Bartonellosis/Cat Scratch Disease (Bartonella henselae)
Overview
Plain-Language Overview
Bartonellosis, also known as Cat Scratch Disease, is an infection caused by the bacterium Bartonella henselae. It primarily affects the lymph nodes, causing them to become swollen and tender, usually near the site of a cat scratch or bite. The infection often starts with a small bump or blister at the injury site, followed by fever and fatigue. Most people experience mild symptoms that resolve on their own, but some may develop more serious complications affecting the skin, eyes, or nervous system. The disease mainly involves the immune system and lymphatic system, leading to localized inflammation and sometimes systemic symptoms.
Clinical Definition
Bartonellosis/Cat Scratch Disease is a self-limited infectious disease caused by the gram-negative bacillus Bartonella henselae, transmitted primarily through cat scratches or bites. The core pathology involves a localized granulomatous lymphadenitis typically affecting regional lymph nodes proximal to the inoculation site. The infection triggers a cell-mediated immune response resulting in lymph node enlargement, tenderness, and sometimes suppuration. Systemic symptoms such as fever, malaise, and fatigue are common, and rare complications include parinaud oculoglandular syndrome, neuroretinitis, and hepatosplenic involvement. Diagnosis is clinically suspected based on exposure history and characteristic lymphadenopathy, with confirmation by serologic testing or PCR. The disease is significant due to its potential to mimic malignancy or other infections and its occasional severe manifestations in immunocompromised hosts.
Inciting Event
Cat scratch or bite introduces Bartonella henselae into the skin.
Contact with cat saliva on broken skin or mucous membranes can transmit the bacteria.
Flea bites on cats facilitate bacterial colonization and transmission to humans.
Handling kittens increases exposure due to higher bacterial load in young cats.
Exposure to contaminated cat claws or fur during play or grooming.
Latency Period
3 to 10 days from inoculation to development of primary skin lesion (papule or pustule).
1 to 3 weeks from inoculation to onset of regional lymphadenopathy.
Systemic symptoms typically develop within 2 to 4 weeks after exposure.
Latency may be prolonged in immunocompromised hosts with disseminated disease.
Diagnostic Delay
Nonspecific symptoms such as fever and malaise often mimic viral infections, delaying diagnosis.
Lack of awareness of cat exposure history leads to missed clinical suspicion.
Misattribution of lymphadenopathy to bacterial lymphadenitis or malignancy causes diagnostic confusion.
Negative routine bacterial cultures delay identification since Bartonella henselae is fastidious.
Serologic testing limitations and variable sensitivity can complicate confirmation.
Clinical Presentation
Signs & Symptoms
Localized papule or pustule at the site of cat scratch or bite within 1-2 weeks.
Regional lymphadenopathy that is tender and may suppurate, typically in axillary or cervical nodes.
Low-grade fever, malaise, and fatigue are common systemic symptoms.
Parinaud oculoglandular syndrome presents with conjunctivitis and ipsilateral lymphadenopathy.
Rarely, hepatosplenic involvement causes abdominal pain and systemic symptoms.
History of Present Illness
Initial papule or pustule at inoculation site develops within days after cat scratch or bite.
Progressive regional lymphadenopathy appears 1 to 3 weeks later, often tender and unilateral.
Associated low-grade fever, malaise, and fatigue are common systemic symptoms.
Lymph nodes may become fluctuant or suppurative in some cases.
In immunocompromised patients, disseminated symptoms such as hepatosplenomegaly or bacillary angiomatosis may occur.
Past Medical History
History of immunosuppressive conditions such as HIV/AIDS or organ transplantation increases risk of severe disease.
Previous cat exposure or ownership is relevant for epidemiologic context.
Prior episodes of lymphadenitis or unexplained fever may suggest recurrent or chronic infection.
No specific genetic predisposition is known, but immunodeficiency syndromes may worsen course.
History of flea infestations in household cats may increase transmission risk.
Family History
No known heritable syndromes are associated with susceptibility to cat scratch disease.
Family members with shared cat exposure may have similar risk of infection.
