DOI: 10.5061/dryad.ksn02v74s
title: Reservoir hosts experiencing food stress alter transmission dynamics for a zoonotic pathogen

description: Anthropogenic environmental change can significantly alter availability
 and quality of food resources for reservoir hosts and impact host-pathogen
 interactions in the wild. The state of the host’s nutritional reserves as
 time of infection is a key factor influencing infection outcomes by
 altering host resistance. Here we combine experimental and model-based
 approaches to better understand how an environmental stressor affects host
 resistance to West Nile virus (WNV). Using American robins (Turdus
 migratorius), a species considered a superspreader of WNV, we tested the
 effect of acute food deprivation immediately prior to infection on host
 viremia. Our results show that robins food deprived of food for 48 hours
 prior to infection, developed higher virus titers and were infectious
 longer than robins fed normally. To gain understanding about the
 epidemiological significance of food stressed hosts, we developed an
 agent-based model that simulates transmission dynamics of WNV between the
 avian reservoir host and the mosquito vector. When we simulated a
 nutritionally stressed host population, the mosquito infection rate rose
 significantly reaching levels that represent an epidemiological risk. An
 understanding of the infection disease dynamics in wild populations is
 critical to predict and predict and mitigate zoonotic disease outbreaks.
description: <strong>Analysis of the Agent Based Model Output for
 mosquito infection rate (MIR). </strong> Using
 both daily and weekly aggregated data generated by the simulation, we
 built models for both model fit and computational efficiency. These models
 were for viral loads with food stress levels and time (with interaction)
 as independent variable. AIC model selection criterion was used to compare
 and determine the best model, which we subsequently report in this
 study. <i>Phase 1</i>. Visualization of the
 data (both by day and by week), we notice that the robins exposed to the
 four stress levels, exhibit an upwards linear trend in MIR with time  and
 heteroscedasticity. Further, with time the variance of MIR increases where
 each stress level also shows linear trend as time increases and the
 variances increases as time increases. We approach the
 analysis of the hypothesis that with low levels of circulating virus and a
 constant number of robins, early in the season the effect of varying
 stress levels of the robin population on MIR will be minimal, using a
 linear model that takes into account the inherent
 heteroscedasticity. <i>Phase
 2.</i><b> </b>During the second phase of the season,
 virus transmission is amplified due to large influxes of susceptible
 robins on two different dates (19 September [day 50] and 10 October [day
 71]). We tested the hypothesis that during this period with increasing
 numbers of susceptible robins, the effect of food stress will magnify the
 between-group (i.e. different host stress levels) differences in the
 MIR. Visualization of the data, we notice that the four
 stress levels, exhibit a quadratic trend, rising during through day 60
 before stabilizing and decreasing. Having only 5 data points for the
 weekly data did not adequately exhibit these quadratic trends, though the
 trend was exhibited more clearly using daily data. Subsequently, we
 conducted the analysis for Phase 2 with daily data. Multiple models for
 viral loads were run for the daily data and AIC model selection criterion
 was used to determine the best model. All ABM analysis
 was conducted using Systat statistical software, R statistical software,
 with the glmmTMB package used to account for heteroscedasticity.
 <strong>Viral Titer Data</strong>
 Viral titer data in log/PFU per 0.1ml of whole blood for American
 robins (Turdus migratorius) that were inoculated subcutaneously in the
 cervical region with 0.1ml of 10<sup>5</sup> log PFU/ml of
 infectious West Nile virus (strain WN02, 1986). We collected whole blood
 (0.05ml) daily through 6 DPI, dispensed it into tube with BA-1 (M199
 medium with Hank’s salts, 1% bovine albumin, TRIS base (tris
 [hydroxymethyl] aminomethane), sodium bicarbonate, 2% fetal bovine serum,
 and antibiotics) and quantified viral titers using the Vero cell plaque
 assay as described by Blitvich et al. 2003. The birds
 are all hatch years that were captured at one location in mid-Michigan
 during fall migration of 2018. The food-stressed birds were deprived of
 food for the 48 hours prior to inoculation and the normal birds' food
 access remained unchanged. All birds were given ad libitum access to
 water.
description: Viral titer data: The limit of detection for assay is 0.7
 PFU/0.1ml. Hence, a bird is considered to be uninfected (0 titer) if they
 fell below this limit. There are no missing data.