Infectious Diseases & Family Medicine & Pediatrics
Cat scratch disease
Cat-scratch disease (CSD) is a bacterial infection caused by Bartonella henselae, A small, facultative intracellular Gram-negative bacillus of the Bartonellaceae family. It is transmitted mainly by cat scratch or bite, and more rarely by contact with cat saliva on a cutaneous wound or mucous membrane. The main vector of feline transmission is the cat flea (Ctenocephalides felis) - cats contaminate each other via flea droppings, without presenting any clinical disease. MGC is the most common cause of persistent subacute regional adenopathy in children and adolescents in North America. Its incidence in Canada is estimated at 4-10 cases per 100,000 population per year, with a predominance in autumn and winter. In the vast majority of immunocompetent cases, the disease is benign and resolves spontaneously within a few weeks to a few months. However, atypical and severe forms do occur - encephalitis, retinitis, hepatic peliosis, bacillary angiomatosis - particularly in immunocompromised patients (HIV, transplant patients, chemotherapy), where Bartonella henselae can cause serious and potentially fatal chronic infections if left untreated.
Pathogen, Transmission, and Clinical Presentation
- Microbiology and transmission cycle of Bartonella henselae : facultative intracellular Gram-negative bacillus - slow growth (14-21 days in culture on blood agar) - fastidious bacterium difficult to culture routinely - two main genotypes: type I (Houston-1) + type II (Marseille) - main reservoir: the domestic cat (Felis catus) - asymptomatic bacteremia in cats (duration: weeks to months) → cat infectious but clinically healthy → 40-60 % of cats are bacteremic to B. henselae in some studies (variable prevalence depending on region + temperate + tropical climates → higher prevalence); inter-feline transmission vector: cat flea (Ctenocephalides felis) - fleas ingest B. henselae during a blood meal on a bacteremic cat → bacteria multiply in the flea's intestine → excreted in flea feces («flea poop») → contaminate the cat's claws and fur → transmission to humans by scratching (inoculation of flea feces into the wound) or biting (saliva loaded by licking the claws) → fleas do not directly transmit the bacteria to humans through their bite ; risk factors for human infection : contact with a kitten (less than 1 year old - bacteremia more frequent and higher than in adults) + exposure to cat fleas + cat scratch or bite + immunodepression (risk of severe form) + high-risk profession (veterinarians + pet shops + animal shelters); other Bartonella species pathogenic to humans: B. quintana trench fever + bacillary angiomatosis + blood-culture-negative endocarditis (in homeless people + alcoholics - vector: body louse) + B. bacilliformis Carrión disease (verruga peruana + Oroya fever - Andes)
- Typical clinical presentation in immunocompetent individuals: inoculation phase (3-10 days after scratching): painless erythematous papule or pustule at scratch site (70-90 % of cases) → evolves in a few days into a vesicle + crust + spontaneous disappearance in 1-3 weeks → often overlooked by the patient as painless and transient - usual site: hands + forearms + legs + face (if licked by cat); regional adenopathy (1-7 weeks after inoculation - cardinal sign of MGC): lymph node(s) draining the skin territory of the scratch: hand scratch → axillary or epitrochlear adenopathy + face scratch → cervical or parotid adenopathy + foot-leg scratch → inguinal or femoral adenopathy - characteristics of adenopathy: unilateral (95 %) + bulky (1-5 cm - sometimes up to 8-10 cm) + tender to palpation + warm + mobile (initially non-adherent) + spontaneous evolution over 2-4 months (progressive resolution) → suppuration in 10-15 % of cases (suppurative adenitis - lymph node abscess → evacuating puncture if under tension); general signs (50-60 % of patients): moderate fever (38-39°C) + asthenia + general malaise + anorexia + headache - general signs usually moderate and transient (1-2 weeks); natural course in immunocompetent patients: complete spontaneous resolution in 2-4 months in 90 % of cases - adenopathy may persist for up to 1 year in 10 % of cases - exceptional recurrence (lasting immunity after primary infection); differential diagnosis of subacute regional adenopathy: lymphoma (Hodgkin + non-Hodgkin) + lymph node tuberculosis + atypical mycobacteria + toxoplasmosis + common bacterial infections (staphylococcus + streptococcus) + infectious mononucleosis (EBV) + tularemia + sporotrichosis + lymph node metastasis.
