Thursday, 31 May 2012

Controlling Dengue Fever with Genetically Modified Mosquitoes


Controlling Dengue Fever with Genetically Modified Mosquitoes

Every year more than 50 million people are infected with Dengue fever, a viral disease that causes fever and acute joint pain. Of these millions who become infected, 25 000 die from the disease annually. Mosquitoes in tropical and subtropical parts of Africa, Asia, South America, the Caribbean and Australia spread dengue fever, which means that 40% of the world’s population, a staggering 2.5 billion people, are at risk(Oxitec Limited, n.d.).

There is no known cure for Dengue fever, nor any vaccine, therefore the effective control of this disease is done through control of the mosquitoes that carry it. Common methods for dealing with mosquito populations include the removal of egg-laying habitats and using insecticides, however, recent research by the Cayman Islands Government in conjunction with British bioengineering company Oxitec has unearthed a new potential mosquito population management strategy. This development involves cultivating a strain of the Aedes aegypti mosquito with an altered genome (Bredow, 2012). Modified mosquitoes are bred and released into wild populations where they interbreed. The progeny inherit the altered genes and these genes inhibit the development of the larvae to the point where they die.

In a normal mosquito cell, a repressor chemical acts to prevent most of a specific gene that produces a protein named tTA from binding to a corresponding binding domain called tetO. Conversely, the genetic modification in the mosquitoes removes the repressor and allows the tTA to bind to the tetO binding domain. This binding causes more tTA proteins to be produced and to bind with tetO to create a cycle of continuous production of the tTA protein. This protein is harmful and damaging to the cells of the mosquitoes and henceforth causes the larvae to die(Oxitec Limited). The following image shows the differences in the tTA gene cycle for repressed and unrepressed binding:

Figure 1: tTA protein production cycle (Oxitec Ltd, n.d.)


When none of the larvae survive to adulthood, they cannot replace the previous generation and the entire population is reduced as a result. A trial was done in the Cayman Islands, where 3.3 million genetically modified (GM) mosquitoes were released over a period of six months in batches of 50,000 animals. By the end of the trial period the number of mosquito eggs being laid was down to 10% of its original volume (Coghlan, 2010). This trial was regarded as a success, and the techniques for controlling mosquitoes in this way are being further explored before widespread use of the technology.

Whilst both males and females with modified genes are needed for the breeding of the genetically modified (GM) insects, only male mosquitoes are released. This is done to prevent any genetically altered mosquito biting a human so that there is no possibility that any of the mosquito’s modified genes could be transferred into humans. Also, because this genetic modification of the mosquitoes causes the offspring to die when still in the larval stage, they do not reach maturity before the genetically altered cells fail thereby preventing them from further reproducing. These considerations are significant for scientists who are using GM organisms because of the ongoing ethical and safety concerns with this technology.

Bibliography

1.         Bredow, R. v. (2012, January 2). Genetically Modified Pests - The Controversial Release of Suicide Mosquitoes. Retrieved March 17, 2012, from Spiegel Online International: http://www.spiegel.de/international/world/0,1518,812283,00.html

2.     Coghlan, A. (2010, November 10). Genetically altered mosquitoes thwart dengue spreaders. Retrieved March 16, 2012, from New Scientist: http://www.newscientist.com/article/dn19717-genetically-altered-mosquitoes-thwart-dengue-spreaders.html

3.         Department of Health - Communicable Disease Prevention and Control Unit. (2012). Dengue Fever Fact Sheet. Retrieved March 17, 2012, from Better Health Channel: http://www.betterhealth.vic.gov.au/bhcv2/bhcpdf.nsf/ByPDF/Dengue_fever/$File/Dengue_fever.pdf

4.          Oxitec Limited. (n.d.). Dengue Fever Information Centre. Retrieved March 17, 2012, from Oxitec: http://www.oxitec.com/our-targets/dengue-fever-and-chikungunya/

5.   Oxitec Limited. (n.d.). Molecular biology. Retrieved March 17, 2012, from Oxitec: http://www.oxitec.com/our-research/molecular-biology/

6.      World Health Organisation. (2012, January). Dengue and Severe Dengue. Retrieved March 17, 2012, from World Health Organisation: http://www.who.int/mediacentre/factsheets/fs117/en/#content





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