Infections do not predict shedding in co‐infections with two helminths from a natural system

Abstract

Given the health and economic burden associated with the widespread occurrence of co-infections in humans and agricultural animals, understanding how coinfections contribute to host heterogeneity to infection and transmission is critical if we are to assess risk of infection based on host characteristics. Here, we examine whether host heterogeneity to infection leads to similar heterogeneity in transmission in a population of rabbits single and co-infected with two helminths and monitored monthly for eight years. Compared to single infections, co-infected rabbits carried higher Trichostrongylus retortaeformis intensities, shorter worms with fewer eggs in utero, and shed similar numbers of parasite eggs. In contrast, the same co-infected rabbits harbored fewer Graphidium strigosum with longer bodies and more eggs in utero, and shed more eggs of this helminth. A positive density-dependent relationship between fecundity and intensity was found for T. retortaeformis but not G. strigosum in co-infected rabbits. Juvenile rabbits contributed to most of the infection and shedding of T. retortaeformis, while adult hosts were more important for G. strigosum dynamics of infection and transmission, and this pattern was consistent in single and co-infected individuals. This host-parasite system suggests that we cannot predict the pattern of parasite shedding during co-infections based on intensity of infection alone. We suggest that a mismatching between susceptibility and infectiousness should be expected in helminth coinfections and should not be overlooked.

Genomic and phenotypic characterization of myxoma virus from Great Britain reveals multiple evolutionary pathways distinct from those in Australia

“…Samples were taken from rabbits with clinical myxomatosis gathered at multiple locations on two sites, the first located in Perthshire in central-eastern Scotland, and the second in North Yorkshire, England, collected as part of other field studies [62, 63, 64, 65]. An early isolate sampled in Belfast, Northern Ireland in 1955, was also sequenced.…”

Parasite–Parasite Interactions in the Wild: How To Detect Them?

“…Next-generation epidemiological models will need to be cross-scales, connecting within-host dynamics and between-host dynamics. This is particularly difficult when the link between infection intensity and transmission is unclear and not readily simplified [58]. Consequently, continued observation and experiments on the effects of parasite co-circulation and interactions on parasite and host communities are crucial to allow generalities to emerge and to feed appropriate modeling approaches.…”

Host allometry influences the evolution of parasite host-generalism: theory and meta-analysis

“…Because our dataset did not include any information on parasite body size, we did not incorporate such relationships into the model, but doing so would be relatively straightforward (though the analysis of such a model may not). Moreover, we have assumed that shedding rate is positively correlated with abundance, but for many parasites the opposite is true: increased within-host abundance increases density-dependence, thereby reducing parasite fecundity such that shedding is actually lower [32,55]. In that case, our parameter λ 0 should be separated out into its component pieces that capture how abundance increases with body size and how shedding rate per parasite decreases with abundance.…”

“…There are, however, several reasons to suspect that host body size might influence a parasite's host diversity. Larger hosts support higher within-host parasite abundances [31], which may influence between-host transmission, for example, by positively or negatively affecting parasite shedding [32]. Host body size also affects key host characteristics, such as longevity and ecological carrying capacity [20], that may affect host availability to parasites.…”