Researchers, using CRISPR/Cas9, seek to genetically modify mosquitoes to dampen the spread of arboviruses in human populations.
Mosquitoes are a group of approximately 3500 species of small arthropodal insects. They have slender, segmented bodies, a pair of wings, three pairs of long hair-like legs, feathery antennae and elongated mouthparts. Mosquitoes, especially females, are an important factor in public health. Females possess a proboscis which can pierce human skin in order to extract blood. Female mosquitoes require the protein and iron contained in blood in order to produce eggs. Not all mosquito varieties feed on human blood, but a significant number do. Although, the loss of blood from its victim is rarely of consequence to them, the saliva of mosquitoes that comes in contact with its victim can cause a rash and itching. Significantly, mosquitoes also serve as a vector by injecting or ingesting (or both) disease-causing organisms.
Mosquitoes aid in the transmission of arboviruses. Arbovirus is a name given to viruses that are transmitted by arthropods. In humans, the virus begins to display symptoms 3-15 days after exposure and may last an equal amount of time. Common symptoms include fever, headache, malaise, encephalitis and hemorrhagic fever. Common diseases include chikungunya, dengue fever, malaria, West Nile virus, yellow fever, Zika virus and filariasis, amongst a host of others. Mosquitoes are responsible for the most number of human fatalities than any other animal; over 1 million humans die a year as a result of mosquito-related diseases. Female mosquitoes use an array of sensory information to find their victims. They can detect exhaled carbon dioxide, body odour, heat and moisture.
Researchers around the world have long sought methods by which the threat of mortality from mosquitoes can be negated. Recently, research published in the Current Biology journal showed that the acidic nature of human sweat plays a vital role in attracting the insect. Researchers sought to genetically pinpoint how mosquitoes detect their victims. The scientists identified a gene named Ir8a, expressed in the antenna of a mosquito, that allows them to smell lactic acid which is present in human sweat. Using CRISPR/Cas9 gene-editing technology, the researchers were able to prevent the manifestation of the gene, making the female Aedes aegypti mosquitoes less interested in humans. Researchers say that the genetic alteration is much less likely to spread mosquito-borne illnesses.
The Aedes aegypti mosquito that the researchers genetically modified is one of the most prevalent mosquito varieties in the world. It lives alongside over half of the world’s population, especially in the tropical, subtropical and temperate regions. The diseases it’s spread kills hundreds of thousands of people a year. Negating the risk posed by the variety would go a long way in ensuring public health. Researchers say that the genetically modified mosquitoes can be released into the wild to combat the spread of arboviruses. However, the practice has garnered some controversy over the potential environmental ramifications such an action might bring.
Researchers have not only focused their efforts on genetic modification, arguing that the study provided them valuable insight into how mosquitoes hunt and feed. This would, in turn, increase the “efficacy of current repellents like DEET or picaridin.” Alternatively, the researchers have claimed that they could employ the discovery to overstimulate the detection mechanism of mosquitoes in order to cajole them away from humans and into traps.
The research comes at a momentous moment for mosquito-borne viruses. As human populations increase, there is a number of hosts that the mosquitoes can source their vital blood resources from. Simultaneously, the size of the human population increases the likelihood of stagnant water that mosquitoes require to lay their larvae in. Particularly, the effects of climate change may help make currently inhospitable parts of the world ideal for mosquito populations, aiding the spread of mosquito-borne arboviruses. In February of 2019, the World Health Organisation announced that there was perceived resistance to insecticides by mosquitoes that could lead to an increase in malaria cases. Conditions seem ripe for an explosion in the mosquito population.
Our assessment is that given the current environmental conditions, new and innovative insect control methods will become vital in the fight against man’s deadliest animal; the mosquito. We believe that this use of CRISPR/Cas9 is essential in understanding the tool better, while still contributing to making life safe on earth.
Image courtesy: https://upload.wikimedia.org/wikipedia/commons/7/7e/Anopheles_stephensi.jpeg, Jim Gathany [Public domain]
Map courtesy: https://upload.wikimedia.org/wikipedia/commons/3/3f/Global_Aedes_aegypti_distribution_%28e08347%29.png, Moritz UG Kraemer, Marianne E Sinka, Kirsten A Duda, Adrian QN Mylne, Freya M Shearer, Christopher M Barker, Chester G Moore, Roberta G Carvalho, Giovanini E Coelho, Wim Van Bortel, Guy Hendrickx, Francis Schaffner, Iqbal RF Elyazar, Hwa-Jen Teng, Oliver J Brady, Jane P Messina, David M Pigott, Thomas W Scott, David L Smith, GR William Wint, Nick Golding, Simon I Hay [CC0]