Mosquitoes with certain mutations can handle large amounts of insecticides. According to a study, this helps to curb the diseases they spread.
Mosquitoes are among the most dangerous animals for humans because they can transmit many diseases. These include malaria, dengue, zika, chikungunya and yellow fever. To date, many of these diseases cannot be treated causally, and there is not an effective vaccination once morest every one, quite apart from the difficulty of reaching everyone with it. One of the most important ways to prevent infection is therefore to fight the mosquitoes themselves – usually through the use of insecticides.
A research team from the National Institute for Infectious Diseases in Japan, in collaboration with scientists from several Southeast Asian and African countries, has now found evidence that many mosquitoes in Vietnam and Cambodia have become resistant to insecticides from the so-called pyrethroid group. These are synthetically produced neurotoxic agents, which means they target the central nervous system of the mosquitoes, which are then quickly paralyzed and ultimately supposed to die. Pyrethroids are widely used worldwide, among other things they play an important role in the fight once morest malaria, but are also a frequently used agent once morest insect pests in agriculture.
For their study, published in the journal Science Advances, the researchers left their laboratories to collect Aedes aegypti tiger mosquitoes in Vietnam, Indonesia, Ghana and Taiwan. These insects are vectors of dengue fever, zika, chikungunya, and yellow fever. Of these diseases, dengue is the most common. It is estimated that between 100 and 500 million people contract it every year, so far mainly in the tropical and subtropical regions of Asia, South America and Africa. Dengue is considered to be the most common mosquito-borne infectious disease caused by viruses.
Dengue also in Europe
The international research team writes in its study that the number of cases has increased 30-fold in the last 50 years. According to experts, climate change might also bring dengue to previously unaffected areas. The Asian tiger mosquito has now also settled in southern Europe and is expanding its habitat further. Dengue infections have already occurred in Spain, Croatia, Madeira and France. This leads to fever with severe headache and body aches, with most sufferers recovering following a few days. However, dengue can also lead to serious complications and even death.
For their study, the scientists sprayed each of their samples with permethrin, a pyrethroid commonly used to control mosquitoes in the areas chosen for the study. They found that only 20 percent of mosquitoes collected in Vietnam died, while samples from other countries died as expected.
In a next step, the researchers analyzed the genomes of those mosquitoes that had survived the insecticide. The result: They found a mutation in a gene called L982W, which has long been suspected of having something to do with resistance in mosquitoes. The team then collected more samples, this time from Singapore and Cambodia, and also examined the genomes of these mosquitoes, specifically focusing on that one specific gene. The researchers came across ten strains with mutations that were similar to those of the resistant mosquitoes from Vietnam. Almost all of these samples came from Cambodia. They also found that certain combinations of mutations increased resistance particularly strongly: Mosquitoes with such a genome were able to cope with a 500 to 1000 times higher amount of insecticide than other females without dying.
The scientists write that up to 78 percent of the samples they collected in Vietnam and Cambodia were insensitive to pyrethroids. They suggest that other countries should start testing mosquitoes for resistance to pyrethroids to determine the true extent of the problems.
Link to study: https://www.science.org/doi/10.1126/sciadv.abq7345
