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Swimmer’s Itch (Cercarial Dermatitis)

What is Swimmer’s Itch? Swimmer’s itch, also known as cercarial dermatitis, is allergic dermatitis caused by a parasitic infection by flatworms from the schistosome family. Schistosomes most commonly associated with infection in humans are from the genera Trichobilharzia and Gugantobilharzia, which use freshwater snails and waterfowl as intermediate and definitive hosts, respectively. Cercariae, the larval stage of the parasite, develop in the bodies of freshwater snails and are released into the water. When exposed to the larvae, humans may become an accidental host as the cercariae can penetrate skin, but cannot complete their life cycle.

Swimmer’s itch is a global disease, most often seen near freshwater lakes during summer. However, there have been outbreaks from brackish water as well. The seasonal aspect of the incidence is thought to be because of the increase in the number of people swimming. Infection can occur in any setting with exposure to water bodies with schistosome-infested snails.

Clinical Presentation of Swimmer’s Itch

  • Tingling, itching, or burning sensation that turns into a maculopapular rash with vesicles measuring 3-8mm in diameter.
  • Papular lesions are only on the parts of the body immersed in the water.
  • Development of the reaction can take 1 hour to 24 hours after exposure and can persist for over 20 days.
  • Severity and speed at which reaction occurs may worsen with repeated exposures.
  • Pruritis can range from mild to intense itching that may cause insomnia.
  • Secondary bacterial infections can occur.
  • Other, less common symptoms can include fever, swelling, nausea, and diarrhea.

Source: Al-Jubury, A., Bygum, A., SusannaTracz, E., Koch, C. N., & Buchmann, K. (2021). Cercarial Dermatitis at Public Bathing Sites (Region Zealand, Denmark): A Case Series and Literature Review. Case Reports in Dermatology, 13(2), 360–365. https://doi.org/10.1159/000516981