Differential drivers of intraspecific and interspecific competition during malaria–helminth co-infection

Abstract

Graphical abstract Both initial infectious dose and the presence of co-infecting parasites can impact the within-host dynamics of infection. In mice infected with malaria, increasing initial infectious doses reduced the time it took for within-host malaria replication to peak, but also reduced the magnitude of this within-host replication. When mice were also co-infected with hookworms (helminths that reduce the availability of red blood cells (RBCs) to malaria parasites), peak within-host malaria replication was delayed. Modelling indicates that this difference during co-infection may be mediated by two factors: a higher background death rate of RBCs during co-infection, in tandem with an increased influx of new RBCs.

Intraspecific density changes the impact of interspecific competitors on parasite infection traits in multiple infections

“…We find that the impact of interspecific competition in both the within and between host environment is only seen at lower intensities of intraspecific competition, as found in another study in the within-host environment looking at effects on host traits (10). A few studies have explored how the intensity of intraspecific parasite competition changes the impact of an interspecific competitor parasite in multipe infections (2,4,10,12,13), but results are not always presented as a function of changing intraspecific densities (e.g. ( 4)).…”

“…In the within-host environment one study showed that the relative impact of interspecific competition on T. urticae growth declined with increasing T. urticae densities (12). Another found that the impact of an interspecific competitor (a helminth macroparasite) on shared host resources (red blood cells) was neglible at higher malaria densities, attributed to more intense intraspecifc malaria competition (10).…”

“…Higher doses of an interspecific competitor may increasingly reduce a focal parasite’s growth (4, 11). Alternatively, higher intraspecific densities (competition) may change the impact of an interspecific competitor on parasite growth or host traits (2, 10, 12), even to the extent that the impact of interspecific competition is no longer apparent at certain (higher) intraspecific densities (10). The relative densities of conspecifics versus interspecific competitors may also affect parasite traits in the between host environment such as whether a parasite establishes on an already infected host (13) and/or movement between infected hosts.…”

“…The effect of inter and intra-specific competition in multiple infection scenarios may depend on the relative densities of each competitor (2,4,(10)(11)(12). Higher doses of an interspecific competitor may increasingly reduce a focal parasite's growth (4,11).…”

Helminth-host-environment interactions: Looking down from the tip of the iceberg

“…Fairlie-Clarke et al (2015) infected mice with Plasmodium chaboudi alone or simultaneously with a single dose of Nippostrongylus brasiliensis larvae. Secondary analysis of their data using statistical and mechanistic models revealed that low-dose Nippostrongylus infection slowed the increase in P. chaboudi parasitemia (Wait et al 2021). However, simultaneous infection of mice with P. berghei and Ascaris suum eggs had no impact on P. berghei parasitemia.…”