Bartonella
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Direct answer
A child with a cat scratch weeks earlier and one tender axillary node should prompt Bartonella henselae before an FNAC for tuberculosis is ordered. Bartonella are small, fastidious, facultatively intracellular gram-negative rods that stain poorly with Gram and best with Warthin-Starry silver; they are culture-negative by routine methods and slow even in enriched or automated systems, so serology and histology carry the diagnosis. Three species define the examinable spectrum: B. henselae — cat-scratch disease (regional lymphadenopathy after a cat scratch or flea bite, usually self-limiting) and, in advanced HIV, bacillary angiomatosis and peliosis hepatis; B. quintana — louse-borne trench fever, now urban homelessness and culture-negative endocarditis; B. bacilliformis — sandfly-transmitted Carrión disease, whose acute phase (Oroya fever) is a dramatic haemolytic anaemia from red cell invasion and whose chronic phase is the vascular tumours of verruga peruana.
What you must remember
- Morphology and staining: pleomorphic gram-negative rods, weakly Gram-staining; Warthin-Starry silver stain demonstrates them in tissue — the name to attach to cat-scratch lymph node histology.
- Vectors and reservoirs: B. henselae — cats are the reservoir and the cat flea (Ctenocephalides felis) the vector; flea faeces inoculated by scratching transmit; B. quintana — human body louse, humans the sole reservoir; B. bacilliformis — Lutzomyia sandflies in Andean valleys.
- Cat-scratch disease: papule at the inoculation site, then regional lymphadenopathy one to two weeks later (axillary, cervical, epitrochlear), tender with overlying red skin, low fever; suppurates in a minority; usually resolves over weeks to months.
- Uncommon CSD presentations to quote: Parinaud oculoglandular syndrome (conjunctivitis with preauricular node), neuroretinitis with a macular star, encephalopathy and seizures in children.
- Bacillary angiomatosis: lobular proliferations of capillaries in skin, bone, liver (peliosis) of severely immunocompromised patients — clinically mimicking Kaposi sarcoma; Warthin-Starry-positive organisms within; treated with prolonged erythromycin or doxycycline.
- Trench fever (B. quintana): the "five-day fever" of trench warfare — relapsing fever, severe shin pain, sterile blood cultures; today it causes chronic bacteraemia and culture-negative endocarditis in homeless, louse-infested populations.
- Carrión disease (B. bacilliformis): acute Oroya fever — fever and severe haemolytic anaemia with organisms filling erythrocytes — then weeks later verruga peruana angiomatous skin lesions; Daniel Carrión's fatal self-inoculation proved both phases one disease.
- Diagnosis and therapy: indirect fluorescent antibody serology is the practical standard, with PCR and prolonged blood culture to confirm; azithromycin shortens bulky CSD; endocarditis needs doxycycline plus gentamicin.
The AIDS-era angiomatosis, and what it taught
Rewind to the early HIV era, before combination antiretroviral therapy: patients with advanced immunosuppression under early NACO-era care in India had no such category yet, but Western cohorts were filling with violaceous skin nodules initially dismissed as Kaposi sarcoma — until biopsies showed not spindle-cell sarcoma but lobular capillary proliferations stuffed with Warthin-Starry-positive bacilli. Epidemiological detective work traced the agent to a new species, Bartonella henselae, and linked the same organism to peliosis hepatis, a blood-filled cystic liver disease in the same patients. The punchline: bacillary angiomatosis melted under prolonged erythromycin or doxycycline — a "tumour" that was a curable infection, reshaping how medicine thinks about vascular proliferation.
The same logic returns today: biopsy, not assumption, separates vascular lesions in HIV patients, and B. quintana serology or weeks-long blood cultures name pathogens routine protocols miss in culture-negative endocarditis.
Where students slip
Two vector errors recur: students credit the scratch itself with transmitting B. henselae directly from claw to blood, when the claw inoculates infected flea faeces — the cat is the reservoir, the flea the amplifier; and they assign trench fever to fleas or ticks rather than the body louse. Second slip: reaching for acid-fast or Gram expectations — Bartonella is the Warthin-Starry organism, and calling lymph node biopsy "negative for AFB, so no diagnosis" misses the granulomatous with stellate microabscesses and silver-positive bacilli that define cat-scratch histology. Third, treatment reflexes misfire: CSD in an immunocompetent child usually needs no antibiotic, and the examinable indications are bulky painful nodes, systemic illness, retinitis or immunocompromise. A final Indian angle for viva: cat-scratch disease is under-recognised rather than absent — with abundant street and household cats and fleas, the index of suspicion, backed by serology, is what finds it.
Frequently asked questions
Which Bartonella species causes cat-scratch disease, and how is it transmitted?
Bartonella henselae, with cats as reservoir and the cat flea as vector; infective flea faeces are inoculated through scratched skin, producing a papule and then regional lymphadenitis.
Why does bacillary angiomatosis mimic Kaposi sarcoma?
Both present as violaceous vascular skin lesions in immunocompromised hosts, but angiomatosis shows capillary lobules with neutrophils and Warthin-Starry-positive bacilli, and it responds to antibiotics.
What distinguishes the two phases of Carrión disease?
The acute Oroya fever phase is an intravascular haemolytic anaemia with bartonellae filling red cells; the chronic verruga peruana phase erupts as angiomatous cutaneous nodules weeks later, both caused by Bartonella bacilliformis.
What is trench fever, and who gets it now?
A relapsing fever with severe shin and back pain transmitted by the human body louse, classically of First World War trenches; today B. quintana also causes chronic bacteraemia and culture-negative endocarditis in homeless populations.
When should azithromycin be given in cat-scratch disease?
For bulky, painful suppurating lymphadenitis, systemic illness, hepatosplenic disease, neuroretinitis, or immunocompromised hosts — while uncomplicated CSD in healthy children is managed supportively.