Translated material
Mosquitoes against fever
Hundreds of millions of people around the world have a fever, and has not yet been able to cope with it. There are no drugs from Dengu, Zika and Chicunga. Experts tried to fight the infection carriers - mosquitoes of yellow -bearing AEDES AEGYPTI, draining the reservoirs where their larvae live, but also to no avail. Mosquitoes continue to bother, and the list of diseases they transfer are continuously replenished.
Maybe the problem will be able to solve if these bloodsuckers are used against themselves? Currently, experts are actively developing this idea in two directions [1]. The first approach involves the creation of transgenic mosquitoes - carriers of a lethal gene. This gene will be transmitted to descendants who will die without reaching maturity . The second approach allows you not to reduce the population, but to replace wild insects with mosquitoes that are not able to transmit infection.
Liquidators
At the beginning of the XXI century, the genetics of the University of Oxford led by Professor Luke Alphey received a transgenic line of mosquitoes A. Aegypti Ox513a. The line contains the theomol of TTAV (variant of the transcription activator suppressed by tetracycline). In the laboratory, mosquito larvae develop in water, into which tetracycline is added. The antibiotic blocks TTAV activity, so mosquitoes live and multiply normally [2].
In natural conditions, without an antibiotic, the gene begins to work, its product prevents the synthesis of other cells of the cell, while enhancing the expression of the TTAV proper, and the amount of protein is avalanche -shaped increases. A huge amount of TTAV blocks the transcription machinery, and the insect dies. The design turned out to be very stable and is already preserved in the 200th generation of transgenic A. Aegypti.
The TTAV gene only works in insect cells, its protein is non -toxic, and frogs, having eaten transgenic mosquitoes, will not suffer. Another advantage of the method is that its action is not aimed at all insects in the district, but to one specific species.
The transgenic line of mosquitoes also contains the DSRED fluorescent marker - a protein, the glow of which is clearly visible when viewing through certain filters. It allows you to easily distinguish wild insects from transgenic.
The laboratory of transgenic larvae is sorted manually: males and females differ significantly in size. Only the Friendly ™ Aedes are released into the world. They do not bite and therefore cannot infect anyone. But they strive for mating and fertilize wild females, conveying the fatal gene to the offspring. Larvae die without reaching maturity, males Friendly ™ Aedes are also dying and are not preserved in the environment.
The implementation of the Friendly ™ Aedes program is engaged in Oxitec, which was founded by Luke Alphaea. The trial production, which took place in 2009 in the Kaiman Islands, showed excellent results. On a area of 0.16 km2, the population of wild mosquitoes decreased by 96%.
Then the company conducted successful tests in Panama and Malaysia, then it was the turn of Brazil. In this country, millions of citizens suffer from Denge’s fever: only in 2015, the virus struck about one and a half million Brazilians, and now cases of infection with the ZIK virus have also become more frequent, so no mosquito studies have passed Brazil.
In cooperation with the University of San Paulo Transgenic mosquitoes in 2011-2013, Bahia (Bahia) was produced in the Brazilian state; During this time, the number of wild A. aegypti decreased by at least 90%. In mid-2016, the Friendly ™ Aedes program was deployed in the San Judas area and in just six months they achieved a reduction in the number of wild larvae by 78%.
In the Brazilian town of Pirasikaba (Piracicaba), the release area was 12 km2, about 60 thousand people live in this territory. On March 30, 2017, Oxitec and the Pirasikabs administration reported that the second year in a row the number of wild mosquitoes is reduced by more than 80% compared to the raw zone, while the number of Friendly ™ Aedes released in 2016 was 59% lower than a year earlier [3].
The company's specialists celebrate victory and are going to expand the program of the program, for which they will need to increase the production of transgenic larvae 30 times (now their Brazilian mosquito farm produces up to 4 million larvae per week).
Do not kill a mosquito , but protect people
While Oxitec with triumph calculating the number of destroyed insects, their colleagues adhere to another tactics. They see their task not to kill mosquitoes, but to protect people from dangerous diseases. Their creatures are designed not to exterminate the wild population, but to change it.
In 2005, an entomologist Scott O'Neill from the University of Monash (Melbourne, Australia) found that mosquitoes that were given blood with Denge or Chicungy viruses or tolerate these viruses, if infected with the intracellular parasite of WolBachia Pipentis. In the same year, but a little earlier, Brazilian scientists from the Oswaldo Cruz Foundation received similar results for the Zika virus.
Together they started the Eliminate Dengue program, headed by Scott O'Neill [4]. Scientists suggested that the parasite is competing with the virus for limited resources of the mosquito cell. It is also possible that Wolbachia activates the owner’s immune system, which helps him fight other infections. Wolbachia parasitizes about 60% of insect species in cells, but A. aegypti is not among them. The laboratory population of infected mosquitoes had to be obtained on purpose.
