The utility of animal surveillance in the detection of West Nile virus activity in Puerto Rico, 2007.

After the isolation of West Nile virus (WNV) from humans, mosquitoes, and chickens in 2007, an analysis of animal surveillance involving multiple species (horses, monkeys, sheep, dogs, and birds) used to track WNV transmission from 2006 to 2008 was performed. During this period 13.4% of all the animal samples collected were seropositive by blocking ELISA for WNV. The most complete island-wide sampling was obtained from horses of which 22% were serologically positive and 96% were confirmed as WNV infections by plaque-reduction neutralization test. Our conclusion from this 3-year study is that animal surveillance is an early indicator of WNV activity before the identification of human cases. Additionally, the results indicated that horses have a greater geographical range and should be continued to be used as sentinels for passive surveillance in the tropics.