How mosquitoes are responsible for the spread of human disease

 

Aedes mosquitoes are a huge problem in the transmission of human diseases, including dengue fever, chikungunya and yellow fever. Insecticides have been widely used in an effort to control them, applied to mosquito larvae habitats, or indoors against adult mosquitoes. However, as with most forms of pest control, Aedes aegypti mosquito populations across the world have started to become resistant to insecticides, which can threaten the success of control interventions designed to prevent the spread of disease and the potential for epidemics.

 

Female Aedes aegypti mosquito as she was in the process of obtaining a "blood meal"

If insecticides are beginning to lose their effectiveness, we must start to look at other avenues of pest control capable of protecting humans against the spread of potentially lethal diseases. Dengue, chikungunya, and zika virus are debilitating diseases that cannot be prevented or treated through vaccine or medication. According to World Health Organization (WHO), the only way to combat dengue, at present, is to control the mosquitoes that spread the disease.

The increasing burden of dengue, and the relative failure of traditional mosquito control programs, highlight the need to develop new control methods. With this in mind, researchers in Brazil have published the results of a trial involving genetically engineered mosquitoes in the journal, “PLOS Neglected Tropical Diseases.” The intention was to reduce the species’ ability to transmit dengue fever through population suppression.

 

“This invasive mosquito and the diseases it carries is a real challenge,” said Professor Margareth Capurro of São Paulo University. “Aedes aegypti is developing resistance to insecticides, and even when we remove breeding sites, they continue to reproduce and transmit diseases because they live in areas that are difficult to treat. This is why we need new tools. We knew that the Oxitec mosquito was a promising tool, so we wanted to independently evaluate its effectiveness here in Brazil.”

 

How “Friendly” Mosquitoes Helped Dropped Disease Spread by up to 95%

The study, which took place in the Itaberaba neighborhood of Juazeiro city in Bahia State, was led by the University of São Paulo and Moscamed, a company that specializes in environmentally friendly pest control. The treatment area included a population of approximately 1,800 people.

 

A company called Oxitec has developed mosquitoes, commonly known as “Friendly Aedes aegypti” mosquitoes. This study spanned over a year and the results of the trial showed that the numbers of the mosquito (Aedes aegypti) that spreads dengue fever, yellow fever, chikungunya, and zika virus were reduced by 95%.

 

“The fact that the number of Aedes aegypti adults were reduced by 95% in the treatment area confirms that the Oxitec mosquito does what it is supposed to, and that is to get rid of mosquitoes,” said Dr. Andrew McKemey, head of field operations at Oxitec. “According to published mathematical models reviewed and recommended by the World Health Organization (WHO) working group on dengue, it would also reduce the number of biting mosquitoes below the disease transmission threshold. The next step is to scale up to even larger studies and run mosquito control projects on an operational basis.”

 

Prior to this study, a self-limiting strain of Aedes aegypti, OX513A, had already reached the stage of field evaluation. Sustained releases of males led to 80% suppression of a targeted, wild Aedes aegypti population in the Cayman Islands, in 2010.

 

This method of control is species-specific. The Oxitec male mosquitoes are released to mate with the pest females, and their offspring die before they can transmit the disease or reproduce because of a self-limiting gene. The mosquitoes also carry a color marker for monitoring, and the insects and their genes do not persist in the environment.

 

Conclusion

The mating competitiveness of the released males was similar to that estimated in the Cayman trials, indicating that environmental and target-strain differences had little impact on the mating success of the OX513A males. This led researchers to believe that the release of these mosquitoes could be the way forward for pest control in a virtually unlimited array of threatened locals.

 

The researchers concluded that sustained release of OX513A males may be an effective and widely useful method for suppression of the Aedes aegypti mosquito. The observed level of suppression would likely be sufficient to prevent disease epidemics in the locality tested and other areas with similar or lower transmission.

*Image Courtesy of Wikimedia Commons