“Accidents waiting to happen” – insights from a simple model on the
emergence of infectious agents in new hosts.
Summary: This study evaluates through modeling 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 analyzed 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 result 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.