Studies of infested lakes and outbreaks in Europe and North America have found cases where infection risk appears to be evenly distributed around the margins of water bodies as well as instances where risk increases in endemic swimmers itch "hotspots". Children may become infected more frequently and more intensely than adults but this probably reflects their tendency to swim for longer periods inshore, where cercariae also concentrate. Stimuli for cercarial penetration into host skin include unsaturated fatty acids, such as linoleic and linolenic acids. These essential fatty acids are found in many edible crops, derived plant oils, sun lotions and creams based on plant oils. Control
Various strategies targeting the mollusc and avian hosts of schistosomes have been used by lakeside residents in recreational areas of North America to deal with outbreaks of swimmers itch. In Michigan, for decades, authorities used copper sulfate as a molluscicide to reduce snail host populations and thereby the incidence of swimmers itch. The results with this agent have been inconclusive, possibly because:

Snails become tolerant
Local water chemistry reduces the molluscicides efficacy
Local currents diffuse it
Adjacent snail populations repopulate a treated areaMore importantly, perhaps, copper sulfate is toxic to more than just molluscs, and the effects of its use on aquatic ecosystems are not well understood.Another method targeting the snail host, mechanical disturbance of snail habitat, has been also tried in some areas of North America and Lake Annecy in France, with promising results. Some work in Michigan suggests that administering praziquantel to hatchling waterfowl can reduce local swimmers itch rates in humans.
Penciclovir is a guanosine analogue antiviral drug used for the treatment of various herpesvirus infections. It is a nucleoside analogue which exhibits low toxicity and good selectivity. Because penciclovir is absorbed poorly when given orally (by mouth) it is more often used as a topical treatment. It is the active ingredient in the cold sore medications Denavir (NDC 0135-0315-52), Vectavir and Fenivir. Famciclovir is a prodrug of penciclovir with improved oral bioavailability. Penciclovir was approved for medical use in 1996. Medical use
In herpes labialis, the duration of healing, pain and detectable virus is reduced by up to one day, compared with the total duration of 2–3 weeks of disease presentation. Mechanism of action
Penciclovir is inactive in its initial form. Within a virally infected cell a viral thymidine kinase adds a phosphate group to the penciclovir molecule; this is the rate-limiting step in the activation of penciclovir. Cellular (human) kinases then add two more phosphate groups, producing the active penciclovir triphosphate. This activated form inhibits viral DNA polymerase, thus impairing the ability of the virus to replicate within the cell. The selectivity of penciclovir may be attributed to two factors. First, cellular thymidine kinases phosphorylate the parent form significantly less rapidly than does the viral thymidine kinase, so the active triphosphate is present at much higher concentrations in virally infected cells than in uninfected cells. Second, the activated drug binds to viral DNA polymerase with a much higher affinity than to human DNA polymerases. As a result, penciclovir exhibits negligible cytotoxicity to healthy cells.