A correct diagnosis of swimmers' itch is not always very easy. Similar external symptoms may occur after insect bites and in some communicable diseases, such as chickenpox, measles, and some venereal diseases. Similar symptoms may also sometimes be induced by plants in sensitive persons. The localization of the affected skin areas is important to consider for the differential diagnosis. A history of bathing or immersion of affected skin areas in water is of course most important for a presumptive diagnosis. However, allergic reactions after exposure to blue-green algae (cyanobacteria) have also been recorded (Solomon and Stoughton 1978).
It should be kept in mind that the cercariae causing swimmers itch in northern regions are released from the snails and swarm in the waters only during short periods in summer and during warm, sunny days. Cnidarians (coelentarates) is a group of marine animals that contain stinging structures known as nematocysts, and include jellyfish, corals, sea anemones, hydroids, etc. Contacts with these animals can induce dermatitis (Black and Szmant 1992). In northern areas, however, there are few representatives of these animals able to produce symptoms in humans.
There is evidence for an antibody response in swimmers' itch patients and serology can be used for diagnostics (Kimmig and Meier 1985; Kolarova et al. 1994; Pilz et al. 1995).
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