- Atypical forms and complications : Parinaud's oculo-glandular syndrome (5-10 % of MGC) : conjunctival inoculation (licking or eye contact) → unilateral conjunctival granuloma (painless erythematous papule + sometimes necrotic - visible with a slit lamp on the inferior fornix) + ipsilateral preauricular or submandibular adenopathy (preauricular ganglion ++ - almost pathognomonic diagnosis if associated with conjunctival granuloma) → spontaneously favorable evolution in 2-4 months → antibiotic treatment accelerates healing ; hepatosplenic involvement (hepatosplenic granulomas - 1-5 % of MGC): more frequent in children - prolonged fever + abdominal pain + hepatomegaly + splenomegaly + moderate elevation of transaminases + abdominal ultrasound: multiple hypoechoic hepatic and/or splenic nodules (granulomas) + abdominal CT → characteristic aspects - spontaneously favorable evolution (2-6 months) + antibiotic therapy accelerates resolution; neurology (0.5-2 % of MGC - especially in children): encephalitis (abrupt onset - convulsions + obnubilation + confusion + altered state of consciousness) + aseptic meningitis + radiculopathy + myelitis + optic neuritis → CSF: lymphocytic pleocytosis + moderate proteinorachy + PCR B. henselae rarely positive on CSF → serology B. henselae positive → overall favorable prognosis (complete cure in 90 % of encephalitis cases in 1-6 months) but risk of neuropsychological sequelae in severe forms; retinitis and stellate neuroretichopaticularis (0.5-1 %): unilateral drop in visual acuity + macular star (star-shaped perimacular lipid deposits - characteristic appearance on fundus) + papilledema → ophthalmological emergency → ophthalmology opinion + urgent antibiotic therapy (risk of permanent visual sequelae); endocarditis with negative blood cultures: B. henselae (+ B. quintana) is one of the major causes of endocarditis with negative blood cultures - echocardiography (vegetations) + serology B. henselae + PCR on surgical valve if resection; bacillary angiomatosis and hepatic peliosis (immunocompromised forms - see below)
Diagnosis, treatment, and special forms
| Clinical situation | Diagnosis | Treatment and follow-up |
|---|---|---|
| Typical MGC — benign form Regional lymphadenopathy — immunocompetent |
The diagnosis of typical cat-scratch disease is essentially clinical and epidemiological in immunocompetent individuals. Further examinations are reserved for doubtful or atypical cases. Clinical diagnostic criteria (3 out of 4 criteria are sufficient - according to revised Margileth criteria): contact with a cat (scratch or bite within the previous 3 weeks) + papule or pustule at the inoculation site (still present or described by the patient) + tender unilateral regional lymphadenopathy in the drainage territory of the inoculation lesion + serology B. henselae positive OR compatible lymph node histology (if biopsy performed); serology B. henselae (indirect immunofluorescence - IFI or ELISA): IgG ≥1:64: compatible with a past or recent infection - IgG ≥1:256 or IgM positive: probable recent infection (IgM peak at 2-4 weeks + IgG persist 1-2 years) - sensitivity 80-95 % + specificity 95-98 % - possible cross-reactions with B. quintana + Coxiella burnetii + Chlamydia + some Gram-negatives (check with referring laboratory) - delay: IgG may not yet be detectable in the first 2 weeks of illness → repeat serology at 2-3 weeks if initially negative and strong clinical suspicion; PCR on sample : PCR B. henselae on lymph node pus (fine needle aspiration) or lymph node biopsy: sensitivity 43-76 % + specificity 100 % → examination of choice if serology negative + strong suspicion + or if diagnosis of certainty is required (immunocompromised child + atypical form) → refer to reference laboratory (LSPQ - Laboratoire de santé publique du Québec); lymph node histology (if excisional biopsy performed - not routinely recommended): epithelioid granulomas with stellate central necrosis + microabscesses + special stains (Warthin-Starry - silver impregnation): Gram-negative rods in necrotic areas + compatible but not pathognomonic; CBC and laboratory workup: moderate hyperleukocytosis + modest eosinophilia (10-15 %) + moderately elevated ESR + CRP + moderately elevated transaminases