We’ve heard how traditional methods to control Aedes aegypti can be harmful to people and the environment, and aren’t very effective in any case. In the film, the reporter then asks Haedes and Aegypta about the Oxitec approach. This is a new technology based on advanced genetic science, which uses the natural instincts of the mosquitoes themselves to track down other mosquitoes and stop them reproducing.
Before taking a look at the Oxitec solution in more detail, you can read a bit more about genes and genetic modification; an incredibly powerful science which has already been central to recent advances in medicine, agriculture and understanding diseases.
Most people have heard of genes – even if it’s not always quite clear what they are, and what they do! A gene is the name given to a section of DNA. In both people and mosquitoes, genes produce proteins that influence everything from height to eye color. Offspring inherit these genes from their parents
‘Genetics’ is the name given to the science of studying and manipulating genes, and understanding how they are passed on from parent to offspring. Over the last 50 years, since the discovery of the structure of DNA, genetics has contributed to many important scientific developments, such as understanding and treating inherited diseases like cystic fibrosis; developing more effective ‘targeted’ cancer medicines, like Herceptin; or enabling us to manufacture large amounts of human insulin to treat diabetics.
Using modern genetics, scientists now have the ability to manipulate and combine genes in many different ways. This allows them to study how genes work, as well as combining different genes in ways that can be enormously useful in medicine, agriculture and other applications.
Genetic modification (GM), also known as genetic engineering, is a biotechnology technique which can be used to add to or alter the genes within an organism. A genetically modified organism, or ‘GMO’, is an organism that has had its existing genes altered, or new genes added, through a process of genetic modification.
Genetically modified organisms were first developed in the late 1970s and since then their use in a range of industries has become widespread. Perhaps without appreciating it many people today are reliant on this biotechnology for medicines and foods.
One of the first products of genetic modification was insulin produced by genetically modified bacteria. Through insertion of the human gene for insulin into the bacteria’s DNA, the bacteria effectively acts as a chemical factory, synthesizing the human protein exactly. This has provided a quick and easy way to produce pure insulin for diabetics.
Since the 1980s, there have been a number of other human proteins produced through genetic engineering, such as growth hormone or blood clotting factors. Genetic modification has also been used in a wide variety of other medical applications: the Hepatitis B and HPV vaccines have been developed using genetic modification, and there is potential for scientists to develop an entirely new field of cancer vaccines based on this biotechnology.
Oxitec has applied the science of genetic modification to the problem of controlling populations of Aedes aegypti.
As we’ve seen earlier in the video, the challenge we face in trying to control Aedes aegypti is to find ways of targeting the mosquitoes where they live; in people’s houses and gardens. What’s more, we need to have ways of doing this which don’t harm people or other animals and plants in the environment, and which avoid the use of chemicals which mosquitoes are often resistant to. One potential approach which meets some of these goals is known as the Sterile Insect Technique or ‘SIT’.
The concept of SIT was first developed in the 1950s. The basic technique is to dose male insects with radiation, which makes them sterile. By ‘sterile’, we mean that although the males do produce sperm and can fertilise the female’s eggs, their offspring are ‘inviable’ – meaning that they die at a very early stage of development.
The sterile males are then released into the environment, where they mate with wild females. Females usually only mate once, so a female which mates with a sterile male doesn’t produce any offspring. As a result, the population as a whole is reduced. Eventually, with enough sterile releases, the population of the target insect in an area can be dramatically reduced or even eliminated.
The Sterile Insect Technique was successfully used to eradicate screw-worm (a pest of cattle) in North America. It has also been successful in reducing populations of other pests, such as eradicating the Tsetse fly, which causes sleeping sickness, in Zanzibar.
SIT uses the natural instincts of the released male mosquitoes to seek out females, so it is much more effective than traditional means at targeting difficult-to-reach pest populations, like Aedes aegypti. It is also species-specific: it affects only the target pest, and doesn’t harm other insects.
Unfortunately, using radiation to produce sterile insects in this way can cause problems. Not surprisingly, being hit by a large amount of radiation isn’t very good for the male insects! Often, irradiated males are very sickly, so wild females prefer not to mate with them. If that happens, they won’t be very effective at controlling the population. While SIT has been used successfully against some insect pests, mosquitoes are easily damaged by the process of irradiation, and to date there have not been any successful programmes of mosquito population control using radiation-based SIT.
Oxitec has developed a new way to control mosquitoes using genetic modification. Our approach is similar to the sterile insect technique, but because we use genetics to stop our insects from reproducing, we eliminate the need for damaging irradiation.
Scientists at Oxitec have developed a way to modify mosquitoes by adding a gene which produces a protein that stops their cells from functioning normally. The gene produces a protein called tTA, which is a special kind of protein able to act as a switch that controls the activity of other genes. Our modified mosquitoes produce high levels of this protein because it actually activates its own gene, producing lots more of itself. Although it’s not toxic itself, it ties up some of the cell’s essential machinery. It can interact with other proteins which are needed for controlling genes in the cell, and in this way it stops the cell from turning on other genes which are essential for it to survive.
All this means that the modified mosquitoes become very sick, and die before reaching adulthood.
If the gene in the modified mosquitoes kills them, how does that make them sterile? That depends on another special property of the gene, and the tTA protein it makes: when the mosquitoes reared in the presence of tetracycline, it stops the tTA from working: in effect, it acts like an antidote.
So when we feed the modified mosquitoes with this supplement in the lab, they stay perfectly healthy. But when the male mosquitoes mate with females in the wild, their children inherit the lethal gene. Tetracycline is not present in the environment in sufficient quantities to allow survival, so without the ‘antidote’ in their diet, the children of the modified mosquitoes die.
Because of this, the Oxitec genetically modified mosquitoes are effectively sterile. When radiation is used to sterilise insects, as we saw earlier, their offspring die at a very early stage of development – before hatching. With the Oxitec technique, the insect’s offspring die later in life, but the effect is the same: when a genetically modified male mates with a wild female, her children will die before reaching adulthood, so the population is reduced.
So why use genetics? As we saw earlier, a major problem with using irradiation is that the released males are often sick, so females may not choose to mate with them. In the video, Aegypta at first seems convinced that she’ll be able to recognise Oxitec’s males and avoid them. With irradiated males, she might – but that’s the clever part of using genetic modification; because Oxitec’s insects don’t have to be irradiated, they are fit and healthy. Like all male mosquitoes, they will naturally seek out females and mate with them. This means that Oxitec’s approach will be much more effective than other treatments, like pesticides, at targeting mosquitoes in difficult-to-reach places – people’s homes and gardens. And unfortunately for Aegypta and her friends, they won’t be able to tell the difference until it’s too late…