Which is more terrible for sharks and mosquitoes? The answer is mosquitoes. Sharks have killed 1035 people in the last 100 years, and mosquitoes can kill 1470 people a day, which is more than 500,000 a year. This is the data that Bill Gates has repeatedly quoted. Mosquito, onlyFemale mosquitoes are the biggest killer of human beings.
Sharks have killed 1035 people in the last 100 years, and mosquitoes can kill 1470 people a day, which is more than 500,000 a year (Source: Bill Gates blog)
On two islands in Guangzhou, China, researchers have virtually eliminated the world's most invasive mosquito species — — Asian tiger mosquito (also known as Aedes albopictus).
Guangzhou is the city with the highest rate of dengue transmission in China. During the mosquito breeding season in 2016 and 2017, the team of Professor Sun Zhiyong, director of the Joint Research Center for Tropical Diseases and Insect Control of Michigan State University, released a large number of Asian tiger mosquitoes per hectare per week in residential areas on two islands. More than 160,000 mosquitoes.
Let mosquitoes deal with mosquitoes and replace harmful mosquitoes with harmless mosquitoes.This is the idea of the team research of Qi Zhiyong. On July 18th, their latest research results areNaturePublished. Compared with previous research by Qi Zhiyong's team, the new trials are larger, are carried out in the community, and can be close to 100% of cleared mosquitoes.
New research toolsScreening of male and female mosquitoes by mechanical and low-dose radiation means combining female mosquito sterilization with male mosquito infectionIt can control mosquito populations, be green, and be low-cost and high-performance.
The research object that Zhi Zhiyong locked in was the Asian tiger mosquito. As the name suggests, the Asian tiger mosquito is a globally powerful and aggressive mosquito that can spread dengue virus, Chikungunya virus, Zika virus. In cooperation with the Guangzhou Municipal Center for Disease Control and Prevention, they selected two residential areas in downtown Guangzhou to verify the effectiveness of dengue prevention and control.
“The principle of mosquito control for mosquitoes is thatWhen the sterilized male mosquito is released and mated with the wild female mosquito, the produced egg cannot be developed.
Previously, the traditional strategy of suppressing the population of Asian tiger mosquitoes has had little effect. One method is to use radiation to sterilize male mosquitoes and then release them in the wild. After the sterilized male mosquitoes are mated with the female females in the wild, the female eggs of the female mosquitoes cannot hatch, and the mosquitoes are suppressed or eliminated by reproductive control. The International Atomic Energy Agency and the Food and Agriculture Organization of the United Nations have successfully used this sterilization technique on a large scale to control important agricultural pests.
It is only this means that has its drawbacks. Radiation will reduce the reproductive competitiveness of sterilized male mosquitoes, and it lacks mating advantages compared with wild male mosquitoes, so the mosquito control effect is not ideal.
Another method allows male mosquitoes to infect a symbiotic bacteria called Wolbachia, which produces cytoplasmic incompatibility when mated with females that do not carry the same Wolbachia type. , causing its eggs to not hatch, thereby inhibiting the number of mosquitoes. Wolbachia is a commensal bacterium that is widely distributed in nature and can be transmitted by eggs. It naturally exists in about 65% of the world's insect population and 28% of mosquito species, carrying different types of Volbak. Eggs produced after mating of male and female insects of the body cannot develop.
But this method is also risky, just adoptMechanical screening of male and female mosquitoes can not be 100% accurate. Once the female mosquito infected with the same type of Wolbachia is accidentally released, it will replace the local population and affect the further implementation of the Wolbachia-based population suppression strategy.
Qi Zhiyong decided to absorb the length of the two means and avoid it short. He and his colleagues irradiated mosquitoes infected with Wolbachia to sterilize female mosquitoes that might be accidentally released, while ensuring that low-dose radiation levels did not affect the reproductive competitiveness of male mosquitoes.
For a two-pronged application, Zhai Zhiyong explained that if you want to pursue maximum population suppression, or population clearance, you must solve the damage caused by a small number of female mosquitoes, then the introduction of radiation can achieve the effect of clearing female mosquitoes. . If the Wolbachia infection technique is used purely, a high degree of compression cannot be pursued in the absence of a 100% efficient male-female separation technique.
In their field trials in Guangzhou, they released millions of mosquitoes that were infected with Wolbachia and had been exposed to radiation. In two years, wild Asian tiger mosquito populations were almost completely eliminated, and the annual number of wild mosquitoes decreased by an average of 83% - 94%, and no mosquitoes were detected for up to 6 weeks. Population genetic analysis showed that the only remaining mosquitoes might have migrated from outside the study area.
Zhai Zhiyong said, “We have been doing this field experiment since 2014. By combining these two techniques, after 2 years, the effect of eradicating the target mosquitoes was finally achieved. ”
The researchers released mosquitoes at the test site. (Source: Qi Zhiyong)
Increased public acceptance
Dengue fever is a mosquito-borne viral infection that can cause severe flu-like symptoms and sometimes can cause fatal complications, while Aedes aegypti and Asian tiger mosquitoes carry dengue fever, Chikungunya and Zika virus. According to the World Health Organization, the incidence of dengue fever has increased 30-fold over the past 50 years. It is estimated that between 50 and 100 million infections occur in more than 100 countries with the disease each year, jeopardizing almost half of the world's population.
