Cat Scratch Disease

Irina Margaritescu, MD, DipRCPath

Bruce R. Smoller, MD

Key Facts

Etiology/Pathogenesis

Domestic cats represent natural reservoir and vectors
Cat scratch disease (CSD) is caused by Bartonella henselae (B. henselae), and bacillary angiomatosis (BA) is caused by both B. henselae and Bartonella quintana

Clinical Issues

History of recent exposure to cats (scratch, bite, lick)
Papules or pustules appear at inoculation site in 3-12 days
Regional lymphadenopathy usually occurs after 10-30 days
Immunocompromised patients develop bacillary angiomatosis, bacillary peliosis, or relapsing fever with bacteriemia

Microscopic Pathology

Cutaneous lesions of CSD show zone of necrosis, fibrin, neutrophils, and nuclear debris in dermis surrounded by mantle of macrophages, lymphocytes, and plasma cells
Cutaneous lesions of BA are characterized by vascular proliferation in lobular pattern
Accompanied by lymphocytes, histiocytes, neutrophils, and nuclear dust of neutrophils and clumps of granular purplish material (masses of bacteria) in immediate vicinity of some vessels

Ancillary Tests

Clinical photograph shows regional submandibular lymphadenopathy

in a case of cat scratch disease. (Courtesy L. Thompson, MD.)

H&E demonstrates the microscopic features of cat scratch disease lymphadenitis, showing hyperplastic follicles

and stellate necrotizing granulomas

TERMINOLOGY

Synonyms

ETIOLOGY/PATHOGENESIS

Environmental Exposure

Natural reservoir and vectors are domestic cats, especially kittens and stray cats
Occasional cases of CSD associated with dog and monkey bites have been reported

Infectious Agents

Bartonella henselae (formerly Rochalimaea henselae)
- Causative agent of CSD, BA, and endocarditis
- Small, pleomorphic, intracellular, slow-growing, weakly gram-negative bacillus
- Houston-1 and Marseille (genotype II) identified as main genogroups
Bartonella quintana
- Causative agent of both trench fever and BA
- Less frequently associated with BA than B. henselae
Bartonella clarridgeiae rarely associated with CSD cases

Pathogenesis

Only genus that infects human erythrocytes and triggers pathological angiogenesis in vascular bed
Highly adapted pathogens that infect and persist in erythrocytes and endothelial cells of host circulatory system through various mechanisms
- Induction of pathological angiogenesis, with concomitant production of pseudoneoplastic lesions in human vasculature (i.e., BA and bacillary peliosis)
- Use of adhesins for endothelial cells
- Incorporation of lipopolysaccharides with low endotoxic potency in outer membrane (antagonistic to host’s innate immune response)
Colonization of secondary foci at considerable distances from primary site of infection, with preference for highly vascularized tissues like heart valves, liver and spleen, or cooler areas of body, such as vascular beds of skin
Response to infection depending on immune status of infected host
- Granulomatous and suppurative response in immunocompetent individuals
- Vasoproliferative response in immunocompromised persons

CLINICAL ISSUES

Epidemiology

Incidence
- At least 9.3 per 100,000 population for CSD
- Greater in regions with higher temperature and humidity
- Incidence peaks in fall and winter months
Age
- CSD affects persons in all age groups, but most are < 21 years (60-80%)
- BA affects children very rarely
Gender
- CSD and BA more common in males

Presentation

History of recent exposure to cats (scratch, bite, lick)
1 or more cutaneous papules or pustules may appear at inoculation site in 3-12 days
Regional lymphadenopathy (most remarkable manifestation) usually occurs after 10-30 days
- Cervical, axillary, or epitrochlear nodes typically involved
Usually mild constitutional symptoms including malaise, anorexia, nausea, fatigue, headache, and low-grade fever
Atypical presentation in up to 10% of cases
- Encephalopathy, neuroretinitis, prolonged fever, arthritis, synovitis, atypical pneumonitis, and endocarditis
- Granulomatous conjunctivitis and ipsilateral preauricular lymphadenitis (Parinaud oculoglandular syndrome) caused by conjunctival inoculation
Visceral involvement with hepatitis/splenitis
Skin manifestation including nonspecific rashes, erythema nodosum, and leukocytoclastic vasculitis
Immunocompromised patients may develop BA, bacillary peliosis, or persistent or relapsing fever with bacteremia
- BA
  - Vasculoproliferative disease that primarily involves skin but can involve other organs
  - Numerous brown to violaceous tumors of skin and subcutaneous tissues
  - Lesions very similar to verruga peruana, the chronic form of Carrión disease (Oroya fever)

Laboratory Tests

Diagnosis of both CSD and BA strongly suggested by history and physical findings
Laboratory findings
- Occasionally, mildly elevated white blood cell count, elevated or diminished platelet count, and elevated erythrocyte sedimentation rate in CSD
- Anemia, leukopenia, CD4(+) cell count < 200/µL in patients with BA and HIV

Treatment

Options, risks, complications
- Most cases of CSD require only supportive and symptomatic care
- Management of mild to moderate infections in immunocompetent patients consists of reassurance, adequate follow-up, and analgesics for pain
- Antibiotic treatment (azithromycin, erythromycin, doxycycline, or gentamicin) is necessary for severe infections, particularly when lymph nodes are severely affected and when organs other than lymph nodes have become involved
- Immunocompromised patients tend to develop more severe Bartonella infections and may require prolonged antibiotic treatment
- Avoidance of unnecessary manipulation, including incision and drainage of lymph nodes, is advisable as this may leave scars without hastening recovery
Surgical approaches
- Occasionally, lymph node aspiration is indicated for symptomatic relief of tender, fluctuant nodes
- Excision of lymph nodes is not justified therapeutically although it may occasionally be indicated for histology