Infectious diseases & Pediatrics & Dermatology & Family medicine
Cat scratch disease
Cat scratch disease (CSD) is a bacterial zoonosis caused by Bartonella henselae, a facultative intracellular Gram-negative bacterium, transmitted to humans mainly by scratching or biting an infected cat (especially a kitten). The bacterium is transmitted from cat to cat by the Ctenocephalides felis flea (cat flea) - infected flea feces contaminate the cat's claws, and the scratch inoculates the bacterium into human skin. MGC is the most common infectious cause of regional adenopathy in children and adolescents in developed countries. Its classic presentation - inoculation papule at the site of scratching + ipsilateral painful satellite adenopathy appearing 1 to 4 weeks after contact + sub-febrile state + asthenia - is highly suggestive and often leads to a clinical diagnosis. Bartonella henselae serology (IgM + IgG) confirms the diagnosis in atypical cases. In the vast majority of cases in immunocompetent patients, MGC is a self-limiting disease that resolves in 2 to 4 months - antibiotic therapy remains debated, but azithromycin is recommended to accelerate resolution of adenopathies. In immunocompromised patients (HIV + transplant patients + chemotherapy), B. henselae can cause severe disseminated forms - in particular bacillary angiomatosis (cutaneous and visceral vascular proliferation) and hepatosplenic peliosis - requiring prolonged antibiotic treatment with doxycycline or erythromycin.
Microbiology, transmission, and clinical presentation
- Bartonella henselae Biology and Transmission Mechanism: Microbiology: Bartonella henselae = Gram-negative bacillus + facultative intracellular bacterium + aerobe → Bartonellaceae family → slow growth on enriched media (BCYE agar + blood agar + hemin) → difficult to culture (2–6 week delay) → culture is rarely performed routinely → related species: B. quintana (trench fever + transmitted by lice) + B. bacilliformis (Peruvian verruga) → B. henselae transmission cycle: reservoir: domestic cat (especially kittens) <12 months) → B. henselae circulates in cats' blood without causing disease in them (healthy carriers + asymptomatic bacteremia) → vector: cat flea (Ctenocephalides felis) → bites bacteremic cat → flea feces (containing B. henselae) contaminate the cat's claws and skin → scratching or biting → inoculation into human skin → IMPORTANT: the flea does not directly bite the human to transmit B. henselae → contamination of claws by flea feces is the mechanism → 40-50 % of domestic cats are seropositive for B. henselae + higher prevalence in warmer regions (more fleas) → human risk factors: contact with cats + especially kittens <12 months + or deep scratches/bites + immunosuppression → severe forms + pathogenesis: B. henselae penetrates skin → phagocytosis by macrophages + dendritic cells → intracellular survival + multiplication → granulomatous reaction in regional lymph nodes (suppurative granulomas with central necrosis) → in the immunocompromised → B. henselae infects endothelial cells → vascular proliferation = bacillary angiomatosis
- Clinical presentation by background and atypical forms: classic presentation of MGC (90 % of cases): incubation: 3-14 days after scratch or bite → inoculation papule or pustule at scratch site → appears in 3-5 days → little noticed → painless or slightly pruritic → disappears in a few weeks → satellite regional adenopathy (1-4 weeks after inoculation): localized in the lymphatic drainage territory of the scratch site → cervical (hand/arm scratch) + axillary ++ (arm/forearm scratch) + inguinal (leg scratch) + variable size: 1-8 cm → firm + painful + overlying skin erythema possible → fluctuation in 10-30 % of cases → spontaneous fistulization in 5-10 % → moderate fever (38-38.5°C) + asthenia + malaise + headache → spontaneous healing in 2-4 months + atypical forms (10-20 % of