No familial clustering of immune defects specifically linked to Bartonella infection has been described.
Genetic predisposition to severe disease has not been established.
Family history is generally noncontributory in typical cases.
Physical Exam Findings
Tender regional lymphadenopathy near the site of cat scratch or bite is the hallmark finding.
Papule or pustule at the inoculation site appearing 3-10 days after exposure.
Low-grade fever and malaise may be present during the acute phase.
Conjunctivitis or Parinaud oculoglandular syndrome if the eye is involved.
Hepatosplenomegaly can be detected in disseminated cases.
Diagnostic Workup
Diagnostic Criteria
Diagnosis of Bartonellosis/Cat Scratch Disease is established by a combination of clinical history of cat exposure and characteristic regional lymphadenopathy. Key diagnostic findings include a history of a papule or pustule at the inoculation site followed by tender lymph node enlargement. Confirmation is achieved through serologic testing detecting antibodies against Bartonella henselae or by PCR amplification of bacterial DNA from lymph node aspirates. Histopathology of lymph node biopsy, if performed, shows necrotizing granulomatous inflammation but is not routinely required. Negative cultures do not exclude the diagnosis due to the fastidious nature of the organism.
Pathophysiology
Key Mechanisms
Intracellular infection of endothelial cells and macrophages by Bartonella henselae leads to localized inflammation and granuloma formation.
Lymphatic spread from the site of inoculation causes regional lymphadenopathy.
Immune-mediated granulomatous response results in necrotizing lymphadenitis with stellate microabscesses.
Endothelial proliferation induced by bacterial factors can cause angioproliferative lesions in immunocompromised hosts.
Bacterial evasion of host immunity through inhibition of phagosome-lysosome fusion promotes persistence.
| Involvement | Details |
|---|---|
| Organs | Lymph nodes are commonly enlarged and tender due to regional lymphadenitis in cat scratch disease. |
Skin serves as the initial site of Bartonella henselae inoculation and local lesion development. | |
Liver and spleen may be involved in disseminated infection causing hepatosplenic granulomas, especially in immunocompromised patients. | |
| Tissues | Lymph node tissue is the primary site of granulomatous inflammation and necrosis in cat scratch disease. |
Skin tissue at the inoculation site shows papule or pustule formation due to local bacterial infection. | |
Vascular tissue involvement occurs in bacillary angiomatosis, causing proliferative vascular lesions. | |
| Cells | Macrophages phagocytose Bartonella henselae and serve as a reservoir for intracellular bacterial replication. |
Endothelial cells are infected by Bartonella henselae, leading to vascular proliferation and granuloma formation. | |
Lymphocytes mediate the immune response causing regional lymphadenopathy characteristic of cat scratch disease. | |
| Chemical Mediators | Interleukin-1 (IL-1) is elevated and contributes to local inflammation and fever in cat scratch disease. |
Tumor necrosis factor-alpha (TNF-α) promotes granuloma formation and systemic symptoms. | |
Vascular endothelial growth factor (VEGF) is upregulated by infected endothelial cells, promoting angiogenesis in bacillary angiomatosis. |
Treatments
Pharmacological Treatments
Azithromycin
- Mechanism:
Inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit of Bartonella henselae.
- Side effects:
Gastrointestinal upset
QT prolongation
Allergic reactions
- Clinical role:
First-line
Doxycycline
- Mechanism:
Inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, effective against Bartonella henselae.
- Side effects:
Photosensitivity
Gastrointestinal upset
Tooth discoloration in children
- Clinical role:
Second-line
Rifampin
- Mechanism:
Inhibits bacterial DNA-dependent RNA polymerase, used in combination therapy for severe cases.
- Side effects:
Hepatotoxicity
Orange discoloration of body fluids
Drug interactions
- Clinical role:
Adjunctive
Non-pharmacological Treatments
Supportive care including analgesics and antipyretics for symptom relief.
Lymph node aspiration or drainage if suppuration occurs.
Avoidance of cat scratches and bites to prevent infection.
