Ivermectin is a drug used extensively in cattle. It is thought that this drug might cross the blood brain barrier in turtles and torts. I have heard of a lot of reptiles, not just turtles and torts, having trouble with this medication. I don't know if this is because of the toxicity of the drug in general, even when given at the correct dosages and frequency, or if the animals have been accidentally over medicated. Clinical signs associated with Ivermectin intoxication are primarily related to general neuromuscular weakness.
Death is a function of paralysis of the respiratory muscles.
Ivermectin binds irreversibly and can take at least 7 days before reversal of clinical signs is observed. Signs and Symptoms Parasites are quite common in wild caught, and yes even captive bred and born reptiles. In the wild many reptiles live with few ill effects caused by the internal parasites that they might be harbouring. Reptiles can also pick up some parasites from eating food items that contain parasites. I'm quite sure they eat food items in the wild that have parasites in them, but again the conditions of captivity can create an environment that causes the parasites to multiply much more easily.