We have a lot of ticks around here, so I check for them after every ride or hike. They do tickle when they crawl on you, so if you respond to that, they don't get a chance to dig in.
Poison ivy is evidence of pure evil in the world. I try to avoid it as much as possible. If you stay on well-travelled trails or ride in a place without trails (there are state forests around here where you can ride wherever you want), it isn't too much of a problem. I have noticed that it pops up in places that have been cut back and are now neglected. It is oportunistic.