Reverse zoonoses: Human-to-animal disease transmission and its one health implications

Public discussion of zoonotic disease nearly always runs in one direction: a virus jumps from a bat, a bird, or a pig into a person, and from there into the headlines. Far less attention is paid to the reverse traffic, in which humans pass their own pathogens back into animal populations. Reverse zoonosis, or zooanthroponosis, has been documented across viruses, bacteria, fungi, and parasites, with consequences that reach from zoo enclosures to national parks to industrial pig farms. This article traces the routes by which human pathogens reach animals, examines three well-studied cases, SARS-CoV-2 in mink and wildlife, methicillin-resistant Staphylococcus aureus in pig farming, and human respiratory viruses in wild apes, and considers what a One Health perspective demands of veterinarians, farmers, conservationists, and physicians alike. The pattern that emerges is consistent: wherever humans keep close, sustained contact with animals, whether through occupation, captivity, or habituation, our own microbes eventually cross the species line, sometimes with consequences as severe as those more readily associated with zoonotic spillover in the opposite direction.