if hepatosplenic involvement - these abnormalities are non-specific but point to an infectious etiology | Treatment of typical MGC in the immunocompetent: benign MGC in the immunocompetent is self-limiting - antibiotic treatment modestly reduces the duration of symptoms, but its clinical benefit in the immunocompetent adult with benign typical form is debated (meta-analyses: modest acceleration of lymph node regression) → decision to treat individually according to severity + symptoms + terrain; recommended antibiotic treatment (if decision to treat): azithromycin (1st line - strongest data): adult: 500 mg PO D1 then 250 mg/d D2-J5 (5 days) - child: 10 mg/kg D1 then 5 mg/kg/d D2-J5 - Bass 1998 meta-analysis (PIDJ): significant reduction in lymph node volume at D30 with azithromycin vs placebo; alternatives: doxycycline 100 mg × 2/d × 10-14 days (adult - CI in children <8 years and pregnant women) + trimethoprim-sulfamethoxazole (TMP-SMX - Septra): 160/800 mg × 2/d × 7-10 days + rifampicin 300 mg × 2/d × 10-14 days (especially in forms with hepatosplenic involvement) + ciprofloxacin: secondary option (limited data in MGC); suppurative adenitis (lymph node abscess): evacuating needle puncture (aspiration of pus - preferred to surgical incision - reduced pain + prevention of skin fistulization) + pus sent for PCR + culture + concomitant oral antibiotic therapy; analgesia and symptomatic measures: paracetamol or ibuprofen if pain + NSAIDs if marked local inflammation + local application of heat to the lymph node (optional - symptomatic relief); follow-up: reassessment consultation at 2-4 weeks to check lymph node regression + if persistence or increase in lymph node volume after 4-6 weeks of treatment → consider lymph node biopsy to rule out lymphoma or mycobacteriosis |
| Atypical forms — visceral involvement Hepatosplenic — neurological — ocular |
Atypical forms of MGC are more frequent in children and adolescents and require a more in-depth diagnostic approach; hepatosplenic involvement (hepatosplenic granulomas): context: child + prolonged fever ≥2 weeks + abdominal pain + hepatomegaly ± splenomegaly — imaging: abdominal ultrasound (first intention): multiple hypoechoic nodules in the liver and/or spleen (2–20 mm) ± hypoechoic halo — abdominal CT scan with contrast: hypodense nodules that do not enhance + sometimes calcified if old — abdominal MRI: hypointense T1 nodules + hypointense T2 nodules (central fibrosis) — serology B. henselae : often strongly positive (IgG >1:512) in these forms — Hepatic PCR (biopsy-guided if diagnostic doubt) + liver function tests: moderately elevated AST + ALT + elevated alkaline phosphatase + normal bilirubin; encephalitis due to B. henselae Cerebral CT: often normal - Cerebral MRI: may show T2/FLAIR hypersignals + sometimes ischemic lesions - EEG: diffuse non-specific abnormalities - LP: normal CSF or mild lymphocytic pleocytosis (50-200 cells) + moderately elevated proteinorachy + PCR B. henselae on CSF: not very sensitive - serology: high IgG + sometimes IgM+; Bartonella retinitis and optic neuropathy: fundus: macular star (star-shaped perimacular lipid exudative deposits) + papilledema + whitish retinal plaques - AFG (angiofluorography): papilledema + vascular diffusion + retinal plaques - OCT (optical coherence tomography): optic nerve edema + perimacular retinal thickening - serology B. henselae high - diagnostic and therapeutic urgency (risk of permanent visual damage) | Treatment of atypical forms of MGC: hepatosplenic forms (hepatosplenic granulomas): prolonged oral antibiotic treatment: rifampicin 300 mg twice daily PO for 4-6 weeks ± azithromycin 500 mg/day PO day 1 then 250 mg/day for 4 days — the combination of rifampicin + azithromycin is preferred in severe or prolonged forms — alternative: doxycycline 100 mg twice daily for 4-6 weeks — TMP-SMX 160/800 mg twice daily for 4-6 weeks — resolution of hepatosplenic nodules: 2-6 months under treatment (sometimes persistent calcifications without pathological significance) — ultrasound follow-up at 1-3 months; encephalitis B. henselae antibiotic treatment recommended, although data are limited (largely self-limiting disease): doxycycline 100 mg × 2/d × 4 weeks (adult) + azithromycin alternative - anticonvulsants if epileptic seizures (levetiracetam + valproate - duration according to control EEG) - corticoids (dexamethasone) : discussed in severe encephalitis (insufficient data - use on a case-by-case basis) - hospitalization + neurological monitoring + resuscitation if status epilepticus; retinitis and optic neuropathy : urgent antibiotic treatment (doxycycline 100 mg × 2/d × 4-6 weeks OR azithromycin × 4-6 weeks) + systemic corticosteroids (prednisone 1 mg/kg/d × 1-2 weeks with gradual taper-off) if significant drop in visual acuity or marked papilledema - urgent ophthalmological opinion + follow-up OCT and fundus at 1 month - visual prognosis : complete recovery in 60-80 % if treated promptly → possible sequelae if treated late; Parinaud's syndrome (oculo-glandular): azithromycin × 5 days or doxycycline × 14 days + local eye care (artificial tears + eyelid hygiene) + spontaneous favorable evolution if untreated but antibiotic therapy accelerates healing |
| MGC in immunocompromised individuals Bacillary angiomatosis — hepatic peliosis |
In immunocompromised patients (HIV with CD4 <100 cells/µL + transplant recipients + chemotherapy + prolonged corticosteroid therapy), Bartonella henselae (and B. quintana) cause distinct and potentially fatal clinical forms - bacillary angiomatosis (BA) and hepatic peliosis (HP) - which differ profoundly from the typical MGC of the immunocompetent; bacillary angiomatosis (BA): cutaneous and visceral proliferative vascular lesions - skin: erythematous or purplish skin papules or nodules (resembling Kaposi's sarcoma lesions) → distribution: trunk + limbs + face + mucous membranes → variable number (1 to several hundred) → firm consistency + easy bleeding on contact → skin biopsy essential (histology + Warthin-Starry + PCR) → essential differentiation from Kaposi's sarcoma (totally different treatment); visceral manifestations of bacillary angiomatosis : bone involvement (bone pain + osteolysis on X-ray + osteomyelitis) + adenopathies (multiple + enlarged) + pleuropulmonary involvement (nodules + pleural effusion) + CNS involvement (intracranial lesions) + persistent bacteremia (blood cultures + lysis centrifugation); hepatic peliosis (PH): dilated intrahepatic (and splenic) vascular cavities filled with blood → hepatomegaly + abdominal pain + marked elevation of alkaline phosphatases + moderately elevated AST/ALT + CT: multiple hypodense hepatic and splenic lesions + liver biopsy (histology + PCR): vascular cavities lined with bacterial clusters (Warthin-Starry) → diagnosis of certainty; diagnostic workup in immunocompromised patients: blood cultures (special medium - lysis centrifugation - Isolator): positive in 20-40 % of Bartonella bacteremias - PCR B. henselae on EDTA whole blood: sensitivity 70-90 % in active bacteremia - serology: often falsely negative in immunocompromised patients (insufficient antibody response) → do not exclude the diagnosis on negative serology - tissue biopsy (skin + liver) + histology + PCR + Warthin-Starry staining | Treatment of bacillary angiomatosis and peliosis hepatis in the immunocompromised: reference treatment : erythromycin 500 mg × 4/d PO × 3 months minimum (ABL + hepatic peliosis) - or doxycycline 100 mg × 2/d PO × 3 months minimum - some experts prefer doxycycline (better intracellular penetration + fewer side effects than erythromycin); severe or disseminated forms (bacteremia + significant visceral damage): doxycycline 100 mg × 2/d IV then PO + rifampicin 300 mg × 2/d PO (synergistic combination) - duration: minimum 3-4 months - if HIV: initiation or optimization of concomitant antiretroviral therapy (ART) → immune restoration → reduced risk of recurrence; duration of treatment: at least 3 months - some experts recommend 4-6 months depending on severity + immune restoration + clinical response - in case of HIV with CD4 200/µL on stable ART for >3 months → doxycycline 100 mg/d or erythromycin 500 mg/d as secondary prophylaxis; frequent relapse (20-40 %) if treatment too short or if immunodepression uncorrected → clinical monitoring + blood cultures + control PCR + visceral imaging; prevention in the immunocompromised patient (HIV CD4 <100): avoid kittens (higher bacteremia) + treat fleas in domestic cats (veterinary antiparasitics - pyrethroids + imidacloprid) + careful disinfection of scratches + no need to eliminate the cat from the household if fleas are controlled |
