Abstract
Host shifts, when a cross-species transmission of a pathogen can lead to successful infections, are the main cause of emerging infectious diseases, such as COVID-19. A complex challenge faced by the scientific community is to address the factors that determine whether the cross-species transmissions will result in spillover or sustained onwards infections. Here we review recent literature and present a perspective on current approaches we are using to understand the mechanisms underlying host shifts. We highlight the usefulness of the interactions between Drosophila species and viruses as an ideal study model. Additionally, we discuss how cross-infection experiments — when pathogens from a natural reservoir are intentionally injected in novel host species— can test the effect cross-species transmissions may have on the fitness of virus and host, and how the host phylogeny may influence this response. We also discuss experiments evaluating how cooccurrence with other viruses or the presence of the endosymbiont bacteria Wolbachia may affect the performance of new viruses in a novel host. Finally, we discuss the need of surveys of virus diversity in natural populations using next-generation sequencing technologies. In the long term, these approaches can contribute to a better understanding of the basic biology of host shifts.
Highlights
In less than eight months, COVID-19 has spread from a few cases in Wuhan, China, to more than eighteen million people in almost everywhere in the world (Coronavirus Research Center, https://coronavirus.jhu.edu/map.html visited on August 6th, 2020)
Phylogenetic analyses suggest that the natural host of this virus is likely bats, and that a possible wild animal sold at the Wuhan food market might be an intermediate host that helped transmission to humans (Lu et al, 2020). This is a classic example of an emerging infectious diseases (EID) — infections recognized in a host population for the first time (Morens and Fauci, 2013)
Some examples include the acquired immunodeficiency syndrome (AIDS) pandemic caused by the human immunodeficiency virus (HIV), which jumped into humans from non-human primates (Sharp and Hahn, 2011; Faria et al, 2014), and Ebola, whose virus shifted from fruit bats to humans (Leroy et al, 2005)
Summary
In less than eight months, COVID-19 has spread from a few cases in Wuhan, China, to more than eighteen million people in almost everywhere in the world (Coronavirus Research Center, https://coronavirus.jhu.edu/map.html visited on August 6th, 2020). Interactions between viruses can lead to different outcomes in fitness of the new infecting virus, affecting the chances of a host-shift These possible interaction effects of cooccurring viruses have not been tested in Drosophila melanogaster (Palmer et al, 2018). Phylogenetic experiments on host-shift as described above, can be repeated with species that naturally host Wolbachia, to test how the presence of this endosymbiont may affect replication of the new virus on different host species (Figure 2). Another essential piece of information to understand host shifts is the knowledge of virus natural host range and frequency of cross-species transmissions in wild populations. This survey will likely give interesting virus candidates to be isolated and subsequently used in the experimental approaches described above
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