Here the danger is not so much to the human population but rather to the livestock exposed to bat bites. In South America a major economic problem existed when large numbers of cattle were lost to rabies and infection. An effort to control and eradicate the vampire bat was initiated in 1968 by the Agency for International Development in cooperation with the Mexican government. The U.S. Fish and Wildlife Service was assigned the task of studying its habits to obtain some clues for its control. Using several different methods of nighttime surveillance, observation of the bat's grooming behavior provided the answer.
Bats are extremely clean, sometimes grooming, licking, and scratching themselves for hours.
The vampire bat, in particular, grooms both itself and its neighbors intensively. A paste-like anticoagulant poison that causes internal bleeding in the bat was smeared on likely areas, fetlocks or shoulders, of cattle that had been bitten. Vampire bats usually return to their victims for more food, so when they attack again, they come in contact with the poison. Back at the roost in the process of grooming, they ingest and spread the poison with the subsequent death of a large percentage of the colony. At the present time, the poison is being used successfully in Mexico, Central and South America.