Cercarial dermatitis

From WikiMD's Wellness Encyclopedia

  • A pruritic rash that occurs as consequence of cercariae penetration of the skin after aquatic exposure to animal (usually avian) schistosomes, often in countries non-endemic to human schistosomiasis.
  • The condition is non-invasive and responsive to symptomatic treatment.
Cercarial dermatitis
Cercarial dermatitis

Other names[edit | edit source]

Swimmer’s itch

Clinical features[edit | edit source]

  • Swimmer’s itch, also called cercarial dermatitis, appears as a skin rash caused by an allergic reaction to certain microscopic parasites that infect some birds and mammals.
  • These parasites are released from infected snails into fresh and salt water (such as lakes, ponds, and oceans).
  • While the parasite’s preferred host is the specific bird or mammal, if the parasite comes into contact with a swimmer, it burrows into the skin causing an allergic reaction and rash.
  • Swimmer’s itch is found throughout the world and is more frequent during summer months.
Cercarial Life Cycle
Cercarial Life Cycle

Lifecycle[edit | edit source]

  • The adult parasite lives in the blood of infected animals such as ducks, geese, gulls, swans, and certain mammals such as muskrats and raccoons. The parasites produce eggs that are passed in the feces of infected birds or mammals.
  • If the eggs land in or are washed into the water, the eggs hatch, releasing small, free-swimming microscopic larvae.
  • These larvae swim in the water in search of a certain species of aquatic snail.
  • If the larvae find one of these snails, they infect the snail, multiply and undergo further development.
  • Infected snails release a different type of microscopic larvae (or cercariae, hence the name cercarial dermatitis) into the water.
  • This larval form then swims about searching for a suitable host (bird, muskrat) to continue the lifecycle.
  • Although humans are not suitable hosts, the microscopic larvae burrow into the swimmer’s skin, and may cause an allergic reaction and rash. Because these larvae cannot develop inside a human, they soon die.
Cercaria Dermatitis
Cercaria Dermatitis

Signs and symptoms[edit | edit source]

Symptoms of swimmer’s itch may include:

  • tingling, burning, or itching of the skin
  • small reddish pimples
  • small blisters
Swimmers Itch Life Cycle
Swimmers Itch Life Cycle

Progression[edit | edit source]

  • Within minutes to days after swimming in contaminated water, you may experience tingling, burning, or itching of the skin.
  • Small reddish pimples appear within twelve hours.
  • Pimples may develop into small blisters.
  • Scratching the areas may result in secondary bacterial infections.
  • Itching may last up to a week or more, but will gradually go away.
  • Because swimmer’s itch is caused by an allergic reaction to infection, the more often you swim or wade in contaminated water, the more likely you are to develop more serious symptoms.
  • The greater the number of exposures to contaminated water, the more intense and immediate symptoms of swimmer’s itch will be.
Austrobilharzia variglandis cercaria
Austrobilharzia variglandis cercaria

Treatment[edit | edit source]

  • Use corticosteroid cream
  • Apply cool compresses to the affected areas
  • Bathe in Epsom salts or baking soda
  • Soak in colloidal oatmeal baths
  • Apply baking soda paste to the rash (made by stirring water into baking soda until it reaches a paste-like consistency)
  • Use an anti-itch lotion

Risk factors[edit | edit source]

Anyone who swims or wades in infested water may be at risk. Larvae are more likely to be present in shallow water by the shoreline. Children are most often affected because they tend to swim, wade, and play in the shallow water more than adults. Also, they are less likely to towel dry themselves when leaving the water.

Prevention[edit | edit source]

To reduce the likelihood of developing swimmer’s itch Do not swim in areas where swimmer’s itch is a known problem or where signs have been posted warning of unsafe water. Do not swim near or wade in marshy areas where snails are commonly found. Towel dry or shower immediately after leaving the water. Do not attract birds (e.g., by feeding them) to areas where people are swimming. Encourage health officials to post signs on shorelines where swimmer’s itch is a current problem.


Cercarial dermatitis Resources
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Contributors: Prab R. Tumpati, MD