No, they've always been here. They are everywhere, literally. The lifecycle begins as an egg that is ingested by a deer while browsing. That egg is from feces contaminated forage or water. The egg travels into the gut and hatches into a larva. The larva then burrows through the intestinal wall and into the muscle or other organs of it's host. The larva then encysts itself and lies in wait.
So to complete that lifecycle, another animal needs to eat the flesh of the infected host and consume the cyst. Then the cyst will hatch and the larva will then grow to an adult tapeworm in say a coyote, bear, wolf or cougar. Then the adult tapeworm will spew millions of eggs that are excreted from the live host.
Then the lifecycle starts over as those eggs are deposited in water and on forage for other creatures to consume.