Zoonotic disease A) is caused by suborganismal pathogens such as viruses, viroids, and prions only. B) is caused by pathogens that are transferred from other animals to humans by direct contact or by means of a vector. C) can only be spread from animals to humans through direct contact. D) can only be transferred from animals to humans by means of an intermediate host. E) is too specific to study at the community level, and studies of zoonotic pathogens are relegated to organismal biology.