| Endocarditis Bartonella Negative blood cultures - native or prosthetic valve |
Bartonella henselae and B. quintana are among the leading causes of blood culture-negative infective endocarditis worldwide - representing up to 3-5 % of all infective endocarditis and 25-30 % of blood culture-negative endocarditis in some series; suggestive epidemiological context: recent feline contact (+ native valvulopathy or prosthetic valve + immunodepression - for B. henselae) or precarious social conditions + alcoholism + homelessness (for B. quintana — vector: body louse); clinical presentation of Bartonella endocarditis: prolonged fever of unknown origin (FUO) + heart murmur + splenomegaly + large vegetations (often >10–15 mm) on aortic or mitral valves + peripheral signs of endocarditis (purpura + Osler's nodes + Janeway lesions + subungual hemorrhages) + often preserved general condition (subacute course); diagnostic workup: blood cultures: negative (despite adequate technique) on standard media → culture on special media (lysis centrifugation + enriched media + prolonged incubation 4–6 weeks) — if blood cultures negative after 5 days → consider fastidious bacterium (Bartonella + HACEK + Coxiella + Brucella + Tropheryma whipplei) → extended serological workup + serology B. henselae + B. quintana (IFA): IgG ≥1:800 → highly suggestive of Bartonella endocarditis (modified Duke - minor criterion) - PCR on blood + PCR on valve biopsy (if surgery): sensitivity 80-95 % on valve - ETT + ETO (vegetations + valve destruction + periannular abscess) + 18F-FDG PET-CT: valvular hypermetabolism + peripheral septic foci; modified Duke criteria including criteria for fastidious bacteria: IgG serology ≥1:800 for Bartonella = minor criterion (Duke 2000) | Endocarditis Treatment Bartonella Medical treatment (native valve - uncomplicated form): doxycycline 100 mg twice daily PO for 6 weeks + gentamicin 3 mg/kg/day IV for 14 days (initial synergistic phase) - alternative if contraindication to doxycycline: erythromycin 1 g four times daily IV for 2-4 weeks then oral switch for 6 weeks; surgical + medical treatment (surgical indications): severe valvular destruction + refractory heart failure + vegetation >15 mm + periannular abscess + recurrent septic emboli → valve replacement (biological or mechanical depending on the patient's condition) + valve biopsy → histology + PCR + culture + follow-up: serology B. henselae every 3 months (decreased IgG while on effective treatment - slow - can remain elevated for 1–2 years) + control TTE or TEE at 3–6 months + control PCR if relapse suspected — prognosis: in-hospital mortality 5–10% % (better than standard bacterial endocarditis with appropriate management) + possible relapse if treatment is too short + recurrence rare if treatment is complete and cause identified + treated; prophylaxis of Bartonella endocarditis in patients at risk: no established primary prophylaxis — in cardiac patients (valvular disease + prosthetic valve) with a cat: strict control of cat fleas (regular veterinary antiparasitic treatment) + disinfection of scratches + awareness of risk + seek medical attention quickly if unexplained fever >1 week |
| Prevention and advice for cat owners Chip Control — Risky Behaviors |
The prevention of AMD relies on reducing exposure to B. henselae via cat flea control and behavioral precautions; modifiable risk factors: kitten ownership (<12 months - higher risk of bacteremia) + flea infestation on the cat (vector of inter-feline transmission) + contact with cat claws or saliva on wounds or mucous membranes; recommended preventive measures - flea control : regular veterinary antiparasitic treatment of the cat (spot-on products - imidacloprid + fipronil + selamectin - applied monthly as recommended by the vet + antiparasitic collar + environmental treatment if heavy domestic infestation - vacuum cleaner + adulticidal products + larvicides on bedding + carpets) → flea control is the most effective preventive measure against MGC; risk behaviors to avoid: do not rub eyes or mucous membranes after