Cat-scratch Disease

Cat-scratch disease is an infection caused by Bartonella henselae, a bacteria to which people are often exposed via contact with cats. Cat-scratch disease is one of the most common causes of chronic lymphadenopathy in children. 

Etiology

  • B. henselae is a fastidious, pleomorphic gram-negative bacillus
  • Cats are the major reservoir for B. henselae; up to 50% of domestic cats test seropositive for the bacteria
  • Transmission from cat-to-cat occurs via a cat flea, ctenocephalides felis, but the flea is not widely believed to cause transmission from cats to humans 
  • Transmission to humans occurs via cat saliva and scratches

Epidemiology

  • There is a higher incidence of b. henselae bacteremia in kittens, cats with fleas, outdoor cats, and stray cats
  • CSD has a worldwide distribution
  • In the US, most cases occur between July and January, and are more common in humid locales
  • There are 22,000 new cases of CSD per year in the US 

Clinical Manifestations

  • Most patients with cat-scratch disease report contact with cats, but many will not recall a scratch or bite. There is a classic presentation, but atypical presentations have also been reported. As diagnostic methods have improved, the spectrum of disease known to be caused by b. henselae has expanded greatly

TYPICAL PRESENTATION

  • In the classic history, a skin lesion develops 7-12 days after a cat bite or scratch
         - The lesion is typically described as a "brownish red papule"
         - The lesion will progress: erythematous --> vesicular --> crusted      
         papule 
         - Lesions last one to three weeks 
  • Regional lymphadenopathy develops one to several weeks after the skin lesion appears
         - Cervical and axillary LAD are the most common sites
         - Affected nodes may be very small or may enlarge to many  
         centimeters
         - Nodes are often tender, warm and erythematous
         - Ten to 30% of nodes eventually suppurate
         - Enlarged nodes may persist for weeks to months
  • Some patients may be febrile, but most patients appear quite well. Fever above 39 degrees is rare 
  • Some patients may have general constitutional symptoms, including sore throat, malaise, rash, and anorexia

ATYPICAL PRESENTATIONS 

  • Prolonged fever of unknown origin (FUO): often patients have fever and generalized symptoms including malaise, fatigue, diffuse adenopathy, and hepatosplenomegaly. CSD is on the differential for all cases of FUO
  • Hepatosplenic Manifestations: hepatosplenic involvement is more common in CSD than originally thought. Patients often present with systemic symptoms, including prolonged fever, malaise, and microabscesses in the liver and spleen 
  • Parinaud Oculoglandular Syndrome: inoculation occurs at the conjunctiva, resulting in non-suppartive, painless conjunctivitis and periauricular (and submandibular) LAD. A conjunctival granuloma may be present at the site of inoculation
  • Neurologic complications: patients with CSD may present with headache, cranial or peripheral nerve abnormalities, and even encephalopathy, changes in mental status, and seizures 
  • Vertebral Ostomyelitis: often presents with insidious back pain
  • Endocarditis: CSD is a common cause of endocarditis. (Treatment includes surgical intervention, valve replacement, and long-term antibiotics)
  • Case reports connect CSD with other disease processes, including Henoch-Schonlein Purpura, EBV infection, ileitis, and acute transplant rejection

PRESENTATIONS IN THE IMMUNOCOMPROMISED HOST

  • Bacillary Angiomatosis: Characterized by nontender, firm, red-to-purple or skin-colored lesions. The lesions may be papular or nodular, and can be difficult to distinguish from pyogenic granuloma, Kaposi sarcoma, and some hemangiomas. If not treated with antiobiotics, dissemination to multiple organs will likely occur, resulting in fever, weight loss, and nausea. Bacillary angiomatosis has become less common as the treatment of AIDS has improved. 
  • Bacillary Peliosis: Characterized by vasoproliferations within the liver, spleen, and occasionally abdominal lymph nodes and bone marrow. 

