7.2.3: Zoonoses
Zoonotic diseases (zoonoses) are those that can be shared between humans and animals. Any animal can potentially carry zoonoses, including pets, livestock, and wild animals. Some animals do not even get infected with the disease, but are simply carriers of the pathogen. Suburban sprawl and climate change are two more recent environmental factors that have forced humans and animals into closer environments. Many zoonotic diseases are also vector borne (transmitted by insect bites), and warmer climates can lengthen the breeding season for mosquitos and other insects (Burke & Weill, 2023). When a zoonotic pathogen finds its way from animals to humans this is called “spillover”. For example, HIV originally infected primates in the 1920s before the human outbreak several decades later (Ellwanger & Chies, 2021). It is estimated that 60% of known infectious diseases and 75% of emerging ones are zoonoses ( Zoonotic Diseases , 2023).
Bats are reservoirs for many viruses that have the potential for spillover, the majority of which do not affect them. It is thought that they are probably the reservoir for the viruses that caused several recent epidemics such as SARS, MERS, and Ebola, as well as the COVID-19 pandemic (Burke & Weill, 2023). While direct or indirect contact with bats was a possible starting point for the COVID-19 pandemic, it has also been postulated that another animal such as a pangolin could have been an intermediary. Environments that allow a lot of direct and indirect contact between humans, live animals of different species, and meat - particularly if there are poor sanitary conditions - increase the risk of spillover events. Wet markets are culturally significant in China and other Asian countries, and it is suspected that human and animal interactions at a wet market in Wuhan, China were the origin of the COVID-19 pandemic (Ellwanger & Chies, 2021).