Written by: Fernanda Ferreira, Elizabeth Jaensch, and Tianli Xiao
We’re back with a new episode of Sit’N Listen, this time all about the world’s most deadly animal: MOSQUITOES. Tune in to learn about the history (and future!) of some of the infamous diseases mosquitoes spread, as well as new tools scientists are using in the fight against mosquito-borne diseases.
Special thanks to Amy Gilson for audio production help.
Feel free to send us any comments, questions, or topic suggestions at firstname.lastname@example.org.
All the best,
The Sit’N Listen team: Amy Gilson, Elizabeth Jaensch, Vini Mani, and Angela She
Elizabeth: Hello, and welcome to Sit’N Listen: a production of Science in the News. We’re a graduate-student run organization at Harvard University committed to generating discussion between scientists and other experts and enthusiasts.
I’m Elizabeth Jaensch, a graduate student in biological and biomedical sciences.
Fernanda: I’m Fernanda Ferreira, a graduate student in the virology program
Tianli: and my name is Tianli Xiao, I’m a graduate student in the immunology program (pause)
Tianli: And today we’re going to talk about mosquitos.
I want to start this podcast off with a brief disclaimer/conflict of interest statement: I HATE mosquitos. Mostly because they, on the other hand, seem to love me, as evidenced by the SEVEN mosquito bites currently on my left ankle. After dozens of summers filled with constant bites and the subsequent itching, I would be happy to never see another mosquito again.
And though it is annoying enough to have pleasant summer evenings marred by the stink of bug repellent and high-pitched buzzing, mosquitoes become even worse when you consider that they are the world’s most deadly animal, killing more than a million people every year by spreading diseases like malaria and yellow fever.
We’ve been trying to stop the spread of these diseases for decades, using a number of different approaches, with varied success. Today we’re going to talk a bit about how we’ve combated mosquitos and their associated diseases throughout history, as well as what new efforts scientists are focusing on and what the future might hold for the spread and livelihood of mosquitoes.
We’re talking about mosquitos today for the same reason many of our listeners may be thinking about them lately: the Zika outbreak that has been going on for the last few months. But even though a lot of the focus has been on Zika lately, there are plenty of other mosquito-transmitted diseases, such as malaria, that have a long history of causing human suffering in many parts of the world.
I’m just going to start off with a brief, general introduction to mosquitoes. There are more than 3000 species of mosquito found everywhere in the world, except a few places like Antarctica and Iceland. They can be found year-round in warm, humid, tropical regions, whereas in more temperate and cold areas they are dormant outside the warm periods.
The life cycle of mosquitos can be categorized into three general stages- the larval stage, the pupal stage and the mature stage. Both the larval and pupal stage occur entirely in water, which is why the most common suggestion for getting rid of mosquitoes is to not allow standing water to accumulate.
As adults, mosquitos actually feed on nectar and other sources of sugar. Only female mosquitoes bite and they do so to get enough nutrients for egg development. Which sounds really sweet and maternal, until you remember that it is during this biting process that diseases like malaria and Zika are transmitted.
Tianli: Definitely not sweet.
Fernanda: Yeah, especially considering that in 2015 there were 214 million cases of malaria worldwide, with an estimated 438,000 deaths, 90% of which were in Africa.
SPEAKING of malaria, this seems like a good opportunity to give a little more background on the diseases we’re focusing on: malaria and Zika. Malaria is caused by single-celled parasites in a genus called Plasmodium. Female mosquitoes in the Anopheles genus, or biological grouping, can carry these parasites; when an infected mosquito bites a person for a blood meal, they transmit the parasite to the new human host.
Symptoms of malaria can linger for many months when not properly treated and can include fever, fatigue, and vomiting, while the most severe cases can lead to seizures, coma, and death. People who are regularly exposed to malaria can develop a partial resistance which keeps symptoms mild on re-infections, but this can disappear within months of removal from a malarial environment.
