More Like this

1. The drivers and consequences of unstable Plasmodium dynamics: a long-term study of three malaria parasite species infecting a tropical lizard

   https://doi.org/10.1017/S0031182018001750  

   Otero, Luisa ; Schall, Jos J. ; Cruz, Virnaliz ; Aaltonen, Kristen ; Acevedo, Miguel A. ( April 2019 , Parasitology)

   Abstract Understanding the consequences of environmental fluctuations for parasite dynamics requires a long-term view stretching over many transmission cycles. Here we studied the dynamics of three malaria parasites ( Plasmodium azurophilum , P. leucocytica and P. floridense ) infecting the lizard Anolis gundlachi , in the rainforest of Puerto Rico. In this malaria–anole system we evaluated temporal fluctuations in individual probability of infection, the environmental drivers of observed variation and consequences for host body condition and Plasmodium parasites assemblage. We conducted a total of 15 surveys including 10 from 1990 to 2002 and five from 2015 to 2017. During the early years, a lizard's probability of infection by all Plasmodium species appeared stable despite disturbances ranging from two hurricanes to short droughts. Over a longer timescale, probability of infection and overall prevalence varied significantly, following non-linear relationships with temperature and rainfall such that highest prevalence is expected at intermediate climate measures. A perplexing result was that host body condition was maximized at intermediate levels of rainfall and/or temperature (when risk of infection was highest), yet we found no significant decreases in body condition due to infection. Plasmodium parasite species composition varied through time with a reduction and near local extinction of P. floridense . Our results emphasize the need for long-term studies to reveal host–parasite dynamics, their drivers and consequences. 

   more » « less
2. Beyond single host, single parasite interactions: Quantifying competence for complete multi‐host, multi‐parasite communities

   https://doi.org/10.1111/1365-2435.14068  

   Stewart Merrill, Tara E. ; Calhoun, Dana M. ; Johnson, Pieter T. J. ( May 2022 , Functional Ecology)

   Understanding parasite transmission in communities requires knowledge of each species' capacity to support transmission. This property, ‘competence’, is a critical currency for modelling transmission under community change and for testing diversity–disease theory. Despite the central role of competence in disease ecology, we lack a clear understanding of the factors that generate competence and drive its variation.

   We developed novel conceptual and quantitative approaches to systematically quantify competence for a multi‐host, multi‐parasite community. We applied our framework to an extensive dataset: five amphibian host species exposed to four parasitic trematode species across five ecologically realistic exposure doses. Together, this experimental design captured 20 host–parasite interactions while integrating important information on variation in parasite exposure. Using experimental infection assays, we measured multiple components of the infection process and combined them to produce competence estimates for each interaction.

   With directly estimated competence values, we asked which components of the infection process best explained variation in competence: barrier resistance (the initial fraction of administered parasites blocked from infecting a host), internal clearance (the fraction of established parasites lost over time) or pre‐transmission mortality (the probability of host death prior to transmission). We found that variation in competence among the 20 interactions was best explained by differences in barrier resistance and pre‐transmission mortality, underscoring the importance of host resistance and parasite pathogenicity in shaping competence.

   We also produced dose‐integrated estimates of competence that incorporated natural variation in exposure to address questions on the basis and extent of variation in competence. We found strong signals that host species identity shaped competence variation (as opposed to parasite species identity). While variation in infection outcomes across hosts, parasites, individuals and doses was considerable, individual heterogeneity was limited compared to among‐species differences. This finding highlights the robustness of our competence estimates and suggests that species‐level values may be strong predictors for community‐level transmission in natural systems.

   Competence emerges from distinct underlying processes and can have strong species‐level characteristics; thus, this property has great potential for linking mechanisms of infection to epidemiological patterns.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

   more » « less
3. Global drivers of avian haemosporidian infections vary across zoogeographical regions

   https://doi.org/10.1111/geb.13390  

   Fecchio, Alan ; Clark, Nicholas J. ; Bell, Jeffrey A. ; Skeen, Heather R. ; Lutz, Holly L. ; De La Torre, Gabriel M. ; Vaughan, Jefferson A. ; Tkach, Vasyl V. ; Schunck, Fabio ; Ferreira, Francisco C. ; et al ( September 2021 , Global Ecology and Biogeography)

   Macroecological analyses provide valuable insights into factors that influence how parasites are distributed across space and among hosts. Amid large uncertainties that arise when generalizing from local and regional findings, hierarchical approaches applied to global datasets are required to determine whether drivers of parasite infection patterns vary across scales. We assessed global patterns of haemosporidian infections across a broad diversity of avian host clades and zoogeographical realms to depict hotspots of prevalence and to identify possible underlying drivers.

   Global.

   1994–2019.

