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Q: What is your company doing?
Oxitec is pioneering a new solution to control harmful insect populations, including the mosquito species Aedes aegypti which spreads Dengue Fever and Chikungunya. According to the Centers for Disease Control and Prevention, approximately 100 million people each year suffer from a case of Dengue Fever – a debilitating and sometimes fatal disease also known as ‘break-bone fever’. Other estimates put the number of infections as high as 400 million people per year and the number of infections is growing rapidly. The same mosquito transmits Chikungunya, a disease with similar symptoms, that is most often found in the Indian sub-continent but which has recently emerged in the Caribbean causing up to 1 million cases in one year.
There’s no available vaccine or specific medication for these diseases so the only way to stop transmission is to control the mosquitoes that spread them.
Oxitec’s approach involves the release of genetically engineered male mosquitoes The Oxitec males mate with the wild females of the same species and the offspring die before they become adults. Following sequential releases in several countries we have shown that the pest population of Aedes aegypti can be reduced by over 90% in urban environments using our genetically engineered strain called OX513A.
Oxitec is the only company in the world offering genetically engineered insects to control Aedes aegypti.
Q. Why don’t insecticides always work to control insect pests?
In recent decades insecticide resistance has increasingly become a problem. Many insecticides previously used to control mosquitoes are no longer effective, and no new chemicals have been introduced in over 40 years. This means that vector control agencies are left with far fewer tools than in the past. The situation is similar for many crop pests: for example, the diamondback moth has become resistant to almost every insecticide used to control it, including both synthetic chemicals and organic pesticides.
When they do work, insecticides can only kill the insects that they touch. This poses an additional problem for mosquitoes like Aedes aegypti, which live in and around people’s homes. To control this mosquito with insecticides, a public health authority needs access to people’s homes on a very regular basis, which is impractical for even the best funded and most organised vector control agencies.
Q. Could the introduced genes in Oxitec’s self-limiting insects be transferred to other species?
No. Our self-limiting insects only produce offspring with other insects of the same species, so they cannot pass the genes on to other species through reproduction. Animals that eat our self-limiting insects cannot take up genes through this route, just as we do not incorporate genes from the food that we eat.
Q. Where did the inserted DNA come from?
The inserted genes themselves are synthetically manufactured, but they are inspired by working systems found in organisms from nature. These sequences are available in DNA databases; we use these databases as a starting point and then adjust the sequences to specifically work in insects. The final genes share little similarity with the DNA in the organisms from which they were originally derived.
The basis of the self-limiting gene, the “tet-off” system, has been used extensively and safely in many other biological systems.
Q. Could Oxitec’s insects develop resistance to the self-limiting gene?
To date we have released over 300 million Friendly™ Aedes aegypti mosquitoes worldwide, and have never seen any evidence of resistance. We check the genetic make-up of our mosquitoes every few generations: these genetics have been stable for over 140 generations, and we expect this to continue. In addition, resistance has never been observed in the field or lab to the Sterile Insect Technique (SIT), a similar technique that uses radiation to render male insects sterile, and which has been used for decades to control insects such as screw-worm.
Nevertheless, mutations can occur in insects, so it’s worth considering what would happen in the highly unlikely event that there was a mutation that made the self-limiting gene ineffective. Because our insects inherit a marker gene, we would be able to identify insects that were resistant through our monitoring programme and stop releases. These insects would have no added advantage in the environment so would still die just like a wild mosquito. Other tools could be applied to control the wild population.
Q. What would happen to an organism that ingested a self-limiting insect?
Eating an Oxitec insect is just like eating a wild one. An animal will get the same nutritional elements – protein, fat, carbohydrate and so on – from an Oxitec insect as they would from the wild equivalent. The proteins created by the introduced genes are non-toxic and non-allergenic so do not affect predators in any way.
Independent studies have shown that Oxitec’s insects are not harmful to animals: predators including fish and other mosquitoes that ate our Friendly™ Aedes aegypti showed no difference from those fed wild Aedes aegypti. This was true even when they were fed diets consisting solely of Friendly™ Aedes aegypti – a much higher level than they would ever eat in the wild.
Q. Are there national or international regulations for releasing genetically engineered insects?
The release of genetically engineered organisms in a particular country is covered by national biosafety regulations and laws. Each country has its own regulatory procedures, although in practice many countries adopt similar processes and standards, including a risk assessment.
The Cartagena Protocol on Biosafety is an international treaty governing movement of genetically engineered organisms between different countries. It was adopted on 29 January 2000 as a supplementary agreement to the Convention on Biological Diversity and entered into force on 11 September 2003. Over 160 countries have agreed that they will put systems in place to implement the Cartagena Protocol through their national laws.
There is now also a growing body of guidance on genetically engineered insects from regulatory bodies around the world such as the World Health Organization, the European Food Safety Authority and the North American Plant Protection Organization.
