Summer has just begun, and we all know what that means: hot weather, shorts, and mosquitoes! However, despite being annoying pests in the summertime, mosquitoes play a vital role in nature. Many small aquatic species and insects rely on mosquito larvae as a source of food; if mosquitoes were to be eradicated from nature, these small fish and insects would surely dwindle in numbers, which, in turn, would reduce the population of many animals that feed on them (e.g., birds of prey and game fish). It should be noted that mosquitoes pose a greater threat than their annoying bites, many mosquito species are known vectors (organisms that transfer infectious diseases from animals to humans or between humans) of many diseases such as malaria, dengue fever, Zika virus and West Nile virus, among many others. Fortunately, those living in Canada and the US do not have to worry too much about contracting these diseases due to their country’s optimal living conditions and the fact that they do not live with mosquitoes year-round due to the cold winter weather. Mosquitoes love wet-land, tropical and sub-tropical environments and thus, tend to multiply faster there and are found in greater numbers in those areas for longer periods of time. Unfortunately, because many countries in these climates have sub-optimal living conditions, those living in these areas are at greater risk of mosquito-borne diseases. Vaccines and anti-viral medications have yet to be developed for many of these mosquito-borne diseases, contributing to the cycle of infection and post-infection treatment or death for a large population of individuals in these areas.
In 2016, a company called Oxitec began creating genetically modified mosquitoes to reduce the incidence of mosquito-borne diseases, specifically, those carried by the mosquito species Aedes aegypti (e.g., malaria, dengue fever, Zika virus and yellow fever). Their research mainly revolves around male mosquitoes, even though they feed on flower nectar and females are the ones that bite humans and animals. In the lab, male Aedes aegypti are injected with a “self-limiting gene” which yields a protein called tetracycline-controlled transactivator (tTAV). tTAV then binds to a specific location on the self-limiting gene called the “tet-O” site to trigger a positive feedback loop which allows the self-limiting gene to create more tTAV. Once tTAV levels have reached a certain point in the bodies of the mosquitoes, it obstructs the mosquitoes’ protein production mechanisms and prevents the production of viral gene products needed for the mosquitoes to survive and they begin to die. When male genetically modified mosquitoes mate with their female counterparts, their offspring inherit this self-limiting gene and die in their larval life stage, before they can reproduce.
These genetically modified are not completely doomed. If their diet contains enough tetracycline, an antibiotic that inhibits tTAV, they will survive. In Oxitec labs, mosquitoes are fed with enough tetracycline to keep them alive while being reared in the lab, before they are released into nature. Fortunately, tetracycline does not exist in sufficient levels in nature, so the genetically modified mosquitoes do not survive.
Oxitec takes extra measures to ensure that their genetically modified mosquitoes are safe for other animal species that interact with them and the natural environment. The genetic modifications made are species-specific; their mosquitoes only reproduce with other members of their species and therefore would not result in the death of other, beneficial insects. Another additional environmental benefit of Oxitec mosquitoes is that they can and have successfully reduced the use of pesticides, as seen in areas, such as Brazil and Panama, where Oxitec mosquitoes projects have been active. Their methods of genetic modification are also environmentally responsible and non-persistent, meaning that their insects cannot become established in the environment. According to a 2016 report, a region in São Paulo, Brazil has seen a 91% decrease in cases of dengue fever in the population. It is hoped that instances of other mosquito-borne diseases continue to decrease as Oxitec mosquitoes become more prevalent.
“Cases of Dengue Drop 91 Percent Due to Genetically Modified Mosquitoes.” Entomology Today, 29 Dec. 2017, entomologytoday.org/2016/07/14/cases-of-dengue-drop-91-due-to-genetically-modified-mosquitoes/.
“Our Technology.” Oxitec, www.oxitec.com/our-technology/.
World Health Organization. (2014). A global brief on vector-borne diseases. World Health Organization. http://www.who.int/iris/handle/10665/111008