West Nile virus ecology in a tropical ecosystem in Guatemala

Abstract

West Nile virus ecology has yet to be rigorously investigated in the Caribbean Basin. We identified a transmission focus in Puerto Barrios, Guatemala, and established systematic monitoring of avian abundance and infection, seroconversions in domestic poultry, and viral infections in mosquitoes. West Nile virus transmission was detected annually between May and October from 2005 to 2008. High temperature and low rainfall enhanced the probability of chicken seroconversions, which occurred in both urban and rural sites. West Nile virus was isolated from Culex quinquefasciatus and to a lesser extent, from Culex mollis/Culex inflictus, but not from the most abundant Culex mosquito, Culex nigripalpus. A calculation that combined avian abundance, seroprevalence, and vertebrate reservoir competence suggested that great-tailed grackle (Quiscalus mexicanus) is the major amplifying host in this ecosystem. West Nile virus transmission reached moderate levels in sentinel chickens during 2007, but less than that observed during outbreaks of human disease attributed to West Nile virus in the United States.

Figure 1.

Guatemala departments where domestic chickens were serially sampled to detect West Nile virus (WNV) transmission, 2004–2005. Numbers 1–7 indicate the department, each representing a different eco-region (see text).

Figure 2.

Sampling sites for assessment of West Nile virus (WNV) transmission in Puerto Barrios, Izabal, Guatemala, 2006–2009. Markers numbered 1–10 indicate locations of selected study sites where chickens and mosquitoes were sampled. A and B represent locations where wild birds were sampled.

Figure 3.

Average mosquito abundance of candidate West Nile virus (WNV) mosquito vectors in relation to monthly incidence of chicken seroconversions across study sites in Puerto Barrios, Guatemala, 2006–2009. Mosquito densities were derived from monthly Centers for Disease Control and Prevention (CDC) gravid and light trap collections at 10 sampling points. Arrows indicate months in which WNV-infected mosquitoes were detected in supplemental collections.

Figure 4.

Climatic data recorded by the Guatemalan National Institute of Meteorology in Puerto Barrios, Guatemala, 2006–2008. (A) Rainfall (mm) and (B) monthly average temperature (°C).

Figure 5.

Seasonal variation in percent of all avian detections during point counts for selected bird species in Puerto Barrios, Guatemala (2006–2008). “Spring” represents Spring migration, “Summer” breeding season, “Fall” fall migration and “Winter” non-breeding season.

Figure 6.

Seroprevalence of adult and juvenile clay-colored thrush (Turdus grayi), and great-tailed grackle (Quiscalus mexicanus) before, during, and after the peak transmission period (May–Nov 2007).