There are currently some good anti-malarial medications, though resistance to anti-malarial drugs is developing among some of the Plasmodium parasite species. For example, scientists have found resistance to the drug chloroquine in Plasmodium falciparum, which is the most deadly version of the malaria parasite. Unfortunately, there is currently no effective vaccine for malaria.
Another disease that has really captured the world’s attention in recent months is zika, which is also spread by mosquitos
The Zika virus, as its name implies, is a virus, not a parasitic microorganism like malaria, and it’s actually carried by a different group of mosquitoes than malaria. It is spread by specific species within a genus of mosquitoes called Aedes, such as Aedes aegypti, which you may have heard of on the news. The Zika virus is a flavivirus, a genus [group] which includes the dengue, yellow fever, Japanese encephalitis, and West Nile viruses, which are also carried by mosquitos. We have known of the existence of Zika in a narrow region along the equator from Africa to Asia since the 1950s, but was mostly contained between monkeys and mosquitoes. Now, there are pandemic levels of the virus in humans in Central and South America and the Caribbean.
Zika infections may result in no symptoms or mild symptoms, including headaches, rash, fever, and joint pains. Adults may also develop Guillian-Barre syndrome, which leads to severe weakness when the nerves throughout the body are damaged. But what the Zika virus is most known for is causing microcephaly, a developmental disorder in the brain that can lead to intellectual disability and a smaller head, as well as other brain-development problems in the babies of mothers infected during pregnancy.
There are no existing medications or vaccines for Zika, though there are vaccines currently available for its relatives Yellow Fever, and Japanese Encephalitis, and many efforts are currently underway to produce a vaccine for Zika.
Fernanda: Given Aedes aegypti’s ability to cause so much heartbreak, it’s not surprising that Marcelo Castro, the Brazilian Health Minister, called Aedes aegypti “Brazil’s public enemy number one”. Nor is it surprising that when Brazil was in the early days of the Zika virus outbreak, it deployed two-hundred and twenty thousand soldiers to educate the general population on how to fight the Aedes aegypti mosquito.
For many people, the idea that 60% of a country’s armed forces took arms against a mosquito is a little shocking, but it turns out that a lot of mosquito elimination programs, especially the first ones to happen, are intimately tied to the military.
In Brazil the military was seen as a great resource of people, who were needed to run around educating the general populace on how to control mosquito populations, but in the past mosquito or disease control was seen as necessary to win a war and no mosquito-borne disease exemplifies this better than malaria.
There are countless examples of armies both thwarted and helped by malaria. For instance malaria in the Italian peninsula protected the Romans from foreign invaders such as Goths and Attila the Hun, and if we fast forward several hundred years the fight for Haiti’s independence may have been a lot different if the French soldiers sent to squash it hadn’t succumbed to malaria, to which they had no immunity.
Elizabeth: Given all these examples it’s not surprising that by the time WWII rolled around, a lot of nations understood that an important part of winning the war was making sure their soldiers were safe from malaria.
Fernanda: Exactly, and the US army is a perfect example of this.
The Office of Malarial Control in War Areas was established in Atlanta in 1942 with the purpose of limiting the number of soldiers affected by malaria and other diseases in southwestern USA, where many military training bases were located.
When the war ended, anti-malarial efforts were continued with the renaming of the Office of Malarial Control in War Areas to the Centers for Disease Control and Prevention, or CDC, in 1946.
With the CDCs founding, anti-malarial efforts were extended to all of southwestern USA, not just the areas around military bases. Getting rid of malaria once and for all required a strong cooperation between the CDC and the state governments in that region, and the main tool used was interior house spraying with DDT.
The numbers for this anti-malarial effort are ridiculous: in 1949 for instance, over 4.5 million households were sprayed. This cooperative program was so effective that by 1951 malaria was declared eliminated in the US and the CDC changed its anti-malarial efforts to one of surveillance in American territories and assistance in the global fight for malaria eradication.
Tianli: But not all anti-mosquito efforts are pushed forth by war. After all, eradication programs don’t end when war does.