Prevention
Pharmacological Prevention
No established antibiotic prophylaxis is recommended after cat exposure.
Prompt antibiotic treatment with azithromycin can reduce symptom duration if early infection occurs.
Non-pharmacological Prevention
Avoid rough play with cats to reduce scratches and bites.
Wash cat scratches or bites immediately with soap and water to reduce bacterial inoculation.
Control flea infestations in cats to decrease Bartonella henselae transmission.
Educate immunocompromised patients to avoid contact with stray or young cats.
Outcome & Complications
Complications
Suppurative lymphadenitis requiring drainage.
Neuroretinitis causing vision loss in ocular involvement.
Bacillary angiomatosis in immunocompromised patients presenting with vascular skin lesions.
Hepatosplenic granulomatous disease in disseminated infection.
Endocarditis is a rare but serious complication.
| Short-term Sequelae | Long-term Sequelae |
|---|---|
|
|
Differential Diagnoses
Bartonellosis/Cat Scratch Disease (Bartonella henselae) versus Lymphadenitis due to Staphylococcus aureus or Streptococcus pyogenes
Bartonellosis/Cat Scratch Disease (Bartonella henselae) | Lymphadenitis due to Staphylococcus aureus or Streptococcus pyogenes |
|---|---|
History of cat scratch or bite preceding lymphadenopathy | Recent skin trauma or local infection with purulent drainage |
Subacute onset with regional lymphadenopathy that is often tender but less fluctuant | Rapid onset with acute painful, erythematous, and fluctuant lymph nodes |
Often self-limited or requires macrolides or doxycycline for Bartonella henselae | Rapid improvement with beta-lactam antibiotics targeting gram-positive cocci |
Bartonellosis/Cat Scratch Disease (Bartonella henselae) versus Tuberculous lymphadenitis
Bartonellosis/Cat Scratch Disease (Bartonella henselae) | Tuberculous lymphadenitis |
|---|---|
Exposure to cats or kittens without tuberculosis risk factors | Exposure to individuals with active pulmonary tuberculosis or endemic area travel |
Subacute lymphadenopathy with noncaseating granulomas and stellate necrosis | Chronic, slowly progressive lymphadenopathy with caseating granulomas |
Positive serology or PCR for Bartonella henselae | Positive acid-fast bacilli stain or culture from lymph node biopsy |
Bartonellosis/Cat Scratch Disease (Bartonella henselae) versus Toxoplasmosis lymphadenitis
Bartonellosis/Cat Scratch Disease (Bartonella henselae) | Toxoplasmosis lymphadenitis |
|---|---|
Direct cat scratch or bite exposure | Exposure to undercooked meat or cat feces in immunocompetent host |
Granulomatous inflammation with stellate microabscesses | Follicular hyperplasia with clusters of epithelioid histiocytes without necrosis |
Positive Bartonella henselae serology or PCR | Positive Toxoplasma gondii IgM or rising IgG titers |
Bartonellosis/Cat Scratch Disease (Bartonella henselae) versus Tularemia
Bartonellosis/Cat Scratch Disease (Bartonella henselae) | Tularemia |
|---|---|
Exposure to cats or kittens | Exposure to rabbits, ticks, or deer flies in endemic regions |
Infection with Bartonella henselae | Infection with Francisella tularensis |
Primary papule at scratch site followed by regional lymphadenopathy without ulcer | Ulceroglandular form with painful ulcer at inoculation site and regional lymphadenopathy |
Bartonellosis/Cat Scratch Disease (Bartonella henselae) versus Lymphoma
Bartonellosis/Cat Scratch Disease (Bartonella henselae) | Lymphoma |
|---|---|
Tender lymphadenopathy following cat scratch or bite | Painless, progressive lymphadenopathy without preceding infection |
Polyclonal reactive lymphadenitis with granulomas on biopsy | Monoclonal lymphoid proliferation on biopsy and abnormal peripheral blood counts |
Localized regional lymphadenopathy near scratch site | Widespread lymphadenopathy involving multiple nodal regions |