Panacur is widely known as a worming agent in Reptiles. Nothing unusual about that. Effective against Roundworms, Tapeworms, Hookworms. Was going to suggest that, but figured it better coming from your Vet. Did your turtles have access to dog or cat poop? Most likely they were eating it. Is your vet experienced with reptiles?
jsc
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"As hard as I've tried, just can't NOT do this"
John Crickmer