Risk of Exposure to Eastern Equine Encephalomyelitis Virus Increases with the Density of Northern Cardinals

Laura K Estep,Victor Hoover,Geoffrey E Hill,Thomas R Unnasch,Joseph Jinright,Stephen Sickerman,Patrick Vander Kelen,Nathan D Burkett-Cadena,John Lusk,Keith Armstrong,Lillian M Stark,José Hernandez,Christopher J W Mcclure,Brenda Hunt,Lark L Coffey

doi:10.1371/journal.pone.0057879

Abstract

For a variety of infectious diseases, the richness of the community of potential host species has emerged as an important factor in pathogen transmission, whereby a higher richness of host species is associated with a lowered disease risk. The proposed mechanism driving this pattern is an increased likelihood in species-rich communities that infectious individuals will encounter dead-end hosts. Mosquito-borne pathogen systems potentially are exceptions to such “dilution effects” because mosquitoes vary their rates of use of vertebrate host species as bloodmeal sources relative to host availabilities. Such preferences may violate basic assumptions underlying the hypothesis of a dilution effect in pathogen systems. Here, we describe development of a model to predict exposure risk of sentinel chickens to eastern equine encephalitis virus (EEEV) in Walton County, Florida between 2009 and 2010 using avian species richness as well as densities of individual host species potentially important to EEEV transmission as candidate predictor variables. We found the highest support for the model that included the density of northern cardinals, a highly preferred host of mosquito vectors of EEEV, as a predictor variable. The highest-ranking model also included Culiseta melanura abundance as a predictor variable. These results suggest that mosquito preferences for vertebrate hosts influence pathogen transmission.

Highlights

Greater richness of host species has been associated with lowered risk of transmission in many studies of vector-borne pathogens
Sentinel flock locations were chosen to optimize the success of that particular monitoring program, sentinel flocks are used for routine surveillance for a range of arbovirus including equine encephalitis virus (EEEV) and West Nile virus (WNV)
A total of 68 chickens seroconverted from a status of naive to positive for EEEV antibodies in 2009 across the 24 sites used in our analyses; 48 seroconverted in 2010 (Table S1)

Summary

Introduction

Greater richness of host species has been associated with lowered risk of transmission in many studies of vector-borne pathogens (reviewed in [1,2]). The mechanism underlying these associations may be either a lowering of competent host density that accompanies an increase in species richness [3,4] or an increase in the proportion of ‘‘wasted’’ interactions – interactions of infectious individuals with noncompetent hosts [4]. One argument against the ubiquity of dilution effects pertains to whether host reservoir competence is related to numerical dominance of the host. Empirical evidence of such a relationship between numerical dominance and reservoir competence is currently lacking [9]

Methods

Results

Conclusion