It is estimated that Every year there are 390 million dengue virus infections, of which 96 million have clinical manifestations, that is, signs and symptoms. And according to the World Health Organization (WHO)estimates indicate that there are 3.9 billion people at risk of being infected by the dengue virus. In the Argentinaduring the season 2022/2023 there was a increase in cases of 47% regarding the epidemiological outbreak of 2019/2020.
In the last two decades, in the context of climate changethe dispersion range of several of the vector-borne diseases (transmitters, in the case of dengue it is the Aedes aegypti mosquito) It has been expanded from tropical and subtropical regions to temperate zones. In 2009, indigenous transmission of the dengue virus was detected for the first time throughout the temperate zone of central Argentina and, since then, the incidence of the disease has been increasing in different provinces.
In this context, the prevention and the surveillance of what happens with him mosquito They are fundamental. A group of scientists from CONICET (who published his findings in the journal Parasites & Vectors) verified that in the Buenos Aires Metropolitan Area (AMBA), and in at least two towns in Salta and Jujuy There are Aedes aegypti mosquitoes that already have genetic mutations that give them resistance to insecticides most used today.
“These are insecticides called pyrethroids. Are the only ones allowed by ANMAT in Argentina for the control of insects in homes, in what is called home-sanitary use. The rest of the insecticides have been banned due to toxicological considerations, environmental impact and risk to people,” he explains. Sheila OnsCONICET researcher in the Insect Neurobiology Laboratory linked to the Center for Experimental and Applied Endocrinology (CENEXA) and lead author of the study.
“These insecticides exert their action because they interact with a protein that is in the membrane of the neurons of mosquitoes (and all insects). The insecticide destabilizes the nervous impulse, causing hyper-excitement, which causes the death of the insect,” he describes.
But it is possible that this protein has changes, a mutation, with respect to the original protein and then it no longer recognizes the insecticide as well. As a consequence, the interaction between the poison and its target of action is no longer efficient: “this is what we have detected in our country, and that is that these mosquitoes have resistance to insecticides,” summarizes the researcher.
Consequences of misuse of insecticides
The research was developed within the framework of the Argentine Network for Surveillance of Resistance to Pesticides used in Public Health (RAReP), and included three geographical points of the party of the silveralong with the Buenos Aires towns of Quilmes, Merlo, La Matanza, Tigre, Lomas de Zamora and Avellaneda. In these places the researchers found a mutation, the R1 genotype (implies a still low resistance), but the majority of mosquitoes are still sensitive. However, in the north of the country the mutations found are two (therefore they correspond to the R2 genotype, linked to high resistance), in the same insects. The areas included in the studies were Tartagal in Salta and Calilegua National Park in Jujuy.
“This leads us to conclude that The resistance in the north is going to be even stronger than in the AMBA. Why does this happen? Because since dengue has existed for longer, more years in that northwest region compared to Buenos Aires, insecticides have been used for longer. And that gave more time for populations to evolve toward developing resistance. We can think that it is a matter of time before these things also begin to happen in Buenos Aires. We have time, then, to plan better and take these data into account to be able to include them in the designs of mosquito control campaigns and try to increase the useful life of insecticides,” summarizes Ons.
The process by which mosquitoes develop changes in their physiology that make them resistant is relatively simple, a product of evolution. In a population of mosquitoes, not all specimens are the same, as is the case among human beings. Some mosquitoes are very sensitive to insecticides, others are not. Some, who live with the population, have these mutations that give them greater resistance.
It may be that insects carrying the mutation associated with resistance are few at times when insecticides are not used. But when the environment is sprayed, what happens? Almost all mosquitoes die, except some of them: this is how the resistant survive. They are the ones who are going to have more chance to reproduce, to lay more eggs. The next generation will inherit that characteristic and therefore it will have a greater proportion of resistant insects precisely because they were the ones that managed to survive the pressure exerted by the insecticide.
“When insecticides are used irrationally, more than necessary and at times that are not appropriate, in places where they are not needed, this resistance is going to occur faster -warns Ons-. If one does not take prudence into account, in addition to unnecessarily throwing poisons into the environment, it is also causing the mosquito population to become resistant more quickly.”
“Fumigation is not always a solution, and It is not done at any time or time of day.. In many squares, parks and gated communities, fumigation is carried out throughout the year or before summer as a ‘preventive’ measure, but that does not work. Here the peak of activity of A. aegypti females is in February and March“, and adding poison outside of that period only favors genetic resistance to chemicals,” he points out. Maria Victoria Micielialso a researcher at CONICET, director of the Center for Parasitological and Vector Studies (CEPAVE) and another of the authors of the research.
Planning and science against dengue
Both the WHO Like its counterpart in Latin America and the Caribbean, the OPSrecommend that a integrated mosquito managementusing all available tools and not just insecticides. One of those tools is the brokenenvironmental planning to not have places that accumulate water, use repellents. And resort to toxic substances in the event of a dengue outbreak, when the situation becomes an emergency. One possibility is alternate chemical insecticides with biological methods, bait trapsamong others that are being investigated.
Monitoring the presence of mosquitoes (which is carried out all year round and is carried out by specialized scientists and technicians), and the surveillance of resistance itself are fundamental within this integrated management of the situation.
In this sense, Ons emphasizes the need to have “un strong scientific system that allows us to have a good design of public policies”. And he adds: “Our research group, together with others, works to generate this information that is then received and used by the Ministry of Health to improve public vector control policy.”
And improving public vector control policy also implies improve the quality of life of the entire population exposed to getting sick. “But It also means saving money. It was estimated, for example, that the 2009 dengue outbreak, which was much smaller than that of 2023, cost the country at least 10 million dollars. The fewer people get sick, the fewer resources that the health system and the State and the private sector have to put into addressing this epidemic – describes Sheila Ons -. So, it is a question of good living, it is a question of the environment, it is a question of public health and it is an economic question as well. The good design of public policies, complemented with the scientific information necessary in our country, will have an impact on all these aspects.”
In addition to the discovery of resistant mosquitoes in the north and center of the country, the research also makes another important contribution: the development of a genetic technique for detecting mutations which speeds up times with respect to the methods used until now.
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