Overview

• Emerging infectious agents that are highly adapted to preferential reservoir hosts, where they establish chronic intraerythrocytic bacteremia.
• Agents-small, curved, facultative fastidious intracellular argyrophilic, hemotrophic Gram-negative rod (bacilli) bacteria.
• Vector transmitted (fleas, ticks).
• Human syndrome-wide variety of clinical syndromes, including, most commonly, cat scratch disease, typified by regional lymphadenopathy after a cat scratch or bite distal to the involved lymph node; worldwide occurrence; estimated >25,000 cases/year in United States; >2,000 cases require hospitalization; almost no fatalities.
• Cats-usually asymptomatic.
• Dogs-emerging clinical syndrome.
• Seasonal; more cases reported between July and January.

Signalment

• Dogs and cats.
• Majority of human patients (80%) <21 years of age; more males than females (1.2:1).

Signs

Causes & Risk Factors

• Contact with domestic kittens and cats (>90%), particularly young cats with fleas.
• Scratched by cat-up to 83%.
• Up to 95% of cats residing in households of affected humans are seropositive.
• Localized infections in immunocompetent; systemic infection in immunocompromised.
• Dogs: risk factors include tick and flea exposure and rural environment.
• Feline bartonella include: Bartonella henselae, B. clarridgeiae, B. koehlerae, B. bovis, B. quintana.
• Canine bartonella include: B. vinsonii ssp. berkhoffii, B. henselae, B. clarridgeiae, B. washoensis, B. quintana, B. rochalimae, B. elizabethae.

Differential Diagnosis

• Benign adenopathy in human children and young adults-most common cause.
• History of contact with a cat.
• Formation of a papule at the site of primary inoculation (scratch or bite).
• Compatible clinical picture-unilateral regional lymphadenitis.
• Exclusion of other identifiable causes.
• Characteristic histopathologic findings.
• Serologic tests-indirect fluorescent antibody for B. henselae.
• Positive skin test no longer used.
• Other causes of lymphadenopathy-lymphogranuloma venereum; syphilis; typical or atypical tuberculosis; other forms of bacterial adenitis; sporotrichosis; tularemia; brucellosis; histoplasmosis; sarcoidosis; toxoplasmosis; infectious mononucleosis; and benign or malignant tumors.
• Dogs: co-infections with other tick-borne diseases (Ehrlichia, Babesia).

CBC/Biochemistry/Urinalysis

Non-contributory

Other Laboratory Tests

• Indirect fluorescent antibody test.
• Enzyme immunoassay-IgG antibodies to B. henselae (Quest Diagnostics Nichols Institute Laboratory, Valencia, CA).
• Culture-on enriched (blood-containing) media in presence of 5% carbon dioxide at 35–37°C; fastidious and slow growing; requires 14–30 days.
• PCR amplification of bacterial DNA from lesions (Galaxy Diagnostics, Research Triangle Park, NC).

Pathologic Findings

• Histopathology of lymph nodes-non-specific inflammatory reaction, including granuloma, microabscess, and necrosis.
• Warthin-Starry silver stain-bacilli.

Drug(s)

• Specific antimicrobials-not efficacious.
• Most cases spontaneously resolve in a few weeks or months.
• Severe cases-antibiotic therapy (gentamicin, doxycycline, erythromycin, azithromycin) based on the antimicrobial susceptibility of B. henselae may be appropriate.
• Dogs-optimal therapy not established but likely long-term (4–6 weeks) antibiotics consisting of macrolides (erythromycin, azithromycin).

Prevention/Avoidance

Immunocompromised people should avoid young cats.

Possible Complications

Uncommon

Zoonotic Potential

The risk of transfer of organisms from infected dogs and cats to people is unknown, although infected cats probably serve as a source of organisms for fleas that are thought to transmit the infection to humans by way of contaminating wounds with infected flea feces (i.e., cat scratch disease).

• Dogs may also serve as chronically infected blood reservoirs for Bartonella species, which may be spread by arthropod vectors to people.

Abbreviations

• PCR = polymerase chain reaction