stroking a cat + immediately and thoroughly disinfect any scratch or bite (water + soap + iodized antiseptic or chlorhexidine) + avoid letting the cat lick open wounds or mucous membranes + do not kiss the cat on the muzzle; patients at particular risk (immunocompromised - HIV CD4 1 year - less frequent bacteremia) to a kitten + rigorous veterinary antiparasitic treatment + don't necessarily eliminate the cat from the household (significant psychological impact - especially HIV) if control measures are respected; information for parents of children: children are the population most exposed to MGC (more frequent contact + fewer precautions) → explain to parents the warning signs (subacute regional adenopathy after scratching) → consult rapidly + reassure them that the disease is usually benign. | Resources in Quebec for managing CF: family doctor or pediatrician: first point of contact for diagnosis and treatment of typical CF + prescription of serology B. henselae (available in private - Biron + Dynacare - and hospital LBM laboratories in Quebec); pediatric infectiology (CHU Sainte-Justine + CHUM + CHU de Québec): atypical forms (hepatosplenic + neurological + ocular) + immunocompromised patients + Bartonella endocarditis; LSPQ (Quebec Public Health Laboratory): PCR B. henselae on tissue samples or lymph node pus + molecular identification of Bartonella species + available via hospital laboratories with forwarding to LSPQ; ophthalmology: Bartonella retinitis + Parinaud's syndrome + emergency if visual acuity declines; cardiology + cardiac surgery: Bartonella endocarditis (CHUM + McGill + Montreal Heart Institute); post-healing follow-up: no particular follow-up required for benign cured MGC - IgG antibodies persist 1-2 years (serology remains positive without significance of active infection) → do not interpret isolated positive IgG serology without clinical context as active MGC → avoid overtreatment of seropositive asymptomatic seropositivity of incidental discovery |
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Persistent subacute regional lymphadenopathy — do not forget MGC: in the case of any unilateral regional adenopathy persisting for more than 3 weeks in a child or young adult, the question of recent feline contact should be asked systematically. MGC is the first cause to be considered, before beginning a work-up to rule out lymphoma or lymph node tuberculosis. Serology B. henselae with a compatible epidemiological context (cat scratches in the preceding 3-8 weeks) is sufficient for diagnosis in the vast majority of cases, avoiding a potentially useless lymph node biopsy and its complications.
Situations requiring urgent medical assessment
Bartonella retinitis (unilateral decrease in visual acuity + macular star on fundus examination) in a patient with recent cat contact → ophthalmological emergency → doxycycline + systemic corticosteroids + ophthalmology opinion the same day.
Acute encephalitis (seizures + altered consciousness) in a child with a history of a recent cat scratch → hospitalization + neurological assessment (MRI + EEG + PL) + serology B. henselae urgent + empirical antibiotic therapy.
HIV patient (CD4 <100) with multiple purplish papular skin lesions, fever, and hepatomegaly → probable bacillary angiomatosis → skin biopsy + Bartonella PCR + doxycycline IV or erythromycin IV + initiation or optimization of ART.
Unexplained prolonged fever + heart murmur + negative blood cultures after 5 days + feline contact or precarious social conditions → Bartonella endocarditis → serology B. henselae + B. quintana + TEE + PCR on blood + infectious diseases and cardiology advice.
Consult at Clinique Omicron
Clinique Omicron physicians evaluate subacute regional lymphadenopathies suspected of cat-scratch disease, prescribing serology Bartonella henselae and initiate the appropriate antibiotic treatment according to clinical presentation. Atypical forms (hepatosplenic, neurological, ocular) are referred to specialized teams 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 medical or infectious disease specialist advice. Atypical forms and cases in immunocompromised patients require specialized medical evaluation.
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