Panacur is also used to deworm hourses. You can get it in a paste form from feed stores. I would suggest using it around 2 weeks after the first time you use it, as it will kill any worms that have hatcheed after the first treatment. A good natural dewormer is Pumpkin - although with box turtles, its hard to get them to eat it. Go with the dosage your doctor recomends. I believe they could have been introduced via bird or other animal droppings.

Parasites are common in turtles and tortoises, but under stress or cramped condition, could become dangerous.

Bill