Fernanda: True, but they all do require an almost military-attention to detail and occasionally the use of martial law. For instance, in 1930 Rockefeller Foundation scientists found Anopheles gambiae mosquitoes, which are one of the most efficient vectors of malaria, in Natal, a port city in Northeastern Brazil. For a few years after this finding, small, local malaria outbreaks would flare up in a city or town in Brazil and be tampered down by local anti-malarial efforts. But in 1938 Brazil ran out of luck and was engulfed in the largest malaria outbreak in the Western Hemisphere. Around 100,000 people were infected and between 14 and 20 thousand died.
To deal with this outbreak, Brazil hired the American Fred Soper, who was allowed to employ martial law in order to control the Anopheles. For instance, the health officials were allowed to enter and inspect every building and property – even if they had to do so by force – and they established blockades on roads to fumigate vehicles.
The work paid off because after a few years Brazil was declared malaria-free, but this didn’t last long. When it comes to mosquito and disease control, constant vigilance is needed to make sure neither old nor new diseases take root in a country. For Brazil and many countries that have at one point or another been declared malaria, yellow fever or dengue-free, the fight against mosquitoes never truly ends after elimination.
Elizabeth: Huh, I don’t know much about Fred Soper. When I think of important scientists in mosquito research and eradication I think of Walter Reed’s work with yellow fever or Sir Ronald Ross’ work with malaria.
Fernanda: Yeah, both of these scientists proved that these diseases were transmitted by mosquitoes and their discoveries immediately spurred efforts to halt disease transmission. But when it comes to the actual game of eradication, Soper may be one of the biggest names in the business.
One of his favorite tools for mosquito destruction was a chemical called dichloro-diphenyl-trichloroethane, which is more affectionately known as DDT. DDT works by causing an affected insects’ nerve cells to fire repeatedly, leading to spasms and death. Despite the deep link between DDT and mosquito-borne diseases in the public imagination, DDT was actually first used by Soper in WWII against typhus, a bacterial disease transmitted by lice that causes a terrible fever. But once DDT was proven extremely efficient with killing lice, it quickly began to be used against all sorts of insects, including mosquitoes.
The 1950s were the “the DDT era of malariology” and complete eradication of mosquitoes became the goal of these DDT-spraying efforts. But just as quickly as DDT was adopted worldwide, mosquitos began to develop resistance. However, because the US government saw the fight against malaria as a great form of Cold War propaganda, DDT was used despite growing examples of mosquito resistance to it.
Given that we’re still dealing with malaria today, it’s clear that the “DDT era of malariology” never led to the global eradication that was expected. DDT failed for two main reasons: (1) mosquitoes quickly became resistant to it and (2) the way DDT was applied, in household interiors, affected only mosquitoes with similar domestic lifestyles. That is, any mosquito that lived outside human dwellings, such as in a nearby forest, and only ventured into houses or near humans for a blood meal would be less affected by DDT than ones spending time inside. Furthermore, not only did DDT fail to eliminate malaria, but it also caused a series of environmental problems, such as the thinning of birds eggshells, that were first presented to the world in Rachel Carson’s Silent Spring.
When everyone was talking about Zika and running around trying to find other tools for fighting Aedes aegypti, DDT’s name came up. This is a highly controversial idea, and most articles framed the decision to bring back DDT as a sort of moral, “lesser of two evils” question: are the dangers of using DDT worth it to get rid of Zika?
Tianli: But why do people keep obsessing over DDT? Aren’t there other ways of getting rid of mosquitoes?
Oh, there are a number of other tools. Mosquito control methods can attack every stage of the mosquito’s life by not allowing mosquitoes to reproduce, not allowing eggs and larvae to mature, killing adult mosquitoes, and preventing mosquitos from actually biting humans.
As I mentioned before, mosquitoes need water to be present and still from when eggs are laid until the young mosquitoes are grown. So one of the most obvious options is to drain standing water, thus disrupting the two important steps in a mosquitoes life cycle: egg development and egg-laying. Beyond that, adult mosquitoes can be killed using insecticides, as we just discussed. Mosquito nets and repellents, used individually or in combination, can keep mosquitos away from human hosts. When mosquito nets are coated in a repellent, they are the most cost-effective prevention method, costing only around $3 apiece and providing 70% greater protection over no net. They do however need to be re-coated every few months, which can be challenging in remote regions.
