‘Accidents waiting to happen’—Insights from a simple model on the emergence of infectious agents in new hosts

Abstract

This study evaluates through modelling the possible individual and combined effect of three populational parameters of pathogens (reproduction rate; rate of novelty emergence; and propagule size) on the colonization of new host species—putatively the most fundamental process leading to the emergence of new infectious diseases. The results are analysed under the theoretical framework of the Stockholm Paradigm using IBM simulations to better understand the evolutionary dynamics of the pathogen population and the possible role of Ecological Fitting. The simulations suggest that all three parameters positively influence the success of colonization of new hosts by a novel parasite population, but contrary to the prevailing belief, the rate of novelty emergence (e.g. mutations) is the least important factor. Maximization of all parameters results in a synergetic facilitation of the colonization and emulates the expected scenario for pathogenic microorganisms. The simulations also provide theoretical support for the retention of the capacity of fast‐evolving lineages to retro‐colonize their previous host species/lineage by ecological fitting. Capacity is, thus, much larger than we can anticipate. Hence, the results support the empirical observations that opportunity of encounter (i.e. the breakdown in mechanisms for ecological isolation) is a fundamental determinant to the emergence of new associations—especially Emergent Infectious Diseases—and the dynamics of host exploration, as observed in SARS‐CoV‐2. Insights on the dynamics of Emergent Infectious Diseases derived from the simulations and from the Stockholm Paradigm are discussed.

Taking Action - Turning Evolutionary Theory into Preventive Policies

“…Although we can understand restricting pathogens from spreading beyond small, local outbreaks as preventing epidemics, we argue that prevention should be used in the context of avoiding emergence in the first place. This shift in epistemics is also strongly supported by the grave predictions regarding the speed with which smaller outbreaks can spread out in an increasingly globalised world (17,61,62), narrowing the time window available for containment measures.…”

Ecological super‐spreaders drive host–range oscillations: Omicron and risk space for emerging infectious disease

“…Colonization requires a steppingstone linkage from bats to humans; or from bats to other potential mammalian species that may be synchronic and sympatric; ecological fitting and sloppy fitness space bridge the nexus for capacity and opportunity (Araujo et al., 2015 ; Morens & Fauci, 2020 ). Focused circumstances, interfaces with considerable propagule pressure and viable steppingstones, are required to complete infection pathways to people (Feronato et al., 2021 ).…”

“…We must assume that unimpeded human travel in the early stages of the outbreak made SARS‐CoV‐2 a globally endemic pathogen with many reservoir hosts capable of producing novel variants transmitted across virtually all ecological interfaces (Figure 3 ) (Deng et al., 2020 ; Kuchipudi et al., 2022 ; Rochman et al., 2021 ) (Figure 2 ). SARS variants originate in isolation both in people and assemblages of domestic, semi‐domestic and wild, free‐ranging mammals; subsequent dissemination of initially focal variants occurs with decreased isolation and increasing connectivity (Figure 3 ) (Brooks et al., 2019 ; Feronato et al., 2021 ; Hoberg & Brooks, 2008 ; Rochman et al., 2021 ). The pattern described above represents a dynamic of humans facilitating opportunity as ecological super‐spreaders in the origins and perpetuation of a global pandemic.…”

“…It is as simple and fundamental as recognizing that SARS‐CoV‐2 requires some level of compatibility between viral S1 and host's ACE2 receptors for infection (Conceicao et al., 2020 ; Damas et al., 2020 ); therefore, almost all mammals must be considered at risk for infection if exposed. A robust modelling platform has shown that EID can occur easily in this manner (Araujo et al., 2015 ; Braga et al., 2018 ; Feronato et al., 2021 ).…”

“…Modelling and empirical studies suggests that subsequent host changes (called oscillations in the SP [Braga et al., 2018 ; Janz & Nylin, 2008 ]) can be achieved directly or by a steppingstone dynamic, e.g., from wildlife to domestic animals to humans and vice versa (Araujo et al., 2015 ; Morens & Fauci, 2020 ), and that fast‐evolving pathogens, such as viruses, retain the capacity to retro‐colonize a previous host species (Feronato et al., 2021 ). Although initial colonization of a new host is achieved through pre‐existing variation, each new host species represents a new selective regime for the colonizing pathogen population.…”