Zoonotic Diseases Zoonotic diseases are diseases caused by agents with animal reservoirs. Some of these diseases are transmitted through a vector, such as plague, and others are not, such as anthrax.   Humans are "accidental hosts" in this cycle, meaning they are not natural reservoirs for the agents in question but are incidentally infected when they have contact with those reservoirs. Other zoonotic diseases can be transmitted through contamination of food or water by animal feces (e.g. E. coli O157), contact with urine or animal hides (e.g. hantavirus or anthrax), or animal bites (e.g. rabies).