Swimmer's Itch (Cercarial Dermatitis)
Swimmer's itch requires only symptomatic treatment with topical corticosteroids, as it is a self-limited condition that resolves spontaneously within days to weeks without antiparasitic therapy. 1
Clinical Recognition and Diagnosis
Swimmer's itch presents as an itchy maculopapular rash developing within hours after freshwater or saltwater exposure, caused by penetration of cercariae from bird schistosomes (most commonly Trichobilharzia species) that cannot complete their lifecycle in humans 1
The diagnosis is entirely clinical based on the characteristic presentation: pruritic papules on exposed skin areas following aquatic exposure, with symptom onset typically within hours 1
No laboratory investigations are needed for swimmer's itch, as eosinophilia is absent and serology/microscopy are not indicated 1
Management Approach
Apply topical hydrocortisone cream to affected areas 3-4 times daily for symptomatic relief 1, 2
The condition resolves spontaneously over days to weeks without treatment, and there are no serious sequelae 1
No antiparasitic medications are indicated, as the cercariae die in human skin and cannot establish infection 1
Reassure patients that this is a self-limited allergic reaction to dying parasites trapped in the skin 1
Critical Distinction: Katayama Syndrome
You must differentiate swimmer's itch from Katayama syndrome (acute schistosomiasis), which requires immediate antiparasitic treatment and corticosteroids 1, 3
Red Flags for Katayama Syndrome:
Fever, urticarial rash, dry cough, and marked eosinophilia (often >5 × 10⁹/L) occurring 2-8 weeks after freshwater exposure in Africa or other endemic areas 1, 3
If this presentation occurs, treat immediately with praziquantel 40 mg/kg as a single dose PLUS prednisolone 20 mg daily for 5 days, with mandatory repeat praziquantel at 6-8 weeks 1, 3
Screen for strongyloidiasis before initiating corticosteroids in patients with tropical exposure to prevent hyperinfection syndrome 3
Never use dexamethasone instead of prednisolone, as it reduces praziquantel levels and causes treatment failure 3
Common Pitfalls to Avoid
Do not order unnecessary testing (CBC, eosinophil count, schistosome serology) for typical swimmer's itch presenting within hours of water exposure 1
Do not prescribe antiparasitic medications (praziquantel, albendazole) for swimmer's itch, as the cercariae are already dead and trapped in skin 1
Do not confuse the timing: swimmer's itch occurs within hours of exposure, while Katayama syndrome occurs 2-8 weeks later with systemic symptoms 1
Epidemiological Context
Swimmer's itch occurs worldwide in both freshwater and saltwater environments, often in outbreaks during warm weather when cercarial shedding from snails increases 1, 4, 5, 6
The condition is temperature-dependent, with higher water temperatures accelerating parasite development and increasing cercarial emergence from infected snails 4, 5, 6
Recent climate warming has led to increased reports of swimmer's itch in European countries, with outbreaks documented in Italy, Denmark, and other regions 4, 5, 6