cases): Parinaud's oculo-glandular syndrome: conjunctival inoculation → follicular conjunctivitis + preauricular or submaxillary adenopathy → classic + MGC with systemic expression: encephalitis + convulsions + optic neuropathy + erythema nodosum + purpura + hepatosplenic involvement (hepatic granulomas) + splenomegaly → CBC: hyperleukocytosis + lymphocytosis + moderate eosinophilia → moderately elevated LDH and transaminases + severe forms in the immunocompromised: bacillary angiomatosis: cutaneous vascular papules or nodules (pinkish-red + fragile + bleeding on touch) → numerous + resembling Kaposi's or hemangiomas → fever + splenomegaly + hepatitis + hepatosplenic peliosis (hemorrhagic cavities in liver + spleen) → disseminated bacteremia + Bartonella endocarditis (valvular vegetations) → rare but severe in HIV + transplant recipients
Diagnosis and treatment
| Appearance / treatment | Data, modalities and protocols | References and recommendations |
|---|---|---|
| Diagnostic — serology, PCR, and histology Bartonella henselae IgM IgG serology — Lymph node PCR — Lymph node biopsy granulomas — Difficult BCYE culture — CBC eosinophilia — LDH transaminases — Lymph node ultrasound — Bubo puncture — Warthin-Starry staining |
Diagnosis of cat scratch disease: clinical diagnosis in typical forms: contact with a cat + especially kitten + recent scratch or bite + inoculation papule at site + painful satellite regional adenopathy → diagnosis often clinical without further investigation → Bartonella henselae serology: reference test for typical and atypical cases: IgM B. henselae: become positive within 1-2 weeks of infection → marker of recent infection → IgG B. henselae: titre ≥1:64 → suggestive (but present in people exposed to cats without MGC - cross-reaction or old infection) → titre ≥1:256 → highly suggestive of active MGC → multiplication × 4 between two sera at 15 days = confirmation + false negatives possible early in infection (serological window) → repeat at 2-4 weeks if negative + clinic still suggestive → Bartonella henselae PCR on biopsy material: aspiration of a fluctuating lymph node + or lymph node biopsy + sensitivity 80-95 % → available from LNM (Laboratoire national de microbiologie - Winnipeg) → gold standard if histology taken → lymph node biopsy + histology: if lymph node resected or biopsied → epithelioid granulomas with suppurative central necrosis (star-shaped) → Warthin-Starry stain (silver): visualizes silver pleomorphic bacilli in small clusters in vascular walls → sensitivity 50-70 % + CBC: moderate leukocytosis + lymphocytosis + mild eosinophilia + CRP + elevated VS → LDH + slightly elevated transaminases if liver involvement → abdominal ultrasound: if prolonged fever + splenomegaly → hypoechoic splenic granulomas (multiple nodules) → lymph node echo: usual structure + central necrosis if fluctuating | Jacomo 2002 — Clinical Microbiology Reviews: *B. henselae* + biology + diagnosis + treatment → comprehensive review → reference Lamps 2004 — Archives of Pathology and Laboratory Medicine: Cat-scratch disease (CSD) + histology + granulomas + Warthin-Starry Bass 1998 — Pediatrics: Pediatric CSD + diagnosis + treatment Public Health Agency of Canada (PHAC) + INSPQ Quebec: CSD + zoonoses Winnipeg: *B. henselae* PCR available MSSS Quebec: CSD + zoonoses + assessment + INESSS Quebec + RAMQ: *B. henselae* serology + CBC + ultrasound reimbursed |
| Treatment based on terrain and clinical presentation Immunocompetent self-limiting — azithromycin 5 days — fluctuating lymph node aspiration — DO NOT incise — immunocompromised bacillary angiomatosis doxycycline erythromycin — duration 3 months — cat flea prevention — avoid scratches — HIV prophylaxis |
