Host Mixing and Disease Emergence

Abstract

Recent cases of emergent diseases have renewed interest in the evolutionary and ecological mechanisms that promote parasite adaptation to novel hosts [1-6]. Crucial to adaptation is the degree of mixing of original, susceptible hosts, and novel hosts. An increase in the frequency of the original host has two opposing effects on adaptation: an increase in the supply of mutant pathogens with improved performance on the novel host [7-9]; and reduced selection to infect novel hosts, caused by fitness costs commonly observed to be associated with host switching [10-17]. The probability of disease emergence will therefore peak at intermediate frequencies of the original host. We tested these predictions by following the evolution of a virus grown under a range of different frequencies of susceptible (original) and resistant (novel) host bacteria. Viruses that evolved to infect resistant hosts were only detected when susceptible hosts were at frequencies between 0.1% and 1%. Subsequent experiments supported the predictions that there was reduced selection and mutation supply at higher and lower frequencies, respectively. These results suggest that adaptation to novel hosts can occur only under very specific ecological conditions, and that small changes in contact rates between host species might help to mitigate disease emergence.

Source–sink plasmid transfer dynamics maintain gene mobility in soil bacterial communities

“…Interspecific conjugation also provides opportunity for plasmid recombination with resident genetic elements, enhancing genomic diversification (2). Furthermore, prolonged source-sink transfer dynamics could promote plasmid host range expansion (30), as also shown for bacteriophage (31). Previously, Dionisio et al (32) noted how multispecies communities might accelerate plasmid spread when a highly conjugative intermediate species enhances plasmid transfer between two poorly conjugative species.…”

Evolution of complex life cycles in trophically transmitted helminths. I. Host incorporation and trophic ascent

“…We suggest (see also Bull, 2006;Benmayor et al, 2009) that the optimal host taxa range resembles the classic optimal diet problem of optimal foraging that determines which food items animals should consume (MacArthur & Pianka, 1966). A parasite benefits by adding extra host taxa laterally at any stage in its cycle, but host expansion is constrained by generalism costs.…”

Microsporidian disease of the invasive amphipod Dikerogammarus villosus and the potential for its transfer to local invertebrate fauna

“…There is a greater understanding of ecological and evolutionary patterns governing the emergence of diseases and adaptation to novel hosts, thanks to several recent studies (e.g. Woolhouse et al 2005;Benmayor et al 2009). However, the emergence of diseases still remain 'inherently' unpredictable (Woolhouse et al 2005) and most of the time is recognized a posteriori, i.e.…”