Lin Lifeng, deputy director of the Guangdong Provincial Center for Disease Control and Prevention, said that the dengue fever epidemic in Guangdong Province still occurs this year.There is no vaccine for dengue fever, and there is no specific medicine. It can only prevent and control the spread of the disease by controlling the vector of mosquitoes..
In Guangdong Province, Asian tiger mosquitoes are the main vector, and the only dengue media in Guangzhou and surrounding areas, while Guangzhou is a city with a high incidence of dengue fever. According to Lin Lifeng, killing adult mosquitoes is only an emergency measures to eliminate mosquitoes. The basic means of prevention and control is to eliminate mosquito breeding sites, that is, to clear or control stagnant water and eliminate the source of mosquitoes.
However, the conventional means can not cure the problem, so the disease control and epidemic prevention department will pin the hope of the root cause on the biologist.
Biologists have two strategies for using genetics to reduce mosquito vectors. One is the suppression of population, that is, by inducing infertility and other means to greatly reduce the population of mosquitoes, so that they cannot maintain the spread of germs. The second is population replacement, which changes the genetic background of wild populations and reduces their inherent ability to transmit germs. The strategy of the Qi Zhiyong team is the former, which releases male mosquitoes with Wolbachia to mate with wild female mosquitoes to sterilize them.
In the experiments of previous years, Zhai Zhiyong limited his research to two isolated islands, and now he moved the laboratory to urban residential areas. The challenge of the latter is that the ecological environment and the breeding grounds of mosquitoes are more complicated, there are more variables to be considered, and the acceptance of this means by local residents is also a problem.
Mosquitoes infected with Wolbachia are harmless to the human body.Evidence shows that since the earth has humans, Wolbacher has always lived in peace with mankind. Wolbachia does not infect humans or mammals through mosquito bites, and no anti-Walbachian antibodies are detected in the blood of people who bite. Wolbachia only survives in host cells, cannot leave insects to grow independently in the environment, and does not infect native enemies that feed on mosquitoes. Biosafety risks from Wolbachia-based mosquito vectors are almost negligible.
In fact, the biggest driving force for local residents to accept the pilot program is the dengue epidemic in previous years. The researchers also reached into a plastic canister with mosquitoes and proved to the public that the test male mosquito did not bite.
Before and after the test, the residents' support rate for mosquito control by mosquitoes increased greatly. (Source: Zhi Zhiyong paper)
The test results are positive for residents' acceptance. According to the survey, only 13.0% of the residents supported the mosquito control before the mosquito test, and 76.4% of the intermediate position and 10.6% of the opposition rate. After the test, the mosquito support rate reached 54.3%.
Residents also really felt the power of science. At two test sites,The wild-type Asian tiger mosquitoes have reduced the bite rate of humans by 96.6% and 88.7%, respectively..
Expected to promote within three years
Low temperature transport of male mosquitoes. (Source: Qi Zhiyong)
Previous studies have been conducted on GM mosquitoes or genetically modified mosquitoes to control Zika virus, but they have not been seen. Qi Zhiyong told DeepTech,In many cases, these studies have been blocked by the government and difficult to accept..
Qi Zhiyong's research methods have nothing to do with genetic modification technology. The method of establishing Wolbachia-infected mosquitoes is by microinjection, the donor is a Wolbachia that is widely found in nature, not a transgenic product, and thus does not introduce any new organism into the environment. In this approach, the mosquito's genes are not transformed and there is no need to tamper with or modify the genes.
Concerning whether this means will eliminate mosquitoes, Zhai Zhiyong said that this method is specifically aimed at Asian tiger mosquitoes and has no effect on other types of mosquitoes. There are about 3,000 species of mosquitoes in nature. There are many kinds of mosquitoes that do not transmit diseases, and some mosquitoes do not bite or suck blood. These mosquitoes are not the target of control. In addition, these methods are mainly aimed at disease-transmitting mosquitoes in human settlements, and those Asian tiger mosquitoes that do not bear the role of transmitting diseases in the wild are not clear targets.
Peter Armbruster, an ecologist at Georgetown University in the United States, commented in Nature during the same period that no single mosquito control method can completely eliminate the transmitted mosquitoes and requires a combination of mosquito control tools. However, the team's “two-pronged approach” is a major advancement, demonstrating a strong potential for mosquito control.
Peter Armbruster pointed out that the team must solve the problemSustainability problem. Once the mosquitoes infected with Wolbachia cease to be released, the migrated wild mosquitoes will inevitably re-establish natural populations.
Today, the team of Qi Zhiyong is actively communicating with the Ministry of Agriculture to submit data on pharmacodynamics.It is hoped that the male mosquito carrying Wolbachia will be approved for application as a microbial insecticide.. Qi Zhiyong is very optimistic about this. He said that such research has recently been registered by the Environmental Protection Agency for microbial pesticides in the United States. It is expected that China will be approved for promotion within one to three years.