bladder bladderneoplasms cancer classification complications control diseasevectors etc freshwatermussels freshwatersnails gastropoda handbooks healtheducation identification latinamerica manuals mollusca mollusks parasiticdiseases parasitology prevention qx675m245s1985 schistosoma snails snailsascarriersofdisease transmission trematoda trematodeinfections tropics wc810h4341990