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Cercarial Dermatitis

Last updated Aug. 25, 2021

Reviewed by: Lester Fahrner, MD

Approved by: Krish Tangella MD, MBA, FCAP

Cercarial Dermatitis (CD) is an itchy skin condition (hypersensitivity reaction) caused by larval penetration of skin, by the larva of Schistosoma cercariae.


What are the other Names for this Condition? (Also known as/Synonyms)

  • Duck Itch
  • Schistosome Cercarial Dermatitis
  • Swimmer’s Itch

What is Cercarial Dermatitis? (Definition/Background Information)

  • Cercarial Dermatitis (CD) is an itchy skin condition (hypersensitivity reaction) caused by larval penetration of skin, by the larva of Schistosoma cercariae. It is a type of flatworm parasite that is normally found in some freshwater and saltwater creatures (snails) and birds
  • Humans are not natural hosts for the parasite, but an accidental skin penetration may occur on exposure to the larva in lakes and rivers, while swimming or bathing. The signs and symptoms of Cercarial Dermatitis infection include skin inflammation, severe itchiness, and ulceration
  • Cercarial Dermatitis is treated through antimicrobial medications and topical applications in case of a severe infection. Generally, the infections are mild and may not require therapy
  • Cercarial Dermatitis is not a serious medical condition and generally, it has an excellent prognosis. The symptoms usually resolves within a few days, since the larva cannot survive in the human body for longer durations

Who gets Cercarial Dermatitis? (Age and Sex Distribution)

  • Any individual who is exposed to freshwater and saltwater bodies may be affected by Cercarial Dermatitis
  • The condition affects both male and female and no gender discrimination is observed
  • No ethnic or racial predominance has been observed. However, individuals in certain geographical regions (mainly in Europe and North America) have a higher exposure incidence

What are the Risk Factors for Cercarial Dermatitis? (Predisposing Factors)

The risk factors for Cercarial Dermatitis include:

  • Exposure to lakes, streams, and ponds contaminated with the parasite
  • Swimmers and divers; generally, the greater the duration of stay in the water, the higher is the risk
  • Walking on shallow waters by a river or lake side, mostly barefoot
  • Europeans and North Americans have a higher risk
  • Poor hygiene and sanitation status
  • Those with open and untreated wounds are at high risk for developing Cercarial Dermatitis in the endemic zones

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Cercarial Dermatitis? (Etiology)

Cercarial Dermatitis is an infection that is caused by a variety of nonhuman Schistosomes through larval penetration. This larva generally does not infect humans. Thus, human beings are not natural hosts for these parasites, but an accidental penetration of the skin may occur. The natural hosts of the larva are small mammals, marine creatures, and water birds.

Human transmission may occur through any of the following methods:

  • Through contaminated water bodies and pools
  • Contact with contaminated feces of the birds and snails

The skin manifestation of the larva leads to Cercarial Dermatitis. The common nonhuman Schistosomes causing the condition include:

  • Schistosoma cercariae
  • Trichobilharzia
  • Gigantobilharzia
  • Ornithobilharzia
  • Microbilharzia
  • Schistosomatium

The larva can enter the body through open wounds and lesions, or even through unbroken skin. This may result in a local allergic reaction, which is followed by the signs and symptoms of Cercarial Dermatitis.

What are the Signs and Symptoms of Cercarial Dermatitis?

The common signs and symptoms of Cercarial Dermatitis may include:

  • When the larva penetrates the skin, it may cause an inflammatory or allergic reaction in the area
  • Severe itching sensation may be felt in the area of larval penetration
  • The skin can ulcerate, and bleed
  • The skin condition can become nodular or may form vesicles
  • There may be single or multiple lesions depending on the number of skin penetrations
  • Any region on the body may be affected, although it is mostly the body part that comes in direct contact with the contaminated water or feces, which is involved

How is Cercarial Dermatitis Diagnosed?

A diagnosis of Cercarial Dermatitis may involve the following tests and exams:

  • Complete evaluation of medical history along with a thorough physical examination of the skin. History of exposure to freshwater or saltwater and the presence of skin lesions are normally sufficient to make a diagnosis
  • Blood tests, such as complete blood count, which may show increased white blood cells
  • CBC with differential may show increased eosinophil, called peripheral eosinophilia
  • Skin biopsy of individual lesion(s)
  • Elevated serum levels of immunoglobulins (antibodies)

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Cercarial Dermatitis?

The following are the complications associated with Cercarial Dermatitis:

  • The individual can develop a severe allergic reaction
  • Secondary infections due to bacteria or fungus from intense scratching of the skin

How is Cercarial Dermatitis Treated?

The treatment of Cercarial Dermatitis may aim at managing the symptoms, especially if they are severe. Typically, the larva dies after a few days in the human body and antiparasitic treatment is not warranted.

  • Steroid creams or oral steroids can help decrease inflammation and other severe signs and symptoms of the infection
  • Usually, antiparasitic treatment is not necessary (as humans are not natural hosts of the parasitic larva)
  • Home remedies may include:
    • Scratching the affected area should be avoided, since it may lead to further swelling and secondary infections
    • Avoid sunlight and hot showers which tend to increase the itching
    • Using an ice pack can help in pain-relief
  • Typically, antihistamines are also not required

How can Cercarial Dermatitis be Prevented?

There are no definitive methods to prevent Cercarial Dermatitis. However the following measures may help avoid the risk factors for Cercarial Dermatitis:

  • Wear appropriate protective clothing in waters where pathogenic infestation is known
  • Avoid walking barefoot in shallow waters by the side of a river or lake
  • Individuals working or dealing with aquatic or marine animals should thoroughly wash and clean their entire body after work
  • While lying or sitting by the riverside, it is always preferable to use a suitable mattress to protect bare skin from direct contact with the sand or soil (which can lead to a higher degree of exposure to the parasite)
  • Wounds should always be covered to protect from superimposed infections
  • Individuals with a history of severe allergic reactions should avoid swimming in water bodies such as rivers and lakes

What is the Prognosis of Cercarial Dermatitis? (Outcomes/Resolutions)

The prognosis of Cercarial Dermatitis is excellent, since it is self-resolving condition in most cases. The Schistosome larva in the human body dies after a few days.

Additional and Relevant Useful Information for Cercarial Dermatitis:

Cercarial Dermatitis is known by a host of terms that include Clam Digger’s Itch, Duck Itch, Lake Itch, Sedge Pool Itch, and Swimmer’s Itch.

What are some Useful Resources for Additional Information?


References and Information Sources used for the Article:


Helpful Peer-Reviewed Medical Articles:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Jan. 22, 2016
Last updated: Aug. 25, 2021