From fields to deep forests
With decades of dedicated research on mosquitoes, Professor Vu Sinh Nam, National Institute of Hygiene and Epidemiology (NIHE), said: Vietnam has recorded more than 200 species of mosquitoes belonging to 17 genera, of which 4 genera can transmit diseases to humans. Anopheles mosquitoes transmit malaria; Culex mosquitoes transmit Japanese encephalitis; Mansonia mosquitoes transmit elephantiasis; Aedes mosquitoes transmit dengue fever caused by the Dengue virus (commonly known as dengue fever in the community).
NIHE experts guide people in Hanoi to eliminate mosquito larvae that transmit dengue fever.
Among the dangerous diseases transmitted by mosquitoes, malaria has been basically controlled. Mosquitoes that transmit this disease are distributed and live in the mountains and forests, remote areas, not really close to people, so the ability to spread the disease is also limited in the mountains and forests, especially for the group of people who go to the forest to sleep in the fields.
Culex mosquitoes that transmit Japanese encephalitis usually breed, rest and spread outside the house, such as in rice fields, rice fields, and bushes, so they are called field mosquitoes. Mosquitoes often fly out to suck blood from animals or people at dusk; they breed and develop a lot in the summer when it is hot and rainy. Thanks to the Japanese encephalitis vaccine, this epidemic is being effectively controlled.
Professor Vu Sinh Nam (right cover) and other scientists have spent decades researching the characteristics of mosquitoes that transmit dengue fever, contributing to solutions to control the disease.
Regarding elephantiasis, the Department of Preventive Medicine (Ministry of Health) said that Vietnam has eliminated it since 2019. Therefore, mosquitoes that transmit elephantiasis are temporarily not a major threat to public health.
Urban mosquitoes wake up with people
Professor Vu Sinh Nam said that among the four disease-transmitting mosquito species, the most "smart" and "intimate" to humans is the Aedes species, of which the Aedes aegypti is the most dangerous. This mosquito is black, with white spots on its body and legs, so it is often called the tiger mosquito.
Aedes mosquitoes always follow human activities closely. Early morning and late afternoon are the two times when Aedes mosquitoes are most active, which is also when people just wake up and come home from work. They "reside" in the house, in dark corners, on clothes or blankets and other items. In particular, female Aedes mosquitoes only like to suck human blood. Only when there is human blood can mosquito eggs develop. This species of mosquito is also known as "bourgeois mosquito", "urban mosquito", because it only chooses to lay eggs in places with clean water.
Mosquito surgery
According to Professor Vu Sinh Nam, to assess the level of "coping" of Aedes mosquitoes with chemicals to kill them, scientists still have to catch larvae and raise them in the laboratory. After about 7 - 10 days, the larvae develop into mosquitoes, at which time the mosquitoes will be tested with chemical doses.
Professor Vu Sinh Nam (right cover) and other scientists have spent decades researching the characteristics of mosquitoes that transmit dengue fever, contributing to solutions to control the disease.
Along with assessing the risk of chemical resistance, studies also assess the life cycle and reproductive capacity of Aedes mosquitoes, thereby determining the most effective mosquito control measures. Mosquito surgery is one measure used for this assessment.
Through meticulous "dissections", the "surgeons" observed the reproductive system (oviducts, ovaries) of female mosquitoes. On the oviduct of the mosquito, each time it lays eggs, it will leave a "button" and a mark. Female mosquitoes lay eggs at most 4-5 times, with 4-5 buttons marked on the oviduct. After spraying mosquito-killing chemicals, if the captured mosquito population has no buttons or few buttons, the spraying is effective.
According to Professor Nam, female mosquitoes live for about a month, sucking human blood every 3-5 days to develop eggs; each time they lay about 100 eggs. In a life span of about 30 days, a female mosquito can produce 300-500 offspring.
More and more "young mosquitoes" carry the virus
NIHE scientists say that dengue mosquitoes have a high degree of euthanasia compared to other mosquito species. For malaria mosquitoes and Japanese encephalitis mosquitoes, they need to suck blood with a certain "dose" of blood enough for eggs to develop. If the amount of blood is less than the required amount, the blood is only enough for food.
"But for Aedes mosquitoes, the more blood they suck, the more eggs they develop. In one meal of blood, Aedes mosquitoes can suck many people. Therefore, if there are 4-5 people in a house, just one Aedes mosquito infected with Dengue virus can easily infect everyone, causing the whole family to get dengue fever," said Professor Nam.
NIHE experts study Aedes mosquitoes
Notably, the latest studies show that previously, Aedes mosquitoes transmitted the virus to their offspring at a very low rate, about 1/4,000 - 1/6,000; but recently the rate of Aedes mosquitoes transmitting the virus to their offspring has been much higher, about 1 - 3%. This fact can change the perspective on the emergence and spread in the community. Previously, they had to suck the blood of infected people to transmit the disease. But now, their offspring, the "young mosquitoes" are born with the virus and can transmit the disease more easily.
"Therefore, if you miss a nest of hundreds of mosquito larvae, 7-10 days later a new batch of mosquitoes will spread out to bite people and transmit the disease. Studies estimate that for every 1 case of dengue fever diagnosed, there are actually about 122 other cases that have been silently infected in the community," Professor Nam noted.
"The existence of the Dengue virus in the community along with the large population of Aedes mosquitoes makes dengue fever persistent and easy to break out. We hope that everyone in the community will join hands to kill larvae and mosquitoes that transmit the disease, and work with the health sector to apply measures to prevent this disease," Professor Nam shared.
Vaccine expectations
Currently, there are two types of dengue vaccines that have been approved in the world: Sanofi Pasteur (France) and Takeda (Japan). Takeda's (Japan) vaccine can protect against all four types of viruses and does not care whether the vaccinated person has had dengue or not. WHO is reviewing and will soon have recommendations on dengue vaccination.
The Ministry of Health is in the process of reviewing and licensing Takeda's dengue vaccine in Vietnam. With the vaccine, the community will have more tools to prevent dengue fever caused by Aedes mosquitoes.
Professor Vu Sinh Nam
Source link
Comment (0)