- by Alison Booth

Science fights back in the war against dengue

With our climate warming, Aedes mosquitoes are spreading to new locations across the globe. The risk of dengue and other vector-borne diseases is rising. To fight back, scientist across the world are coming up with novel strategies for combatting the mosquito and the disease. Let’s take a look at a few of them, starting with the diet pills that aim to stop mosquitoes biting.

 

Diet pills could be the key to stopping Aedes aegypti mosquitoes from biting us, according to researchers at Rockefeller University in New York City. As you may be aware, only female Aedes mosquitoes bite. Understanding exactly why they nibble us led the researcher to this novel ‘diet pill’ approach to stopping the spread of dengue

Like other female mosquitoes, female Aedes bite us because they need the protein in our blood to produce their eggs. They only take what they need. Once they’ve had their fill, they won’t bite again until they’ve produced their eggs. But when they extract the small amounts of our blood that they require, they inject us with some of their saliva. Mosquitoes infected with dengue, pass the virus on.

Neurobiologist Leslie Vosshall came up with the wild idea that if we could trick mosquitoes into believing they had already had their fill of our blood, their desire to bite us would diminish. In her research, Vosshall fed some mosquitoes a solution of human appetite-suppressants and compared their behaviour to a control group. She found the mosquitoes given the ‘diet’ solution were far less inclined to seek out human scent than the control group.

Although it is early days in this research, initial findings are promising. If the method is ever used to suppress the appetites in the wild, it can’t rely on a drug intended for humans. An alternative would need to be developed that only affects mosquitoes to avoid any unintended side effects. If developed on a larger scale, it could potentially reduce how often mosquitoes bite and thus the spread of mosquito-borne diseases such as dengue.

 

Novel mosquito repellents

 

For our second example, researchers at the University of Wisconsin–Madison investigating new ways bacteria could be used to kill mosquitoes accidentally uncovered a compound that works as a mosquito repellent. They have taken that compound, which is obtained by purifying extracts of the microbes, and produced a mosquito repellent that is effective against a number of mosquito species, including Aedes aegypti. The repellent is still effective when used in lower doses than other repellents, making it potentially more cost-efficient. However, there is still a great deal more research to do in this area, and researchers haven’t established how safe these mosquito-repelling bacterial compounds are for humans.

It’s not only bacteria that scientists have resorted to in their quest to deter mosquitoes. Lavender is a plant loved by many for its scent and medical properties. One of its other properties is less well-known: it’s also a mosquito repellent. In a bid to discourage Aedes mosquitos, leaders in the Marunda area of North Jakarta have turned to lavender for help, planting 2,000 of the purple flowering shrubs. The Marunda community has already formulated a second plan for eliminating the mosquitoes: introducing betta fish to their ponds to feast on mosquito larvae – a technique similar to the use of guppy fish we’ve written about.

A number of natural mosquito repellents are also becoming commercially available. Cinnamon oil, for example, has been shown to kill mosquito larvae. Researchers in Taiwan have previously suggested that the product could be a better-smelling alternative to established chemical pesticides. A Sri Lanka-based company, Cinnamon Hill, is marketing an insect repellent spray made with cinnamon leaf and bark oil, while lemon eucalyptus oil, lavender and neem oil are also commonly used.

 

Mosquito birth control

 

Our fourth and fifth approaches look at ways of reducing Aedes populations using new forms of mosquito birth control. Research carried out at the University of Arizona and San Jose State University manipulated a specific gene code (a set of rules by which information encoded in genetic material is translated into proteins) that they believe plays a vital role in the formation of mosquito eggs. During their research, the team bred some female mosquitoes with a disrupted gene code for the EOF1 protein. The results showed that the majority of eggs produced from these females were unviable. Most significantly, the EOF1 protein is unique to mosquitoes and, therefore, any insecticide produced to target it would be less likely to be harmful to other life forms.

University of Florida researchers are also looking into reducing the mosquito population through a form of birth control, this time exploring a technique known as ‘satyrization’. Here a male mosquito from one species mates with a female from a different species. When satyrization occurs, the female is unable to produce the hybrid offspring. Not only is her egg not fertilised, but her reproductive system becomes infertile.

While researchers hoped cross-species mating between Aedes aegypti and Aedes albopictus in regions where the two types of mosquitoes co-exist might reduce the mosquito populations, their studies revealed that mosquitoes learn to avoid cross-species mating within a few generations. They also found that when the species where separated, the mosquitoes lost all they had learnt within six generations. There is still more research to be done. New insights could help us predict how Aedes populations interact as they invade new regions.

 

Fighting dengue infection

 

Looking beyond mosquito birth control to treating dengue infection, an article published by Lahore University of Management Sciences suggests a common natural spice could offer a breakthrough in dengue treatment. Cloves contain eugeniin, a chemical thought to have the ability to halt the production of dengue viral components. Eugeniin could potentially prevent the creation of a mature dengue virus, halting its ability to replicate.

With so many potential new tools emerging in the fight against dengue, we’d love to hear about your own novel research or techniques in your own battle against the disease and its Aedes vector.