Florida’s climate has been a suitable breeding ground for mosquitoes, but climate change could make temperatures apt for them to spread diseases for longer throughout the year, experts say.
Although the malaria vector, the Anopheles quadrimaculatus mosquito species, never disappeared from the state, Florida has kept the disease at bay, for the most part, because of mosquito surveillance efforts and people’s limited exposure to the insects, disease ecology researchers Sadie Ryan and Courtney Murdock said.
Globally, as temperatures warm, mosquitoes are able to breed faster, lay more eggs and bite more people, said Ryan, a professor at the University of Florida.
Additionally, higher temperatures also accelerate the growth of the parasite — Plasmodium vivax in the seven cases coming out of Sarasota County — that causes mosquitoes to spread malaria, according to the Centers for Disease Control and Prevention. However, since the malaria cases in Sarasota and dengue cases in Miami-Dade County haven’t spread elsewhere, Ryan and Murdock said they are not too worried.
Not all mosquitoes or the kinds of malaria they spread are the same, though. Species have different temperature thresholds of conditions where they can thrive, Ryan said.
“Obviously, once the proteins are cooking, they’re not really doing well anymore, and they’re not going to be flying around biting people and infecting them,” she said. “But sort of the flip side of that is: If it’s really too hot for a tropical mosquito to live, it’s probably really uncomfortable for humans, and so we start facing all the other issues of extreme heat.”
Hence, mosquitoes will move to areas of the world that were previously too cold or not humid enough. It is unclear how this will impact Florida since most of the research is based in South America and Africa, where malaria is most common and deadly.
Research indicates that mosquitoes are expanding to higher altitude areas in the highlands of South America and mountainous regions of eastern Africa as lower altitudes become too hot, according to an Associated Press article.
Just as the suitable areas for vectors are shifting in Africa and South America, the same could happen in the U.S. Ultimately, the spread of mosquito-borne diseases depends on how humans interact with mosquitoes. Screened windows and doors, air-conditioning, limited time outdoors and insecticide treatments help keep mosquito populations from getting out of control.
While the spread of malaria in other continents doesn’t directly affect Florida, a traveler could unknowingly contract the disease elsewhere and infect a mosquito in the state, which is how the spread in Sarasota must have started, Ryan said. Someone may not show any malaria symptoms because the parasite can go dormant and hide in the person’s liver.
“Malaria can’t travel by itself, and we have the vectors that can transmit it,” Ryan said. “We have the climate that is suitable for those vectors to be around. Particularly, Anopheles quadromaculatus that we think is the main malaria vector still hanging out in Florida. So, yes, it’s a low probability, but it’s not a zero probability.”
The mosquitoes humans co-exist with nowadays are highly domesticized, said Murdock, a professor at Cornell University. She is an expert on how mosquitoes transmit diseases. In the two-week lifespan of anopheles, they live in small areas and only experience those micro-climates, which Murdock studies.
For example, mosquitoes have adapted to breeding in standing water at construction sites, she said.
“If you have more urbanization, you’re going to have more concrete,” Murdock said. “You’re going to have a lot of surfaces that absorb heat, and then radiate heat slowly throughout the day; you’re going to have a lot of the built environments; you’re not going to have a lot of air flows. These can create pockets of warmer areas relative to the non-urban outskirts.
“This can have important implications for the temperatures and relative humidities mosquitoes experience, which will affect the environmental suitability for these diseases.”
Still, climate change research, particularly in Florida, focuses on the larger-scale impact of natural disasters, taking precedence over the micro-climates that are most relevant to mosquitoes.
