Effects of weather on mosquito biology, behavior, and potential for West Nile virus transmission on the Southern High Plains of Texas

The threat of emerging and resurgent vector-borne diseases associated with weather conditions, global climate change, and biologic attacks is of major concern. West Nile virus (WNV) first appeared in the United States in the summer of 1999. Since then it has spread rapidly across the nation and continues to be a threat to humans, domestic animals (particularly horses), and wildlife.

The goal of this project was to model the factors involved in the WNV maintenance and transmission cycle. Mosquito surveillance to determine mosquito community dynamics and WNV infection in mosquito populations has been ongoing in Lubbock County, TX (33.65°N; 101.81°W; 975 m elevation), since the summer of 2002. West Nile virus was first detected in Lubbock County in late summer 2002 and has continued to appear each summer. The occurrence of WNV in mosquitoes collected over a three-year period was determined and related to very diverse annual weather conditions during those years in order to determine trends in WNV occurrence.

Differences in weather conditions between study years was reflected in differences in mosquito collections and WNV maintenance and transmission. In the Lubbock area, 2003 was a drought year, and Culex tarsalis Coquillett dominated mosquito collections due to an abundance of stagnant pools that allowed for the proliferation of this species. Additionally, a large number of mosquito pools tested positive for WNV. The following year, however, was a wet year, and Aedes vexans Meigen, a floodwater species, dominated mosquito collections. During 2004, the number of WNV-positive mosquito pools was reduced by two-thirds, despite testing approximately the same number of pools. Modeling mosquito populations and WNV occurrence in relation to weather patterns revealed interesting trends. Both of these were predicted by weather conditions, typically rainfall and temperature, in the weeks prior to collection of WNV infected mosquitoes. By understanding the factors that drive mosquito populations and the occurrence of WNV, future patterns of disease occurrence can be predicted and efficient mosquito control operations can be initiated prior to a major disease outbreak.

Models which explain when and why disease transmission occurred are important as related to effective surveillance and control activities as well as with respect to climate change and the potential for biologic attacks. Climate change is expected to increase the geographic distribution of many vector-borne diseases, and especially mosquito-borne diseases. Malaria, among other diseases, has already reappeared in regions in which it had previously been eradicated. Global warming that is projected to occur with climate change will allow for the geographic range of many mosquito species to be expanded, with the potential for these species to carry new diseases into naïve areas. Additionally, climate change is expected to increase the frequency of extreme events such as floods and droughts, which have previously been shown to facilitate the outbreak of various mosquito-borne diseases. Models of disease transmission will help public health officials initiate effective surveillance and proactive control strategies to prevent the further spread of disease. Acts of terrorism involving biologics is also of major concern. Models of disease transmission will aid in distinguishing between natural outbreaks of disease and a biologic attack. Understanding how a disease outbreak was initiated is also critical for effective surveillance and control operations, since biologic attacks could involve genetically altered pathogens, thus potentially requiring a different means of disease treatment or control.