Cat Scratch Disease and Bartonellosis

Prepared and reviewed by the PrepElephant Academic Review Team

First published 14 Oct 2026 · Spot an error?

Reference basis: Ananthanarayan and Paniker's Textbook of Microbiology; Harrison's Principles of Internal Medicine; Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases

On this page

Direct answer
What you must remember
Comparing the Bartonella species
Where the exam tries to catch you
Frequently asked questions
Related topics

Direct answer

Cat scratch disease is a self-limiting regional lymphadenopathy caused by Bartonella henselae, a fastidious gram-negative bacillus transmitted mainly by scratches or bites from cats and by cat fleas. Bartonellosis is the wider group of infections caused by Bartonella species, including bacillary angiomatosis in HIV and trench fever caused by Bartonella quintana. Most cases of cat scratch disease resolve without antibiotics, while immunocompromised patients need targeted treatment.

What you must remember

Causative organism: Bartonella henselae is a slow-growing, fastidious gram-negative bacillus; Bartonella quintana causes trench fever.
Cat scratch disease: a papule at the inoculation site, followed one to three weeks later by tender regional lymphadenopathy, usually axillary or cervical.
Parinaud oculoglandular syndrome: granulomatous conjunctivitis with ipsilateral preauricular nodes, typically after contact with a cat.
Histology: stellate necrotising granulomas in the node; Warthin-Starry silver staining can demonstrate the bacilli.
Bacillary angiomatosis: proliferation of vascular lesions in the skin and viscera, seen in advanced HIV with low CD4 counts.
Trench fever: Bartonella quintana is transmitted by the human body louse and causes relapsing fever with shin pain.
Carrion disease: Bartonella bacilliformis is sandfly-borne and causes Oroya fever and verruga peruana.
Treatment: supportive care for uncomplicated cat scratch disease, antibiotics such as azithromycin for severe cases, and a prolonged course of erythromycin or doxycycline for bacillary angiomatosis.

Comparing the Bartonella species

A 9-year-old child develops a tender axillary node two weeks after a kitten scratched her arm, and the node has no other obvious cause. The table shows how the species differ by vector and by the disease they cause, and students should keep the vector, host and organ involvement together when answering.

Species	Vector or reservoir	Main disease
Bartonella henselae	Cat; cat flea	Cat scratch disease; bacillary angiomatosis
Bartonella quintana	Human body louse	Trench fever; chronic bacteraemia; endocarditis
Bartonella bacilliformis	Sandfly	Carrion disease (Oroya fever and verruga peruana)

Most cat scratch disease in children is benign and follows a predictable course. Kittens are the commonest source, and the organism persists in cats without causing them harm. Some nodes suppurate, and fine-needle aspiration may be needed to exclude tuberculosis and other causes. Diagnosis rests on the history of cat contact, the typical nodal pattern and serology or PCR, since routine culture rarely grows the organism.

Where the exam tries to catch you

Questions on this topic often test whether the candidate knows which Bartonella disease belongs to which host and how the diagnosis is made.

Trap: cat scratch disease needs antibiotics in every case. Correct: it is usually self-limiting over weeks to months, and antibiotics are reserved for severe, prolonged or complicated disease.
Trap: bacillary angiomatosis occurs in immunocompetent children. Correct: it is an AIDS-associated illness that occurs with low CD4 counts.
Trap: Bartonella grows readily on routine culture. Correct: it is fastidious and slow-growing, so diagnosis relies on serology, PCR or histology with silver staining.
Trap: Parinaud oculoglandular syndrome is a separate disease. Correct: it is a presentation of cat scratch disease with granulomatous conjunctivitis and preauricular nodes, though other organisms can cause it.

Frequently asked questions

What is the typical presentation of cat scratch disease?

Cat scratch disease typically presents with a small papule at the inoculation site, followed one to three weeks later by tender regional lymphadenopathy, usually axillary or cervical. Low-grade fever and malaise may accompany the nodes. The illness is usually self-limiting over weeks to months.

What histological finding is characteristic of cat scratch disease?

Cat scratch disease shows necrotising granulomas with stellate microabscesses in the lymph node. Warthin-Starry silver staining can demonstrate Bartonella bacilli in tissue. Histology alone is not diagnostic, so serology or PCR is commonly added.

What is Parinaud oculoglandular syndrome?

Parinaud oculoglandular syndrome is a granulomatous conjunctivitis with ipsilateral preauricular or cervical lymphadenopathy. It is most often caused by Bartonella henselae after contact with a cat, though Francisella tularensis is another recognised cause. The eye findings are usually unilateral.

Which vector transmits Bartonella quintana?

Bartonella quintana is transmitted by the human body louse, and it causes trench fever, characterised by relapsing fever and shin pain. It is also associated with chronic bacteraemia and culture-negative endocarditis in homeless adults. Hygiene and louse control are the main preventive measures.

How is bacillary angiomatosis treated?

Bacillary angiomatosis is treated with a prolonged course of erythromycin or doxycycline, often for several months. It occurs in people with advanced HIV, and lesions can appear as vascular skin papules or visceral masses. Relapse is common if treatment is stopped early.