Q. Have Oxitec’s insects been independently evaluated?
Yes. Independent collaborators around the world have conducted extensive testing on our insects, including:
- The Institute Pasteur, France
- The Gorgas Memorial Institute, Panama
- The Institute for Medical Research, Malaysia
- The Department of Agriculture and Food, Western Australia (DAFWA)
- The University of Crete, Greece
- SAOAS, Morocco
- Gangabishan Bhikulal Investment and Trading Limited (GBIT), India
- The University of Colorado
- Cornell University, New York
- The United States University of Health Sciences (USUHS)
- The Center for Medical and Veterinary Entomology (CMAVE), Florida
- The Mosquito Research and Control Unit (MRCU), Cayman Islands
- Moscamed, Brazil
- University of São Paulo, Brazil
Q. What is the lifespan of Oxitec mosquitoes?
Oxitec mosquitoes tend to live less than one week. Females that have mated an Oxitec male lay eggs which hatch into larvae, but do not develop into adults.
Q. How do you rear mosquitoes if the offspring die?
In a production facility, the larvae are given an antidote in their rearing water from the tetracycline family which inactivates the self-limiting gene. This enables us to rear large numbers of mosquitoes. Those that are released cannot access this antidote in the right quantities and/or at the right time and so the self-limiting gene works effectively, as demonstrated by field trials in different countries.
Q. Could you eradicate Aedes aegypti?
We don’t believe that worldwide eradication of Aedes aegypti is possible or practical, because the mosquito lives around humans and has managed to spread across the world by travelling with people as they move around. However, it may be possible to completely eradicate Aedes aegypti from certain limited localities such as islands. This would require strict monitoring at points of entry, to ensure it is not reintroduced.
Q. Do all offspring of Friendly™ Aedes aegypti die?
When reared in ideal conditions in the laboratory, a very small number of larvae can live to adulthood, but even these “survivors” are very sickly. With the added pressures of the wild, is is unlikely that any offspring will survive. However, even if a very small number of larvae did make it to adulthood, this would be negligible compared to the number of mosquitoes removed from the environment by our solution.
Q. Would Oxitec’s mosquitoes reduce insecticide use?
Projects with our mosquitoes in Brazil, Panama and the Cayman Islands have successfully reduced the population of Aedes aegypti by more than 90% within 4-9 months. That level of suppress
Q. Do you release only male mosquitoes?
Our sorting methods are very efficient and precise, allowing us to release almost all males, which do not bite. In our trial in Panama, only one female was released for every 10,000 males. If any females are released, they have been reared in the lab and so are disease free. They will die within a few days after release, a significantly shorter lifespan than wild females, and just like the males they will carry the self-limiting gene.
Q. What are the risks if a female Oxitec mosquito bites someone?
The bite of an female Oxitec mosquito is the same as the bite of a wild Aedes aegypti. The proteins of the two introduced genes are not expressed in the mosquito saliva, so a person bitten by a female mosquito would not be exposed to these proteins. In addition, these proteins are non-toxic and non-allergenic.
Q. If Aedes aegypti is controlled, could another species like Aedes albopictus move in?
A year-long trial of our Friendly™ Aedes aegypti in Panama found no evidence that suppressing Aedes aegypti increased numbers of Aedes albopictus. Additionally, Aedes aegypti is the major threat in terms of ability to spread disease, as it feeds almost exclusively on humans, while Aedes albopictus is considered only a secondary vector of disease. So even if the numbers of Aedes albopictus were seen to rise after suppression of Aedes aegypti, the disease threat would still be significantly reduced.
Q: What is Dengue Fever and how is it spread?
Dengue fever is a severe, flu-like illness that affects infants, young children and adults. There is neither specific medicine nor vaccine for dengue fever. Dengue fever is transmitted by the bite of an Aedes aegypti mosquito infected with any one of the four versions of the dengue virus (and a fifth serotype of dengue has now been discovered in Malaysia). Symptoms appear in 3–14 days (average 4–7 days) after the infective bite. Dengue haemorrhagic fever (DHF) and Dengue Shock Syndrome (DSS) are potentially lethal complications, particularly in children, and early clinical diagnosis and careful clinical management by experienced physicians and nurses is necessary to reduce the number of fatalities.
Dengue can only be transmitted by the bite of an infected mosquito and only the female mosquitoes bite. The main vector is the mosquito Aedes aegypti, which originated from Africa and has spread around the world, largely in the last 50 years and, as it has done so, dengue fever has increased dramatically.
The global numbers of dengue cases have grown 30 fold in only 50 years because current control methods, relying mostly on insecticides are not adequate to control this mosquito. New approaches are needed.
Q: What is Chikungunya and how is it spread?
Chikungunya is a viral disease transmitted to humans by infected mosquitoes. It causes fever and severe joint pain. Other symptoms include muscle pain, headache, nausea, fatigue and rash.
The disease shares some clinical signs with dengue, and can be misdiagnosed in areas where dengue is common. There is neither vaccine nor specific medication for the disease. Treatment is focused on relieving the symptoms.
Until recently the disease occurred mainly in Africa, Asia and the Indian subcontinent. In recent decades mosquito vectors of chikungunya have spread to Europe and the Americas. In 2007, disease transmission was reported for the first time in a localized outbreak in north-eastern Italy. In December 2013 the first case was reported in the Caribbean and within in 12 months there were an estimated 1 million cases and 11 cases of locally acquired chikungunya have been reported in Florida in 2014 (CDC).
