Mosquitoes and ticks can carry vector-borne diseases such as Lyme disease, West Nile virus, and Zika virus, and transmit them to humans. Anticipated climatic changes will create more habitat that is suitable for ticks and mosquitoes. The new habitat ranges will increase the number of mosquitoes and ticks in the Midwest, increasing the risk of vector-borne disease transmission to humans.
Warmer winter and spring temperatures will allow mosquitoes and ticks to expand their ranges further north and increase their populations. Days with extremely cold temperatures that have historically helped control pest populations are expected to decrease and allow more mosquitoes and ticks to survive and reproduce. Warmer temperatures can also speed up the development periods for ticks and mosquitoes, reducing the time it takes for them to mature and incubate diseases. Longer periods of warmer temperatures will enlarge the window of time for ticks and mosquitoes to obtain a virus, transmit the virus, and spread it across a wider geographic range.
To reproduce, mosquitoes require standing water, which can arise from rainfall and flooding. Spring rainfall is expected to increase in the Midwest, meaning there will be more breeding habitat for mosquitoes. While projected summer drought conditions can limit the spread of mosquitoes, the use of containers for rainwater collection and storage during droughts are prime breeding sites for mosquitoes. Coupled with higher temperatures, the Midwest is projected to see larger mosquito populations and more mosquito species expanding their range into the region due to increased precipitation and flooding.
It is important to note that other changes, such as human impacts on the landscape, can also increase the distribution and transmission of vector-borne diseases. Development and other land use changes, for instance, can bring humans into closer contact with mosquitoes and ticks, as well as deer, birds, and other wildlife that also carry disease vectors, increasing the risk of disease transmission.
Indiana is already experiencing some of these impacts. From 2013 to 2017, the Hoosier state had 132 average Lyme disease cases reported annually – more than double the average annual cases from the previous five-year period. Also, the number of mosquitoes in Marion County, where Indianapolis is located, increased 500 percent from 1981 to 2016. This increase is consistent with observed changes in temperature and precipitation during that time.