They can get sick, but it's usually from something being off in their habitat. They are pretty hardy little animals. (not saying they can't or don't get sick for other reasons) getting their uvb and basking on point is the most important thing. Keeping their habitat sanitary is also very important. Just like any other animal they naturally carry some parasites in their system. If their habitat is kept reasonably sanitary their immune systems keeps it in check, but some like Coccidia depend on being reingested as part of their life cycle, so if poop is left for them to track through it can cause a flare up.