Diagnosis

  • Patient may present with the typical story: exposure to cats, a primary lesion, and then regional LAD. Recall, however, that many patients will not recall a bite or scratch
  • When CSD is considered, the differential diagnosis often includes: tularemia, brucellosis, toxoplasmosis, TB, malignancy (leukemia, lymphoma), and sarcodiosis 
  • If CSD is suspected, serologic testing can be carried out via an enzyme immunoassay (EIA) or immunofluorescent antibody (IFA) test. A sensitive PCR test does exist, but it is less widely available
  • The orgnism can be cultured from affected nodes, but this process is difficult and can take up to 6 months 
  • Biopsy of nodes or other affected tissues may be carried out, especially when the diagnosis is unclear. Biopsy material may demonstrate silver staining of the organism by the Warthin-Starry stain and the presence of granulomas, which may help differentiate cat -scratch from other etiologies of lymphadenopathy
  • Even with serologic testing, diagnosis of CSD usually combines evidence from the history, serologies, epidemiology, and clinical picture. A diagnostic tool has been suggested, with diagnosis confirmed if three of the following are present:
  1. Cat or flea contact, regarless of presence of an inoculation site
  2. Negative serologies for other causes of LAD, sterile pus aspirated from a node, a positive PCR assay, and/or liver/spleen lesions seen on CT scan 
  3. Positive EIA or IFA with titer ratio greater than or equal to 1:64
  4. Biopsy showing granulomatous inflammation consistent with CSD or staining with Warthin-Starry silver stain

Treatment

  • In the immunocompetent, most cases are self-limited and only require supportive care. 
         - Most cases resolve within 2-4 months
         - Enlarged nodes may persist for months to years
         - Warm compresses may be applied to the affected nodes
         - Anti-pyretics and analgesics may be used as needed 
         - Many patients wil replapse within 6 months with or without treatment
  • Antimicrobials: No antimicrobial regimen has been shown to cure B. henselae. Many studies of antiobiotic treatment show little or no improvement in immunocompetent patients. Even so, many suggest antimicrobials may shorten the disease course in patients with severe symptoms and/or immunodeficiency
         - Antibiotics that have shown the highest efficacy include: Doxycycline,
         erythromycin, rifampin, penicillin, gentamicin, ceftriaxone, ciprofloxacin,
         and azithromycin. The optimal duration of therapy has not been
         determined
         - No antimicrobial therapy is effective for treating cats
  • Patients with bacillary angiomatosis and bacillary peliosis require treatment with antibiotics, as these condtions may be fatal. Treatment regimens include erythromycin ethylsuccinate for at least three months. Rifampin may be added for severe cases. Treatment often results in significant improvement, but improvement may take over a month, and relapses are common if the treatment duration is not extended 
  • Suppurative, painful nodes may be treated with needle aspriation. Surgical excision is rare and not recommended, as there is a risk for chronic drainage and sinus tract formation
  • Case studies suggest that there may be a role for corticosteroids in treating CSD, but they are not recommended at this time as more research is needed

Prevention

  • Control fleas in cats and other pets
  • Avoid stray cats
  • Teach children to play carefully with their cats to avoid being scratched or bitten
  • The cat does not need to be removed from the home
  • Testing cats for B. henselae infection is not recommended 
  • Clean all scratches and bites carefully. Encourage children to practice good hygiene after coming into contact with any animal, wild or domestic

References
1. Batts, S and Demers DM. Spectrum and Treatment of Cat-Scratch Disease. Pediatric Infectious Disease Journal. 2004;23:1161. 
2. English R. Cat Scratch Disease. Pediatrics in Review. 2006;27:123. 
3. Florin T, Zautis T, Zautis L. Beyond Cat Scratch Disease: Widening Spectrum of Bartonlla henselae Infection. Pediatrics. 2008;121:e1413.  
4. Klotz SA, Ianas V, Elliott SP. Cat Scratch Disease. American Family Physician. 2011;83;2:152. 
5. Wallace S. Snakes, Snails and Puppy Dog Tails: Teach patients to practice proper hygiene around animals to reduce their risk of contracting zoonotic infections. AAP News. 2003;23:66. 

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