Another one from the old articles, though I think this is actually the last; GP Clinical, September 2006, written by GP Dr Raj Thakkar.
Pathogen: Bartonella henselae, a G-ve organism which is carried by fleas. Rabbits, dogs and monkeys can sometimes cause infection, though cats are the most common. Up to 70% of cats have a history of infection. It can be transmitted to humans by biting or even licking as well as scratching, and also, not surprisingly, by bites from the infected fleas.
Epidemiology: 80% of cases occur in the under-21s; most of these are under 10. (Article illustrated with rather cute picture of child cuddling kitten, to make the point.)
- 1 – 2 weeks after the scratch, an erythematous papule develops at the site. This can become vesicular or sometimes suppurative.
- Within 2 – 3 weeks this heals without scarring.
- There is usually a single regional lymph node (the article didn’t say whether this develops at the same time as the papule or later) enlarged to around 2 to 4 cm with mild tenderness. However, in 10 – 15% of cases there are painful suppurative nodes, often associated with constitutional symptoms.
- Lymphadenopathy usually resolves within three months, though it can take up to two years.
- Severe systemic features can occur in up to 25% of the infected; they include fever, malaise, anorexia, headache, and splenomegaly. Always consider cat scratch disease as a differential diagnosis in a child with unexplained fever.
- Complications are due to bacterial seeding, which can involve just about any organ.
- Encephalitis, cerebellar ataxia, myelitis
- Erythemas (multiforme, nodosum, marginatum)
- Thrombocytopenic purpura
- Arthropathy, sometimes severe
- Parinaud’s oculoglandular syndrome; unilateral conjunctivitis with preauricular lymphadenopathy
Diagnosis: Serology. Bloods also show markedly raised ESR, raised CRP, often eosinophilia, and sometimes abnormal LFTs.
Treatment and prognosis: Often self-limiting. Azithromycin can help the lymphadenopathy. Immunocompromised patients, or those with systemic features/complications, can be treated with rifampicin or (in adults) ciprofloxacin.
The feline culprit should have flea treatment, but doesn’t need to be removed from the household. The infected person should avoid contact with the immunocompromised or with those at risk of endocarditis.