Context: Diseases caused by coronaviruses, such as COVID-19, are zoonotic, meaning they are transmitted between animals and people.As the novel coronavirus has spread across continents, studies are underway to better understand its origin and how it is transmitted.

• According to the World Health Organisation (WHO), SARS-CoV was transmitted to humans from civet cats, and MERS-CoV from dromedary camels.
• Both the viruses, however, are believed to have originated from bats and subsequently passed on to other animals.
• While researchers are yet to conclude how the novel coronavirus, which was first detected in China’s Wuhan, originated, many believe it could be traced back to bats.
• Many studies over the years have found bats to be a natural reservoir for a large number of zoonotic viruses that have caused outbreaks in many countries in the past. These include rabies, Marburg, Nipah and Hendra viruses. 
• Researchers at the Wuhan Institute of Virology in China were able to trace the origin of the SARS virus to these bats in a remote cave in the country’s southeastern Yunnan province.
• Research suggests that bats, which make up a quarter of all mammal species, have developed stronger immune systems through the process of evolution which enabled them to fly.
• Studies have shown that when bats fly, the energy requirements in their bodies cause cells to break down into bits of DNA which are then released. While most organisms would treat such DNA particles as foreign invading bodies, in bats such responses are more muted. 
• Due to this weakened response, bats do not develop inflammations, which can cause a considerable toll on the body’s energy. This phenomenon is believed to be the reason so many viruses can exist in their bodies. 
• In a 2007 study at the American Society of Microbiology that predicted the emergence of a SARS-like coronavirus epidemic. Coronaviruses are well known to undergo genetic recombination, which may lead to new genotypes and outbreaks.

How do germs spread between animals and people?
Zoonotic transmission can occur in any context in which there is companionistic (pets), economic (farming, etc.), predatory (hunting, butchering or consuming wild game) or research contact with animals.

• Contamination of food or water supply: Eating or drinking contaminated food can cause various types of diseases in humans.
• Direct contact: While petting or touching animals, and bites or scratches.
• Indirect contact: Coming into contact with areas where animals live and roam.
• Vector-borne: Being bitten by a tick, or an insect, like a mosquito or a flea food-borne

Type of disease that passes from an animal or insect to a human

• Ebola: There are 6 species of Ebola Virus identified till date namely Zaire, Bundibugyo, Sudan, Taï Forest, Reston and Bombali.It is Transmitted to people from wild animals and spreads in the human population through human-to-human transmission. Its host are fruit bats of the Pteropodidae family.
• Nipah: It is transmitted to humans from animals (such as bats or pigs), or contaminated foods and transmitted directly from human-to-human.Its host are Fruit bats of the Pteropodidae family.
• Zika: It is transmitted primarily by Aedes mosquitoes and infected people can transmit Zika through transfer of body fluids including sexual intercourse.
• Avian/Bird Flu: It is caused by H5N1 virus, a subtype of the influenza A virus. Human infections occur through infected bird-to-human contact or contact with surfaces and objects  contaminated by their droppings but Human-human transmission is limited.
• Swine Flu: It is caused by H1N1 virus. It occur in people with direct exposure to pigs spread from person to person, similar to seasonal influenza viruses.
• Kyasanur forest disease: It is caused by Kyasanur Forest disease Virus(KFDV), a member of the virus family Flaviviridae. Rodents, shrews and monkeys after being bitten by an infected tick are the common host by which its transmission to humans occur after a tick bite or contact with an infected animal.
• Rabies: It is caused by Ribonucleic Acid(RNA) virus that is present in the saliva of a rabid animal.It is transmitted to humans following a bite of a rabid animal.
• West Nile Virus: It is caused by the West Nile Virus.Birds are the natural host which transmits it to humans through bites from infected Culex mosquitoes.
• Monkeypox: It is caused by monkeypox virus transmitted to people from wild animals such as rodents and primates and Human-to-human transmission caused by contact with lesions, body fluids, respiratory droplets and contaminated materials.
• Dengue: It is caused by Dengue virus belonging to the genus Flavivirus of the family Flaviviridae and it is transmitted to humans by the bite of an infected female Aedes Aegypti mosquito.
• Hantavirus: They are family of viruses which are spread mainly by rodents.It does not spread from one person to another and can be contracted if someone comes in contact with a rodent that carries the virus.
• Malaria: It is caused by Plasmodium parasites which is transmitted to humans through the bite of infected female Anopheles mosquitoes.