Plants you buy from reputable sources have generally been treated with Potassium Permanganate before being shipped. Those plants should be safe.
If you want to disinfect plants yourself, you can use a 1:20 bleach solution and put the plants in that for a couple of minutes. Years ago, I left mine in too long and managed to kill all my plants, so I don't use bleach anymore.
Potassium Permanganate is safer for plants, but you need to be careful with it. Wear gloves and eye protection. It also stains anything it comes in contact with, so you might want you wear some old clothes as well. Don't use it on a windy day. You don't want it blowing into your face and you don't want to inhale it.
Mix a teaspoon of PP with 10 - 15 gallons of water. You can leave the plant in that for 10, even 20 minutes and they should be fine.
PP won't kill leaches, but it is good for most other parasites and diseases.