Swimmer’s itch is a dermatological disease of a parasitic nature caused by infection of the skin with larvae (cercariae) of schistosomes (one of the genera of flatworms or trematodes). Symptoms of this condition are skin itching, the appearance of red spots and papules on the skin, urticaria and allergic edema. In rare cases, there is an increase in temperature, dry cough, dizziness. Diagnosis is based on the results of a dermatological examination and the patient’s medical history. Usually, the treatment of the disease is symptomatic, the use of specific antiparasitic agents is not required.
Swimmer’s itch (cercarial dermatitis) is a parasitic skin disease caused by the introduction of cercariae (larvae of some trematodes) into the tissues and accompanied by a pronounced allergic reaction. Schistosomes and related flatworms have a complex life cycle, with cercariae usually embedded in the body of the final host, where they transform into adults.
Swimmer’s itch is most often found in Africa and Asia, where a warm climate contributes to the development of trematodes in freshwater stagnant reservoirs. Most often, pathology affects children due to the thinness of the skin and increased reactivity of the body at this age.
Despite the fact that some types of schistosomes and other trematodes can cause parasitic diseases of the urinary tract and intestines in humans, the cause of swimmer’s itch is extremely rare for the above parasites. Usually this disease is the result of the introduction of cercariae (larvae) of trematodes that parasitize the body of waterfowl, and in this case a person acts as a “random host”. The inability of parasite larvae to the conditions of the human body largely determines the peculiarities of the course of swimmer’s itch.
Most often, cercariae are found in warm shallow reservoirs with fresh stagnant water. A prerequisite is the habitation of some species of mollusks in the lake, acting as an intermediate host for trematodes – in their body, the transformation of miracidia into cercariae occurs. When bathing a person in such a pond, the larvae of the parasite first attach to the surface of the skin, and then with the help of a gnawing apparatus penetrate into its thickness.
The cause of the first symptoms of swimmer’s itch are hydrolytic enzymes secreted by parasite larvae for deeper penetration into tissues, as well as mechanical irritation. Enzymes have strong immunogenic and allergenic properties, therefore, a pronounced inflammatory reaction occurs at the site of penetration of cercariae and in the course of their movement.
Since humans are not the final host for these parasites, they soon die in the thickness of the skin. The decay products of cercariae increase the inflammatory reaction, which is observed in the final stages of swimmer’s itch, after which spontaneous recovery occurs.
With secondary infection with schistosome larvae, the manifestations of the disease become much more pronounced, various common symptoms may be added. The reason for this is that during the first episode of swimmer’s itch, the body is sensitized by the decay products of cercariae, and with subsequent infections, an allergic reaction develops much faster, leading to more severe symptoms.
The first manifestations of swimmer’s itch develop very quickly – literally a few minutes after bathing in a pond where flukes and their larvae live. If there is primary contact with this parasite, then the symptoms are poorly expressed, the picture of the disease is erased. 10-15 minutes after bathing, skin itching occurs in the area of penetration of cercariae, after 1-2 hours, small red spots appear there, completely disappearing for 6-12 hours. After that, no other symptoms of swimmer’s itch are usually observed, provided there is no further contact with the pathogen. During this episode, the body is sensitized and hypersensitivity to the antigens of schistosome larvae develops.
If there is secondary contact with cercariae, the clinical picture of swimmer’s itch becomes more pronounced and severe. After the initial manifestations (severe itching, burning and the development of erythematous rash), the spots do not disappear, papules form in their place for 1-2 days – sometimes their development may be delayed, and they appear for 5-10 days. Often, swelling and a rash resembling urticaria occurs on the affected area of the skin.
Also, with this form of swimmer’s itch, common symptoms may appear – dry cough, headaches, and an increase in body temperature. Manifestations of the disease persist for 2-3 weeks, after which spontaneous recovery is observed. A possible complication of swimmer’s itch may be a secondary bacterial infection introduced by the patient himself when combing the affected areas of the skin.
In the diagnosis of swimmer’s itch, the method of dermatological examination, questioning and examination of the patient’s anamnesis is used, in controversial cases, a skin biopsy on the affected areas and histological examination can be performed.
- Anamnesis and objective data. Patients with swimmer’s itch complain of persistent itching, soreness and burning in the affected area. When questioned, it turns out that the first symptoms of the disease appeared shortly after bathing in a freshwater reservoir. Upon examination, an erythematous rash is detected in the form of red spots with a diameter of 1-4 millimeters, with a more severe course of the disease, papules of 2-4 millimeters in size can be determined.
- Morphological examination. The histological picture in swimmer’s itch is represented by signs of nonspecific inflammation (arteriole dilation, edema, neutrophil infiltration) and lysis of epidermal cells. Sometimes cercariae can be detected under a microscope.
- Other tests. Occasionally, against the background of the development of cercariosis of the urinary tract, intestines or other organs occurs, therefore it is recommended to analyze feces and urine for the eggs of these parasites.
Swimmer’s itch treatment
In clinical dermatology, the treatment of swimmer’s itch is usually nonspecific, aimed at reducing the activity of allergic and immunological reactions of the body. Antihistamines are used, in severe cases, calcium preparations and glucocorticoids are prescribed. Externally, anesthetics (anesthetic oil solution, lidocaine) are applied to reduce soreness, zinc ointment is used to relieve itching and reduce inflammatory manifestations. If schistosomiasis is detected, complex anthelmintic therapy is prescribed.
Prognosis and prevention
The prognosis of simple swimmer’s itch, not complicated by schistosomiasis, is favorable – all manifestations of the dermatological disease disappear without a trace after a few hours (with initial contact) or days. This condition may pose some danger to young children who still have poorly formed immune defense mechanisms. Therefore, in their regard, it is especially important to adhere to the rules of prevention of swimmer’s itch – to avoid bathing in reservoirs with abundant aquatic vegetation and in habitats of waterfowl. After bathing in any fresh pond or contact with water from it, you must immediately wipe yourself with a dry towel and replace wet clothes. Also, do not come into contact with water from lakes or ponds if there are instructions about the prohibition of bathing near them.