Zoonosis: Back to the Future of Parasites, Humans, and Living Together, such is their Destiny

Abstract

Most biological pathogens have a zoonotic origin, meaning at some point in the history of our planet, they “spilled over” (i.e., were transmitted) from animals to humans to become pathogens. Today, as human populations expand, urbanize, and encroach on wildlife habitats, interactions at the human–animal–environment interface are more frequent, facilitating these spillover events and increasing the risk of emerging disease in humans. Other factors, as agricultural intensification, wildlife trade, deforestation, and global travel further amplify the risk of such spillover, or cross-species transmission. Once introduced into human populations, some pathogens adapt to efficient human-to-human transmission, leading to outbreaks, epidemics, or pandemics.