Fernando Bernardini

A Step Ahead in the Fight Against Resistant Mosquitoes

After experiencing a peak in dengue fever cases in 2015, Latin America has enjoyed falling rates of the disease in the past two years. According to the World Health Organization (WHO), in 2017 more than 570,000 dengue fever cases were recorded in the region, well below the 2.1 million cases recorded in 2016. Incidences of zika and chikungunya is also falling. This represents a small victory in the fight against the Aedes aegypti mosquito, vector transmitter of the three diseases. Although cases are declining, populations of resistant mosquitoes are on the rise. In practice, this poses a new obstacle to be overcome in controlling the insect.

Effective control of the Aedes aegypti mosquito began in the 1940s during World War 2, when the spread of dengue fever cases drew the attention of epidemiological authorities due to the intense displacement of people during the war. The insect of African origin traveled the world and ended up adapting very well to urban areas. The high temperatures and humidity typical of tropical climates have made developing cities, such as Latin American capitals, ideal homes for the mosquito (which has translucent wings and white stripes on their bodies and legs and is smaller than the common mosquito’s species, called Culex).

According to WHO estimates, the Aedes aegypti mosquito infects at least 390 million people with the dengue fever virus per year worldwide. This clearly makes it necessary for countries to continue investing in vector-fighting methods, especially due to the increase in mosquito resistant populations.

Since the 1980s, the mosquito has been controlled with the use of a chemical group known as pyrethroids, which are found in virtually all insecticides available on the market. However, some mosquitoes naturally carry an enzyme that deactivates the power of pyrethroids. Acting very much like a "shield", this makes them resistant to the products based on this chemical group.

Fernando Bernardini
Fernando Bernardini
Fernando Bernardini
Environmental Science Product Development Manager, Crop Science Division at Bayer

The mosquito's growth cycle is very fast and it only takes seven days for the insect to grow from an egg to an adult. There is a portion of mosquitoes that have a natural defense against pyrethroids, and therefore are not affected by the current treatments. On the other hand, the susceptible mosquitoes (that have no natural protection) continually die under the effect of pyrethroids. This led to a worrying increase in the resistant population of Aedes aegypti.

Faced with such high rates of mosquito populations that no longer react to available insecticides, in the last five years we have endeavored to identify and develop a new mode of action effective against the Aedes aegypti. At Bayer Vector Control research centers in Paulínia (Brazil), Monheim (Germany) and Clayton (United States), we perform ongoing tests on resistant mosquitoes to find new ways to combat them.

Over the next two years, Bayer researchers will work closely with renowned research and vector control organizations on laboratory and practical tests to study very complex issues. Among the variables, it will be necessary, for example, to understand the best methods of application for a new solution to overcome physical and natural barriers of the cities (buildings, walls, trees, etc.) and reach the mosquitoes. Another important factor is to find out the ideal consistency of the product particles so that it hits the insects before evaporating. These are some details that once answered will help to develop new effective treatments against resistant Aedes aegypti.

The first outcomes of these studies are quite promising. However, the road to overcoming the obstacles of combating the Aedes aegypti is long and has no shortcuts.

In order to fulfill the commitment of Bayer to use science and innovation to improve people’s lives all over the world, we must not only acknowledge the achievements in the fight against vector-borne diseases such as dengue, but also be mindful of the environmental, socio-economic and/or political emerging challenges. This we are doing as we continue to invest in research and the forging of strategic partnerships to offer society the most advanced and safest insect control products and solutions.

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