Deer and ticks have a parasitic relationship. In parasitic relationships, one organism is harmed, while the other organism benefits. This is often written as (+,-) in scientific shorthand.
Although the parasite harms its host in this type of relationship, it is rarely the goal of the parasite to kill its host. This would mean the parasite would no longer have a place to live and gain nutrients. Parasites and hosts typically evolve together; the host adapts to become more resistant to the parasite and the parasite adapts to be able to feed off the host again. Other examples of parasitic relationships include aphids and rose plants, as well as orchids and trees.