Treatment of cat scratch disease according to terrain: immunocompetent - typical mild to moderate form: CGD is a self-limiting disease → spontaneous cure in 2-4 months without treatment → symptomatic treatment: analgesics + NSAIDs if lymph node pain → azithromycin: recommended to accelerate resolution of adenopathies (faster reduction in lymph node size) → Bass 1998 - Pediatrics (RCT): azithromycin vs placebo → significant reduction in lymph node size at D30 → dosage: adult → 500 mg D1 then 250 mg D2-J5 + child → 10 mg/kg D1 then 5 mg/kg D2-J5 → or azithromycin 500 mg/d × 5 days + duration of antibiotic treatment is limited as no effect on complete resolution in simple forms → aspiration of a fluctuating lymph node: if very painful + fluctuating lymph node → fine needle aspiration for symptomatic relief + sampling for PCR → DO NOT incise (risk of persistent fistulization) → NO systematic surgical excision → atypical forms with systemic involvement (encephalitis + hepatosplenic + optic neuropathy): more prolonged antibiotic treatment → doxycycline 100 mg × 2/d × 2-4 weeks → or azithromycin + bacteremia → rifampicin may be added; immunocompromised (HIV + CD4 <100 + transplanted) - bacillary angiomatosis + peliosis: treatment mandatory + long → doxycycline 100 mg PO × 2/d: treatment of choice → minimum duration 3 months → or erythromycin 500 mg × 4/d × 3 months → if severe bacteremia → doxycycline IV → relapse prevention: prolong treatment as long as immunosuppression persists → HIV : ART improves prognosis → frequent relapses if CD4 remains low → Bartonella endocarditis: doxycycline + gentamicin × 6 weeks → valve replacement if necessary; prevention: control fleas in cats (antiparasitic products) → regular treatment of cats against fleas → avoid being scratched or bitten by cats → wash hands after contact + disinfection of any scratch or bite with soap and water → immunocompromised: avoid kittens <12 months + or stray cats + if domestic cat → regular antiparasitic treatment against fleas. | Bass 1998 — Pediatrics (RCT): Azithromycin vs. placebo + Cat Scratch Disease → reduced lymph node size on Day 30 → reference + Jacomo 2002 — Clinical Microbiology Reviews: Bacillary angiomatosis + doxycycline treatment + erythromycin + duration → Rolain 2004 — Journal of Antimicrobial Chemotherapy: B. henselae + antibiotic susceptibility → Angelakis 2014 — Infectious Diseases Clinics of North America: Cat Scratch Disease + immunocompromised + treatment + CDC + IDSA 2021 STI/Bartonella guidelines + ASPC + INSPQ Quebec: Cat Scratch Disease + prevention + treatment + INESSS Quebec + RAMQ: azithromycin + doxycycline reimbursed + cat antiparasitic treatment → veterinary advice |
| Differential diagnosis and special situations Lymphadenopathy lymphoma — toxoplasmosis — tuberculosis — tularemia — lymphogranuloma venereum — mononucleosis — cervical adenopathy in children — Parinaud's syndrome — MGC encephalitis — splenomegaly granulomas — prolonged fever |
Differential diagnosis of cat scratch disease according to presentation: isolated regional adenopathy → main differential diagnosis: lymphoma (painless + hard + persistent + no scratch context → biopsy if doubtful) + toxoplasmosis (lymphocytosis + cervical adenopathy + Toxoplasma serology) + lymph node tuberculosis (cervical adenopathy + QuantiFERON + context) + tularemia (Francisella tularensis - contact with rabbits + hares + ticks + axillary or inguinal adenopathies) + LGV (lymphogranulomatosis venereum - inguinal adenopathies + ITSS context + PCR Chlamydia) + infectious mononucleosis (posterior cervical adenopathies + angina + Monospot) + common bacterial adenitis (staphylococcus + streptococcus - redness + warmth + rapid fluctuation) → oculo-glandular syndrome: follicular conjunctivitis + pre-auricular adenopathy → differential: adenovirus + ocular herpes + trachoma + tularemia + sporotrichosis + leishmaniasis → encephalitis and neurological involvement: differential with viral encephalitis (EBV + enterovirus + herpes) → MRI + LP + serologies → context of recent cat scratch + B. serology. henselae positive → specific situations in Quebec: prolonged fever + splenomegaly + multiple hypoechoic splenic nodules on echo in a child or adolescent + ATCD of cat contact → evoke hepatosplenic MGC → B. henselae serology + abdominal ultrasound → treatment with doxycycline if persistent form + unexplained prolonged febrile state in an immunocompromised patient + vascular skin lesions (red papules + bleeding) → bacillary Bartonella angiomatosis → skin biopsy (Warthin-Starry + PCR) → urgent doxycycline | Jacomo 2002 — Clinical Microbiology Reviews: Cat Scratch Disease (CSD) + atypical forms + differential diagnosis + Bass 1998 — Pediatrics: Pediatric CSD + Angelakis 2014 — Infectious Diseases Clinics: CSD in immunocompromised patients + bacillary angiomatosis + Lamps 2004 — Archives of Pathology: histology + Warthin-Starry stain → diagnosis + ASPC + INSPQ Quebec: zoonoses + CSD + prevention + treatment + INESSS Quebec + RAMQ: *B. henselae* serology + abdominal ultrasound + CBC + skin biopsy → reimbursed + infectious disease consultation for atypical forms or immunocompromised patients + IDSA 2021 |
ℹ️
Cat-scratch disease is the most common infectious cause of regional lymphadenopathy in children and adolescents. In a patient with a recent cat scratch or bite and ipsilateral painful satellite lymphadenopathy, the diagnosis is often clinical, and Bartonella henselae serology confirms it. In immunocompetent individuals, the illness is self-limiting within 2–4 months—azithromycin hastens resolution. In immunocompromised individuals (HIV+ CD4 <100), B. henselae can cause bacillary angiomatosis (vascular skin lesions) and hepatosplenic peliosis, requiring doxycycline for at least 3 months. Never incise a fluctuant lymph node—aspiration only.
Situations Requiring Urgent Infectious Disease Evaluation
Immunocompromised (HIV CD4 <100 + transplant + chemotherapy) + pink-red vascular skin lesions (papules + nodules bleeding to the touch) + fever + splenomegaly + painful bone lesions → bacillary angiomatosis with Bartonella → urgent skin biopsy (Warthin-Starry + PCR B. henselae) → doxycycline 100 mg twice daily PO for at least 3 months → urgent infectious disease consultation → severe prognosis without treatment.
Child with prolonged fever (>2 weeks) + asthenia + splenomegaly + abdominal pain + multiple hypoechoic splenic and hepatic nodules on ultrasound + history of recent contact with a kitten → Hepatosplenic MGC → *B. henselae* serology + CBC + LDH + transaminases → if persistent form → prolonged doxycycline or azithromycin → echo monitoring at 2–4 weeks.
Patient with recent cat scratch + development of persistent, very large (>5 cm), indurated adenopathy with no improvement after 4-6 weeks + no fever or positive B. henselae serology → Rule out lymphoma → Excisional lymph node biopsy + repeat serology + CT scan → DO NOT treat empirically without confirmed diagnosis.
Consult at Clinique Omicron
Clinique Omicron's doctors diagnose cat scratch disease clinically (cat scratch + satellite adenopathy) and with B. henselae serology. henselae serology, prescribe azithromycin if accelerated cure is desired, perform fine needle aspiration if painful fluctuating lymph node, refer to infectiologist for atypical forms or immunocompromised patients, and provide preventive advice (cat antiparasitic treatment + avoid scratching). Consultations are available at several points of service in Quebec, and via telemedicine. To book an appointment, visit cliniqueomicron.ca.
The content of this page is for informational purposes only and does not substitute for the advice of a physician or infectious disease specialist. In immunocompromised patients, any vascular skin lesion or prolonged fever with a history of cat contact should raise suspicion for Bartonella infection and requires urgent medical evaluation.
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