Infectious Dose Affects the Outcome of the Within‐Host Competition between Parasites

Abstract

The ecological and epidemiological processes underlying the success of parasites competing within individual hosts are not yet clear. We investigated one idea: that increasing one parasite's infectious dose might decrease the success of its competitor. We reared uninfected larvae of the mosquito Aedes aegypti and exposed them to two concentrations of the microsporidium Vavraia culicis and of the protozoan Ascogregarina culicis. The rate at which Vavraia produced its infectious spores depended on its dose and that of its competitor: when the dose of Vavraia was high, only the higher dose of Ascogregarina slowed the production of spores, but when the dose was low, either dose of Ascogregarina did. Ascogregarina was least likely to produce oocysts when its competitor's dose was high and the mosquito was reared with little food. This was due to the mosquito's preadult mortality induced by Vavraia. Our results show that increasing the dose of a parasite can increase its deleterious effects on a coinfecting parasite. Since dose increases with a parasite's prevalence, such dose effects could lead to an epidemiological feedback that ultimately eliminates one of the parasites.

Cost of co-infection controlled by infectious dose combinations and food availability

“…It is tempting to compare the eVects of co-infection on the host with the ones on the parasites that we reported earlier (Fellous and Koella 2009). Interestingly, the development of the parasites and that of the host were rarely aVected by infectious dose and food availability in the same fashion.…”

“…Prevalence was 100% for all infectious treatments. The present paper strictly focuses on the eVect of co-infection on a host's phenotype; the results for parasite transmission are accordingly detailed in a separate article (Fellous and Koella 2009).…”

Make New Friends and Keep the Old? Parasite Coinfection and Comorbidity in Homo sapiens

“…For coinfecting species, the sequential order of establishment, infectious dose, and density of established parasites infl uence infectious outcomes of secondarily invading species (Fellous and Koella 2009 ). Coinfecting species may inhibit the establishment of new parasites through direct competition or competitive inhibition (e.g., monopolizing host resources), ultimately reducing infection intensity or pathogenesis of one or more species (Lafferty et al 1994 ;Fredensborg and Poulin 2005 ).…”

“…At the same time, infecting species may competitively inhibit establishment or replication by other species (Lim and Heyneman 1972 ;Fredensborg and Poulin 2005 ). As such, coinfection may increase, decrease, or have no effect on host fi tness, depending on the individual species involved (Fellous and Koella 2009 ).…”

Synergistic effects of dual parasitism in Daphnia magna under nutrient limitation

“…Host and parasite traits are sensitive to environmental factors such as food availability and quality, which interact to affect parasite virulence levels (feLLous & KoeLLa 2009;VaLe et al 2013;Duncan et al 2014). The outcome of the interaction between host and parasite depends on the amount of energy available for the host, the allocation of this energy towards life history responses, and the need and capacity of the parasite to exploit this (smith & hoLt 1996;BeDhomme et al 2004;PeDerson & fenton 2007;miDeo 2009;cressLer et al 2014).…”