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A mosquito sits on a stick on April 9, 2009 in Martinez, California.
(Photo: Justin Sullivan / Getty Images)
We often think of climate change in terms of extreme weather, but the effects of global warming go well beyond natural disasters. Scientists believe that climate change will also make the world more welcoming to mosquitoes and the diseases they carry. To make matters worse, new research shows that climate change can also be a supercharged evolution of mosquitoes.
Zika, West Nile and dengue are just a few of the deadly viruses that spread to mosquitoes. Human diseases such as these are also borne by animals such as birds and rodents, which do not always have symptoms. But if a mosquito bites an infected animal, it can then transmit the disease to other animals, including humans. That's why many disease prevention efforts focus on: control mosquito populations – a task on the verge of becoming much more difficult.
Insects like it hot
The mosquito species differ in the mode and location of their eggs, but they all like water. Some species lay their eggs in the soil, others directly in ponds or in flooded containers. Eggs are sensitive to moisture and, in the case of soil-related eggs, heavy rainfall causes them to hatch. While climate change is making many places hotter, wetter and more exposed to extreme weather conditions, mosquito habitats are changing. It spreads diseases to new places and worsens epidemics in already afflicted places.
According to Sadie Ryan, lead author of the study and professor of medical geography at the University of Florida, these viruses have been discovered mostly in the tropics, but they have now begun to appear in new places. "Humans are very good at moving both insects and their pathogens around the world," she said in a press release.
Dengue incidents, for example, have increased by 3,000% over the last 50 years and the virus continues to spread to new countries. Another study estimates that disease-carrying mosquitoes expand their reach by more than 150 km each year. In 2016, the Centers for Disease Control and Prevention (CDC) investigated the number of counties in the United States that A. albopictus and reported a 10% increase in a single year.
The threat motivated researchers, like CDC scientists, to develop better ways to predict epidemics. "We have done a lot of work on the predictions," said Gabriela Paz-Bailey, an epidemiologist at the CDC office in Puerto Rico, where she is responsible for monitoring mosquito-borne diseases such as dengue and zika.
Paz-Bailey and her family had just settled on the island when Hurricane Maria hit. "We feared an increase in the number of vector-borne diseases after the hurricane," she said. Paz-Bailey was particularly concerned about the epidemics of dengue and Zika, both diseases being permanent threats on the island.
"There are some theories about high winds that reduce the number of mosquitoes shortly after a hurricane," said Paz-Bailey. But if windstorms usually kill adult mosquitoes, their eggs can survive. And tropical storms of stagnant water are causing insect populations to rebound quickly. "Not only moisture and humidity, but all the debris left after the hurricane are ideal breeding sites."
After Hurricane Florence devastated communities in North Carolina last September, for example, many residents reported an increase in the number of active mosquitoes. Scientists suspect that floodwaters have accelerated the hatching of otherwise dormant mosquito eggs found in the soil. Two weeks after the pbadage of the storm, an entomologist noted the population of a particular species, Psorophora ciliata, had ballooned by more than 15 times.
This giant mosquito species, affectionately called & # 39;gallinipper,& # 39; delivers a memorable bite that has pinched "a pinch of gallon of your blood." Fortunately, the gallinipper rarely carries dangerous pathogens. But if it started? After all, mosquitoes (and viruses) are evolving.
Accelerate the evolution of mosquitoes
Mosquito species considered troublesome may soon become a threat to public health. A recent study published in the journal Biology of communication, shows that climate change can really accelerate the evolution of mosquitoes. Matthew Wills, a paleobiologist at the University of Bath, collaborated with scientists from York and Beijing to understand how climate influences the speed of evolution, a process called speciation.
"If we look at the last 195 million years …[back] The speculation rates are much higher than others, "says Wills. Researchers focused on the effects of temperature and the amount of carbon dioxide in the atmosphere. while climate change is changing both. "We found that there was a connection with temperature," says Wills, but, surprisingly, "the link with carbon dioxide seems [even] stronger."
During the study, the team examined 550 previously published evolutionary family trees. These described different species of mosquitoes, their kinship and their separation from their predecessors. But the data forest was full of contradictions. The team scanned each tree and combined the data to create a more complete and accurate "tree" of mosquito relationships.
The team then used fossil recordings and mutation rates known to badign dates to major changes in mosquito evolution. The fossil record provided physical evidence, and known mutation rates confirmed how quickly mosquitoes could adapt over time. This revealed a decisive link: historically high temperatures and carbon dioxide levels both increased mosquito speciation rates.
Although researchers do not know exactly why, they badume that increasing carbon dioxide levels is beneficial for plants. "We think of [mosquitoes] We have blood meals here, but many species also feed on plants. "The Wills team proposes that carbon dioxide boosts food supplies for mosquitoes and that abundant resources support more species, thus offering a chance to evolve.
According to Wills, mosquito diversity means more opportunities for disease transmission. "More species of mosquitoes can produce more species of parasites."
To be clear, an accelerated evolution does not necessarily mean that all the mosquitoes will fly suddenly with incurable viruses. It simply means that mosquitoes will have more opportunities to spread diseases.
Until now, scientists have not found evidence that the speciation rate has already increased. Wills suggests that this could happen in a few decades, but it could also happen much more slowly. "Part of the problem is we do not know," he says. The team method was based on data of several thousand years, but it does not predict the near future. "Of course, it's a concern." To a certain extent, the precise moment of rapid evolution does not begin: science predicts that we will soon have a problem, whether tomorrow or in 50 years.
When Hurricane Maria swept over Puerto Rico, the island suffered, but thankfully, there was no outbreak of dengue or Zika after the storm. This does not mean that the next hurricane will not cause an epidemic. It is time to treat climate change – and its impact on disease – as the serious threat to public health.
This story originally appeared on mbadif, an editorial partner site that publishes scientific stories of scientists. Subscribe to their newsletter and follow Mbadive on Facebook and Twitter.
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