{"id":4653,"date":"2016-04-29T15:27:08","date_gmt":"2016-04-29T15:27:08","guid":{"rendered":"http:\/\/www.lifeandnews.com\/articles\/?p=4653"},"modified":"2016-04-29T15:27:08","modified_gmt":"2016-04-29T15:27:08","slug":"to-fight-zika-lets-genetically-modify-mosquitoes-the-old-fashioned-way","status":"publish","type":"post","link":"https:\/\/www.lifeandnews.com\/articles\/to-fight-zika-lets-genetically-modify-mosquitoes-the-old-fashioned-way\/","title":{"rendered":"To fight Zika, let’s genetically modify mosquitoes \u2013 the old-fashioned way"},"content":{"rendered":"

Jeffrey Powell<\/a>, Yale University<\/a><\/em><\/span><\/p>\n

The near panic caused by the rapid spread<\/a> of the Zika virus<\/a> has brought new urgency to the question of how best to control mosquitoes that transmit human diseases. Aedes aegypti<\/em> mosquitoes bite people across the globe, spreading three viral diseases: dengue<\/a>, chikungunya<\/a> and Zika<\/a>. There are no proven effective vaccines or specific medications to treat patients after contracting these viruses.<\/p>\n

Mosquito control<\/a> is the only way, at present, to limit them. But that\u2019s no easy task. Classical methods of control such as insecticides are falling out of favor<\/a> \u2013 they can have adverse environmental effects as well as increase insecticide resistance<\/a> in remaining mosquito populations. New mosquito control methods are needed<\/a> \u2013 now.<\/p>\n

The time is ripe, therefore, to explore a long-held dream of vector biologists<\/a>, including me: to use genetics to stop or limit the spread of mosquito-borne diseases. While gene editing technologies have advanced dramatically in the last few decades, it is my belief that we\u2019ve overlooked older, tried and true methods that could work just as well on these insects. We can accomplish the goal of producing mosquitoes incapable of transmitting human pathogens using the same kinds of selective breeding techniques people have been using for centuries on other animals and plants.<\/p>\n

\n \"\"<\/a>
\n Technicians from Oxitec inspect genetically modified Aedes aegypti mosquitoes in Campinas, Brazil.<\/span>
\n Paulo Whitaker\/Reuters<\/span><\/span>
\n <\/figcaption><\/figure>\n

Techniques on the table<\/h2>\n

One classic strategy for reducing insect populations has been to flood populations with sterile males<\/a> \u2013 usually produced using irradiation. When females in the target population mate with these males, they produce no viable offspring \u2013 hopefully crashing population numbers.<\/p>\n

The modern twist on this method has been to generate transgenic males that carry a dominant lethal gene that essentially makes them sterile; offspring sired by these males die late in the larval stage, eliminating future generations. This method has been promulgated by the biotech company Oxitec<\/a> and is currently used in Brazil<\/a>.<\/p>\n

Rather than just killing mosquitoes, a more effective and lasting strategy would be to genetically change them so they can no longer transmit a disease-causing microbe.<\/p>\n

The powerful new CRISPR gene editing technique could be used to make transgenes (genetic material from another species) take over a wild population. This method works well in mosquitoes<\/a> and is potentially a way to \u201cdrive\u201d transgenes into populations<\/a>. CRISPR could help quickly spread a gene that confers resistance to transmission of a virus \u2013 what scientists call refractoriness.<\/p>\n

But CRISPR has been controversial, especially as applied to human beings, because the transgenes it inserts into an individual can be passed on to its offspring. No doubt using CRISPR to create and release genetically modified mosquitoes into nature would stir up controversy. The U.S. Director of National Intelligence, James Clapper, has gone so far as to dub CRISPR a potential weapon of mass destruction<\/a>.<\/p>\n

But are transgenic technologies necessary to genetically modify mosquito populations?<\/p>\n

\n \"\"<\/a>
\n Examples of successful artificial selection of various traits through the years. In the center is a cartoon of the \u2018block\u2019 scientists would like to select for in mosquitoes so they can\u2019t pass on the virus.<\/span>
\n Jeff Powell<\/span>, Author provided<\/span><\/span>
\n <\/figcaption><\/figure>\n

Selective breeding the old-fashioned way<\/h2>\n

Genetic modification of populations has been going on for centuries with great success. This has occurred for almost all commercially useful plants and animals that people use for food or other products, including cotton and wool. Selective breeding can produce immense changes in populations based on naturally occurring variation within the species.<\/p>\n

Artificial selection using this natural variation has proven effective over and over again, especially in the agricultural world. By choosing parents with desirable traits (chickens with increased egg production, sheep with softer wool) for several consecutive generations, a \u201ctrue breeding\u201d strain can be produced that will always have the desired traits. These may look very different from the ancestor \u2013 think of all the breeds of dogs derived from an ancestor wolf.<\/p>\n

To date, only limited work of this sort has been done on mosquitoes<\/a>. But it does show that it\u2019s possible to select for mosquitoes with reduced ability to transmit human pathogens. So rather than introducing transgenes from other species, why not use the genetic variation naturally present in mosquito populations?<\/p>\n

Deriving strains of mosquitoes through artificial selection has several advantages over transgenic approaches.<\/p>\n