   Avian haemosporidian parasites (generaPlasmodium,Haemoproteus,LeucocytozoonandParahaemoproteus).

   We amalgamated infection data from 53,669 individual birds representing 2,445 species world‐wide. Spatio‐phylogenetic hierarchical Bayesian models were built to disentangle potential landscape, climatic and biotic drivers of infection probability while accounting for spatial context and avian host phylogenetic relationships.

   Idiosyncratic responses of the three most common haemosporidian genera to climate, habitat, host relatedness and host ecological traits indicated marked variation in host infection rates from local to global scales. Notably, host ecological drivers, such as migration distance forPlasmodiumandParahaemoproteus, exhibited predominantly varying or even opposite effects on infection rates across regions, whereas climatic effects on infection rates were more consistent across realms. Moreover, infections in some low‐prevalence realms were disproportionately concentrated in a few local hotspots, suggesting that regional‐scale variation in habitat and microclimate might influence transmission, in addition to global drivers.

   Our hierarchical global analysis supports regional‐scale findings showing the synergistic effects of landscape, climate and host ecological traits on parasite transmission for a cosmopolitan and diverse group of avian parasites. Our results underscore the need to account for such interactions, in addition to possible variation in drivers across regions, to produce the robust inference required to predict changes in infection risk under future scenarios.

    

   more » « less
4. Multi-Scale Drivers of Immunological Variation and Consequences for Infectious Disease Dynamics

   https://doi.org/10.1093/icb/icz138  

   Becker, Daniel J. ; Downs, Cynthia J. ; Martin, Lynn B. ( July 2019 , Integrative and Comparative Biology)

   The immune system is the primary barrier to parasite infection, replication, and transmission following exposure, and variation in immunity can accordingly manifest in heterogeneity in traits that govern population-level infectious disease dynamics. While much work in ecoimmunology has focused on individual-level determinants of host immune defense (e.g., reproductive status and body condition), an ongoing challenge remains to understand the broader evolutionary and ecological contexts of this variation (e.g., phylogenetic relatedness and landscape heterogeneity) and to connect these differences into epidemiological frameworks. Ultimately, such efforts could illuminate general principles about the drivers of host defense and improve predictions and control of infectious disease. Here, we highlight recent work that synthesizes the complex drivers of immunological variation across biological scales of organization and scales these within-host differences to population-level infection outcomes. Such studies note the limitations involved in making species-level comparisons of immune phenotypes, stress the importance of spatial scale for immunology research, showcase several statistical tools for translating within-host data into epidemiological parameters, and provide theoretical frameworks for linking within- and between-host scales of infection processes. Building from these studies, we highlight several promising avenues for continued work, including the application of machine learning tools and phylogenetically controlled meta-analyses to immunology data and quantifying the joint spatial and temporal dependencies in immune defense using range expansions as model systems. We also emphasize the use of organismal traits (e.g., host tolerance, competence, and resistance) as a way to interlink various scales of analysis. Such continued collaboration and disciplinary cross-talk among ecoimmunology, disease ecology, and mathematical modeling will facilitate an improved understanding of the multi-scale drivers and consequences of variation in host defense.

    

   more » « less
5. Similar parasite communities but dissimilar infection patterns in two closely related chickadee species

   https://doi.org/10.1093/ornithology/ukad033  

   Theodosopoulos, Angela N. ; Grabenstein, Kathryn C. ; Larrieu, Mia E. ; Arnold, Vanessa ; Taylor, Scott A. ( July 2023 , Ornithology)

   Hemosporidian parasite communities are broadly similar in Boulder County, Colorado, between two common songbirds––the Black-capped Chickadee (Poecile atricapillus) and Mountain Chickadee (Poecile gambeli). However, Mountain Chickadees appear more likely to be infected with Plasmodium and potentially experience higher infection burdens with Leucocytozoon in contrast to Black-capped Chickadees. We found that elevation change (and associated ecology) drives the distributions of these parasite genera. For Boulder County chickadees, environmental factors play a more important role in structuring hemosporidian communities than host evolutionary differences. However, evolutionary differences are likely key to shaping the probability of infection, infection burden, and whether an infection remains detectable over time. We found that for recaptured birds, their infection status (i.e. presence or absence of detectable parasite infection) tends to remain consistent across capture periods. We sampled 235 chickadees between 2017 and 2021 across a ~1,500-m elevation gradient from low elevation (i.e. the city of Boulder) to comparatively high elevation (i.e. the CU Boulder Mountain Research Station). It is unknown whether long-term hemosporidian abundance trends have changed over time in our sampling region. However, we ask whether potentially disparate patterns of Plasmodium susceptibility and Leucocytozoon infection burden could be playing a role in the negative population trends of Mountain Chickadees.

    

   more » « less