The emergence of a new coronavirus (SARS-CoV-2, the etiologic agent of COVID-19) in Wuhan, China, creates a sense of deja vu with the severe acute respiratory syndrome (SARS-CoV) epidemic in China in 2003. Coronaviruses are enveloped, positive-stranded RNA viruses of mammals and birds. These viruses have high mutation and gene recombination rates making them ideal for pathogen evolution. In humans, coronavirus is usually associated with mild disease, the common cold. Previous emerging novel coronaviruses, such as SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV), which emerged in the Middle East in 2012, were associated with severe and sometimes fatal disease. MERS-CoV was less pathogenic than SARS-CoV, with the most severe infections mainly in individuals with underlying illness.
Phylogenetic analysis of SARS-CoV-2 suggests an initial single-locus zoonotic spillover event in November 2019, and subsequent human-to-human respiratory transmission. The SARS epidemic in 2003 was followed soon after by avian influenza H5N1 in 2006, centered on the Asian continent and Middle East. Other surprising viral zoonoses that have caused serious disease include Nipah encephalitic virus in pigs and humans in southeast and south Asia in 1999–2014, and large-scale Ebola virus epidemics in 2014–2016 and 2018–2019 in west and central Africa. Taken together, these events represent wake up calls regarding disease emergence in the 21st century and the importance of human diseases originating from indiscriminate contacts with infected animals.
There is an increasing focus on the human–animal–environment disease interface, as encompassed in the One Health concept. Mortalities, disability-adjusted life-years and billions of dollars of economic losses from these infections demand action and investment in prevention to face novel challenges to human and animal health. Research has led to better understanding of the nature and drivers of cross-species viral jumps, but the detail is still elusive. No reservoir population of bats for SARS and MERS-CoV or Ebola virus has been definitively identified. Forensic examination has clarified the human infection sources and multispecies involvement in these diseases, with some species confirmed as competent hosts (eg, camels for MERS-CoV), bridge (or amplifying) hosts (eg, pigs for Nipah virus, nonhuman primates for Ebola virus) or dead-end hosts. The crucial checkpoint is the jump and bridging of the viruses to humans, which occurs most frequently through animal-based food systems.
Comment: Zoonotic or agricultural bridging of novel pathogens from domestic and captive wildlife needs urgent attention, along with attention to the human appetite for meat. This approach may be achieved for coronavirus threats by substantially reducing the trade of risky species of wild caught animals for food or other purposes, and a culturally sensitive ban on the sale of these animals in wet markets.
In some parts of Africa, prevention of Ebola virus and future coronavirus threats require shifts in food habits, a transition from bushmeat being a cultural norm or primary source of protein, and by discouraging agricultural development that brings bats into increased contact with humans or livestock. In the Middle East, re-evaluating and improving infection prevention and control measures for camel farms, a recent introduction coincident with the emergence of MERS-CoV, represents another prevention strategy.