Scitech | Fighting mosquitoes with mosquitoes

An Integrative Approach to Mosquito Control

The pungent stench of mosquito coils and repellent sprays, and the claustrophobic experience of sleeping under nets are familiar to those who venture out from underneath the protection of the well-established public health infrastructure and temperate climate available in select countries. However, half of the world’s population – approximately 3.2 billion people – inhabit regions of the globe where the endemic mosquito population could serve as a vector (disease carrier) for the transmission of several parasitic and viral human pathogens. The most common of these mosquito-borne pathogens include malaria, Chikungunya virus, Dengue virus, West Nile virus, Yellow fever virus, and the Zika virus. These mosquito-borne illnesses claim about one million lives every year, with young children being disproportionately affected.

Basic vector control strategies, which rely on targeting breeding grounds, controlling larval populations, and using insecticides have been crucial in reducing the transmission of mosquito-borne illnesses. However, a truly effective vector control strategy would require basic vector control techniques to be implemented in conjunction with more sophisticated approaches, such as the use of genetically-modified mosquitoes. This integrative and modern approach will be the next step in successfully reducing the mortality (death within a population) and morbidity (sickness in an area) caused by mosquito-borne illnesses. This integrative strategy would be of particular importance in dealing with the current Zika virus pandemic; which has gained notoriety due to its rapid geographic expansion and its association with severe neurological complications such as Guillain Barré syndrome and fetal microcephaly.

Within the past decade, the Zika virus was brought to the forefront of global public health consciousness, with progressive epidemics in Micronesia (2007), French Polynesia (2013), and Latin America (currently ongoing). The virus is transmitted by the Aedes aegypti and Aedes albopictus species of mosquitoes, and over the last couple years has caused localized epidemics in Argentina, Colombia, Brazil, El Salvador, Guatemala, Paraguay, and Venezuela, as well as recent outbreaks in the southern United States and Singapore.

The controversial debate over the use of genetically modified mosquitoes to curb the spread of mosquito-borne illnesses has become salient in the context of the Zika pandemic. This strategy involves the introduction of a dominant gene in the mosquito’s genome, which doesn’t affect the normal development of the larvae, but results in the death of the mosquito before it reaches adulthood, if outside of laboratory conditions. As male mosquitoes are not directly responsible for disease transmission, genetically-modified specimen are then periodically released into the environment, where they mate with wild female mosquitoes to produce developmentally arrested larvae. As such, the transgenic males are able to competitively inhibit wild males from producing viable larvae. This ultimately results in a rapid decline in the local mosquito population, as well as a decline in the transmission of the diseases transmitted by mosquitoes. Field studies conducted in the Cayman Islands, Brazil, Panama, and Malaysia were resoundingly successful in reducing the local A. aegypti mosquito population by 80 to 95 per cent.

Despite successful field studies, concerns about the possibility of environmental damage and a general public distrust of genetically-modified organisms (GMOs)are some of the current obstacles to widespread implementation of a transgenic mosquito strategy in Zika virus affected-areas. While some of these concerns arise from a legitimate fear of upsetting delicate ecosystems, they are often exacerbated by misinformation; it is the responsibility of the scientific community to accurately communicate the benefits of this strategy to the general public while directly challenging outlets of misinformation.

The concern about the potential ecological impact of introducing genetically modified mosquitoes into the environment is valid and must be continuously addressed. Releasing a new species into the environment could potentially upset delicate ecosystems by inadvertently affecting other species that are ecologically-dependent on mosquitoes. To date, however, no field studies conducted to date have found any significant downstream ecological effects. It is also important to note that the A. aegypti mosquito is usually an invasive species and is unlikely to be central to environmental stability. The potential for any serious ecological impact is also limited by the fact that the transgenic mosquitoes contain lethal genes that directly affect their ability to successfully reproduce. This environmental concern, however, is not to be dismissed lightly, and future field studies must continue to diligently monitor the regional ecological impact of releasing transgenic mosquitoes. This will be crucial in informing any potential large scale implementation of this strategy in other regions where A. aegypti is a public health concern. If any ecological effects are reported in future studies, then further release of transgenic mosquitoes can be halted or adjusted accordingly.

The recent outbreak of theZika virus in southern Florida has prompted public health officials to seriously consider using genetically modified mosquitos as a vector control method. In a nonbinding referendum, 58 per cent of voters in Monroe County, Florida favoured the release of transgenic mosquitoes, however 65 per cent of voters in the neighbourhood of Key Haven (Monroe County) – where the trial is to take place – were opposed to the test. This is despite the fact that the U.S. Food and Drug Administration reviewed the study proposal and concluded that “the proposed field trial will not have significant impacts on the environment.” While we wait for the decision of the Florida Keys Mosquito Control Board on whether or not they will use transgenic mosquitoes, it is important to reiterate the need to better engage the public regarding the benefits of GMOs, while challenging misinformation and those who propagate it.

Opposition to transgenic mosquitoes – or any other GMO – often stems from a general distrust of corporate and government interests and dogmatic adherence to the view that humans should not alter the environment. Although it is reasonable to demand transparency from government bodies and biotechnology companies regarding the potential risks of specific technologies, there is also a responsibility to accept results from evidence-based scientific studies and allow future research to be conducted at a reasonable pace. The argument that humans should not alter their environment – even if it is in a responsible and controlled manner – is unjustified; genetic modification strategies like selective breeding have played a vital role in the development of complex societies. This is not to say that calling for responsible environmental stewardship or a comprehensive risk-assessment of new technologies is not warranted.

With approximately a million deaths attributed to mosquito-borne illnesses every year, it is a humanitarian imperative to have an effective and scientifically-informed vector control strategy. Influential environmental organizations – usually situated in developed countries – that spread misinformation about genetic modification to regions of the world that are facing an immediate public health crisis are misusing their power. Responsible environmental advocacy must prioritize human well-being.

While the use of fogging machines, insecticides, and mosquito nets have been moderately successful in controlling mosquito populations, more sophisticated approaches like the use of transgenic mosquitoes must also be cautiously implemented. The success of recent field studies as well as the immediate threat of emerging pathogens, like the Zika virus, stresses the importance integrating transgenic mosquitoes into any serious global vector control strategy. With climate change increasing the geographic range and the invasive potential of mosquitoes – and their associated human pathogens – it is crucial to properly communicate the benefits of GMOs and dispel public misconceptions.

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