Malaria is a severe illness that affects millions of people worldwide each year. In South America, it continues to circulate, with over 600,000 cases recorded annually. Brazil, Colombia and Venezuela report the largest totals.
The leading malaria vector
The mosquito chiefly responsible for transmitting malaria in the region is Anopheles darlingi. After biting an infected person, the mosquito may carry the parasite and transmit it when it bites somebody else.
For that reason, reducing populations of this mosquito is among the most important measures for cutting malaria cases.
A research team from the Harvard T.H. Chan School of Public Health conducted a major investigation to gain a clearer understanding of this mosquito.
They gathered more than 1,000 mosquitoes from 16 sites in six countries: Brazil, Peru, Colombia, Venezuela, Guyana and French Guiana. The collection sites covered forests, wetlands, farms, mining areas and cities.
Examining mosquitoes from such varied settings allowed the team to assess how this species behaves throughout South America.
A more complete view of mosquito genes
Rather than examining only small sections, the scientists analysed the mosquito’s complete genetic make-up. This gave them a clearer picture of how the species is changing over time.
Previous studies were based on limited information, whereas this approach revealed how the mosquito adapts to and survives in differing environments. It also uncovered patterns that had not previously been detected.
As the first large-scale study of this type in the Americas, it represents an important advance.
Anopheles darlingi is becoming more difficult to kill
One of the study’s key discoveries is that Anopheles darlingi is developing resistance to insecticides, the chemicals used to kill mosquitoes and lower their numbers.
“Insecticide resistance has only been sporadically documented in Anopheles darlingi, which have not been subject to intensive insecticide-heavy campaigns like those elsewhere in the world,” said Jacob Tennessen, lead author of the study.
“We were not expecting to see resistance-related genes evolving as much as we did, and in so many different countries. Resistance may be driven by agricultural insecticides rather than those used for vector control specifically.”
In other words, the mosquito is gradually becoming able to survive exposure to these chemicals. Insecticides used in agriculture may also be contributing to the development of this resistance.
Mosquito populations vary by location
The team also established that mosquito populations differ between places. Mosquitoes in Guyana, for instance, are markedly different from those in Venezuela.
These variations indicate that the species adapts to local conditions. Its characteristics change according to whether it lives in a forest, city or agricultural area.
Consequently, one approach may not succeed in every location. A control measure that works in one country might be ineffective in another.
A rapidly adaptable species
Anopheles darlingi is highly adaptable and able to survive in a broad range of surroundings. It can live in natural habitats, including forests, as well as human-made environments such as farms and cities.
Activities including agriculture and mining may affect the way this mosquito evolves. The species can adjust rapidly to such changes, helping it survive and continue transmitting malaria.
This adaptability makes it a resilient and persistent carrier of disease.
Why the study is important
The findings give scientists a stronger understanding of malaria transmission in South America. They also demonstrate why controlling the disease is becoming increasingly challenging.
“Malaria remains stubbornly persistent in South America, and there is a risk that dangerous drug-resistant strains of the malaria parasite could evolve in the Americas and then spread elsewhere,” said Jacob Tennessen.
“Our study plays a major role in revealing the evolutionary dynamics of a primary malaria vector, providing new insights into Anopheles darlingi biology that could help improve methods for blocking disease transmission.”
However, the researchers stress that further work is necessary before public-health policies are changed.
“This was basic research rather than an applied study,” said study co-author Daniel Neafsey. “Additional research is required before any policy changes are implemented.”
The way forward
The research marks a substantial advance in malaria understanding. It makes clear that mosquitoes are changing, and that older control methods could become less effective over time.
Scientists must now develop more effective and intelligent ways to manage them. The more that is known about how these mosquitoes change, the easier it will be to identify stronger responses.
The work also provides direction for future research into other mosquito species in the Americas. Better knowledge of these insects will help scientists prepare for emerging challenges.
Malaria remains a concern, but studies such as this offer hope for improved control in the future.
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