Zoonosis
Infectious diseases transmitted from animals to humans.
A zoonosis (pl.: zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen transmitted from a non-human animal to a human. Major modern diseases such as Ebola and salmonellosis are zoonoses, and most human diseases originated in non-humans. Of the pathogens known to infect humans, a significant majority are zoonotic in origin. Transmission can occur through various routes, including direct contact such as bites and saliva, as seen in rabies, or through the air, as with influenza. While human infection with animal influenza viruses is uncommon due to poor transmissibility, avian and swine influenza viruses possess high zoonotic potential and can recombine with human strains, occasionally sparking pandemics like the 2009 swine flu. HIV, originally a zoonotic disease transmitted to humans in the early twentieth century, has since evolved into a human-only pathogen. Host genetics are crucial in determining which animal viruses can replicate in humans; dangerous viruses are those requiring few mutations to do so, as such mutations may arise randomly in animal reservoirs. Zoonotic diseases frequently emerge through spillover events from animal reservoirs to human populations, driven by environmental factors such as deforestation, land-use change, and human encroachment into wildlife habitats. Tropical regions with high biodiversity and rapid population growth are hotspots for disease emergence. Climate change alters the distribution of vectors like mosquitoes and ticks, affecting transmission dynamics. Urban wildlife, including rodents and birds, can spread diseases such as leptospirosis, hantavirus, and histoplasmosis. A One Health approach integrates human, animal, and environmental health to manage these risks. The rise in new zoonotic diseases is linked to environmental changes, unsustainable agriculture, wildlife exploitation, and increased human mobility.
- field
- Infectious disease epidemiology
- known_for
- Diseases transmitted from non-human animals to humans
- key_fact
- Approximately 60% of known human infectious diseases are zoonotic in origin
- transmission_modes
- Direct (air, bites, saliva) and indirect (food, water, vectors)
- examples
- Ebola, salmonellosis, rabies, HIV (originally zoonotic), avian and swine influenza
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.
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