Pathogen transmission is a complex process that scales from allocation of a host's energy to immune defense to contacts between individuals. I'm particularly interested in how heterogeneity in host resources (i.e., food availability) influences wildlife physiology and behavior and how these effects scale up to determine infection spread across landscapes. For many wildlife, interactions between consumers and their resources are being heavily modified by human activities that subsidize animals with novel and abundant food. Both intentional and unintentional forms of "resource provisioning" (e.g., bird feeders and fruit plantations) have been responsible for the emergence of virulent pathogens in wildlife and humans, encouraging a better understanding of how these resource shifts influence infection processes and when and where food supplementation may amplify pathogen transmission. My research combines simple theoretical models, meta-analysis and comparative methods, and field studies of vampire bats to better understand how resource provisioning influences pathogen transmission across scales. See below for brief summaries of my projects and approaches.
linking consumer–resource and host–pathogen theory
Most epidemiological models ignore bottom-up relationships between hosts and their resource base, but integrating resource dependence into mechanistic frameworks of infection can have serious consequences for the local and spatial spread of pathogens. Past work has shown that resource-dependent host immune defense (i.e., resistance) can prevent pathogen invasion even in the face of resource-improved fecundity, survival, and contact rates. At larger scales, improving a moderate to large proportion of host habitat can allow virulent pathogens to invade a metapopulation and spread across all occupied patches, increasing spillover risk. Continued work in this area is now examining how variation in patch quality influences host colonization rates between habitat types and exploring the consequences for metapopulation persistence and infection dynamics. Future projects also principally aim to better link resource improvement effects on within- and between-patch host processes (e.g., spatially realistic and individual-based models).
resource supplementation and wildlife health
Much of my work on linking infectious disease dynamics and consumer–resource interactions is motivated by the applied example of how human activities accidentally and intentionally subsidize wildlife populations with food. I've compiled a large dataset of how host–pathogen interactions respond to resource provisioning and used meta-analysis to show that substantial variation in decreased or increased infection outcomes can be attributed to pathogen taxonomy and the type of feeding employed. In particular, infection with bacteria and viruses tends to be elevated with supplemental feeding, and intentional forms of feeding (e.g., recreational bird feeding, management) exacerbate pathogen transmission more so than wildlife foraging on anthropogenic food in urban habitats. I am also collaborating on a large-scale study of how food subsidies impact the stress, immunity, and disease state of urbanized white ibis (Eudocimus albus) and on a synthetic review of how intentional wildlife feeding activities for conservation, management, and tourism can be improved to limit pathogen transmission. Some of my in-progress comparative work is more broadly testing how innate host species traits shape whether resource provisioning will increase or decrease infection; for example, wildlife species with large home ranges may be more prone to increased infection if supplemental feeding artificially inflates host density, aggregation, and contact.
vampire bat ecology and epidemiology
The common vampire bat (Desmodus rotundus) is the primary reservoir host of rabies virus throughout Latin America, with this pathogen being spread on a potentially nightly basis when blood-feeding bats forage on wild mammals. Livestock expansion into rainforest habitats could provide vampire bats with an abundant and stable food source, which could decrease stress from starvation and in turn improve antiviral immune defenses that help resist lethal rabies infection. I am currently conducting mark–recapture studies across 12 field sites in Peru and Belize where local densities of livestock prey vary to explore the consequences of this diet shift for vampire bat stress, immune function, and infection with rabies virus, Bartonella, and Mycoplasma. More intensive laboratory work funded by a NSF DDIG is using a transcriptomics approach to quantify differential immune gene expression between study sites that contrast markedly in livestock density and to develop better immunological tools for this important reservoir host species. We are also using population genetics to infer connectivity between bat colonies and to test if and how between-patch movement is influenced by livestock density and distribution. Relationships between resources, antiviral defense, and connectivity are being built into a spatially explicit model of vampire bat rabies dynamics using approaches from likelihood-based inference and parameter estimation.
persistence and network dynamics of bacteria in bats
Bats are notorious as important reservoirs for zoonotic viruses, yet we understand far less about their role in the spread of zoonotic bacteria and how such pathogens are maintained in wild populations. I have an emerging interest in understanding the dynamics of two bacterial (and potentially zoonotic) pathogens, Bartonella and hemoplasmas. Infection prevalence within our Belize and Peru vampire bat populations is quite high, ranging from 40% to nearly 100%. We are currently building some simple theory to explore the role that bat–bat contact plays in Bartonella transmission (as opposed to vector–bat contact) and more generally building a time series of these infections within Belize to later confront these models with data. Phylogenetic studies are also exploring the evolution of these pathogens across bat species and examining their zoonotic potential through tree building. I am also interested in testing for cross-species transmission of these pathogens in Neotropical bats through phylogenetic comparative approaches and network-based models of pathogen sharing to understand which types of bat species may be most central to transmission within bat communities.
distribution and impact of mercury exposure on bats
Mercury is a widespread contaminant that has neurotoxic effects on many wildlife taxa. Such impacts have been minimally studied in bats, which could be especially prone to negative fitness consequences of chronic mercury exposure owing to their slow life histories and ubiquitousness in anthropogenic environments where contamination is likely. Mercury exposure could also have distinct effects on bat immune defense, as bats may have components of their immune systems that are unique among mammals. Our work in the vampire bat system has shown that even concentrations of mercury considered sublethal correlate with distinct shifts in bat innate immunity. Ongoing work aims 1) to assess mercury concentrations in other Neotropical bat species and 2) to test if this particular sensitivity of bat susceptibility to chronic mercury exposure is a widespread phenomenon throughout the order Chiroptera.
social epidemiology of zoonotic pathogens
Lastly, I am interested considering the socioeconomic drivers of resource provisioning and how these feeding practices feed back into human risk of zoonotic disease. Some very preliminary work of mine suggests a tight correlation between state-level bird feeding activities and the incidence of salmonellosis in the United States. Other work has been examining cryptosporidiosis in the United States and illustrating links between this (partly) zoonotic pathogen, livestock density, and social inequality. A fruitful area of work will eventually be to test associations between socioeconomic status (e.g., poverty), frequency of accidental resource provisioning (e.g., garbage), and infection outcomes in synanthropic urban wild species (e.g., raccoons, small rodents, songbirds, corvids).