Finally, we can get into some more scienc-y approaches. A method that has previously had some success in insect population control is releasing males that have been sterilized, often using radiation, into the wild. This is called the sterile insect technique. Because female mosquitos only mate once, if they mate with a sterile male, they will produce no offspring. Although this method has proved successful in eliminating screwworms in Mexico and Belize and Tsetse flies, which carry sleeping sickness, in Zanzibar, it can be a little tricky. There are plenty of other, non-sterile mosquitoes in the wild that the females can mate with, and it’s possible that the sterilization method makes males less fit to survive and mate in the wild. Lastly, multiple releases of large number of males are necessary to see a decrease in the mosquito population, which would require a sort of “mosquito factory” to keep churning out large numbers of sterile males, which could be difficult to implement and very gross to think about.
Oxitec, a British biotechnology company, is actually currently working on a method to control Aedes aegypti mosquito populations using the Sterile insect technique. But instead of irradiating the mosquitoes, they are using more specific genetic modifications. They are inserting a gene into male mosquito genomes that causes all their offspring to die. This method should avoid some of the problems with general reproductive fitness that can accompany radiation, though the problems of needing repeated releases and generating large numbers of mosquitoes still remain.
Fernanda: Okay, so the sterile insect technique has its issues, but the idea of releasing genetically modified mosquitoes into the wild to do our work for us is interesting, especially with recent advances in genome editing technology. Are they any other ways we could modify mosquitoes to reduce the threat they pose to us, other than sterilization?
Absolutely! Scientists have long hoped for more creative ways to prevent mosquitoes from spreading disease. One of the ideas is to make the mosquitoes unable to carry malaria by giving them a malaria resistance gene. As a matter of fact, scientists are currently designing mosquitos that carry an antibody gene against malaria, which would make them poor hosts for the Plasmodium parasite. If mosquitoes cannot carry this parasite, they cannot infect us with malaria when they bite. But to make these strategies viable, scientists would need to find a way to change the genome of an entire mosquito population, which is a quite daunting task. It’d be impossible to capture every single mosquito and change their genome one by one! But what if we make the mosquitos do the work for us, to spread the gene to the entire population themselves?
Imagine if we genetically modify a mosquito in the lab and give it resistance to malaria, and we release it to mate with wild mosquitoes. The lab mosquito will pass the malaria resistance gene to its descendents, making all the new-born mosquitoes immune to the malarial parasite. These offspring will grow up to mate with other wild mosquitoes and the cycle repeats. After a few generations, the entire mosquito population will carry malaria resistance, and they will no longer cause malaria when they bite humans.
Elizabeth: Hold on, that’s really not how inheritance works…
Mosquitos, just like us, have two different copies of each of their genes, which are also known as alleles: one they inherit from their mothers and one from their fathers. When they reproduce, they randomly pass on just one of the alleles of each gene to their offspring. So if we have a mosquito with one copy of a gene, modified to give it malaria resistance, from its father, but only a normal copy of the gene from its mother, there is only a 50% chance that any given one of its offspring will inherit the resistance gene.
Fernanda: So after the first generation, only 50% of an engineered mosquito’s offspring will inherit the malarial-resistance gene. In the second generation, only half of this 50% will inherit the gene; this represents only 25% of all the offspring at this point. Which means the number of offspring with the gene will keep dividing by half with each generation till absolutely no mosquitoes carry that gene!
Tianli: You’re both right: to change the genome of an entire mosquito population, we need this malaria resistance gene to be passed on to an offspring more than 50% of the time. This is where the idea of gene drive comes in.
