DOI: 10.5061/dryad.zw3r228cd
title: Host-pathogen interactions under pressure: a review and meta-analysis of stress-mediated effects on disease dynamics

description: Human activities have increased the intensity and frequency of natural
 stressors and created novel stressors, altering host-pathogen
 interactions, and changing the risk of emerging infectious diseases.
 Despite the ubiquity of such anthropogenic impacts, predicting the
 directionality of outcomes has proven challenging. Here, we conduct a
 review and meta-analysis to determine the primary mechanisms through which
 stressors affect host-pathogen interactions and to evaluate the impacts
 stress has on host fitness (survival and fecundity) and pathogen
 infectivity (prevalence and intensity). We assessed 891 effect sizes from
 71 host species (representing seven taxonomic groups) and 78 parasite taxa
 from 98 studies. We found that infected and uninfected hosts had similar
 sensitivity to stressors and that responses varied according to stressor
 type. Specifically, limited resources compromised host fecundity and
 decreased pathogen intensity, while abiotic environmental stressors (e.g.,
 temperature and salinity) decreased host survivorship and increased
 pathogen intensity, and pollution increased mortality but decreased
 pathogen prevalence. We then used our meta-analysis results to develop
 Susceptible-Infected theoretical models to illustrate scenarios where
 infection rates are expected to increase or decrease in response to
 resource limitation or environmental stress gradients. Our results carry
 implications for conservation and disease emergence and reveal areas for
 future work.  
description: We conducted a systematic literature search and meta-analysis to
 evaluate the impacts of three broad types of environmental stressors on
 disease dynamics. First, we confirmed that pathogen exposure in laboratory
 studies typically negatively affected host fitness. We then proceeded with
 our main meta-analyses focused on two specific questions: Q1) were
 stressor fitness effects more severe for infected vs. uninfected hosts?,
 and Q2) was infectivity more susceptible to environmental stress than host
 fitness traits? To address these questions with data from primary studies,
 we used infection intensity and prevalence as proxies for infectivity and
 survivorship and fecundity as proxies of host fitness.
 To identify studies that evaluated the effects of environmental
 stressors on infectivity and host fitness traits in host-parasite systems,
 on February 9th of 2021, we conducted a systematic literature search in
 Web of Science using the search terms: (parasit* OR pathogen* OR disease)
 AND (environment* OR temperature OR pollution OR resource OR provision* OR
 toxi* OR contamination) AND (infection OR load OR yield OR resistance) AND
 ("birth rate" OR "death rate" OR surviv* OR mortality
 OR reproduct* OR fecundity). We limited our search to journal articles
 published in English between 2010 and 2020 and scanned titles and, if
 relevant, abstracts of all 20,684 hits. This initial screening effort was
 split and carried out by two experienced independent reviewers (AVS and
 BW). We identified ten additional studies from references of selected
 studies. One experienced reviewer or two student reviewers further
 examined articles documenting effects of environmental stressors on
 infectivity and host fitness. We classified stressors
 into three groups: 1) environmental factors, which can vary naturally but
 are also subject to human-induced perturbation (hereafter “endogenous
 environment”); 2) presence or quantity of chemical pollutants (hereafter
 “chemical pollution”), that lead to negative expected outcomes for hosts;
 and 3) resource availability for hosts (hereafter “resource
 limitation”).   
description: # Host-pathogen interactions under pressure: a systematic review and
 meta-analysis of stress-mediated effects on disease dynamics Data from
 experimental research evaluating the effects of stress (resource
 limitation, environmental stress, and pollution) on host-parasite
 interactions. Empty cells are present because the screened papers only
 reported one or few statistics that could be recorded. Included is also
 the code for the meta-analysis evaluating the effects. Our code ignores
 the empty cells from the database.