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TellUs: Genetically Modified Mosquitos

The Amazon’s role in disease regulation

The Amazon basin encompasses some of the world’s most harmful and serious diseases within its grasps, including: malaria, dengue and leishmaniasis just to name several. Every year there are approximately 400,000-600,000 cases of malaria reported within the Amazon. This is a pretty staggering figure!

Let us start with how the rainforests provide a valuable ecosystem service. Rainforests reduce the risk of infectious disease by controlling the populations of disease vectors (mosquitoes and rats etc), by sustaining healthy populations of pest predators (bats and snakes etc). Now this is all well and good until curveballs are thrown into the occasion, like deforestation. I’m going to put this into perspective and give an example. The loss of forest cover has been shown to have an effect on the abundance and behaviour of Anopheles darlingi, a malaria-carrying mosquito. Also deforestation reduces predators, an example being removing tree roosting sites for bats and because mosquitos cannot fly high, removing vegetation clears a path for them. This is backed up again by a study stating that deforested areas have up to a 300-fold increased risk of malaria infection compared to protected forests. 

It’s important to note that although we are focusing on population control in particular, the Amazon also helps to limit waterborne diseases and forest fires, resulting in respiratory diseases. Deforestation has again been linked to an increase in both these diseases. 

Case study

Between October 2015 and January 2016 in Brazil there were nearly 4000 cases of microcephaly in newborn babies. This is a disease where the brain and skull don’t develop properly in the womb and leads to extreme physical and mental disabilities. Before then there were just 150 cases reported yearly. The culprit appeared to be a mosquito-borne virus called Zika (other factors were also at play). The Zika virus was first detected in 1947 in the Zika Forest of Uganda.

The Zika virus is spread by the Aedes mosquito. Aedes is already responsible for infecting millions across the world with yellow fever, dengue and chikungunya. Dengue alone makes 50 to 100 million people ill every single year. Increasing urbanisation and and poverty creates a fertile environment for the mosquito by increasing breeding sites. The Aedes larva has been shown to thrive in discarded plastic bottles filled with stagnant rainwater. 

One solution from 2015, to address the Aedes mosquito outcry was developed by a biotech company. They genetically modified the male Aedes mosquito to produce sterile offspring. The GM mosquito is then let free to mate with wild females. This caused a sudden drop in Aedes numbers. However they’re notorious for bouncing back, so for this solution to be successful it would have to be happening regularly. 


Drawing of the Mesocyclops
However an alternative solution of biological control showed to be highly successful, firstly in communities in Vietnam. The approach promotes the spread of the natural predator of the Aedes larva. The Mesocyclops is a crustacean that devours the mosquito. As the female Aedes lay their eggs in containers of water, it proved successful to spread the crustacean from container to container. This can be done by volunteers within the community. Sustaining a healthy population of Mesocyclops allowed for the almost total elimination of the mosquito, with no cases of dengue or other diseases associated with the Aedes two years after the community involvement began. What’s amazing is that every community has its own native Mesocyclops species!

Therefore the moral of the experiment here is how nature can and will balance out on its own, if we do not interrupt its natural state. However if we do, nature is very resilient and can bounce back extremely well. Also it demonstrates the need to conserve all biodiversity, not just the cuddly and cute!

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Check out my previous blog: https://www.tellusabouttheenvironment.com/2019/09/tellus-no-amazon-without-sahara-desert.html
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