I don't know how diatomaceous earth is used internally for parasites. It's just very small spiky silica particles that mechanically injure the exoskeletons of insects if they get it on them. I would think it would be really irritating to internal membranes of any animal that ingested it. Just getting it on my skin makes me kind of itchy. But I see by a google search that people offer it for sale as a dewormer.