Coevolution of virulence and immunosuppression in multiple infections

Abstract

Many components of host-parasite interactions have been shown to affect the way virulence (i.e. parasite-induced harm to the host) evolves. However, coevolution of multiple parasite traits is often neglected. We explore how an immunosuppressive adaptation of parasites affects and coevolves with virulence in multiple infections. Applying the adaptive dynamics framework to epidemiological models with coinfection, we show that immunosuppression is a double-edged sword for the evolution of virulence. On one hand, it amplifies the adaptive benefit of virulence by increasing the abundance of coinfections through epidemiological feedbacks. On the other hand, immunosuppression hinders host recovery, prolonging the duration of infection and elevating the cost of killing the host (as more opportunities for transmission will be forgone if the host dies). The balance between the cost and benefit of immunosuppression varies across different background mortality rates of hosts. In addition, we find that immunosuppression evolution is influenced considerably by the precise trade-off shape determining the effect of immunosuppression on host recovery and susceptibility to further infection. These results demonstrate that the evolution of virulence is shaped by immunosuppression while highlighting that the evolution of immune evasion mechanisms deserves further research attention.

How parasite interaction strategies alter virulence evolution in multi‐parasite communities

“…In the case of immune suppression, previous theory suggests that as the strength of symmetric immune suppression increases, host exploitation should increase as well (Choisy and de Roode ; Kamiya et al. ), whereas our results predict the opposite. This difference arises from how immune suppression within hosts is parameterized.…”

“…Thus, following Kamiya et al. () future studies may simultaneously model both the evolution of the strength of these interactions, and within‐host exploitation rates, in order to ascertain the conditions under which cross immunity and spite will ultimately increase or decrease the mortality of coinfected hosts.…”

“…, Kamiya et al. ; although interaction strength may be asymmetric) and empirically (de Roode et al. ; Bell et al.…”

Two parasites, virulence and immunosuppression: how does the whole thing evolve?

“…Thus, the consequences of immunosuppression for the evolution of virulence in a system allowing for multiple infections are not straightforward. Kamiya et al [2] embrace this challenge. They create an epidemiological model in which the probability of co-infection trades off with the rate of recovery from infection, via immunosuppression.…”

“…Also, this relationship is predicted to vary with the shape of the trade-off underlying the costs and benefits of immunosuppression. In sum, Kamiya et al [2] provide a comprehensive analysis of an important problem in the evolution of host-parasite interactions. The model provides clear predictions, and thus can now be tested using the many systems in which immunosuppression has been detected, provided that the traits that compose the model can be measured.…”