I don't know of any human parasites that are carried by land snails, nor can I imagine what the mode of transmission from snail to human might be, unless you ate them raw. However, fresh water snails are the carriers of one of the most serious human parasitic diseases, schistosomiasis. Three different species of schistosomes, or blood flukes, infect humans, and they are a major public health problem in many parts of the world, especially areas with poor sanitation. Snails become infected when the water they live in is contaminated by human excrement. The parasite passes through larval stages in the body of the snail, culminating in a final larval stage that leaves the snail, and is free-swimming in the water. This larva is capable of burrowing directly into human skin, and humans become infected when they enter the water. Once in the human body, the larvae migrate to the blood stream, where they mature into full-grown blood flukes. Each of the three species of human schistosomes uses a different family of fresh water snails as its intermediate host. I don't remember what they all are - I believe one of them uses snails in the family Hydrobiidae. Schistosomes are flukes - flatworms - but unlike most flatworms, they are not flat. They are slender and cylindrical, an adaptation for living in blood vessels. Other species of schistosomes infect other mammals, and birds, and each schistosome species has particular fresh water snails that serve as its host, and cannot use other snail species. Sometimes the free-swimming larvae of waterbird schistosomes will burrow into human skin. They can't infect humans, but die in the skin, causing an irritating alergic condition know as "swimmer's itch". That's all I can remember. If you want more information on this, I'll get out my parasitology books when I go home tonight. Regards, Paul M.