After a 26-year absence, Auburn School of Forestry and Wildlife Sciences Assistant Professor of Disease Ecology Sarah Zohdy and wildlife sciences undergraduate student Victoria Ashby have discovered the species in Mobile. Ae. aegypti was thought to have been eliminated from the state.
“Our Centers for Disease Control and Prevention-funded research has not only allowed for the detection and molecular confirmation of the mosquito in the state, but over the last year we have documented the spread of the mosquito from central Mobile to all of Mobile County,” Zohdy said.
The study was conducted from July 2016 to September 2017. Mosquitoes were collected twice a month from the grounds of various tire shops, gas stations, abandoned buildings and open containers quantified to estimate larval abundance. A total of 1,074 mosquitoes were collected, with Ae. aegypti being detected most commonly in the 36606 area code of southwest Mobile, where there were more open containers than any other area in the city.
Since 1991, Ae. aegypti was thought to have been displaced in Alabama by another container-breeding mosquito, Ae. albopictus, because Ae. albopictus larvae are better competitors with resource-limited habitats and the males are capable of mating with Ae. aegypti and rendering the females sterile. Despite these advantages, Mobile is the ideal habitat for Ae. aegypti reintroduction or for remnant populations to persist because the city’s maritime traffic and its diverse mix of urban, suburban, rural and industrial environments allow the mosquito to find different habitats where it can either escape from Ae. albopictus or have the competitive upper hand.
The detection of Ae. aegypti confirms that Alabama residents could be at risk to contract several mosquito-transmitted diseases. “This work demonstrates that citizens of Alabama may be exposed to the mosquito vector of Zika, chikungunya and Dengue fever viruses,” Zohdy said.
Zika virus spreads to people primarily through the bite of an infected Aedes species mosquito (Ae. aegypti and Ae. albopictus). Female mosquitoes become infected by ingesting microbes from a person’s blood while biting them and then passing those microbes to the next person’s blood stream. Once infected, the mosquito is then thought to remain infected and able to pass on the virus throughout the remainder of its life, or about two to four weeks. During this period they may take three to four blood meals, biting up to four or five people during their lifespan. Ae. aegypti is particularly problematic because it will also bite during the day and is very adaptive to different environments.
Specific geographic areas of greatest risk are correlated to the existence of the Aedes species. The Centers for Disease Control and Prevention (CDC) have developed estimated-range maps using models that predict potential geographic ranges where the Zika-transmitting mosquitoes would likely survive and reproduce based on local and historical records and suitable climate variables. According to the 2017 maps, the Zika-transmitting mosquito species are very likely to exist throughout the southeastern U.S. and as far west as California and as far north as Delaware.
Despite the state of Alabama being an ideal habitat for mosquitoes that transmit Zika virus, very little mosquito surveillance data has been collected from around the state. Zohdy said that because of their research efforts and the discovery of Ae. aegypti, her team is now working with the Alabama Department of Public Health.
According to the CDC, there were 449 symptomatic Zika virus disease cases reported within the U.S. in 2017, with three reported in Alabama and two in Georgia. The majority of cases were instances of travelers contracting the disease from affected areas. Seven cases were acquired through presumed local mosquito-borne transmission, including two in Florida and five in Texas.
Zohdy’s team is now conducting research in all 67 counties in Alabama to determine how widespread Ae. aegypti and Ae. albopictus are across the state.