A gene drive system is a genetic system that increases the chance of a gene being passed on to the offspring. Remember that mosquitoes have two copies of their genes, known as alleles? Let’s name them allele A and allele B. If the malaria resistance gene is present on only one allele, when the mosquito breeds, allele A will be passed on to its babies half of the time and allele B will be passed on the other half of the time. Thus the gene only has 50% chance of being passed to its children. To improve the odds of passing on the malaria resistance gene, we have to make sure it is present in BOTH allele A and allele B. This way, regardless whether allele A or B is passed on, the progeny will receive malaria resistance.
How can we make sure that the gene is found in both alleles? Assuming we can get the resistance gene into one allele, for instance allele A, how can we create a system where allele B will automatically get the resistance gene from allele A? Well, we can actually take advantage of the cell’s natural repair mechanisms. When there is a break in the DNA, the cell will want to fix the break. Here’s one way that works: Let’s say that allele B has a break in its DNA. Because the cell wants to make the right repairs, it will reference allele A as a correct copy of this DNA sequence, and as it makes its repairs, it will copy the information from allele A to allele B. So we can use this natural mechanism to engineer resistance in both alleles. If we insert a resistance gene in allele A, then cause a break in allele B, the cell will be fooled into copying the resistance gene into allele B as it fixes the break. Then all the alleles that are passed onto offspring with have this resistance gene.
But how do we make sure that the DNA is cut in the exact right place we need it to be for this to work?
Elizabeth: Sounds like a job for CRISPR!!
Tianli: Yes, we can use CRISPR. CRISPR is a recently developed tool that allows scientists to edit genomes quickly and precisely. The CRISPR system includes a protein that cuts DNA, called cas9, and a special guide that tells cas9 where to cut the DNA, so it doesn’t just cut in random places in the genome. If you’re interested in learning more about CRISPR, you can check out our previous episode of Sit’N Listen dedicated entirely to this new technology.
Since CRISPR can make very specific cuts in DNA, which is exactly what we need for our gene drive, we will insert the Cas9 and the guide along with the malaria resistance gene into allele A. The guide is designed to target allele B, which does not have any insertion. So Cas9 will cut allele B, and the cell will repair the DNA, like we said, using allele A as a reference. When allele B is fully repaired, it will contain not only the resistance gene, but also the CRISPR machinery.
Fernanda: So not only will all of this mosquito’s offspring be resistant to the malarial parasite, they will also have in their genomes the tools to make sure both their alleles have the resistance gene. So they can pass it on to all their progeny as well. And so on and so on.
Tianli: correct. And this isn’t the only strategy using CRISPR as gene drive systems. For instance, some labs used a CRISPR gene drive to insert a gene that would specifically kill all the female mosquitos. So when these modified mosquitoes mate with wild mosquitoes, only male offspring will survive. If there’s no female offspring, eventually the mosquito population runs out of females to mate with and the population number will drastically drop. Scientists are still coming up with many other clever ways to either prevent mosquitos from harboring disease or killing entire populations very quickly.
Fernanda: is this system ready to use in the field?
Tianli: well, there are several criteria we have to consider when we design a gene drive system. First, we want a gene drive that can quickly spread a gene to the entire population. For instance, if the gene drive system spreads the malaria resistance gene too slowly, only some mosquitos become immune to malaria and people are still going to get sick. Second, the gene drive system cannot dramatically decrease the mosquito’s ability to survive. As we learned from the process of evolution, individuals that are not fit for survival are less likely to reproduce and pass on their traits. Since the whole point of a gene drive system is to pass on a trait to as many offspring as possible, creating less fit specimens would kind of defeat the purpose. Furthermore, it would be ideal to create a gene drive system that can be modified afterwards, possibly by releasing mosquitoes with a “reversal” drive that can stop the existing one. If ever something goes wrong, having a stop button that either stops the gene drive from continuing to spread or further modify it would be very useful.
While the incorporation of CRISPR technology into gene drive system meets a lot of these criteria, many within and outside of the scientific community are still cautious when it comes to applying them in the field. Since the ability to change the genome of an entire specie is so powerful, there are still significant hurdles to overcome before we can safely implement them. For instance, genome editing technology still needs to be more precise to avoid cutting genomes at undesired places, which could create undesired mutants in the wild. Furthermore, some closely-related species may mate with each other, although the chances of this are pretty low. This could lead to undesired genome changes in a non-targeted species. Lastly, fail-safe mechanisms still have to be developed in case something goes wrong in the field to inactivate the gene drive system. All in all, the scientific community is taking the safety issue very seriously, and are collaborating with other scientists and politicians to come up with ways to safely use gene drives.
