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Infectious Disease and Microbiology – Cat-Scratch Disease (Bartonella Infections)
Cat-scratch disease is typically a self-limited acute illness characterized by regional lymphadenopathy with or without fever and constitutional symptoms. It is most commonly caused by Bartonella henselae. In addition to classic lymphadenitis, B. henselae infection may present as fever of unknown origin, hepatosplenic granulomatous disease, neuroretinitis, or encephalopathy. Other medically important Bartonella species include Bartonella quintana, the historical cause of trench fever and a cause of persistent bacteremia, endocarditis, and bacillary angiomatosis, and Bartonella bacilliformis, which causes Oroya fever.
In the United States, the incidence of cat-scratch disease is approximately 10 cases per 100,000 person-years, with an estimated 24,000 recognized cases annually. The disease occurs worldwide and shows seasonal variation in temperate climates, with most cases occurring between August and January. It primarily affects immunocompetent individuals, and about 80% of cases occur in persons younger than 21 years. Most cases are self-limited and present with regional adenopathy. Bartonella quintana is globally endemic and associated with body louse transmission, while Bartonella bacilliformis is transmitted by sand flies and occurs at altitudes above 1 km in the Andes.
Cats, particularly kittens and those infested with fleas, are the natural reservoir of B. henselae. A history of cat exposure is reported in approximately 90% of patients, and about 60% recall a scratch. B. quintana outbreaks are associated with homelessness and poor socioeconomic conditions, where infestation with the human body louse (Pediculus humanus) facilitates transmission. Immunocompromised patients, especially those with advanced HIV infection, are at increased risk of chronic Bartonella infections such as bacillary angiomatosis and bacillary peliosis.
Prevention includes limiting exposure to cat scratches, bites, and licks, especially in immunocompromised individuals. Control of cat fleas may reduce transmission risk.
Bartonella species are fastidious, gram-negative, aerobic rod-shaped bacteria capable of intracellular survival. Infection leads to an inflammatory response and granuloma formation, particularly in lymph nodes. B. henselae accounts for the vast majority of cat-scratch disease cases.
The illness often begins with a small erythematous papule or pustule at the site of inoculation that may persist for weeks. Regional lymph nodes draining the affected area enlarge and become tender. Fever and malaise occur in approximately 30% of patients. Neuroretinitis may present with decreased visual acuity, and encephalopathy may manifest as mental status changes. In HIV-infected individuals, B. henselae bacteremia may cause progressive fatigue, weight loss, recurrent fevers, and hepatomegaly.
Trench fever due to B. quintana typically presents after an incubation period of 3–38 days with sudden onset of chills and fever. Symptoms such as headache, retro-orbital pain, and conjunctival injection are nonspecific. Bacillary angiomatosis presents with red-to-purple papules or nodules that may ulcerate or bleed. Bacillary peliosis involves blood-filled cystic lesions within visceral organs such as the liver or spleen.
On physical examination, regional lymphadenopathy is the most common finding. A primary inoculation lesion may be visible. Parinaud’s oculoglandular syndrome, characterized by conjunctivitis, conjunctival granuloma, and preauricular lymphadenopathy, occurs in approximately 5% of patients. Visceral involvement may produce hepatosplenomegaly.
Laboratory findings may show mild leukocytosis with occasional eosinophilia. Bartonella species can be isolated from blood using specialized culture techniques. Serologic testing with indirect fluorescence assays is widely used; titers greater than 1:256 strongly suggest active infection. If results are equivocal, repeat serology after two weeks may assist diagnosis. Ultrasound of enlarged lymph nodes may help evaluate suppuration and guide aspiration. Histopathology typically shows granuloma formation, and special stains such as Warthin–Starry or tissue PCR may support the diagnosis.
Diagnosis is suggested by compatible clinical findings, history of cat exposure, positive serology, characteristic histopathology, and exclusion of other causes of lymphadenopathy, particularly mycobacterial infections and suppurative adenitis.
Although cat-scratch disease is usually self-limited, antibiotics may hasten resolution. Azithromycin (500 mg orally once, then 250 mg daily for four additional days) is commonly used in adults. Neuroretinitis has been treated with doxycycline plus rifampin, although evidence is limited. Bacillary angiomatosis limited to the skin is treated with erythromycin (500 mg four times daily) or doxycycline (100 mg twice daily) for 8–12 weeks. Bacteremia requires at least four weeks of therapy, and longer courses (2–3 months) are recommended in HIV-infected patients, persistent fever, or endocarditis. Alternative agents include rifampin, ciprofloxacin, and trimethoprim-sulfamethoxazole.
If lymph node suppuration occurs, needle aspiration is preferred over incision and drainage to relieve pain and promote recovery. Valve replacement may be required in Bartonella endocarditis.
Lymphadenopathy usually resolves over several months. One episode appears to confer lifelong immunity. In immunocompetent individuals, fever resolves promptly with or without therapy. In HIV-infected patients, resolution of fever may take longer, although bacteremia typically clears within a week of treatment.
Uncomplicated cat-scratch disease has an excellent prognosis. Complications, including retinitis, encephalopathy, or severe systemic disease, occur in 5–14% of cases. Encephalopathy typically develops weeks after the acute illness and may present with seizures; recovery is usually rapid. Inflammatory organ involvement without angiomatosis or peliosis has been reported in patients with AIDS, affecting the liver, spleen, lymph nodes, heart, and bone marrow.
