Zoonosis

Lore & Background

Zoonoses have different modes of transmission. In direct zoonosis the disease is directly transmitted between non-humans and humans through the air (influenza), bites and saliva (rabies). Host genetics plays an important role in determining which non-human viruses will be able to make copies of themselves in the human body. Dangerous non-human viruses are those that require few mutations to begin replicating themselves in human cells. Zoonotic diseases frequently emerge through spillover events, in which pathogens are transmitted from animal reservoirs to human populations. The likelihood of spillover is influenced by environmental and anthropogenic factors, including deforestation, land-use change, and increased human encroachment into wildlife habitats.

Reader's Guide

Zoonotic diseases account for a substantial proportion of infectious diseases affecting humans, with up to 75% of emerging infectious diseases being zoonotic in origin. Disease emergence hotspots are often located in tropical regions where high biodiversity coincides with rapid human population growth and environmental disruption. Climate change further contributes by altering the distribution of vectors such as mosquitoes and ticks. Urban wildlife, including rodents, pigeons, bats, and raccoons, can increase contact between humans and animals, creating opportunities for zoonotic disease transmission. A One Health approach is used to address zoonotic disease risks by integrating human, animal, and environmental health. The emergence of zoonotic diseases originated with the domestication of animals, and recently there has been a rise in frequency of appearance of new zoonotic diseases. A study led by researchers at the University of California, Davis estimated that approximately 1.67 million undescribed viruses exist in mammals and birds, up to half of which may have the potential to spill over into humans.

Did You Know?

• HIV was a zoonotic disease transmitted to humans in the early part of the 20th century, though it has now evolved into a separate human-only disease.
• Rabies is a zoonotic viral disease affecting mammals, including wildlife such as bats and raccoons.
• Approximately 1.67 million undescribed viruses are thought to exist in mammals and birds, up to half of which are estimated to have the potential to spill over into humans.