Why are there so few (or so many) circulating coronaviruses?. Issue 9 (September 2021)

• Record Type: Journal Article
• Authors: Rice, Benjamin L.; Douek, Daniel C.; McDermott, Adrian B.; Grenfell, Bryan T.; Metcalf, C. Jessica E.
• Is Part Of: Trends in immunology. Volume 42:Issue 9(2021)
• Page Start: 751
• Page End: 763
• Publication Date: 2021-09
• Subjects: viral ecology -- cross-reactivity -- landscape of immunity -- antigenic space; Immunology -- Periodicals; 571.96
• DOI: 10.1016/j.it.2021.07.001
• Languages: English
• ISSNs: 1471-4906

Abstract

Abstract : Despite vast diversity in non-human hosts and conspicuous recent spillover events, only a small number of coronaviruses have been observed to persist in human populations. This puzzling mismatch suggests substantial barriers to establishment. We detail hypotheses that might contribute to explain the low numbers of endemic coronaviruses, despite their considerable evolutionary and emergence potential. We assess possible explanations ranging from issues of ascertainment, historically lower opportunities for spillover, aspects of human demographic changes, and features of pathogen biology and pre-existing adaptive immunity to related viruses. We describe how successful emergent viral species must triangulate transmission, virulence, and host immunity to maintain circulation. Characterizing the factors that might shape the limits of viral persistence can delineate promising research directions to better understand the combinations of pathogens and contexts that are most likely to lead to spillover. Highlights: Coronaviruses have emerged repeatedly in human history, indicating that exposure may be common. Evidence suggests that the emergent coronaviruses have the capacity to infect a broad range of hosts, invade these via a variety of host cell receptors, evolve rapidly during the emergence process, and, in the case of the endemic coronaviruses, persistently circulate by avoiding sterilizing immunity. From this, we hypothesize that a diverse set of emerging coronaviruses might be found within the human pathogen pool. However, only four endemic coronavirus species are known (HCoV-229E, -NL63, -OC43, and -HKU1), which exhibit limited genetic diversity within species. The interaction between infection parameters such as transmission and virulence, and the pattern of immune crossprotection against existing endemic viruses, warrant further study to understand the trajectory of novel coronaviruses and to explain why so few can establish endemic transmission.