Although they already thrive in south Louisiana’s warm, wet weather, mosquitoes generally inflict little more damage than an itchy, raised bump. But as climate change pushes temperatures higher, the viruses carried by the unofficial state bird are likely to proliferate faster, increasing its threat of infecting human beings with West Nile, Zika and dengue.
New Orleans’ average daily temperature has already risen 0.8 degrees since 1981, to 70.5; Lafayette is up 0.5 degrees to 68.1. As the trend continues, the state’s number of 79- to 84-degree days – the ones ideal for mosquito activity – could grow by nine to 14 per year, depending on the city, according to a report by the nonprofit Climate Central.
In addition, the changing climate’s promise of more intense rain and wetter tropical storms might make it easier for some mosquitoes to multiply in the aftermath of a downpour, said James Diaz, LSU professor of environmental and occupational health. More precipitation can create more breeding areas, so it’s increasingly important for residents and businesses to check their property for standing water.
“As climate change occurs and we get hotter and longer summers and shorter and warmer winters, the diseases that are transmitted by arthropods are going to increase,” Diaz said. “The mosquito season … mirrors the tropical storm and hurricane season, and as we see more storms, we’re going to see more mosquito-borne disease outbreaks.”
Easily distinguished by their white-striped legs, the aggressive Aedes albopictus and Aedes aegypti excel at spreading viruses. West Nile is the most common mosquito-borne virus in Louisiana, but should the Zika and Dengue viruses enter the state, they would pose a significant health threat, said Diaz and Jennifer Breaux, a New Orleans research entomologist.
The pair drop their eggs in standing water, especially human-made containers ranging from old tires to children’s playground equipment to small plastic bottle caps – anything that can hold water.
“Albopictus is very dangerous because it lives around your house,” Diaz said. “It lives in your backyard. It lives in the saucers under your potted plants. It lives in your upturned garbage can top that you’ve forgotten to bring in and you’ve left outside during the heavy rains like we’re having right now. And it will bite you again and again.”
Louisiana is also home to several species of Culex mosquitoes, which can also carry West Nile but breed in drainage catch basins and septic systems.
It takes two bites for mosquitoes to spread a virus. The first bite on a host animal establishes the virus inside the insect, and the second passes it on. Between those two bites, pathogens incubate and grow inside the mosquito, working their way up from the gut into the saliva.
Heat allows pathogens to multiply faster, so the mosquito needs less time to start infecting people. The same heat makes the insects more active, which means more biting.
In Louisiana, cases of West Nile virus historically arise between late June and July and stop by November. A New Orleans resident reported a serious case recently, going beyond the usual flu-like symptoms to affect the nervous system. But as the state’s already mild winters see further warming, Breaux said scientists have logged cases as early as January.
“A random one will pop up and you’re going, ‘What is this? This is not supposed to happen,'” said Breaux, who works for the New Orleans Mosquito, Termite and Rodent Control Board. “It’s that lack of seasonal stability that’s bringing these issues with the mosquitoes themselves.”
A 2018 Climate Central report said New Orleans could see at least 14 more days per year with conditions ripe for disease spread: days when the average temperature falls between 79 and 84 degrees. That report looked only at temperature trends during the spring, summer and fall, leaving out ”disease danger days” during the winter.
Lake Charles was expected to have 11 additional days, and Monroe, 12. Baton Rouge, Lafayette and Alexandria each was projected to see nine more days.
Local agencies such as New Orleans’ mosquito control board perform their own routine checks in known mosquito breeding grounds, Breaux said, monitoring tire piles and spraying larvicide by truck or airplane where needed. But residents and businesses must do their part to limit population growth.
“This is happening on a very micro scale; this is happening in someone’s backyard,” Breaux said. “We try to address the issues that are city issues like the tire dumps, like the swales in the road and the puddles of water in the parks. We can definitely handle that, but if I can’t get all of our neighbors to check their backyards for their wheelbarrows, and their kids’ toys, we’re still going to have a huge problem.”
Diaz said researchers are studying a number of innovative methods for controlling mosquito populations, beyond raining insecticide from the sky. They include sending in tiny crustaceans called copepods to gobble mosquito larvae and sterilizing male mosquitoes, which prefer flower nectar over blood. After Hurricane Katrina, some residents received bags of guppies to place in abandoned swimming pools, where they ate the mosquito larvae.
But Breaux said insecticides will always remain an important tool in combating extreme outbreaks.
Ultimately, she said, vigilance from all parties will be key to managing any threats posed by the whining insect.
“There’s a whole lot we can do about these impending climate changes, and whatever it’s going to do, leave that to the experts,” she said. “What people can do is help us figure out how to handle this at the level of our communities.”
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