In Brazil, scientists are tackling the spread of diseases such as dengue and Zika with, yes, mosquitoes. If that tactic proves successful, it could be good news for us too. ‘Due to climate change, such diseases are also advancing in Europe.’
It must become the largest ‘mosquito factory’ in the world. At a yet to be determined location in Brazil, the World Mosquito Program (WMP) wants to set up a nursery where five billion mosquitoes roll off the proverbial belt every year. Their mission: to go out and multiply, decimating dengue, zika and chikungunya virus infections.
The mosquitoes are infected with the bacterium Wolbachia pipientis. It occurs naturally in about half of all insect species, but not in the Aedes aegypti mosquito that spreads dengue, Zika and chikungunya. Scientists discovered that mosquitoes carrying the bacteria are less able to transmit infectious diseases.
If such a mosquito drinks blood from someone who is infected with the dengue virus, for example, bacteria and virus in the mosquito’s body compete with each other. As a result, the virus is less able to multiply and the chance that it will be passed on to the next victim decreases.
Once infected, mosquitoes pass the bacteria on to their offspring via the eggs. The principle behind the control method is simple: if you release enough mosquitoes infected with Wolbachia, they will pass the bacteria on to their wild counterparts, making all mosquitoes less good disease spreaders.
“This is a very interesting technique,” says mosquito and infectious disease expert Bart Knols. “A major advantage is that the method is very targeted and has no adverse effects on ecosystems, as is the case with large-scale use of insecticides.”
In an experiment in Indonesia, WMP researchers released mosquitoes in some parts of the city of Yogyakarta, but not in others. In the ‘treated’ zones, the number of symptomatic dengue infections fell by three-quarters. “A promising result,” says Knols.
In Brazil, the WMP has already tested the method in several cities, and the reduction ranged from almost 70 percent to less than 40 percent in Rio de Janeiro. For an optimal result you need to be able to release enough mosquitoes in different places, and that turned out not to be obvious in slums. “This is a valuable additional weapon in the fight against infectious diseases,” says entomologist Ruth Müller (Institute of Tropical Medicine). “But it is not a miracle solution that makes all other methods obsolete.”
The question is also how long the method will remain effective. Bacteria and virus are involved in an evolutionary arms race in mosquitoes. There is a chance that a virus will be able to win the battle against the bacteria due to accidental genetic mutation. And the more mosquitoes with Wolbachia flying around, the greater the chance. Just as widespread use of pesticides can lead to resistance. “That problem has not yet been observed,” says Knols. “But it would mean that this method loses its power in one fell swoop.”
Genetically engineered mosquitoes
In the meantime, scientists are also working on other ways to use mosquitoes as a weapon. The American company Oxitec is developing genetically modified Aedes aegypti mosquitoes. Males are given a gene that only gives them male offspring that do not sting and are therefore harmless. Releasing genetically modified males should reduce the number of dengue infections. The company announced last month that its method will be deployed on a large scale in the Marshall Islands, and was previously authorized to release 2.4 billion mosquito males in Florida.
The Target Malaria research consortium wants to use genetically modified malaria mosquitoes to combat the spread of malaria in a similar way. Their sterile males cannot produce viable offspring. The ambition is nothing less than to eradicate mosquito populations, including malaria. This disease affects about 250 million people every year and claimed more than 600,000 victims in 2021.
Because genetic modification is involved, these methods are encountering more resistance, including from environmental organization Friends of the Earth. “Of course you have to investigate the safety of this properly,” says Knols. “But when you see the toll these diseases take, I think we should give each method a chance.”
The Brazilian mosquito factory must run at full capacity in 2024. The WMP wants to release mosquitoes in various places in Brazil over the next ten years, to protect around 70 million people against infectious diseases. It would be the first time that the method has been applied on such a large scale.
The WMP hopes to be able to roll out the technology in other countries as well. Dengue alone occurs in more than 100 countries. According to the World Health Organization (WHO), about half of the world’s population is at risk.
Scientists in Europe are also experimenting with the Wolbachia technique. Earlier this month, Italian researchers published the results of a field trial in Rome. “Diseases such as dengue are on the rise in Europe due to climate change,” says Müller. “This technique can therefore also be useful in Europe.”
2023-04-26 01:00:56
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