Association of Climate Factors and Dengue Case Counts in Florida

Abstract

Dengue fever (DENF) is a common arboviral disease globally that is caused by four serotypes of the dengue virus (DENV -1, -2, -3, and -4) and transmitted through the bite of Aedes genus mosquitoes. The incidence of DENF has grown substantially over time, from 505,430 cases reported in 2000 to the World Health Organization, to 6.3 million cases and more than 7,300 DENF deaths reported in 2023. Although historically DENF cases have been limited to tropical climates, new areas at higher latitudes could become at risk for DENF with the vector’s habitable range changing as a result of climate change. One possible mechanism whereby changing climate could influence DENF patterns is via the reduction of extrinsic incubation period (EIP) of DENV. Our objectives were to: describe how climate in Florida affects the probability of Aedes aegypti mosquitos surviving the EIP, determine how mosquito survival and EPI length are related to DENF case counts in Florida, and to identify environmental conditions among states in the Southeast United States that may impact the probability of a mosquito surviving through the EIP of DENV. We created heat maps using Python code to graph the calculated probability that a mosquito survives the EIP (PSE) against relative humidity and temperature with points representing the environmental conditions of each month in the three selected Florida counties averaged over the years between 2009-2024. Additional heat maps were produced for the five selected counties from Georgia, Alabama, southern Texas, and Louisiana using the same method as the Florida counties. We used Python to graphically display the relationship between PSE and DENF case counts for each Florida county of interest. Our results indicated that in all three Florida counties we investigated, from June to September, between 7 and 10% of Aedes genus mosquitoes will survive long enough to transmit DENV after becoming infected. We found that case counts in the three Florida counties appear to be closely correlated with the PSE curve. Given the average monthly PSEs over the year, every county we examined in Georgia, Alabama, Louisiana, and Texas also has the potential for yearly DENF outbreaks similar to Florida. Our findings suggest that climate factors like temperature and humidity influence mosquito survival and ultimately the time required for DENV to incubate within the mosquito. This raises serious concern about the impacts of climate change on vector-borne diseases such as DENF, and state and county health departments should be aware of how climate and travel patterns could influence the transmission of DENV amongst their state populations.