Globalization, land use, and the invasion of West Nile virus

Abstract

Many invasive species that have been spread through the globalization of trade and travel are pathogens. A paradigmatic case is the introduction of West Nile virus (WNV) into North America in 1999. A decade of research on the ecology and evolution of WNV includes three findings that provide insight into the outcome of future pathogen introductions. First, WNV transmission in North America is highest in urbanized and agricultural habitats, in part because the hosts and vectors of WNV are abundant in human-modified areas. Second, after its introduction, the virus quickly adapted to infect local mosquito vectors more efficiently than the originally introduced strain. Third, highly focused feeding patterns of the mosquito vectors of WNV result in unexpected host species being important for transmission. This research provides a framework for predicting and preventing the emergence of foreign vector-borne pathogens.

Fig.1

An American robin (Turdus migratorius) and its nestlings. Robins flourish in human altered landscapes and appear to play a key role in WNV amplification across many regions of North America. Photo Credit: Bruce Lyon.

Fig. 2

Spread of WNV throughout the Americas. The map shows the year that WNV was first detected in a state, province, or country. The box-plot shows the temporal pattern of WNV incidence at the state-level following WNV arrival. The y-axis shows the relative number of WNV neuroinvasive cases (the fraction of the maximum observed in that state) that occurred in each state in each year, starting with the year WNV was first detected. The number of states included in each column is shown above the box.

Fig. 3

Anthropogenic processes that facilitate the introduction and establishment of novel pathogens and increase their transmission. Trade, travel, and animal movement introduce new pathogens. Climate, hosts, and the abundance and feeding ecology of vectors determine establishment and transmission intensity. Land use modifies animal communities that serve as hosts and vectors for pathogens and climate change alters pathogen and vector demographic rates. Image Credit: Google & Tele Atlas (Aerial photos); Edward Canda (rice paddy); Photos8.com (corn field); L. Hufnagel (air traffic map); Dori (dori@merr.info) (smokestacks); Scott Bauer, USDA (tick); Richard Kuhn, Purdue Department of Biological Sciences (virus); NASA (clouds); John Montenieri, CDC/PHIL (flea); Others: Marm Kilpatrick.

Fig. 4

West Nile virus ecology across an urbanization gradient in the northeastern and mid-western United States. WNV is transmitted primarily by C. pipiens mosquitoes among a wide range of birds, but American robins (outlined) are a key amplification host. The diversity of avian hosts decreases with urbanization, while C. pipiens abundance appears to increase. Image credit: USGS (Mosquito); Others: Marm Kilpatrick and Ryan Peters.