Many infectious disease agents are transmitted to humans or animals by blood-feeding insects or ticks, termed disease vectors. Vector-borne diseases pose an enormous public health burden, causing an estimated 700,000 deaths per year worldwide. Mosquitoes are the most important vectors of human disease, transmitting many different parasitic and viral pathogens including those that cause malaria, filariasis, dengue, chikungunya, Zika, and yellow fever.

For more information:
https://www.who.int/news-room/fact-sheets/detail/vector-borne-diseases

Today, control of vector-borne diseases is largely accomplished using drugs to prevent or treat human infection by the disease-causing agent (pathogen) and pesticides to prevent or reduce the vector populations thereby decreasing their transmission of the pathogen. However, pathogens develop resistance to widely used drugs, and vectors develop resistance to frequently used pesticides. Moreover, effective drugs are not available for some pathogens, such as arboviruses. Vaccines are available for some but not all vector-borne diseases. Environmental management, which aims to eliminate potential breeding sites of disease-carrying vectors, also is being used. However, the utility of this measure is limited by the difficulty in finding and removing all possible breeding sites. This situation creates an urgent need to look for new and alternative control measures.

For more information:

https://www.who.int/westernpacific/activities/integrating-vector-management
https://apps.who.int/iris/bitstream/handle/10665/272533/9789241514057-eng.pdf, https://apps.who.int/iris/handle/10665/204588

Mosquitoes can transmit disease causing agents (pathogens) through their bite. Female mosquitoes require nutrients found in blood to support the development of their eggs. Therefore, only female mosquitoes bite humans or other animals to obtain that blood, while male mosquitoes feed exclusively on plants. If the human or animal the female mosquito bites is infected with a suitable level of a pathogen capable of being transmitted by mosquitoes, the female mosquito can pick the pathogen up when she takes a blood meal. She may then be able to pass that pathogen to the next human or animal she bites.

Some pathogens cannot be transmitted by mosquitoes in this way. To be transmitted to the next person, the pathogen must survive the mosquitoes’ digestive system, ideally to multiply and make its way back into the mosquitoes’ mouthparts. Many blood-borne pathogens, like HIV and hepatitis viruses, have not been found to survive in mosquitoes. Moreover, the pathogen and the mosquito must be compatible – only certain pathogens can survive and multiply in certain mosquito species. For example, malaria parasites only can be transmitted by Anopheles mosquitoes. Finally, the pathogen also must be compatible with the human or animal host. Some animal pathogens cannot live in humans, and vice versa. For example, certain malaria parasites that cause disease in birds cannot infect humans.

Yes, several biological control approaches are being taken against mosquitoes.

• Fish: Among the more conventional biocontrol approaches, fish such as those in the genus Gambusia (aka “mosquitofish”) have been employed for controlling mosquito breeding in water bodies, such as rice cultivation areas, for decades.
• Bacteria: Some isolates of the bacteria Bacillus thuringiensis and Bacillus sphaericus are widely used to control mosquitoes and are sold for use by gardeners and property owners as an alternative to chemical pesticides.
• Fungi: Fungi such as Beauveria bassiana and Metarhizium anisopliae are readily available biological control agents for use against mosquitoes. For example, Beauveria bassiana is an active ingredient in some of the mosquito control products of In2Care, a mosquito trap developed to protect humans against mosquitoes that transmit the Zika, chikungunya, yellow fever, and dengue viruses.
• Genetic: Genetic biocontrol approaches are also being applied to mosquitoes. Genetic biocontrol methods can be used to reduce the numbers of mosquito vectors or limit their ability to carry one or more pathogens. For example, three versions of the Sterile Insect Technique are being tested in Aedes aegypti, a mosquito responsible for transmitting dengue, yellow fever, Zika and other human pathogenic viruses. These techniques include: classical Sterile Insect Technique employing radiation-induced sterilization to reduce productive mating; Incompatible Insect Technique that exploits certain effects of the intracellular bacterium Wolbachia to prevent productive mating; genetically engineered mosquitoes which contain genes that are lethal to the next generation of mosquitoes. A different type of method, meant to have persistent effects, uses Wolbachia bacteria in a way that permanently immunizes the mosquito Aedes aegypti against infection by dengue, yellow fever, and Zika viruses.

For more information:

https://www.youtube.com/playlist?list=PLbopRNGowKJ9dtCMDZ9_LQRHyw084vgIP
https://www.iaea.org/topics/sterile-insect-technique/mosquitoes

https://www.in2care.org/
https://www.oxitec.com

https://mosquitomate.com/
https://www.worldmosquitoprogram.org/

Although conventional insecticide-based tools have been a mainstay in fighting insect disease vectors, they have limitations. Insecticide-based tools required continuing reapplication that can be costly to maintain and insecticide resistance is an ongoing problem. Insecticide-based tools historically have been less effective against some mosquito vectors, such as those of arboviral diseases, due to the difficulty of reaching their breeding sites. WHO has taken the position that new tools are urgently needed for vector-borne diseases.

For more information:

https://www.who.int/news-room/fact-sheets/detail/malaria
https://www.who.int/teams/global-malaria-programme/reports/world-malaria-report-2021
https://www.who.int/publications/i/item/9789240015791
https://www.who.int/news-room/fact-sheets/detail/dengue-and-severe-dengue
https://www.who.int/news/item/14-10-2020-who-takes-a-position-on-genetically-modified-mosquitoes

Genetic biocontrol can be applied to other disease vectors besides mosquitoes. For example, Sterile Insect Technology has been used to control the tsetse fly vector of African trypanosomiasis (sleeping sickness). Some researchers also are studying the applicability of genetic biocontrol to ticks.

Some human and animal diseases, such as Lyme disease and plague, are transmitted directly or indirectly by rodents. For these, the same types of genetic biocontrol methods proposed to reduce invasive rodents for conservation purposes might also be useful for public health.

For more information:

https://www.iaea.org/sites/default/files/20305482024.pdf
https://www.cdc.gov/rodents/index.html

Conventional control methods include drugs to prevent or treat human infection and disease, vector control tools based on chemical pesticides such as spatial application of insecticides and use of insecticide-impregnated nets, as well as environmental management efforts to decrease the habitat where vectors breed and housing improvement to reduce human exposure.

These methods are all important, but they have not been able to fully solve the public health problem posed by vector borne diseases. Conventional vector control methods can be extremely costly to maintain and insecticide resistance is a problem in the mosquitoes that transmit either malaria or common arboviral diseases. It is widely recognized that current tools likely will be insufficient to eradicate malaria. For example, the World Health Organization reports that progress against malaria has plateaued in recent years and the situation remains precarious, especially in sub-Saharan Africa. They also report that global incidence of dengue has grown dramatically, with about half the world’s population at risk from dengue and other viral diseases carried by the same mosquito species.

For more information:

https://www.who.int/news-room/fact-sheets/detail/malaria

https://www.who.int/teams/global-malaria-programme/reports/world-malaria-report-2021

https://www.who.int/news-room/fact-sheets/detail/dengue-and-severe-dengue   

Although there are major ethical as well as technical reasons not to consider using gene drive in humans, some scientists have speculated about ways that gene drive might be used to prevent a population of animals from becoming infected with pathogens that could sicken them and/or subsequently be transmitted to people. Animals can serve as a “reservoir” for some diseases, meaning that the disease-causing pathogen can live, grow and multiply in the animal. Depending on the type of pathogen, humans may be able to catch the disease either directly from the animal reservoir (such as through a bite, ingestion of infected meat, or interaction with pathogen-containing animal excrement in the environment) or indirectly via the intervention of a vector, such as a mosquito or a flea, that carries the pathogen between the animal and the human. Gene drive has been proposed as a possible way to spread a resistance trait through the target population of animals, analogous to immunizing or “vaccinating” the animals against the pathogen. This could both protect the animal and ultimately reduce the risk of human exposure to the pathogen. Examples of proposed uses include making bats resistant to coronaviruses or mice resistant to Lyme disease. However, this concept is still in a very preliminary stage of development.

For more information:

https://www.statnews.com/2021/07/01/could-editing-genomes-of-bats-prevent-future-coronavirus-pandemics-two-scientists-think-its-worth-a-try/

https://www.media.mit.edu/projects/preventing-tick-borne-disease-by-permanently-immunizing-mice/overview/