© Josh Sager – July 2012
Mosquitoes are a common pest in many areas around the worlds and have been known to carry numerous diseases which can be transmitted to humans. Efforts to reduce mosquito populations and combat the spread of mosquito-borne illnesses have taken many forms, including the draining of swamps and the uses of chemical pesticides, treated mosquito nets, and scent-based repellants. In recent years, the research surrounding mosquito control has begun to include the use of genetic modification on mosquitoes.
Many species of mosquitoes carry diseases which can cripple or kill humans. Among the diseases which can be transmitted by mosquitoes, Eastern Equine Encephalitis, West Nile, Dengue Fever, Yellow Fever and Malaria have been the most devastating on human life; millions of people have died due to these diseases. In the face of such serious diseases, governments have taken extreme measures to combat the top vector (mode of transmission) of transmission—the bite of a common mosquito.
In the past, mosquito outbreaks have been combatted through conventional means of killing mosquitoes and interrupting the mosquito life-cycle. These methods often are time consuming (draining swamps), expensive, of limited effectiveness (mosquito netting), or involve the use of toxic chemicals (pesticide spraying). With the rise of genetically engineered organisms, scientists have begun developing a pest control method that they claim is cheap, effective, and completely devoid of toxic chemicals: the creation of mosquitoes with a killer gene that prevents them from successfully breeding in the wild.
The genetically modified mosquitoes which are closest to widespread use are created by the UK based Oxitec. These mosquitoes are designed to fight Dengue fever by diminishing the local population of mosquitoes through a suicide gene. Oxitec’s genetically modified mosquitoes are designed to die if they do not have access to the antibiotic tetracycline and to be unsuccessful in producing viable offspring. While they are growing in a lab, these mosquitoes are constantly exposed to tetracycline but, once released, they begin to die off. These mosquitoes are intended to breed with normal mosquitoes and produce dead offspring, thus gradually killing off the species of mosquito and halting the spread of mosquito-borne illnesses.
The Oxitec mosquitoes have been released in several locations, including the Grand Cayman Islands, Brazil, and Key West (Florida). The initial results of these tests suggest that the mosquitoes are successful in decreasing the populations of mosquitoes and that the GE mosquitoes have no effect on humans (all of the GE mosquitoes are male, thus will not bite humans). Unfortunately, these tests only show a very limited picture of the results of GE mosquito usage and give no information about the long-term effects of such genetic modifications.
While a good idea in theory, there are many problems which can be created when humans release a genetically modified or alien (non-indigenous) species into an environment. Among the most severe potential problems, the is the possibility of unanticipated genetic expressions in the modified mosquitoes, the potential for new allergic reactions, and the ripple effect of altering a link in the ecosystem are the three largest issues.
When humans modify an organism on the genetic level, there is always the potential for unforeseen genetic expressions. Simply put, this means that a genetic alteration to an organism may have effects other than the one intended by the scientist. For example: altering a gene which controls the reproductive viability of an organism may also change the metabolism or immune system of the organism in a way which was never intended. As current level of human knowledge about the genetic codes of organisms is not perfect, there is always the potential for accidents when we attempt to alter the genetics of an organism.
It is possible that the genetic alterations of mosquitoes only do what is intended, but there is also the possibility that we will discover side effects—side effects which are impossible to fix once the GE mosquitoes have been released into the wild. There are literally innumerable ways in which genetic modifications can express in unforeseen ways—some of these expressions are harmless, but many are dangerous—but here are a few of the worst-case scenarios:
- It is possible that human alterations to these mosquitoes could make them capable of carrying diseases which are not currently spread by mosquitoes (ex. HIV); we may eradicate the spread of some diseases, only to facilitate the transmission of worse ones in the mutated mosquitoes.
- As not all mutated larvae die, it is possible that these mosquitoes will simply become a new species and replace the current mosquitoes. It is possible that these mosquitoes would be hardier (due to their exposures to antibiotics) than the non-mutated mosquitoes, or otherwise more dangerous than the current species.
- We do not know whether or not GE mosquitoes have similar environmental tolerances to non-mutated ones, thus there is the possibility that the alterations to mosquitoes will allow them to live in normally inhospitable climate—thus spreading the vector of disease to a larger geographic area (ex. increasing mosquito populations in colder areas).
Ironically, the largest danger of genetically modified mosquitoes was near-perfectly expressed in the 1997 movie “Mimic”. In this movie, cockroaches begin to carry a deadly disease and need to be exterminated—the method of extermination chosen is the use of a genetically modified cockroach which is toxic to other cockroaches and sterile. While this plan works to kill off the carrier cockroaches, the modifications to the “Judas” cockroaches have the unanticipated side effect of causing them to grow to immense sizes, breed quickly, and loosely mimic human behavior; needless to say, the new breed of roaches proves to be very dangerous, and arguably a worse threat to humans than the original disease. While this movie’s content is dramatically over-inflated, it demonstrates the very real problem that nobody can predict the final result of genetic modification.
In addition to the potential for unforeseen genetic expressions, there is the potential that the new mosquitoes may provoke allergic reactions to some people. Insect bites and stings are common sources of allergic reactions in humans and it is entirely possible for the modified mosquitoes to provoke a reaction in humans. As all of the mosquitoes released are male (which don’t bite humans), there was never any testing to see whether or not the modified mosquitoes pose a significant risk for allergic reactions in humans. Some offspring of these mosquitoes survive, and many of these will inevitably be females that will bite humans; if there is a potential for serious allergic reactions, or even anaphylactic shock, due to bites from the female offspring, it could pose a serious health risk. It would be terribly ironic if, in an attempt to stop the transmission of mosquito-borne illnesses, we were to develop a type of mosquito which causes severe reactions in humans even without a disease.
The unforeseen danger of anaphylactic shock due to genetically modified organisms is a real risk and has already cost lives. In the 1990s, scientists developed a soybean with increased nutrients derived from the genetic material of a Brazil nut. Unfortunately, since some people are allergic to nuts, this led to deaths from people unknowingly ingesting Brazil nut genetic material through their soybeans. If such an unforeseen allergic reaction were to happen with mosquitoes, the results would be extremely hazardous and could cause many deaths before it was gotten under control.
Even if the genetically modified mosquitoes are completely successful and there are no unforeseen genetic expressions or allergic reactions, there is a danger inherent to removing a link in the ecosystem. While they are a danger to us, mosquitoes are a vital component of an ecosystem and serve as a food supply for many other organisms. If the mosquito populations were to be decimated insectivores (ex. bats) would suffer. In the vacuum created by the loss of mosquitoes, organisms which feed on mosquitoes would lose a significant source of food and would likely decline in population; this decrease in population would further distort the natural ecosystem and could unbalance it.
The demise of a species of mosquitoes could not only affect insectivores, but also other pests. It is possible that the depopulation of a species of mosquito would increase the population of other pests—such as biting flies or other species of mosquitos. In the event of another species being given an advantage due to the demise of mosquitoes, it is very likely that an entirely different set of problems will be created; the new dominant species may carry other diseases or be more pervasive than the now-decimated mosquitoes, thus we may create more problems than we solve.
Ultimately, it is important that any genetically modified organism go through vigorous, independent, and long-term testing before it is released into the wild. Genetic engineering is a new and dangerous technology, thus it must be handled with care. Unfortunately, the Oxitec genetically engineered mosquitoes have not been tested rigorously, yet have been released within the United States. Only time will tell as to the effects of this release, and we must only hope that this experiment does not result in worse problems than we currently are facing due to mosquito-borne illnesses.