The emergence of West Nile virus in mosquito populations of the New Mexico Rio Grande
In the fall of 2002, a new surveillance program was initiated to document the first appearance of West Nile virus (WNV) in New Mexico. Several dead birds and horses had tested positive for WNV in eastern and central New Mexico in the late summer of 2002, but no humans or mosquitoes were found to be infected. It was expected that the first human cases in the state would be reported in the following summer, and that WNV would be detected in mosquitoes. The surveillance program was designed to identify the species of mosquito acting as WNV vectors in New Mexico, and to record the pattern of emergence of WNV in a naïve ecosystem. The study focused on a 750 km stretch of the Rio Grande river valley, between southern Colorado, through New Mexico, and into Texas. The river valley was expected to be the primary focus of WNV emergence in New Mexico. A total of 53,668 mosquitoes were collected from 32 sites in 2003. The surveillance program was refined and refocused on the city of Albuquerque in 2004. A total of 25,973 mosquitoes were caught at 27 sites from Albuquerque.
The pattern of WNV emergence in New Mexico was consistent with introduction throughout the valley in late 2002 or early 2003, followed by a period of buildup through the spring and early summer of 2003. The first WNV-positive mosquitoes from the Rio Grande were reported in mid-July of 2003, with the first human cases occurring at the end of July. Mosquitoes from throughout the statewide study area were found to carry WNV. Three species tested positive for WNV in New Mexico: Cx. tarsalis, Cx. salinarius and Cx. quinquefasciatus. In 2003, 72 positive mosquito pools were found, and 71 pools from Albuquerque tested positive in 2004.
In addition to the study of WNV emergence, the effectiveness of several trapping methods was analyzed, and an extensive survey of mosquito community structures was conducted, representing the first such effort in New Mexico in over 50 years.