The Bat People (1974)

Dr. John Beck, a newlywed, takes his wife Cathy on a spelunking adventure in Carlsbad Cavern. During their expedition, he is bitten by a fruit bat and undergoes a bizarre transformation into a vampire bat. As he tries to find help from a fellow physician, his attempts at treatment only worsen his affliction. Unbeknownst to him, Dr. Beck begins a violent rampage that draws the attention of Sergeant Ward, who is determined to uncover the truth behind the mysterious killings linked to the doctor’s unsettling change.