Cat scratch disease

What is cat scratch disease?

Cat scratch disease (CSD) is a bacterial infection that affects the lymph nodes. It is also known as cat scratch fever or subacute regional lymphadenitis.

Who gets cat scratch disease?

Risk factors for acquiring cat scratch disease (CSD) include:

• Owning a cat younger than 12 months
• Getting licked, bitten, or scratched by an infected kitten
• Contact with a cat if you have broken skin or mucosa
• Petting an infected cat
• Owning at least one kitten or cat with fleas
• Being immunocompromised
• Working with kittens and cats eg, veterinarians and veterinary nurses.

CSD can occur in people of all ages but is most common in children and adolescents. The majority (80%) of patients with cat scratch disease are less than 21 years old.

A primary lesion of cat scratch disease on the cheek - note the infra-auricular lymphadenopathy (CSD-patient2)

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What causes cat scratch disease?

Patients with CSD have usually suffered a scratch or bite from a cat or kitten which is infected with the bacteria Bartonella henselae, a common infection in young cats. It is also known as Rochalimaea henselae.

The bacteria is passed from cat to cat via fleas. In the absence of fleas, an infected cat cannot pass the infection to uninfected cats.

Once infected, the bacteria are present in saliva deposited in the cat’s fur and claws.

What are the clinical features of cat scratch disease?

A small red raised spot develops at the site of contact with an infected cat’s saliva after 3–10 days. This changes into a fluid-filled blister that later forms a crusty sore. It is often mistaken for an insect bite. Most are found on the hands, arms, face, or neck as people often hold kittens close to their chest and face. The sore usually heals without scarring in several days or months.

The nearest lymph nodes become swollen and tender, most often those in the head, neck, and armpit. This is known as regional lymphadenopathy. The lymph nodes may swell to 10–12 cm in the first two weeks of the disease. On questioning, patients often recall being licked, bitten, or scratched by a cat in the previous 1–8 weeks.

About 50% of patients will experience additional signs and symptoms including:

• Fever
• Malaise/fatigue
• Headache
• Nausea and vomiting
• Sore throat
• Rash
• Stomach pains
• Conjunctivitis.

How do clinical features vary in differing types of skin?

Erythema of the initial spot may not be apparent in darker skin types. Instead, it could appear darker than the surrounding skin or violaceous/purple.

What are the complications of cat scratch disease?

Less common problems occur in about 10% of patients. These may include:

• Parinaud’s oculoglandular syndrome (POS), characterised by an inflamed lump in the eye and swollen lymph glands in front of the nearby ear
• Bacillary angiomatosis, especially in HIV or otherwise immunocompromised patients
• Bacillary hepatitis and splenitis (infection of the liver and spleen)
• Erythema nodosum (red lumps on the shins)
• Sepsis
• Encephalopathy
• Bacterial endocarditis
• Neuroretinitis.

Encephalopathy is an uncommon complication of CSD that occurs one to six weeks after the lymph glands swell up. The abrupt symptoms of fever, seizures, and coma can be frightening. With hospitalisation and high doses of antibiotics, most patients recover completely.

Immunocompromised patients (such as solid organ transplant recipients or people with HIV) can present with atypical manifestations such as thrombocytopaenic purpura, haemophagocytosis, and visceral disease resembling lymphoproliferative disorders.

How is cat scratch disease diagnosed?

There is no single established ‘gold standard’ test to diagnose cat scratch disease.

Previously, diagnosis was often based on the presence of three of the four following criteria:

• Contact with a cat and the presence of a scratch or lesion on the skin, eye, or mucous membranes
• Regional lymphadenopathy, after excluding all other possible causes
• Positive skin test for cat scratch disease — no longer used as the skin test antigen is not widely available and not as specific as other tools
• Suggestive biopsy of skin or lymph node.

Diagnostic testing is not routinely performed if characteristic clinical signs are present, although may be indicated in those with atypical signs, unresolving systemic symptoms, or diagnostic uncertainty:

• Serology — indirect immunofluorescence assay (IFA) can be performed to identify past or current infections depending on immunoglobulin G (IgG) titre levels
• Culture — Bartonella henselae is a slow-growing gram-negative bacteria that can be grown from skin and blood samples
• Polymerase chain reaction (PCR) based tests — testing for B. henselae can be performed on blood or tissue, however generally has poor sensitivity.

See also: Laboratory tests for bacterial infections.

What is the differential diagnosis for cat scratch disease?

• Bacterial adenitis
• Viral-associated lymphadenopathy – eg, associated with cytomegalovirus, Epstein-Barr virus, HIV
• Mycobacterial infections
• Toxoplasmosis
• Other infective causes of lymphadenopathy – eg, Yersinia pestis, histoplasmosis, sporotrichosis, nocardiosis
• Malignancy-related lymphadenopathy and lymphoma
• Congenital or acquired cysts
• Sarcoidosis
• Kawasaki disease
• Kikuchi-Fujimoto disease

What is the treatment for cat scratch disease?

General measures

Pain and fever can be managed by increasing fluid intake and simple analgesics. Warm moist compresses to affected lymph glands may decrease swelling and tenderness.

Specific measures

Treatment of uncomplicated cat scratch disease remains controversial. As CSD is a benign and self-limiting condition, with most cases of regional lymphadenopathy resolving spontaneously in 2–4 months, no specific treatment is usually necessary.

However, some studies suggest that certain antibiotics including azithromycin, doxycycline, gentamicin, rifampicin, trimethoprim + sulfamethoxazole, or ciprofloxacin may significantly shorten the duration of lymphadenopathy. Antibiotics are warranted in patients with severe or persistent symptoms, disseminated disease, or immunodeficiency.

In rare cases, large pus-filled lymph nodes may persist for one to three years. The pus may need to be repeatedly drained using a needle.

How do you prevent cat scratch disease?

• Wash hands thoroughly with water and soap after playing with a cat.
• Wash any cat bites/scratches right away with running water.
• Avoid petting or touching stray cats.
• Avoid letting cats lick any open wounds.
• Immunocompromised people should try to adopt cats older than 1 year of age.
• If you own a cat:
  • Control fleas with flea products approved by your veterinarian, using flea combs, and by vacuuming your home frequently.
  • Keep your cat’s claws trimmed.
  • Arrange regular routine check-ups for your cat with a veterinarian.
  • Try to keep your cat indoors to reduce contact with fleas or other infected animals.

What is the outcome for cat scratch disease?

Cat scratch disease spontaneously resolves in approximately 90–95% of children, and is managed symptomatically with pain relief, antipyretics, and warm compresses. In disseminated infection, the recovery process might take several months to a year, and the extent of complications varies depending on which organ systems are affected. CSD can be debilitating in immunocompromised patients.

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