Cat-scratch disease is typically a self-limited acute illness characterized by regional lymphadenopathy with or without fever and constitutional symptoms. It is most commonly caused by Bartonella henselae. In addition to classic lymphadenitis, B. henselae infection may present as fever of unknown origin, hepatosplenic granulomatous disease, neuroretinitis, or encephalopathy. Other medically important Bartonella species include Bartonella quintana, the historical cause of trench fever and a cause of persistent bacteremia, endocarditis, and bacillary angiomatosis, and Bartonella bacilliformis, which causes Oroya fever.
In the United States, the incidence of cat-scratch disease is approximately 10 cases per 100,000 person-years, with an estimated 24,000 recognized cases annually. The disease occurs worldwide and shows seasonal variation in temperate climates, with most cases occurring between August and January. It primarily affects immunocompetent individuals, and about 80% of cases occur in persons younger than 21 years. Most cases are self-limited and present with regional adenopathy. Bartonella quintana is globally endemic and associated with body louse transmission, while Bartonella bacilliformis is transmitted by sand flies and occurs at altitudes above 1 km in the Andes.
Cats, particularly kittens and those infested with fleas, are the natural reservoir of B. henselae. A history of cat exposure is reported in approximately 90% of patients, and about 60% recall a scratch. B. quintana outbreaks are associated with homelessness and poor socioeconomic conditions, where infestation with the human body louse (Pediculus humanus) facilitates transmission. Immunocompromised patients, especially those with advanced HIV infection, are at increased risk of chronic Bartonella infections such as bacillary angiomatosis and bacillary peliosis.
Prevention includes limiting exposure to cat scratches, bites, and licks, especially in immunocompromised individuals. Control of cat fleas may reduce transmission risk.
Bartonella species are fastidious, gram-negative, aerobic rod-shaped bacteria capable of intracellular survival. Infection leads to an inflammatory response and granuloma formation, particularly in lymph nodes. B. henselae accounts for the vast majority of cat-scratch disease cases.
The illness often begins with a small erythematous papule or pustule at the site of inoculation that may persist for weeks. Regional lymph nodes draining the affected area enlarge and become tender. Fever and malaise occur in approximately 30% of patients. Neuroretinitis may present with decreased visual acuity, and encephalopathy may manifest as mental status changes. In HIV-infected individuals, B. henselae bacteremia may cause progressive fatigue, weight loss, recurrent fevers, and hepatomegaly.
Trench fever due to B. quintana typically presents after an incubation period of 3–38 days with sudden onset of chills and fever. Symptoms such as headache, retro-orbital pain, and conjunctival injection are nonspecific. Bacillary angiomatosis presents with red-to-purple papules or nodules that may ulcerate or bleed. Bacillary peliosis involves blood-filled cystic lesions within visceral organs such as the liver or spleen.
On physical examination, regional lymphadenopathy is the most common finding. A primary inoculation lesion may be visible. Parinaud’s oculoglandular syndrome, characterized by conjunctivitis, conjunctival granuloma, and preauricular lymphadenopathy, occurs in approximately 5% of patients. Visceral involvement may produce hepatosplenomegaly.
Laboratory findings may show mild leukocytosis with occasional eosinophilia. Bartonella species can be isolated from blood using specialized culture techniques. Serologic testing with indirect fluorescence assays is widely used; titers greater than 1:256 strongly suggest active infection. If results are equivocal, repeat serology after two weeks may assist diagnosis. Ultrasound of enlarged lymph nodes may help evaluate suppuration and guide aspiration. Histopathology typically shows granuloma formation, and special stains such as Warthin–Starry or tissue PCR may support the diagnosis.
Diagnosis is suggested by compatible clinical findings, history of cat exposure, positive serology, characteristic histopathology, and exclusion of other causes of lymphadenopathy, particularly mycobacterial infections and suppurative adenitis.
Although cat-scratch disease is usually self-limited, antibiotics may hasten resolution. Azithromycin (500 mg orally once, then 250 mg daily for four additional days) is commonly used in adults. Neuroretinitis has been treated with doxycycline plus rifampin, although evidence is limited. Bacillary angiomatosis limited to the skin is treated with erythromycin (500 mg four times daily) or doxycycline (100 mg twice daily) for 8–12 weeks. Bacteremia requires at least four weeks of therapy, and longer courses (2–3 months) are recommended in HIV-infected patients, persistent fever, or endocarditis. Alternative agents include rifampin, ciprofloxacin, and trimethoprim-sulfamethoxazole.
If lymph node suppuration occurs, needle aspiration is preferred over incision and drainage to relieve pain and promote recovery. Valve replacement may be required in Bartonella endocarditis.
Lymphadenopathy usually resolves over several months. One episode appears to confer lifelong immunity. In immunocompetent individuals, fever resolves promptly with or without therapy. In HIV-infected patients, resolution of fever may take longer, although bacteremia typically clears within a week of treatment.
Uncomplicated cat-scratch disease has an excellent prognosis. Complications, including retinitis, encephalopathy, or severe systemic disease, occur in 5–14% of cases. Encephalopathy typically develops weeks after the acute illness and may present with seizures; recovery is usually rapid. Inflammatory organ involvement without angiomatosis or peliosis has been reported in patients with AIDS, affecting the liver, spleen, lymph nodes, heart, and bone marrow.
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