartonella henselae, the causative agent of cat scratch disease (CSD) in humans. While most infected cats remain asymptomatic carriers with chronic bacteremia lasting months to years, bartonellosis can occasionally cause clinical disease including endocarditis, uveitis, fever, and lymphadenopathy. Understanding feline bartonellosis is essential for the NAVLE due to its zoonotic significance and the role veterinarians play in public health prevention.

The prevalence of B. henselae bacteremia in cats ranges from 25-40% worldwide, with higher rates in warm, humid climates where flea infestations are more common. Seroprevalence varies regionally, from 6% in Illinois to 33% in Florida. Kittens and shelter/stray cats demonstrate higher infection rates than adult owned cats.

Species	Reservoir	Clinical Significance	Zoonotic Potential
B. henselae	Cats (primary)	Most common; CSD agent; endocarditis, uveitis	High - Cat scratch disease
B. clarridgeiae	Cats	Second most common in cats; less pathogenic	Moderate - Atypical CSD
B. koehlerae	Cats	Rare; described in feline endocarditis	Low - Endocarditis reported
B. vinsonii berkhoffii	Dogs (cats accidental)	Pericarditis, osteomyelitis in cats	Moderate

Etiology

Causative Agent

Bartonella species are small (0.3-0.6 by 1.0-1.7 micrometers), fastidious, facultative intracellular, Gram-negative bacteria belonging to the family Bartonellaceae. They are pleomorphic, non-capsulated, non-sporing rods that invade and replicate within erythrocytes and vascular endothelial cells. The bacteria are highly hemin-dependent and require enriched blood-containing media for culture, with primary isolation requiring 5-45 days of incubation.

Bartonella Species Affecting Cats

High-YieldB. henselae is the most clinically significant species. Cats can be co-infected with multiple Bartonella species simultaneously. Remember: Cats are RESERVOIR hosts (carry without disease), while humans and dogs are ACCIDENTAL hosts (develop clinical disease).

Route	Mechanism	Clinical Significance
Flea-mediated	Contaminated flea feces in bite wounds	Primary cat-to-cat transmission; ESSENTIAL for maintenance in population
Scratch/Bite	Flea dirt under claws or in saliva	Primary route to humans; kittens higher risk due to play behavior
Blood transfusion	Infected donor blood	Screen feline blood donors; documented cause of infection
Cat fights	Bite wounds; blood contact	Risk factor; outdoor cats more affected

Transmission and Epidemiology

Vector-Borne Transmission

The cat flea, Ctenocephalides felis, is the primary vector responsible for transmission of B. henselae among cats. The transmission cycle is as follows:

Flea ingests blood from bacteremic cat during feeding
Bacteria replicate within the flea gut (6-8 days post-feeding)
Bacteria shed in flea feces ("flea dirt") - viable for greater than 9 days in environment
Contaminated flea feces inoculated into host via flea bite wound, cat scratch, or skin abrasion
Cat-to-cat or cat-to-human transmission occurs through contaminated claws (flea dirt under nails)

Transmission Routes Summary

Risk Factors for Infection

Age: Kittens less than 1 year old have higher bacteremia levels and longer duration of infection
Flea infestation: Essential for transmission; flea control eliminates risk
Geographic location: Warm, humid climates (favors flea survival); highest in southern US states
Housing status: Shelter, stray, and feral cats have higher prevalence
Lifestyle: Outdoor access, multi-cat households increase risk

NAVLE TipWhen a question describes a flea-infested kitten and asks about zoonotic disease transmission, think Bartonella first. The key association is: FLEAS = BARTONELLA. No fleas = no transmission, even if the cat is bacteremic.

Presentation	Clinical Signs	Notes
Subclinical (Most Common)	No clinical signs; chronic bacteremia	May persist months to years; zoonotic risk
Acute Febrile Illness	Fever (48-72 hours), lethargy, anorexia	Self-limiting; may follow stress or surgery
Lymphadenopathy	Regional or generalized lymph node enlargement	Granulomatous inflammation
Uveitis	Anterior uveitis: aqueous flare, miosis, hypopyon, conjunctival hyperemia	Include in DDx for feline uveitis; responds to doxycycline
Endocarditis/Myocarditis	Fever, murmur, arrhythmias, CHF signs; vegetative valvular lesions	Rare but life-threatening; aortic valve commonly affected
Stomatitis/Gingivitis	Oral inflammation, halitosis	Association proposed but not definitively proven
Neurologic	Ataxia, seizures, behavioral changes	CNS involvement rare; case reports

Pathogenesis

B. henselae is highly adapted to the feline host, allowing long-term survival with minimal host pathology. Following inoculation, bacteria enter the bloodstream and invade erythrocytes and vascular endothelial cells. The bacteria possess several virulence factors including Type IV secretion systems that deliver effector proteins to host cells, promoting bacterial uptake and anti-apoptotic effects.

