Multiple-genotype infections and their complex effect on virulence

Abstract

Multiple infections are common. Although in recent years our understanding of multiple infections has increased significantly, it has also become clear that a diversity of aspects has to be considered to understand the interplay between co-infecting parasite genotypes of the same species and its implications for virulence and epidemiology, resulting in high complexity. Here, we review different interaction mechanisms described for multiple infections ranging from competition to cooperation. We also list factors influencing the interaction between co-infecting parasite genotypes and their influence on virulence. Finally, we emphasise the importance of between-host effects and their evolution for understanding multiple infections and their implications.

Experimental evolution with a multicellular host causes diversification within and between microbial parasite populations-Differences in emerging phenotypes of two different parasite strains

“…Alternatively, virulence may change to maximize parasite replication and transmission (Anderson and May ; Alizon and Michalakis ; Bose et al. ). If virulence is too high, the host dies too early and parasite replication is low.…”

“…The altruistic specialization of cell types resulting in increased production efficiency has been shown for other microorganisms including the Bacillus genus (Strassmann et al 2000;Deng et al 2015;van Gestel et al 2015). Alternatively, virulence may change to maximize parasite replication and transmission (Anderson and May 1982;Alizon and Michalakis 2015;Bose et al 2016). If virulence is too high, the host dies too early and parasite replication is low.…”

Diversity and Multiplicity of P. falciparum infections among asymptomatic school children in Mbita, Western Kenya

“…The carriage of multiple distinct parasite clones by an individual is reported to enhance the development of multiple strain specific anti-parasite immunity. However, due to an intense intra-host competition, harbouring multiple distinct parasite clones is also implicated in high gametocyte production and emergence of highly virulent and drug resistant parasite strains 32,[39][40][41][42][43] .…”

Assessment of the Relationship Between Gametocyte Density, Multiplicity of Infection and Mosquito Infectivity in Plasmodium Falciparum Infections

“…The result showed that, MOI and gametocyte density account for about 68.1% of the variations in mosquito infection prevalence. These results can be explained by the emergence of highly virulent and infectious parasite strains due to intense intra-host competition and high recombination rates among the distinct infecting clones [45,46,47]. Another plausible explanation for the association between MOI, gametocyte density and mosquito infection prevalence found in this study may be due to a strategic investment by the parasite to maximise either in-host survival or between-host transmission [42,48,49,50] At relatively low MOI, the level of intra-host competition is relatively low and the P. falciparum parasites reduce the conversion rates to enhance asexual replication and in-host survival through a reproductive restraint process.…”