Viral Ecology and the Maintenance of Novel Host Use

Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520, USA.
The American Naturalist (Impact Factor: 3.83). 04/2006; 167(3):429-39. DOI: 10.1086/499381
Source: PubMed


Viruses can occasionally emerge by infecting new host species. However, the early phases of emergence can hinge upon ecological sustainability of the virus population, which is a product of both within-host population growth and between-host transmission. Insufficient growth or transmission can force virus extinction before the latter phases of emergence, where genetic adaptations that improve host use may occur. We examined the early phase of emergence by studying the population dynamics of RNA phages in replicated laboratory environments containing native and novel host bacteria. To predict the breadth of transmission rates allowing viral persistence on each species, we developed a simple model based on in vitro data for phage growth rate over a range of initial population densities on both hosts. Validation of these predictions using serial passage experiments revealed a range of transmission rates for which the native host was a source and the novel host was a sink. In this critical range of transmission rates, periodic exposure to the native host was sufficient for the maintenance of the viral population on the novel host. We argue that this effect should facilitate adaptation by the virus to utilize the novel host--often crucial in subsequent phases of emergence.

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    • "Our data structure show that in the long-term, genetic differences among host clones become dominant, while earlier, erratic effects, possibly caused by setting up the initial populations, may contribute to the overall variation. The parasite's adaptive evolution during these times seems unlikely (as compared to similar experiments with bacteriophages (Dennehy et al. 2006), but cannot be ruled out. The nearly perfect bimodal distribution seen in the long-term persistence data is not seen in a previous study on individual host infection data (Ebert 2008) where within host–parasite replication of two isolates of H. tvaerminnensis from Finland (Octosporea bayeri) was assessed in 22 new host clones from three populations in Germany and nine clones from the parasite's native range. "
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    • "This is evidenced, for example, by rabies spillover from domesticated dogs to the threatened Ethiopian wolf Canis simensis (see Randall et al. 2006), Rinderpest virus from African domesticated cattle to wild ruminants (Kock et al. 1999) and Aleutian disease (caused by a highly pathogenic parovirus) from domesticated American mink to wild counterparts (Nituch et al. 2011). In this manner, alternative host populations have been shown to act as sinks, if continually but not constantly, exposed to source viral particles from a native host (Schmidt and Ostfeld 2001; Dennehy et al. 2006). "
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