Using DyMSiM to model the response of important disease vectors to urban environments and climate in Tucson, Arizona

Climate is an important control on populations of disease vectors such as Aedes aegypti and Culex quinquefasciatus mosquitoes. In addition to climate, urban environments play a large role in the ability for many disease vectors to establish themselves in a given area. Aedes aegypti are a purely urban mosquito. These container breeding insects do not live outside human inhabited areas. They feed primarily on humans and transmit the Dengue Virus which currently infects over 100 million people per year world wide. Most of these cases are found in urban tropical environments. Culex quinquefasciatus are also predominantly urban mosquitoes and are a principal transmitter of West Nile Virus in Tucson, Arizona. This disease is found throughout the United States and in 2006 infected 150 people and caused 10 fatalities in Arizona.

Urban environments provide ideal habitats to Aedes aegypti and Culex quinquefasciatus mosquitoes. Urban areas tend to have increased amounts of impermeable land cover which allows the formation of standing water where mosquitoes can breed. Clogged gutters and outside containers are perfect environments in which mosquito larvae and pupae can survive and develop. In addition, urban environments provide increased amounts of permanent water sources, especially in arid environments such as the Southwest United States. Coy ponds, man made wetlands, and neglected pools are ideal breeding grounds for mosquitoes. Irrigation in urban environments may also increase mosquito populations by providing a water source in otherwise drier environments. Lastly, urban areas tend to be warmer due to the urban heat island effect. Warmer conditions allow for quicker mosquito development, increased viral replication within a mosquito, and extend the season in which the mosquito can survive.

Improved understanding and modeling of climate effects on mosquito populations is needed to help predict and mitigate disease epidemics. This study reports on the development of a dynamic mosquito simulation model (DyMSiM) driven in part by climatic data. Model inputs include daily temperature, precipitation, and evaporate rates that influence mosquito population development and mortality in relation to temperature, population density, and water availability. These factors are considered through all phases of the mosquito life cycle from ovulation, though the larvae and pupae stages, and finally emergence into an adult. The model also allows calibration for different land covers, irrigation, and urban island effect. In this study, the model is utilized in order to construct historical predictions of aegypti and quinquefasciatus populations in Tucson Arizona. Several runs will be performed with common climate data but different urban settings. This includes different irrigation schemes, patterns of impermeable surfaces, and the presence or absence of standing water. Ultimately, the study seeks to identify the role urban environments and climate play on mosquito populations and disease.