Dengue fever, as a disease that rages in tropical and subtropical regions, was listed by the World Health Organization (WHO) as one of the top ten global health threats in 2019. According to WHO estimates, 100 to 400 million people worldwide are infected with dengue fever each year, and the patients will have symptoms such as high fever and severe joint pain.
The culprit responsible for the spread of dengue fever is the well-known Aedes aegypti mosquito, which is the most important vector for the transmission of dengue fever. In the past, in order to prevent the spread of dengue fever, some areas chose to block the vector, that is, to reduce the number of Aedes aegypti mosquitoes. The idea of this approach is correct, but the implementation has little effect. Insecticides to kill mosquitoes basically cannot curb the spread of dengue fever.
Members of the World Mosquito Project are releasing modified mosquito seeds.
Use mosquitoes to kill disease
However, this passive situation has turned around in recent years. In the past 10 years, scientists have released some modified mosquitoes in certain cities to resist the spread of mosquito-borne diseases. This modification is not complicated, it just makes Aedes aegypti carry a kind of bacteria that they do not originally have in their bodies-Wolbachia. According to a preliminary analysis by the World Mosquito Project (WMP), dengue infection rates have dropped by 76% in some areas where modified mosquitoes are released. This result also strengthened their confidence in further promoting the use of Wolbachia modified mosquitoes.
In fact, Wolbachia naturally exists in many insects, and based on the characteristics of this bacteria, there are many ways to prevent the spread of mosquito-borne diseases. One method is to create a batch of special male mosquitoes. The Wolbachia contained in these male mosquitoes is different from that of wild female mosquitoes, so that when male mosquitoes mate with female mosquitoes, the Wolbachia of the two are different. Will produce cytoplasmic incompatibility. The result is that the eggs laid by female mosquitoes cannot hatch, which can quickly reduce the mosquito population.
However, there is an easier way for Aedes aegypti. The natural Aedes aegypti itself does not contain Wolbachia, and once Wolbachia enters the body of Aedes aegypti, it can prevent many viruses, including dengue fever virus, from replicating. As a result, the number of viruses in the mosquitoes will drop drastically, and even if they bite humans, they will not spread the disease.
This strategy has been practiced on a small scale in 2015, when WMP released a batch of Aedes aegypti infected with Wolbachia in Townsville, Australia. After 4 years of testing, only 4 cases were reported locally. Dengue fever infection case. In 2019, at the annual meeting of the American Association of Tropical Medicine and Hygiene, WMP’s epidemiologists once again brought optimistic results. In Yogyakarta, Indonesia, the number of dengue fever infections dropped by 76% after two and a half years after the release of the modified mosquito area compared with the control area. In Niteroi, Brazil, the number of infections of chikungunya (an infectious disease infected by the chikungunya virus and transmitted by the Aedes mosquito) has dropped by 75%.
The scale of these studies is small, and the conclusions are based on the statistical data of the local health department, so there may be errors in the data. But in the view of WMP members, “this is still a positive signal”, so it may be time to carry out a larger experiment.
Change the lives of 300,000 people
Just do it, the research team directly selected an area of 26 square kilometers in Yogyakarta, where about 300,000 residents live. They divided the area into 24 regions, 12 of which will release specially selected modified mosquitoes, which carry a type of Wolbachia that has been compared and screened many times. This bacteria can effectively deal with 4 kinds of dengue fever. The subtype of the virus.
The entire team needs to collaborate in various areas to release a batch of modified mosquitoes at the test site every two weeks. This process lasts up to 28 weeks. Since the first release of modified mosquitoes, about 10 months later, the proportion of modified mosquitoes in the local mosquito population has risen to 80%.
The researchers recruited some volunteers with fever symptoms in 24 areas for dengue fever testing. Among volunteers who came to the test area, the proportion of dengue fever positive was 2.3%, while in the control area, the proportion of dengue fever positive was 9.4%. Simply put, the release of modified mosquitoes can reduce the proportion of dengue fever infections by 77%. The probability of hospitalization due to dengue fever will also drop by 86%. At the same time, the research team used a computer-built model analysis to show that when individuals are more exposed to mosquitoes infected with Wolbachia, people’s risk of getting dengue fever is much lower.
In the later stages of the experiment, the researchers found that Wolbachia had begun to spread towards the control area, infecting mosquito populations in these areas. After the experiment was over, the research team also began to release modified mosquitoes in the control area. They wanted to completely eradicate dengue fever in this 26 square kilometers area.
In December 2020, WMP submitted to WHO the data of this large-scale experiment carried out in Yogyakarta. According to the WHO advisory group, they are preparing to list Wolbachia mosquitoes as one of the recommendations for controlling dengue fever. WMP is currently seeking approval from the WHO to allow UN agencies to invest in the release of modified mosquitoes in more places. Currently, the price of this method to protect individuals from dengue fever is less than US$10 per person, and WMP plans to reduce the cost to less than US$1 per person.
Of course, after releasing the mosquitoes, how long can protect the local residents is also a question worth considering. Judging from the data currently available, in some places where testing was conducted earlier, the level of Wolbachia transmission in mosquitoes can still maintain a high level within 10 years.