Elizabeth: So Tianli, you’ve been talking about different ways to use gene drives, including basically killing off entire populations. But what would even happen if we took this a step further and completely eliminated mosquitoes from the planet? I’m not even going to pretend I’m not pro this idea, since it seems like for humans wiping out the mosquito population only brings positive effects: no more itchy bites, no more buzzing in our ears and, most importantly, no more mosquito-borne diseases.
Fernanda: But while we might rejoice in the disappearance of mosquitoes, are there any animals that might miss them if mosquitoes are completely eradicated? Do mosquitoes provide any benefits to our ecosystem that we’re not considering?
Back in 2010 the scientific journal Nature explored these issues in a news feature titled “A World Without Mosquitoes”. I’m sorry to have to report, Elizabeth, that mosquitoes do provide benefits in many ecosystems: they can act as pollinators, food for birds, fish, mammals, etc.; and they also process organic matter.
The tricky part comes in parsing out whether mosquitoes would actually be missed if they were eliminated. And here, it becomes clear in the Nature news feature that there is some debate amongst scientists. Basically, whether eliminating a mosquito does or doesn’t affect an ecosystem will depend on how important the mosquito is in that environment and how quickly it could be replaced by another organism. For instance, in a tropical rainforest mosquitoes might make up a large part of a bat’s diet but if they are eliminated from the rainforest we believe bats would be able to quickly change their feeding habits to other insect species. However in a much less diverse environment, the biomass contributed by mosquitoes might be vital for the future of the other organisms in the habitat.
On the other hand, if we focus just on humans, would the health benefits of mosquito eradication makeup for the potential environmental effects? The majority of the scientists seem to believe that they do. Getting rid of malaria, dengue, and yellow fever amongst others would very quickly eliminate a lot of human suffering.
Luckily for us, some of the new forms of mosquito control that Elizabeth and Tianli spoke of earlier allow for the targeted elimination of only a few mosquito species. This way we can eliminate only the Anopheles and Aedes of the world that spread disease, without killing mosquitoes that are both harmless to humans and important members of their ecosystem.
But that ecosystem is changing as we speak as global warming is broadening the areas in which some of these mosquitoes can live.
That’s a good point. The global distribution of many mosquito species is largely determined by local temperatures. Mosquitoes such as Aedes aegypti like tropical temperatures, and they suffer a decrease in their mobility and in their ability to imbibe blood at lower temperatures. So, while global trade and travel has always introduced mosquitoes to new areas, with global warming these mosquitoes can actually survive and establish populations in these new areas. For example, Aedes aegypti mosquitoes, which carry Zika, were originally found in tropical and subtropical zones, but have now spread to every continent except Antarctica.. They have even been found surviving winters in Washington D.C., which is much further north than expected!
Temperature can affect mosquitoes in other ways as well. Maria Diuk-Wasser of Yale’s School of Public Health told Scientific American that “The direct effects of temperature increase are an increase in immature mosquito development, virus development and mosquito biting rates, which increase contact rates (or biting) with humans”.
It is, however, important to point out that climate change will affect each mosquito population differently. Modeling studies of global warming and mosquitoes of the Aedes genus, which carries the Zika virus among others, point to an increase in both geographic distribution and in dengue transmission.
But when it comes to malaria, research suggests that global warming will not make the situation worse, simply change who is in danger of catching malaria. The Eltahir research group at MIT studies the effects of global warming and has a number of research projects looking at how climate change affects vector-borne diseases. In a paper from 2013, they explored the potential consequence of temperature increases and changes in rainfall patterns on rates of malaria in West Africa. Their research showed that while the areas with malaria transmission will be altered in West Africa, the total number of cases will probably continue to be the same.
