The members of a cult carrying their sacred parasite
The worshiped spinal parasite was a kind of gastropod parasite that was worshiped by a cult based in the Juab County, Utah, who believed it was the second coming of Jesus Christ. To ensure the parasite's continued survival, the cult would implant the parasite into young, unsuspecting transients to serve as its host by inserting it into the lower section of the spine. The sentient parasite would then apparently take control over their mind and body while adversely leading to an accelerated decay of the host's bones, causing osteoporosis, arthritis, and kyphosis of the spine. Due to this, upon the behest of the parasite, the cult would ritualistically beat the host to death once the conditions worsened and start the process all over again. The life span of hosts varied between a few days to several months.
The cult, comprised of 47 members, was a small community that settled in the Sevier Desert for the express purpose of worshiping the parasite undisturbed. All citizens were perfectly willing and entirely devoted to serving the parasite's whim, even using a commerical bus to pick up potential hosts passing through the area. They were seemingly led by a man named Milsap and an unnamed woman who acted as the bus driver, taking their orders directly from the parasite.
In 2000, FBI Special Agent Dana Scully investigated the murder of a 22-year old backpacker, who had been missing for six months, after it was found that his skeleton showed signs of damage usually associated with advanced age. Scully later followed their unmarked bus to a gas station, where she questioned gas station owner about the murder. After discovering that Scully was a physician, the attendent broke her car's engine by filling the tank with watered down gasoline, then directed her to the house of Mr. Milsap in the next town over for a phone. Once there, she found out that the line was dead and was offered to stay for the night, reluctantly agreeing for lack of other options.
The next day, Scully was awoken by Milsap who told her it was an emergeny and asked her to take a look at a hiker having a seizure downstairs. The man, Hank Gulatarski, was, unbeknownst to her, the most recent host for the creature, and the townsfolk had hoped that Scully could somehow treat his declining state. It wasn't long before Scully discovered the mollusc burrowing inside Hank's back and upon repeated failure to remove it, she attempted to make a run for the highway to get help. Hank immediately gathered up the rest of the town after she left, recapturing Scully, who was forced to watch as Hank allowed the cult to stone him to death. The parasite was then transferred to Scully, despite her pleas that she was pregnant. In the nick of time, Special Agent Doggett arrived with local police and managed to cut out the parasite from Scully's nape before finally shooting it to death in front of the devastated townsfolk. (TXF: "Roadrunners")