Schistosomatid dermatitis (cercariasis)

Schistosomatid dermatitis (cercariosis, swimmer's itch, water itch, cercarial dermatitis) is a parasitic disease characterized by skin changes caused by larvae (cercariae) of certain types of trematodes.

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Epidemiology of schistosomiasis dermatitis (cercariosis)

Penetration of cercariae through human skin is possible only in those bodies of water that contain intermediate hosts of such schistosomes - pulmonary mollusks. Most cercariae die in the skin, causing inflammatory reactions. Most often, schistosomatid dermatitis is caused by cercariae Tr. ocellata and Tr. stagnicolae.

Trichobilharzia eggs enter the water with the hosts' feces, from which miracidia hatch, penetrating into mollusks of the genera Lymnaea, Planorbis and others, where parthenogenetic reproduction and development of larvae to the cercaria stage occur. Cercariae emerge from the mollusks and penetrate through the skin into the body of ducks and other waterfowl, where their development continues. After 2 weeks in the hosts' circulatory system, the parasites reach sexual maturity.

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What causes schistosomiasis dermatitis (cercariosis)?

The causative agents of schistosomatid dermatitis are larvae (cercariae) of schistosomes of the Schistosomatidae family, which parasitize in the adult state in the circulatory system of waterfowl (ducks, seagulls, swans, etc.). Humans are not a specific host for them. Sometimes dermatitis can be caused by cercariae of schistosomatids of mammals (rodents, etc.). Currently, there are more than 20 species of schistosomes whose cercariae are capable of penetrating human skin.

Pathogenesis of schistosomiasis dermatitis (cercariosis)

The cause of human infection is the ability of schistosomatid cercariae to actively penetrate the skin. Cercariae cause mechanical (often multiple) lesions of the skin and have a toxic and sensitizing effect on the human body, contributing to the introduction of a secondary infection. Cercariosis is especially severe in children.

Edemas with lysis of epidermal cells develop at the sites of cercariae penetration into human skin. As cercariae migrate, infiltrates of leukocytes and lymphocytes appear in the corium. As a result of the developed immunological reaction, schistosomatids in human skin die, and their further development ceases.

Symptoms of schistosomiasis dermatitis (cercariosis)

Within 10-15 minutes after penetration of the skin by cercariae, typical symptoms of schistosomatid dermatitis (cercariosis) appear: skin itching, and an hour after bathing, a spotted rash appears on the skin, disappearing within 6-10 hours. In highly sensitive individuals, local and general urticaria, allergic edema and severe itching of the skin may occur.

With repeated infection, the dermatitis symptoms are more acute: erythema and red papules form on the skin, accompanied by severe itching. Hemorrhages appear in the center of some papules. Papules appear on the 2nd-12th day after infection and persist for up to 2 weeks. Occasionally, skin edema and blisters occur. Schistosomatid dermatitis (cercariosis) ends with spontaneous recovery. Pigmentation persists at the site of the papules for several weeks.

Differential diagnosis of schistosomiasis dermatitis (cercariosis)

The diagnosis of schistosomatid dermatitis (cercariosis) is based on the appearance of characteristic changes in the skin upon contact with water in reservoirs where mollusks and ducks live (swimming, fishing, irrigation work, etc.). Cercariosis is differentiated from reactions to insect bites and other dermatitis.

Schistosomatid dermatitis (cercariosis) has a favorable prognosis.

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Treatment of schistosomiasis dermatitis (cercariosis)

Symptomatic treatment of schistosomiasis dermatitis (cercariosis) is carried out by prescribing desensitizing (diphenhydramine orally 0.05 g 2-3 times a day) and local anesthetics (5-20% oil solution of benzocaine or anesthesin). Zinc ointment and starch baths are also used. In severe cases, the use of glucocorticoids is indicated. In the development of schistosomiasis, treatment is carried out with anthelmintics.

How to prevent schistosomiasis dermatitis (cercariosis)?

For personal prevention of cercariosis when in contact with water (when swimming, washing clothes, playing in the water, fishing, etc.) you should:

• avoid shallow areas of water bodies (or their zones) overgrown with aquatic vegetation where ducks live (coastal areas devoid of aquatic vegetation are safer);
• if it is necessary to stay in water for a long time, use protective clothing and footwear (boots, trousers, shirt) to protect against attacks by schistosomatid cercariae;
• after contact with water in a “suspicious” area of the reservoir, thoroughly wipe the skin with a hard towel or dry cloth and
• quickly change wet clothes.

Public prevention of cercariosis includes:

• equipping internal city water bodies where there is a risk of people becoming infected with cercariae with signs prohibiting swimming and playing in the water;
• regulation (reduction) of the number of mallards in urban water bodies used for recreational purposes;
• regular cleaning of reservoirs (or the most visited areas of reservoirs) from aquatic vegetation.