Global warming will have an effect on mosquito-borne diseases, but predicting what this effect will be will require models that explore not only different mosquito species and diseases, but that also take into consideration the consequences of global warming on different geographic locations.
Tianli: Even without these potential changes, mosquitoes are already a huge threat to human health, and controlling the diseases they spread could save hundreds of thousands of lives every year. But we still don’t have vaccines for some of these diseases, and parasites are developing resistance to drugs as mosquitoes are developing resistance to insecticides.
Fernanda: And even though scientists are working on new ways to control the mosquito population and spread of disease using genetic modifications, they, their regulating bodies, and the general public are understandably proceeding with caution before introducing these new mosquitoes into the wild.
Elizabeth: Earlier, I mentioned that the company Oxitec has created a genetically modified Aedes aegypti mosquito that cannot reproduce. They have already tested these mosquitoes in small areas of Brazil, Panama, and Grand Cayman, where they have reduced the populations of this species by 90%. Oxitec is now planning to test their version of the sterile insect technique on Aedes aegypti mosquitoes in the Key Haven, which is near Key West in Florida.
Since genetically modified animals are regulated as “animal drugs”, the Food and Drug Administration, or FDA, is responsible for approving this trial. They released a preliminary report in March that agrees with Oxitec that releasing these mosquitoes will not have a significant impact on the environment in general. This may be partially due to the fact that these mosquitoes are designed to die with their engineered trait, so the engineered genes shouldn’t run wild in the general population.
However, many critics say that these mosquitoes shouldn’t be regulated as drugs, and that the FDA isn’t qualified to make such environmental assessments. The FDA says it did work the the Environmental Protection Agency and the CDC on this project, but maybe with the rise in genome editing technologies we will need to look at establishing new regulatory systems.
But even with these previous successes and the agreement of the FDA on the environmental impacts, many people are still worried about this release. Some residents of Key Haven have even organized petitions to prevent the testing. The general worries of genetically modified organisms are carried over to the mosquitoes in this case, and many citizens are worried about unintended consequences the release .The FDA had a public comment period that closed May 13, and Oxitec cannot proceed with the test until the FDA gives the go-ahead, which they will not do until they have gone through all the public comments.
Elizabeth: But, for now, we do have a lot of tools like nets and repellent to help prevent mosquito bites, and as Fernanda mentioned, diseases like malaria have been eliminated in some parts of the world. And as a biologist, though caution is needed, I’m really excited about the idea of genetic modifications and what they might be able to accomplish. In lab settings, gene drives have been effective in allowing new genes to be passed on to 99% of mosquito offspring. But as Tianli and Fernanda mentioned, we have a long way to go both in terms of technology and understanding the environmental consequences before we jump into anything.
But we also have to decide, when the opportunity to save over a million lives every year arises, what risks are we willing to take?
History of mosquito and disease eradication programs:
Spielman, Andrew and D’Antonio, Michael. Mosquito: The Story of Man’s Deadliest Foe. 2001.
Sit’N Listen – CRISPR:
CRISPR gene drive technology:
Esvelt, Kevin, Church, George, and Lunshof, Jeantine. “‘Gene Drives’ and CRISPR Could Revolutionize Ecosystem Management”. Scientific American. 2014.
Malaria gene drive:
Pennisi, Elizabeth. “Gene drive turns insects into malaria fighters.” Science. 2015.
Debate about application of CRISPR in the field:
Pennisi, Elizabeth. “Gene drive workshop shows technology’s promise, or peril, remains far off.” Science. 2015.
Nature article on eliminating mosquitoes:
Fang, Janet. “A World Without Mosquitoes.” Nature 466:432-434. 2010.
Mosquito-borne diseases and global warming:
Scientific American’s EarthTalk: “Mosquito-borne Diseases on the Uptick – Thanks to Global Warming.” EarthTalk, Scientific American. 2013. http://www.scientificamerican.com/article/mosquito-borne-diseases-on-the-uptick-thanks-to-global-warming/
Oxitec Florida Keys Project: