Buzzing Trouble: Mosquitoes on the Rise in Canada Amid Climate Change
Exploring Solutions with Genetically Modified Species and CRISPR Technology
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This week, we delve into the topic of mosquitoes, often regarded as the world's deadliest animal.
In today's world, climate change is revealing its unmistakable presence through various indicators. One prominent sign we are currently witnessing in Canada is the occurrence of more frequent and increasingly severe wildfire seasons. While multiple factors contribute to this situation, the combined influence of climate change and climate variability stands out as one of the most critical causes. It is important to recognize that the effects of climate change extend beyond wildfires and can have far-reaching consequences, including an increase in mosquito populations. The United Nations’ Intergovernmental Panel on Climate Change report identified mosquito-borne diseases (MBDs) as the infectious diseases that are most sensitive to climate change. This recognition underscores the significance of understanding the relationship between climate change and the prevalence of MBDs.
In this article, we will learn about the following topics:
Explore the connection between climate change and the rise of mosquitoes.
Delve into how climate change can contribute to the proliferation of mosquitoes and
Examine the cutting-edge technologies employed for mosquito control
Cover the diverse projects wherein scientists are genetically editing mosquitoes to wipe out mosquito-borne diseases.
What are mosquito-borne diseases?
Mosquitoes are small insects that feed on blood, which also allows them to ingest any viruses or parasites present in the blood. These viruses and parasites find a conducive environment within mosquitoes and can be transmitted to another individual through the mosquito's saliva when it bites. Only female mosquitoes bite humans. In this way, mosquitoes play a significant role in the spread of various diseases, including parasitic infections like Malaria and Filariasis, as well as viral illnesses such as Yellow Fever, Chikungunya, West Nile virus (WNV), Dengue fever, and Zika. These diseases, which are transmitted from mosquitoes to humans or animals, are commonly referred to as "mosquito-borne diseases" (MBDs). In simple terms, MBDs spread when mosquitoes bite infected individuals and acquire viruses. When these mosquitoes subsequently bite other people, they can transmit the virus, leading to the spread of the disease. MBDs collectively affect approximately 390 million people worldwide each year, causing considerable suffering.
More MBDs in warmer, wetter world
While it is true that MBDs are typically confined to tropical regions where the hot and humid climate favors their life cycle, the effects of climate change in Canada, such as increased ambient temperatures, changes in precipitation, decreased number of frost days and extreme weather events are expected to contribute to the increased spread of certain “foreign1” MBDs within the country. In the past two decades, there has been a notable 10% increase in “endemic2” MBDs in Canada, primarily attributed to the effects of climate change. Additionally, it is anticipated that WNV will increase in both the rural and urban areas and the other currently endemic arboviruses (i.e. EEEV and CSGV) will increase in the rural areas.
Mosquitoes lay their eggs in water, especially in slow-moving or stagnant water sources. An increase in precipitation provides more breeding sites for female mosquitoes to lay their eggs. Additionally, warmer temperatures between 22 and 27 degrees Celsius are ideal for the mosquito life cycle, as it takes less than 10 days for an egg to develop into an adult mosquito. Therefore, with more warm days, the developmental time of mosquitoes is accelerated, resulting in earlier emergence and the potential for additional generations to occur.
In addition to supporting mosquito’s survival and accelerating their development, scientists suggest that climate change can modify the physiology of mosquitoes, enhancing their ability to transmit diseases to humans. Climate change can also prolong the duration of disease transmission and impact the movement patterns of disease vectors/reservoirs/humans.
Preventive Measures to avoid mosquitoes
Mosquitoes are widespread in most parts of Canada between May and September. While they can bite at any time, they are more active during dusk and dawn. To protect yourself from these blood-sucking insects, it is advisable to cover exposed skin by wearing long pants, loose-fitting shirts with long sleeves, and using insect repellent containing DEET or Icaridin. Additionally, it is important to eliminate potential breeding grounds by removing or emptying containers that can collect water, such as buckets, flower pots, birdbaths, and discarded tires. Regularly cleaning and changing the water in pet bowls and bird baths is also recommended.
Why Eliminating MBDs challenging ?
Eliminating MBDs poses significant challenges due to various reasons. These diseases have complex transmission cycles involving mosquitoes, humans, and animal reservoirs. Mosquitoes, as primary carriers of MBDs, exhibit high adaptability and resilience, allowing them to develop resistance to insecticides and modify their breeding habits to survive in diverse conditions. Eradicating these diseases entirely may require addressing the reservoirs, which presents logistical and scientific challenges.
Furthermore, MBDs disproportionately impact communities with limited access to healthcare, sanitation, and preventive measures. This disparity is particularly prominent in parts of the world, making elimination efforts more complex. Addressing socioeconomic factors and healthcare disparities is crucial for effectively eliminating MBDs, necessitating comprehensive approaches that go beyond solely medical interventions.
What Scientists are doing to tackle MBDs
In the past, mosquito control efforts relied on insecticide sprays and larvicides, but these methods had limitations. They posed risks to human and ecosystem health, and mosquitoes quickly developed resistance, rendering the insecticides ineffective. Another approach involved introducing natural predators like fish, dragonflies, and copepods to control mosquito populations, but these methods had limited scope and potential consequences.
In recent years, scientists worldwide have been harnessing advanced Genetic Pest Management (GPM) strategies to combat mosquitoes and the diseases they transmit. Under GPM, two approaches are being used:
A. Population Replacement
In population replacement, genetically modified mosquitoes are introduced to replace the wild mosquito population with individuals that have reduced ability to transmit diseases or have other desired characteristics.
1. CRISPR-Edited Mosquitoes: that eliminate other mosquitoes
Before diving deep into CRISPR-edited mosquitoes, first let’s understand the basics of CRISPR-Cas9.
What is CRISPR ? CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats is a revolutionary gene editing tool that allows scientists to precisely modify the DNA of organisms, including mosquitoes. It consists of two main components: a Cas9 protein, which acts as a pair of "molecular scissors," and a guide RNA (gRNA), which directs the Cas9 protein to the specific target sequence in the mosquito's DNA.
In order to spread the anti-pathogen genes using this method, scientists rely on a concept known as the gene drive. Gene drives are genetic mechanisms (using CRISPR) that bias inheritance, increasing the chances of a specific gene being passed down to offspring. This approach creates a cascade effect, as the modified mosquitoes reproduce and pass on their altered genes, gradually reducing the overall population of disease-carrying mosquitoes.
Another approach focuses on manipulating the mosquitoes' ability to reproduce. By altering the genes responsible for fertility or sex determination, scientists can generate sterile male mosquitoes or ensure the birth of predominantly male offspring. This disrupts the natural reproductive cycle and reduces the number of breeding females, leading to a decline in mosquito populations over time.
The potential use of gene drives to eliminate entire populations of mosquitoes has become more realistic.
"Development of a Gene Drive System in the Malaria Mosquito, Anopheles stephensi" (Gantz et al., 2015): This study focused on developing a gene drive system in Anopheles stephensi, another important malaria vector. The researchers used CRISPR/Cas9 to introduce a gene disruption in the double sex gene, resulting in the generation of predominantly male mosquitoes. The successful implementation of the gene drive system demonstrated the potential for population modification.
"A CRISPR–Cas9 Gene Drive System Targeting Female Reproduction in the Malaria Mosquito Vector Anopheles gambiae" (Hammond et al., 2016): The researchers used CRISPR/Cas9 to create a gene drive system targeting female reproduction in Anopheles gambiae mosquitoes. By disrupting a specific gene involved in female fertility, they achieved a significant reduction in egg production, providing a potential strategy for population suppression. It is important to note that this experiment was conducted under controlled laboratory conditions.
"CRISPR-Based Gene Drive Strategies for Control of Insect Pest Populations" (Marshall & Akbari, 2018): This review article explores the applications of CRISPR-based gene drive strategies for controlling insect pest populations. It discusses various approaches, including population suppression and population modification, using examples from studies conducted on mosquitoes, fruit flies, and agricultural pests.
Field Trial of genetically modified mosquitoes were conducted by the company Oxitex in various locations, including Grand Caymans, Malaysia, Brazil, and Florida. Aedes aegypti mosquitoes were engineered with a self-limiting gene that causes the offspring to die before reaching adulthood. When released into the wild, the modified male mosquitoes mate with wild female mosquitoes. As a result, the offspring inherit the self-limiting gene, leading to a reduction in the local mosquito population over time.
2. Wolbachia Method: A bacteria that fights disease
Another approach of population replacement is the use of Wolbachia bacteria. Wolbachia is a type of bacteria that naturally infects many insect species, including mosquitoes. Over the past eight years, scientists have conducted extensive research on utilizing Wolbachia, a bacterium found in fruit flies, to combat the transmission of the dengue virus by mosquitoes. This innovative approach involves the transfer of Wolbachia bacteria from fruit flies to the mosquitoes responsible for dengue virus transmission. It is worth noting that despite being marketed as a "non-GM strategy," the artificial infection of mosquitoes with Wolbachia bacterium undeniably falls within the realm of genetic modification. This is due to the transfer of the complete bacterial genome, encompassing more than 1,500 genes, from the original fruit fly host to the mosquitoes.
Wolbachia has been found to inhibit the replication and transmission of certain mosquito-borne diseases, such as dengue, Zika, and chikungunya viruses. This strategy thus aims to reduce mosquito's ability to transmit diseases.
The World Mosquito Program (formerly known as the Eliminate Dengue Program) has set up projects in 12 countries and their Wolbachia mosquitoes have reached more than 10 million people (as of June 2022).
Field trials of Wolbachia-infected mosquitoes have been carried out in countries like Australia, Brazil, Indonesia, Vietnam, and Colombia. These trials have shown promising results, with evidence of reduced disease transmission in areas where Wolbachia has been established within the mosquito population.
One example of a successful program is the Wolbachia program in the city of Townsville, Australia. Following the release of Wolbachia-infected mosquitoes, there was a significant reduction in dengue transmission, with no reported local dengue cases since the program's implementation. This method is safe, self-sustaining and cost-effective method of preventing MBDs.
B. Population Suppression
The other strategy, population suppression uses gene editing to reduce mosquito populations so that there are fewer mosquitoes to pass on the pathogen.
CRISPR-Edited Mosquitoes: Resistant to Diseases
This approach aims to introduce genetic changes that render mosquitoes unable to transmit diseases or make them resistant to malaria parasites.
To make mosquitoes resistant to parasites or viruses, researchers identify key genes in the mosquito that are involved in the transmission of the pathogen. By modifying these genes using CRISPR technology, they aim to disrupt the mosquito's ability to harbor or transmit the pathogen.
"CRISPR/Cas9-mediated gene knockout of Anopheles gambiae FREP1 suppresses malaria parasite infection" by Zhang et al. (2015): A team of scientists from John Hopkins University were first to show that deleting a gene from mosquitoes can make them resistant to malaria parasites. This study used CRISPR/Cas9 to knockout (deletion) a gene called Fibrinogen-related protein 1 (FREP1) in Anopheles gambiae mosquitoes, resulting in reduced susceptibility to malaria parasite infection. These CRISPR-mosquitos showed slower pre-adult development, were less likely to feed on blood meals when given the opportunity and laid fewer and less viable eggs when compared to un-modified mosquitoes.
Conclusion
As we confront the reality of an increasingly interconnected world and the threats posed by climate change, it is clear that proactive measures are crucial to safeguard public health. Embracing GM technology as a tool to combat mosquito-borne diseases not only offers a sustainable solution but also mitigates the environmental and health risks associated with harmful pesticides. Although the concept may initially sound like science fiction, we must recognize its potential life-saving impact.
CRISPR and Wolbachia based GM techniques certainly has the potential to control or even wipe out mosquito populations. However, before doing so, scientists must carefully weigh the ethical implications of using this tool at a species level. Further research and extensive field testing are necessary before genetically engineered mosquitoes are considered for release into the natural environment. Careful evaluation of ecological impacts, regulatory considerations, and public acceptance is vital to ensure the safe and responsible application of these technologies.
We would love to hear your opinion on the use of genetically modified mosquitoes!
As we emerge from the pandemic, it is crucial not to forget the lessons learned, particularly the globalization of diseases. With the effects of climate change and climate variability, the spread of diseases is likely to accelerate. Therefore, maintaining awareness and preparedness for potential disease crises is vital.
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Foreign MBDs: Yellow Fever, Chikungunya, Dengue fever, Zika, Malaria, Filariasis
Endemic MBDs in Canada: West Nile virus, Eastern equine encephalitis virus (EEEV) and two California serogroup viruses (CSV): Jamestown Canyon virus and snowshoe hare virus.
GPM is completely new knowledge to me.Thank you for the detailed article and video links.