Mosquitoes can transmit deadly diseases, such as West Nile fever. Is it possible to prevent this by using drones that will scatter more mosquitoes in the air?
Mosquitoes are much more than an annoying and itchy nuisance; They also transmit serious diseases that need to be protected against. The climate crisis and the increase in temperatures lead to the prosperity of mosquito populations, and in the last decades There was an increase In different regions of the world, the number of infections from mosquitoes infected with diseases, such as the Zika virus and dengue fever. In recent months, Israel has seen an unusual outbreak of West Nile fever, which is transmitted to humans by mosquito bites. and which resulted in the death of dozens of Israelis.
In a new study, edited by researchers The global mosquito program (WMP) - a non-profit organization that works against mosquito-borne diseases - and published in Science Robotics, compared the effectiveness of dispersing mosquitoes infected with Wolbachia bacteria in the ground environment compared to dispersal using a drone - an unmanned aircraft. From the planes, large quantities of mosquitoes infected with the bacteria were released into the air in order to reduce the amount of mosquitoes in a large area in the Fiji Islands.
Wal-what?
The main defensive measures used today against mosquitoes are mainly actions to prevent their reproduction, such as reducing stagnant water sources, alongside monitoring actions and pest control made by the authorities. But what if it were possible to "cure" the mosquitoes of the diseases so that they would not infect us? in research published in the journal Nature found that infection with Wolbachia bacteria gives the mosquito resistance to the virus that causes dengue fever - although the researchers are not entirely clear how. study Another from 2016 showed that the Zika virus was not found in the salivary glands of mosquitoes in Brazil infected with Wolbachia bacteria.
The Wolbachia bacterium was discovered 100 years ago and during that time a number of important and interesting properties were discovered in it; One of them is its ability to protect its hosts from other disease agents. in mosquitoes, for example, it activates genes that may improve the activity of their immune system.
One of the surprising abilities of Wolbachia, which is being used more and more, is to disrupt the reproductive systems of mosquitoes, especially mosquitoes. It was found that when a male mosquito infected with Wolbachia bacteria mates with a female, then the mosquito produces infertile eggs. This means that it is possible that this mechanism can be used as a way to harm the reproduction of mosquitoes in a certain area. Such a strategy can be effective if the distribution of infected males is in huge numbers, which will increase the statistical chance that females will mate with them and not with the other mosquitoes, which do not carry the bacteria.
Cure the mosquitoes
According to the article in Science Robotics, a number of experiments were conducted in the last decade, mainly in areas that suffered from high rates of dengue fever, during which hundreds and thousands of "Wolbachia-infected" mosquitoes were scattered in the hope that they would mate with the mosquitoes and eventually reduce the population and stop the disease. Such experiments were conducted, among others, in Australia, Indonesia, Vietnam, Brazil and Colombia, and showed the spread of Wolbachia bacteria among high rates in the mosquito population. In some cases they exceeded 90 percent.
The real test of the success of the method is whether the infection rates of the mosquitoes led to a decrease in the infection rates in humans. in an experiment conducted Between the years 2015-2020 in three cities in Colombia, the researchers dispersed male mosquitoes infected with Wolbachia bacteria. An examination of records of hospitals and clinics in the three cities revealed that in the years 2019-2021 there was a 94-97 percent decrease in dengue fever morbidity compared to data from the ten years before the start of the experiment. Further strengthening of the connection between the mosquito dispersal operation and morbidity was obtained from the segmentation of the residential areas of the patients. In neighborhoods where mosquitoes were scattered, dengue morbidity was 47 percent lower than in other neighborhoods. That is, not all of the decrease in morbidity is explained by the infection with the bacteria, but it is certainly a significant part.
Mosquitoes in freefall
In a study of the global mosquito program, the team flew drones over an area of 2 square kilometers, in the town of Nausori in the Fiji Islands - an area with high amounts of mosquitoes, which was chosen, among other things, because of the flat ground that made it easier to plan and operate the flight. For 16 weeks, with some short breaks due to technical problems, about 31,000 mosquitoes infected with Wolbachia were released - an average of 155 mosquitoes per hectare. A year later, a repeated test in the field showed that a frequency of infection with the bacteria was recorded in about 60 percent of the mosquitoes - the same results as the dispersion made from the ground.
The purpose of the study was to test the quality and effect of the dispersal from the drones compared to ground dispersal, and the effect on the morbidity data in the area has not yet been tested. The ground method has logistical and safety challenges. To ensure complete coverage of mosquitoes over a certain area, the basic release process involves walking or driving through the release area while manually opening small containers containing live mosquitoes, with the goal of achieving even distribution. This method limits the possibility of carrying out the dispersion in larger areas. According to the researchers, the experiment was successful and not only did the release with the help of the drone achieve a similar result to the existing methods, it also took a third of the time compared to the ground release process.
As part of the experiment, an automatic mosquito release system was developed, which can release small groups of mosquitoes in fixed doses over a wide area from the UAV. Each drone can contain 160,000 adult mosquitoes. The mosquitoes are cooled and anesthetized in high-density insulated containers, where one of the challenges is to maintain constant conditions of temperature and humidity so as not to harm the mosquitoes and so that they do not kill each other inside the container. Before they are released, the system wakes them up and releases them into the wild, about 150 mosquitoes at a time. The freed mosquitoes were dyed with a special phosphorescent substance so that they could be identified later and recaptured. It was found that the unique release mechanism had no negative effects on the effectiveness in infecting the local mosquito population with the bacteria.
Is it also in Israel?
The researchers emphasize that there is no single effective method, and successful prevention of "mosquito epidemics" always requires an integrated approach, but what are the chances that one day we will also see drones here in the skies of Israel to disperse infected mosquitoes? "We are trying to understand the feasibility of this method in Israel," says Dr. Shai Reicher, Director of the Pest and Pest Control Division at the Ministry of Environmental Protection. "Currently, integrated pest control based on the principles of prevention, detection, monitoring and treatment - even if mostly chemical at this stage - can provide an answer to various hazards of sanitary pests, including mosquitoes."
in the Ministry of Environmental Protection Promotions throughout the year Thousands of observations of mosquito larvae and hundreds of captures of adult mosquitoes. The office does not often use or recommend repellents, and mainly focuses on reducing the amount of mosquitoes at the source. "Biological control, such as the use of sterile mosquitoes, may well position itself in the future as a preferred solution over the use of chemicals," notes Reicher. "As much as such a method sounds logical and trivial, it is still in its infancy and we are at a stage where we are still learning its effectiveness. There are places where it didn't help at all or helped very minimally."
Along with the effectiveness of the method, it turns out that there is also quite a bit of technical complexity to adapt the treatment to the local mosquito population. "In order to use sterile mosquitoes of a certain type, a special breeding line has to be produced to produce the specific species of that mosquito," Reicher explains. "In each environment, the mosquitoes behave and reproduce a little differently, and there is also genetic variation. For example, the genetic type of West Nile fever in Israel is different from the one in Cyprus, and treatment there will not necessarily be beneficial here," he says. "This means that even if there is a company somewhere in the world that uses such a mosquito, it is impossible to import the mosquitoes here. This requires local development adapted to the specific species present here. As of today, there is no development in Israel that can provide an answer to the specific species of mosquito that is responsible for West Nile fever infection."
"It is a very complex system that needs to take into account the biology and behavior of the local population, the amount of individuals per unit area and the mosquito's flight distance. These are processes that need to be tested on a scientific level. Right now, we don't have enough evidence to say that this is a good enough method to focus so much effort on. As soon as we know that it will be effective in the long term, we will be happy to integrate it in Israel", he concludes.
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