Key Pathogenic Mechanisms

Intra-erythrocytic persistence: Bacteria replicate within red blood cells, protected from immune surveillance
Endothelial cell invasion: Via invasome-mediated uptake; triggers vasoproliferative responses
Relapsing bacteremia: Cyclic blood-borne infection lasting weeks to months
Immune evasion: Antibodies are NOT protective; seropositive cats can be reinfected

Test	Advantages	Limitations	Clinical Use
Serology (IFA/ELISA)	Most sensitive for exposure; widely available	Low positive predictive value (39-46%); cross-reactivity; titers persist post-treatment	Better for ruling OUT infection (high NPV 87-97%)
PCR	Detects active infection; species identification	Intermittent bacteremia = false negatives; sensitivity suboptimal from blood alone	Best on tissue, LN aspirate, aqueous humor; repeat testing improves sensitivity
Blood Culture	Gold standard; confirms active infection	Requires 2-6 weeks incubation; fastidious organism; prior antibiotics reduce yield	Research/reference labs; enrichment culture with PCR improves sensitivity
Western Blot	Species-specific antibody detection	Limited availability; research use primarily	Confirmatory testing

Clinical Signs in Cats

The majority of cats naturally infected with Bartonella species remain asymptomatic subclinical carriers. When clinical signs do occur, they are typically associated with stress, immunosuppression, or concurrent disease.

High-YieldMost infected cats are ASYMPTOMATIC. On the NAVLE, if asked about a healthy, bacteremic cat without clinical signs, remember that treatment is NOT recommended for asymptomatic carriers. Only treat cats with documented clinical disease attributable to Bartonella.

Drug	Dose	Duration	Notes
Doxycycline	5-10 mg/kg PO q12-24h	4-6 weeks minimum	First-line; give with food/water to prevent esophagitis
Pradofloxacin	4.5-5 mg/kg PO q24h	4-6 weeks	Fluoroquinolone; combination with doxycycline may improve efficacy
Azithromycin	10 mg/kg PO q24h or q48h	Variable	NOT first-line; rapid resistance development; use with caution
Enrofloxacin	5 mg/kg PO q12h	4-6 weeks	Alternative; retinal toxicity risk - do not exceed dose
Combination Therapy	Doxycycline + Fluoroquinolone	6-8 weeks or longer	May be required for therapeutic elimination; better outcomes reported

Diagnosis

Diagnosis of feline bartonellosis is challenging due to the high prevalence of subclinical infection and the difficulty in attributing clinical signs to Bartonella in the face of positive test results. A combination of testing modalities and clinical context is required.

Diagnostic Testing Options

Indications for Testing

Cat with clinical signs compatible with bartonellosis (uveitis, endocarditis, lymphadenopathy, fever)
Feline blood donor screening (REQUIRED)
Cat belonging to immunocompromised person
Human household member diagnosed with Bartonella-related disease

NAVLE TipTesting and treatment of HEALTHY cats is NOT recommended, even if seropositive. A positive serology or PCR in an asymptomatic cat does not indicate disease - it indicates exposure/carriage. Only pursue diagnostics and treatment in cats with compatible clinical signs.

Population	Clinical Syndrome	Key Features
Immunocompetent	Cat scratch disease (typical)	Papule at inoculation site; regional lymphadenopathy (2-3 weeks post-exposure); self-limiting
Immunocompromised	Bacillary angiomatosis, Peliosis hepatis	Vasoproliferative lesions; hepatosplenomegaly; potentially fatal
Any	Endocarditis	Culture-negative; aortic valve vegetations; requires surgical valve replacement
Any	Neuroretinitis	Optic disc edema, macular star pattern; vision loss

Treatment

Treatment is recommended ONLY for cats with documented clinical disease attributable to Bartonella infection. The goal is to reduce bacteremia and resolve clinical signs, though complete elimination of infection is difficult to achieve.

Antibiotic Treatment Options

Treatment Key Points

Complete clearance of bacteremia may not be achievable with any antibiotic regimen
Relapse after treatment discontinuation is common
Monitor response to treatment - clinical improvement supports diagnosis "ex juvantibus"
Avoid azithromycin as sole therapy due to rapid macrolide resistance
Strict flea control is ESSENTIAL concurrent with treatment

Zoonotic Considerations and Public Health

Cat scratch disease (CSD) is the most common manifestation of B. henselae infection in humans. Approximately 24,000 cases occur annually in the United States, predominantly in children under 15 years old. Veterinary personnel are at increased risk - one study found Bartonella DNA in 28% of veterinary staff.

Human Disease Manifestations

Prevention Recommendations (CDC/ABCD Guidelines)

Flea control: Year-round flea prevention on ALL cats - this is the SINGLE most important measure
Wound care: Wash cat scratches and bites promptly with soap and water
Nail trimming: Keep cats' claws trimmed short
Avoid rough play: Especially with kittens; avoid allowing cats to lick open wounds
Immunocompromised persons: Adopt cats greater than 1 year old; indoor-only lifestyle; consider testing
Declawing NOT recommended: No evidence it reduces transmission risk

High-YieldNAVLE questions frequently test owner counseling. Key points: (1) Flea control eliminates transmission risk even from bacteremic cats, (2) No vaccine exists for cats or humans, (3) Prophylactic antibiotic treatment of healthy cats is NOT recommended, (4) Immunocompromised owners should adopt adult cats (greater than 1 year), not kittens.

Differential Diagnosis

For Feline Uveitis

FeLV, FIV, FIP, Toxoplasma gondii, systemic fungal infections (Histoplasma, Cryptococcus, Blastomyces, Coccidioides), FHV-1, neoplasia (lymphoma, melanoma), trauma, lens-induced uveitis

For Fever and Lymphadenopathy

FIP, lymphoma, other infections (mycobacterial, fungal), reactive lymphadenopathy

For Feline Endocarditis

Other bacterial endocarditis (Streptococcus, Staphylococcus, E. coli), FIP

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