Q: Do all mosquitoes spread Dengue Fever or Chikungunya?
No. Aedes aegypti is the species of mosquito which is primarily responsible for spreading dengue. Also, only female mosquitoes can spread dengue or chikungunya. Males do not bite or spread disease (in fact males cannot bite). Other Aedes species such as Aedes albopictus, can also spread dengue and chikungunya, but Aedes aegypti is the main vector and it is this species that is responsible for almost all of the dengue epidemics. Aedes albopictus is often cited as a dengue vector and can indeed spread the disease but it is not very efficient. Other mosquito species bite humans but do not spread dengue fever.
Q: Could the dengue virus mutate and find a way to be spread that gets around your mosquitoes?
The dengue ‘virus’ is actually four viruses (or sub types) and a fifth has been identified in Malaysia. They are all transmitted by this species of mosquito. It is clear the virus will mutate – but if you can reduce the mosquito population below the level where it can transmit the disease on an epidemic level you can prevent outbreaks.
Our system works by reducing the number of mosquitoes rather than by blocking the virus in the mosquito. If it did block the virus, you might expect the virus to find a way around that ‘block’. Instead we focus on reducing the sheer numbers of the mosquitoes to trace levels. In effect this is the same strategy people try today (with insecticides) with the exception that our approach has been proven as far more effective in field trials in different countries.
Q. Could the use of tetracycline when rearing mosquitoes spread antibiotic resistance?
The problem of antibiotic-resistant bacteria is a significant challenge to health, driven by the substantial use of antibiotics in medicine and animal husbandry. That is why we minimize use, monitor it, and have subjected it to detailed review.
We use the antibiotic tetracycline in the rearing process, but the chance of any antibiotic-resistant bacteria surviving on the released mosquitoes is extremely low. We only rear larvae with tetracycline. When they develop into pupae they are washed several times in fresh water as part of the sorting process and then reared without tetracycline. When the pupae then metamorphose into adults, they expel their gut bacteria, meaning any tetracycline-resistant bacteria in the larval gut are highly unlikely to be continued into the adults. In addition, the cuticle (skin of insects) is a very inhospitable environment for bacteria: it is smooth and dry, unlike human skin which harbours many different bacteria species.
In the United States, the Food and Drug Administration (FDA), along with experts from the Centers for Disease Control & Prevention (CDC) and Environmental Protection Agency (EPA), examined the use of tetracycline as part of their Environmental Assessment for a project with Friendly™ Aedes aegypti in the Florida Keys. They concluded “the likelihood of the adverse effects associated with development of anti-microbial resistance is extremely low and the risk is negligible”.
Q: How is tetracycline used or not used in the rearing process?
Oxitec larvae are reared in the presence of tetracycline. Pupae are washed several times in fresh water as part of the sorting process. They are then reared in fresh water, with no tetracycline. When larvae become pupae and metamorphose into adults, they expel their gut bacteria, meaning any tetracycline-resistant bacteria in the larval gut are highly unlikely to be continued into the adults. In addition, the cuticle (skin of insects) is a very inhospitable environment for bacteria; it is smooth and dry, unlike human skin which harbors many different bacteria species. Therefore, the chances of any bacteria surviving on the cuticle of the mosquitoes is extremely low.
The adult mosquitoes emerge from the pupal case onto the surface of clean water and are not exposed to any tetracycline thereafter.
At Oxitec, we take our stewardship of antibiotic use very seriously. That’s why we minimize use, monitor it, and have subjected it to detailed review.
Q: Is there the potential for the spread of antibiotic resistance from Oxitec’s solution?
The problem of antibiotic-resistant bacteria is a significant challenge to health, driven from the many substantial uses of tetracycline in therapeutic and animal husbandry, and one that Oxitec takes extremely seriously. That is why we minimize use, monitor it, and have subjected it to detailed review.
Oxitec has submitted over 283 pages of data and information to the Food and Drug Administration (FDA), and after exhaustive review by an interdisciplinary team of scientists including members from the Centers for Disease Control & Prevention (CDC) and Environmental Protection Agency (EPA), the FDA concluded that: “the likelihood of the adverse effects associated with development of anti-microbial resistance is extremely low and the risk is negligible”. For a review of the data here are the links to Oxitec’s publicly available Environmental Assessment and the FDA’s publicly available evaluation of the data.
In the Florida Keys, the facility in Marathon where the mosquitoes would be reared uses very low quantities of tetracycline. Even at maximum production capacity, the facility would produce less tetracycline waste per week than one person takes per day to treat acne: two 500 mg pills is a standard dose for tetracycline per day for acne, half of which is simply excreted in urine.
Q. Could Oxitec’s insects survive by finding the tetracycline antidote in the environment?
No – tetracycline is not present in sufficient quantities in the environment to inactivate the self-limiting gene. Peer-reviewed studies have shown that even in areas with high levels of tetracycline, such as poultry farms, there is not enough of the antidote to allow Friendly™ Aedes aegypti to survive.