Overwintering of West Nile virus in a bird community with a communal crow roost

Diego Montecino-Latorre,Christopher M. Barker

doi:10.1038/s41598-018-24133-4

Abstract

In temperate climates, transmission of West Nile virus (WNV) is detectable rarely during the coldest months (late fall through early spring), yet the virus has reappeared consistently during the next warm season. Several mechanisms may contribute to WNV persistence through winter, including bird-to-bird transmission among highly viremic species. Here we consider whether, under realistic scenarios supported by field and laboratory evidence, a winter bird community could sustain WNV through the winter in the absence of mosquitoes. With this purpose we constructed a deterministic model for a community of susceptible birds consisting of communally roosting crows, raptors and other birds. We simulated WNV introduction and subsequent transmission dynamics during the winter under realistic initial conditions and model parameterizations, including plausible contact rates for roosting crows. Model results were used to determine whether the bird community could yield realistic outbreaks that would result in WNV infectious individuals at the end of the winter, which would set up the potential for onward horizontal transmission into summer. Our findings strongly suggest that winter crow roosts could allow for WNV persistence through the winter, and our model results provide synthesis to explain inconclusive results from field studies on WNV overwintering in crow roosts.

Highlights

West Nile virus (WNV; family Flaviviridae, genus Flavivirus) was introduced into New York in 19991 and spread rapidly across the continent, reaching California in 20032
In bird communities exposed to extended cold seasons, it would be expected that WNV could fade out in the absence of other transmission mechanisms; the virus consistently reappears during the warm season
We hypothesized that crow-to-crow transmission is the primary maintenance mechanism for WNV infection through the cold season, we initially identified the range of values for the crow-to-crow transmission parameter that yielded the largest fraction of realistic WNV outbreaks that resulted in viremic birds at the end of winter

Summary

Introduction

West Nile virus (WNV; family Flaviviridae, genus Flavivirus) was introduced into New York in 19991 and spread rapidly across the continent, reaching California in 20032. WNV overwintering mechanisms supported by field or laboratory findings include vertical transmission to mosquitoes in winter rest, continued vector-bird transmission through the winter at low rates, direct transmission between avian hosts (predation scavenging and others pathways such as fecal-oral transmission) or recrudescence of viremia in chronically infected birds[19,20,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44]. Field studies have reported that crows within a communal roost are frequently stained with feces of other crows and they exhibit preening behavior that could subject them to oral infection[29], infected birds used the same roosts as healthy birds[29] and WNV-positive dead crows have been recovered during cold periods when mosquitoes are not blood feeding[27,29,57]

Methods

Results

Discussion

Conclusion