What can animal coronaviruses tell us about emerging human coronaviruses?

Diseases are continually emerging. A conservative estimate is that there is one new human disease every eight months, with even more emerging in animals. In 2008, the UK Government’s Foresight programme investigated the potential threat of new and emerging diseases.1,2 Of the eight categories of diseases that were considered to be particularly important, three were prescient of the present severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. These were novel diseases, zoonotic infections and acute respiratory diseases.1 The successful control of global diseases is dependent on a number of factors. The most common natural control comes from sufficient members of the population having immunity to the infection (ie, herd immunity). However, this can break down when either the pathogen mutates, as we regularly see with influenza viruses, or the host becomes immunosuppressed. Herd immunity can be enhanced by vaccination, but with newly emerging diseases there is insufficient time to develop, test, regulate and produce effective vaccines to influence the first ‘wave’ of an epidemic. So, as we are now with the present SARS-CoV-2 pandemic, we need to understand the pathology, epidemiology, viral shedding patterns and survival outside of the host to make informed but intuitive decisions for disease control. Coronaviruses are enveloped, single-stranded, positive-sense RNA viruses that infect a wide variety of species, including people, livestock and companion animals. These viruses display exceptional genetic plasticity, driven by the accumulation of point mutations and recombination events. This genetic variation is responsible for the emergence of viral strains with increased virulence, different tissue tropism and/or an expanded host range. Coronaviruses are currently classified within four genera, Alphacoronavirus , Betacoronavirus , Gammacoronavirus and Deltacoronavirus (Box 1). Many alphacoronaviruses and betacoronaviruses have their origin in bats, while gammacoronaviruses and deltacoronaviruses tend to have their origin in birds. Box 1: ### Representative viruses within the four coronavirus genera