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

Abstract

The majority of organisms host multiple parasite species, each of which can interact with hosts and competitors through a diverse range of direct and indirect mechanisms. These within‐host interactions can directly alter the mortality rate of coinfected hosts and alter the evolution of virulence (parasite‐induced host mortality). Yet we still know little about how within‐host interactions affect the evolution of parasite virulence in multi‐parasite communities. Here, we modeled the virulence evolution of two coinfecting parasites in a host population in which parasites interacted through cross immunity, immune suppression, immunopathology, or spite. We show (1) that these within‐host interactions have different effects on virulence evolution when all parasites interact with each other in the same way versus when coinfecting parasites have unique interaction strategies, (2) that these interactions cause the evolution of lower virulence in some hosts, and higher virulence in other hosts, depending on the hosts infection status, and (3) that for cross immunity and spite, whether parasites increase or decrease the evolutionarily stable virulence in coinfected hosts depended on interaction strength. These results improve our understanding of virulence evolution in complex parasite communities, and show that virulence evolution must be understood at the community scale.

Indirect interactions among co-infecting parasites and a microbial mutualist impact disease progression

“…There were three treatments in which both parasites were inoculated: simultaneous co-inoculation, sequential inoculation with C. cereale inoculated first, and sequential inoculation with R. solani inoculated first. Following inoculations, we surveyed leaves as described above for Experiment 1 at 10 time points (1, 3, 4, 5, 6, 7, 9, 10, 11 and 12 days after inoculation with R. solani), except leaves inoculated first with C. cereale then second with R. solani were observed at nine time points (3,4,5,6,7,8,10,11, and 12 days after inoculation with R. solani).…”

“…These interactions can alter the impact of parasites on host fitness [4], with implications for host population dynamics [5]. Further, they can impact parasites themselves, with potential effects on parasite transmission [6] and parasite evolution [7]. While these within-host interactions among co-infecting microbes have gained much attention [8][9][10][11], most studies focus on one interaction between two microbes.…”

Occurrence of Honey Bee (Apis mellifera L.) Pathogens in Wild Pollinators in Northern Italy

“…Multiple infections are common in natural environments; nonetheless, we have a limited understanding of the interactions occurring among the involved pathogens ( Armitage et al., 2022 ). Often, multiple infections reduce pathogen virulence due to antagonism ( Garbutt et al., 2011 ), but in other cases, synergistic interactions may increase virulence and reduce the host lifespan ( Clay and Rudolf, 2019 ; Armitage et al., 2022 ).…”

Identification and distribution of pathogens coinfecting with Brucella spp., Coxiella burnetii and Rift Valley fever virus in humans, livestock and wildlife

“…Infection with multiple pathogens has dramatic effects on disease dynamics and outcomes. Many theories predict that infection with multiple pathogens will result in the evolution of increased virulence (Alizon & Van Baalen, 2008 ; Clay & Rudolf, 2019 ; May & Nowak, 1995 ). Likewise, multiple infections may lead to worse host outcomes regardless of evolutionary stable strategies, such as in disease emergence or epidemic settings, which is highlighted by studies of human immunodeficiency virus (HIV) and Mycobacterium tuberculosis (Pawlowski et al., 2012 ); helminths ( Heligmosomoides polygyrus ) and bacteria ( Bordetella bronchiseptica ) (Lass et al., 2013 ); and Mycoplasma spp.…”