Good day, i would like to know if topical parasiticide that you apply to a dog's back is poisonous or harmfull to a pregnant woman if she touches the dog?

Yes: Topical flea and tick preparations found in either topical drops or flea collars are known to cause neurotoxicity and organophosphate poisoning in humans if they come into direct contact. A better option for parasite control is oral medication given to the dog. Avoid touching dogs that have been treated with topical meds since the medication can easily rub off on your hand.