Since the bacterium is transmitted to descendants only on the maternal line, scientists have to release the females infected with Wolbachia . However, these females, although they bite, are safe for humans, because they cannot tolerate the virus.
Within the framework of Eliminate Dengue, infected mosquitoes were released in more than 40 regions of Australia, Vietnam, Indonesia, Colombia and Brazil. For 10–20 weeks, the parasite infects up to 90% of the local A. Aegypti and persists in the population for at least five years. This method differs favorably with the Friendly ™ Aedes program, which requires the annual release of transgenic males. Unfortunately, Wolbachia does not apply over long distances. To saturate Brazil with infected mosquitoes, Fiocruz is ready to produce about 12 million larvae per week.
Brazil is one of the few countries where the Eliminate Dengue program is implemented in large cities. Sometimes it creates unexpected difficulties. Some slums of Rio de Janeiro are inaccessible, entering them is associated with risk. In addition, it turned out that mosquitoes infected with parasites are sensitive to insecticides, therefore, in natural conditions, their number is rapidly falling. Scientists had to engage in selection for three months, increasing the stability of laboratory mosquitoes to the level of their wild relatives.
Eliminate Dengue is not the only program that uses Wolbachia to combat mosquitoes. In Singapore, they plan to infect A. aegypti to get barren offspring (the bacterium affects the fertility of the hosts). In the USA and China, with the help of Wolbachia they are going to fight the Asian tiger mosquitoes A. albopictus , which are also tolerated by Denge and Chicungan.
Problems of effectiveness
Both methods significantly affect the state of the populations of wild A. aegypti , but people are more interested in how these measures affected the incidence. And scientists do not know this yet. The reduction in the number of potential media does not mean that people have become less sick: few surviving mosquitoes can transmit the virus very effectively.
In July last year, Oxitec announced that in Pirasikab for a year the number of diseases of the fever of Denge decreased from 133 to 12, that is, by 91%. Other municipalities report a reduction by only 52%. However, fever occurs with outbreaks, and the current lull is not necessarily connected with transgenic mosquitoes. This can only be a natural break between two episodes. To make the final judgment on the effectiveness of both programs, long and large -scale epidemiological studies are needed.
The effectiveness of the Eliminate Dengue program is studied in the Indonesian city of Jokyakarta. Denge's incidence is tracked for more than two years in 24 districts, where about 14,500 people live. In half of these areas, mosquito infected Wolbachia will be released. A large -scale study is also planned in Vietnam. Meanwhile, Oxitec attracts independent experts to develop an experiment scheduled for 2018.
Another big problem is money. Eliminate Dengue did not count the costs, but he will try to make the program no more than $ 1 per person. Oxitec spends more. Only for experiments in Pirasikab in two years it took at least 1.1 million dollars - about $ 10 per resident of the treated territory.
While scientists determine the effectiveness of their projects and think about what means and power they will need to implement them, natural selection does not doze off. Over time, both lines of modified mosquitoes may lose their advantage, because insects will gain resistance to the action of a lethal gene, and viruses will adapt to joint existence with Wolbachia .
Meanwhile, new lines of transgenic mosquitoes are ripening. At the University of San Paulo, in the laboratory of Professor Margareth Capurro, the Brazilian partner OxiteC, develop the A. Aegypti line, which will allow insect cells to recognize the Denge virus enzyme and give the cell a signal of self-destruction. The gene is not flying and over time will spread throughout the population.
American researchers, led by George Dimopoulos, professors of the University of Jones Hopkins, manipulate their own mosquitoes of the Dome receptor or Januscinase Nor , placing them under the promotor, which is activated when the mosquito gets drunk with blood [5]. The promoter only works in the fatty body of insects, which performs, inter alia, the functions of the immunocompetent organ. The increased activity of Dome genes and Nor affects the synthesis of many fatty proteins and suppresses the infection of several serotypes of the Denge virus, but not Zika and not chicunga. Genes do not reduce the life of mosquitoes, but significantly worsen their fertility.
Experts believe that the creation of a market for transgenic insects, which provides potential customers with a choice depending on the desired result, will be useful to health services.
Natalia Reznik
2. Www.oxitec.com/our-solution/technology/the-science/
3. Www.oxitec.com/oxitecs-friendly-aedes- 81-suppress-wild -aedes-aEGYPTI-CAPAPEPEPELDORADO-PIRACICABA-SECOND-YEAR-PROET/
4. Callaway E. Infected Mosquitoes Fight Zika // Nature. 2016. 539. R. 17–18.
5. Jupatanakul N., Sim S., Angleró-Rodríguez Yi, Souza-Neto J, Das S, Poti Ke, et al. Enginereds Aegypti Jak/Stat Pathway-Mediated Immunity to Dengue Virus // Plos New Trop Dis. 2017. 11 (1): E0005187.