[Origin of SARS-CoV-2 theories, keys and unknowns of an emerged disease.]

In the midst of the SARS-CoV-2 public-health pandemic emergency, it is important to understand its zoonotic origin and how an animal virus finally infects humans. Identifying the circumstances in which a virus jumps species boundaries to infect humans so productively is objective of this work and will help us to determine the epidemiology and pathogenisis of this agent. Nowadays, it is known that bats serve as reservoir hosts for virus progenitor, but determine the possibility of a potential intermediate host of SARS-CoV-2 is still a challenge. Scientific investigations stablish the natural selection theory as the most probable (natural selection in an animal host before zoonotic transfer or acquired mutations in humans following crossing species barrier). It is necessary to find out how SARS-CoV-2 emerged, its rapidly spreads within a community and the optimal context in which this virus binds to human receptor. One Health is a multisectoral, collaborative and transdisciplinary approach which allows a cooperative working between animal and human health that will help us to introduce some possible control measures that might reduce the spread of the virus; improving sanitary management, identifying new outbreaks and preventing future zoonotic and pandemic events.