Swimmer’s itch occurs when free-swimming cercariae penetrate the skin of humans (incidental host) and cause an allergic skin reaction (types I and IV hypersensitivity). Human schistosomes may additionally cause systemic schistosomiasis. Cases are less often due to human schistosomes (e.g., Schistosoma haematobium, Schistosoma japonicum, Schistosoma mansoni, Schistosoma mekongi, Schistosoma intercalatum). The Trichobilharzia genus is commonly implicated. Swimmer’s itch is most often caused by non-human schistosomes (over 20 species), particularly avian schistosomes. What is the Cause of the Disease? Etiology Children may be at a higher risk due to more exposure to shallow water and they may be less likely to towel dry. Resident or migratory birds (definitive hosts), snails (intermediate host), and humans (incidental host) must all be present in order for a person to contract swimmer’s itch. Presence of hosts is also an important factor. Warm months may increase intermediate host snail populations leading to increased transmission. Cases primarily occur in shallow freshwater however, cases associated with saltwater exposure have also been reported. Swimmer’s itch occurs worldwide and is commonly observed in bodies of water with on-shore winds. One study reports 6.8 episodes per 100 water exposure days. Who is at Risk for Developing this Disease?įrequency and duration of open-water activity increases the incidence of swimmer’s itch. Skin manifestations of viral causes such as viral exanthems or more defined entities such as varicella/zoster, rubeola, rubella, herpes simplex, should be suspected if a patient is immunocompromised or has not received routine immunizations. Lesions are limited to areas which have been in contact with foliage. For contact dermatitis (poison ivy), patient reports history consistent with poison ivy or other similar exposure. Insect bites (mosquitoes, bed bugs, chiggers, scabies) present with patient history consistent with arthropod exposure. The patient will have diffusely distributed follicular lesions. Hot tub folliculitis generally occurs following recent exposure to hot tub, whirlpool, swimming pool, or waterslide water. Seabather’s eruption usually occurs after saltwater exposure and tends to affect areas of skin covered by clothing or hair (opposite to swimmer’s itch). Several conditions should be considered in the differential diagnosis of swimmer’s itch. Histopathology may show spongiosis, dermal edema, and mixed inflammatory infiltrate. Serologic tests are not commonly done, but the leukocyte differential may show peripheral eosinophilia. The distribution of the rash only manifests where the patient has had direct contact with infested water.ĭiagnosis of swimmer’s itch is based on clinical suspicion. Days to weeks post-exposure, the patient may exhibit purpuric lesions, vesicles, or pustules. Patients may present in the first hours post-exposure with erythematous macules, which can progress to papules, with or without urticaria. Characteristic findings on physical examination Subsequent reactions develop more rapidly and may be more severe. It is important to note that the initial reaction may be mild and go unnoticed by the patient. Additionally, patients may have experienced similar episodes in the past. Friends and relatives participating in water activities may be symptomatic. Patients may have participated in shallow, fresh water activities during warm months. Patients may present with tingling, burning, or itching of the skin occurring hours to days after water exposure itching may be mild initially with progression of worsening intensity. Are You Confident of the Diagnosis? What you should be alert for in the history
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