Photo courtesy of pets.intervet.it
Currently the only truly effective prevention of cercarial dermatitis is to forbid swimming in infested areas as no other effective strategies are known which would be both ecologically and financially acceptable. (In the past several states applied copper sulfate, a moulluscide, to to their lakes to kill the intermediate snail hosts and thus interrupt transmission. However, it is unknown what the long term consequences of using this chemical may be on the ecology of the lake.) In a recent study it was attempted, by means of medication of ducks, to kill the different stages of Trichobilharzia in order to interrupt the parasitic cycle. For this the effectiveness of praziquantel on the parasitic stages in the final host (preadults, adults, eggs or fully developed miracidia) was tested in experimentally infected dwarf mallards (Anas platyrhynchos, hemerot.) and mallards (Anas platyrhynchos platyrhynchos). During therapy of ducks with patent Trichobilharzia infection, onefold or twofold application of this drug (1 x 500 mg/duck, 1 x 300 mg/duck, 2 x 200 mg/duck) only prevented the releasing of eggs with hatchable miracidia for up to 24 hours. Only a threefold application of 200 mg/duck in 24 h intervals led to a permanent reduction of detectable miracidia. Application of praziquantel in low doses (30 or 40 mg per duck and day) did not reduce the number of released miracidia. Medication with praziquantel led to a strong shift of adult worms located in the enteric veins of the ducks to the liver veins in a little as 3 hours and examinations by electron microscopy revealed changes in the worms' surface and damage of the tegument.
New developents in the study of swimmer's itch have lead to the revelation that perhaps systemic treatment should be considered for this seemingly harmless cutaneous eruption. It has always been assumed in man that these cercariae die within the epidermis, and that humans are dead-end hosts for this organism. Newer studies, however, suggest that the human clinical disease is not limited to the exposed surfaces of the body. In the study, 80 ceracariae were applied to human skin, producing the characteristic eruption. Yet none of the infective larvae were detectable on biopsy. This implies that infective larvae may migrate in the human body via the circulatory system. Data from other animal models indicate that cercariae transform into schistosomula and migrate within the mammalian host, especially to the lungs. These worms can survive for days within mammalian organs and feed on red blood cells. Systemic treatment with ivermectin early in the disease is proposed as a treatment consideration until the ramifications of this infestation are better understood. Most of the species of flukes implicated with swimmer's itch are sensitive to ivermectin.