Estimating R0 for tick-borne pathogens: multiple transmission pathways and seasonal dynamics
The basic reproductive number of a pathogen (R0) is the per generation growth in infected individuals in a fully susceptible population. It is a key parameter in epidemiology because R0>1 is a threshold condition for a pathogen to establish and persist. Using extensive field and lab-derived data, we have expanding previous R0 for tick borne pathogens by incorporating alternative transmission pathways, pathogen-pathogen interactions and tick-host seasonal dynamics. Using global sensitivity analyses, we assess which factors more strongly influence R0, which sends us back to the lab and field to measure them more carefully.
LAB MEMBERS: Ching-I Huang, Danielle Tufts, Sarah States, Evelyn Rynkiewicz
COLLABORATORS: Stephen Davis (Royal Melbourne Institute of Technology)
Coinfection of tick-borne pathogens: how do pathogens interact?
The geographic spread of Babesia microti has followed that of Borrelia burgdorferi and experiments have shown a higher rate of transmission of B. microti when hosts are also infected with B. burgdorferi. We investigate whether these pathogens interact with each in in a longitudinal study of tick and host coinfection in field sites in Connecticut, Maine and Rhode Island. Mice tissue, blood, and larval ticks are screened for both pathogens using PCR. Infection data of individual hosts are then analyzed using multi-state Markov and Generalized Linear Models to assess the direction and intensity of interactions.
In controlled laboratory infections simulating field conditions, we are testing how the host immune system influences Borrelia-Babesia interactions in white-footed mice and transmission to ticks. Mice are infected via bites from infected nymphs either simultaneously or at a lag between pathogens. Introducing time lags into the experiment allows for a more realistic representation of how hosts become infected in nature. We then analyze and compare immune gene profiles of hosts in each infection treatment group and at multiple time-points over the course of infection.
LAB MEMBERS: Danielle Tufts, Evelyn Rynkiewicz and Max McClure
COLLABORATORS: Sergios-Orestis Kolokotronis (State University of New York Downstate) and Stephen Harris
Biodiversity and human health: what are the links?
The effect of biodiversity declines on human health is hotly debated, but empirical assessments are lacking. Lyme disease provides a model system to assess relationships between biodiversity and human disease because the etiologic agent, Borrelia burgdorferi, is transmitted in the United States by the generalist blacklegged tick (Ixodes scapularis) among a wide range of mammalian and avian hosts. The ‘dilution effect’ hypothesis predicts that species-poor host communities dominated by white-footed mice (Peromyscus leucopus) will pose the greatest human risk because P. leucopus infects the largest numbers of ticks, resulting in higher human exposure to infected I. scapularis ticks. We assessed these theoretical prediction and test alternative hypotheses by comparing I. scapularis nymphal infection prevalence, density of infected nymphs and B. burgdorferi genotype diversity at sites on Block Island, RI, where P. leucopus dominates the mammalian host community, to species-diverse sites in northeastern Connecticut.
LAB MEMBERS: Samantha Kay, Danielle Tufts, Ching-I Huang
COLLABORATOR: Stephen Davis (Royal Melbourne Institute of Technology)
Linking host and pathogen diversity
Diverse host communities are expected to host higher pathogen diversity if different hosts act as ‘niches’ for different strains of the pathogen (the ‘multiple niche polymorphism’ hypothesis). A key assumption is that pathogens or their genetic variants are differentially adapted – or specialized, to different hosts. We are investigating the tradeoff in generalist-specialist host exploitation strategies among strains of a tick-borne bacterium, Borrelia burgdorferi sensu stricto, the in the United States. Using deep amplicon sequencing of samples from a 6-year-long study, laboratory experiments and mathematical modeling, we are testing the hypothesis that host specialization and antigenic distance traits are important drivers of Bb diversity, community structure and host specialization evolution.
LAB MEMBERS: Danielle Tufts, Evelyn Rynkiewicz, Max McClure, Elsbeth Kane
COLLABORATORS: Yi-Pin Lin (New York State Department of Health, Wadsworth Center), Sergios-Orestis Kolokotronis (State University of New York Downstate), Ben Adams (University of Bath), Katharine Walter
Tick life cycle, behavior and climate: Optimal foraging model for tick host-seeking behavior
We have constructed a foraging model of nymphal tick off-host behavior, taking into account the trade-off that a tick faces between the reward of finding a host and the various costs associated with finding that host. Preliminary findings show that: (1) rising temperatures may increase or reduce the risk of tick desiccation, dependent on relative humidity; (2) tick questing changes qualitatively as tick leaf litter and the ambient relative humidity cross the Critical Equilibrium Humidity, a physiologic threshold below which the tick cannot maintain a steady state water balance. Check out Max McClure’s conference poster presented at EEID 2017!
LAB MEMBERS: Danielle Tufts, Christina Olbrantz, Max McClure
COLLABORATORS: Justin Pool and Tom Daniels (Fordham University)