ZOONOSES

Zoonoses, or zoonotic diseases, are caused by infectious agents that are transmissible under natural circumstances from vertebrate animals to humans. Zoonoses may arise from wild or domestic animals or from products of animal origin. Zoonoses have been known since early hystorical times. There are biblical references to plague, a bacterial zoonosis mainly transmitted to humans by fleas; and some historians contend that a disease first described by Thucydides during the Plague of Athens (430–425 B.C.E.) was typhus, a louse-borne zoonosis (Zinsser). Certain zoonoses, such as yellow fever, malaria, and rabies, are well known to the general public, but a vast number of lesser-known zoonoses exist in limited cycles in different parts of the world. There are undoubtedly many zoonoses lurking in nature that have the potential to cause serious public health consequences if introduced into humans. This is, in fact, what may be our greatest concern about zoonoses—not the diseases that we know they are capable of causing, but the hidden potential of what diseases might arise in the future. Examples that foster our concern include the emergence of AIDS (acquired immunodeficiency syndrome) from nonhuman primates, which has developed into one of the most significant infectious disease threats in the world today, and the crossing of the species barrier of certain influenza virus strains that have led to large human pandemics. Diseases such as AIDS and influenza have their origins as zoonoses, but they subsequently adapted to human-to-human transmission.