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Imminent risk of dengue in Brazil: how does the Aedes aegypti mosquito behave?

High probability of dengue affect 500 Brazilian cities and another 1,880 municipalities are in a state of readiness., as shown by the data of the rapid examination of the level of infection, conducted by "Aedes aegypti" (LIRAa). This is the mosquito responsible for transmission of dengue, zika and chikungunya viruses, as well as yellow fever in urban environments. According to the latest LIRAa data, which analyzes the proportion of households that may be the target of mosquitoes, cities such as Rio de Janeiro or Brasília are among the main capitals ready for dengue epidemics. This is a recurring situation every time the summer season comes, which lasts from December to March.

Dengue is a disease caused by the spread of a virus that is present mainly in areas with a tropical and subtropical climate. Today, according to the World Health Organization (WHO), there is no treatment for this disease, and the main goal of prevention will be to develop effective vaccines against four serotypes or dengue virus strains. Dengvaxia® vaccine (CYD-TDV), created by Sanofi Pasteur laboratories, and others, such as the Butantana lab in Brazil, recently sold to the American multinational companies Merck Sharp and Dohme (MSD), is already being commercialized. or the Osvaldo Cruz Foundation's Biomanganos Institute (Fiocruz) in collaboration with the pharmaceutical company GlaxoSmithKline (GSK).

Fiocruz is a biomedical and environmental research institution founded in Rio de Janeiro since 1900, which is one of the main research poles against dengue spread throughout the world. Rafaela Bruno, head of the Osvaldo Cruz Institute’s Molecular Insect Laboratory (IOC), one of Fiocruz’s oldest sectors, explores the behavioral changes of the Aedes aegypti mosquito after it has been infected with a virus, mainly dengue or zika. This biologist explains in an interview with RT for the current risks of the dengue epidemic, as well as the characteristic behavior of the transmitting mosquito.

RT: What is the risk of a dengue epidemic in the current Brazilian context?

RB: One summer, the risk of epidemics is always inevitable. This is due to the fact that an increase in precipitation and high temperatures typical of this season are an excellent combination for breeding mosquitoes.

Aedes aegypti develops better and faster at elevated temperatures. their Eggs are kept for up to one year. in a dry environment and with the emergence of a more humid and warmer climate, eggs stop developing and give rise to new Aedes aegypti mosquitoes, carriers of dengue and zika, among others.

RT: How does increasing the number of mosquitoes affect the spread of this virus?

RB: "Aedes aegypti" is still the only known carrier of dengue. The more mosquitoes of this type, the greater the likelihood that they will bite an infected person and pass the virus to another person.

Rafaela Bruno, Head of the Insect Molecular Laboratory, Osvaldo Cruz Institute.

"Dengue continues to be one of the most dangerous viruses, because it is present throughout the year, the incidence is higher in the summer, but infection can occur at any time of the year."

Rafaela Bruno, Head of the Insect Molecular Laboratory, Osvaldo Cruz Institute.

This is a mosquito prefers to eat human bloodthus, the transmission is usually transmitted from one person to another, having as a carrier of this particular mosquito. However, the virus is transmitted only when it is in the replicative phase of a person, that is, with an advanced disease.

RT: What is the main risk at this time?

RB: Currently, the greatest fear is caused by the chikungunya virus, which is also transmitted by the Aedes aegypti virus. So far, there have been no strong outbreaks, but this year the number of chikungunya cases is already higher than in previous years. Some groups are investigating to find out why in a certain period the virus ceases to circulate or gives way to others, but we do not yet know the specific reasons.

In addition to the specific care for chikungunya, dengue fever continues to be one of the most dangerous viruses, since it is present throughout the year. In the summer, the incidence is higher, but infection can occur at any time of the year due to the four existing serotypes, in any region of the country there can always be one circulating one.

RT: Where does the infection cycle begin?

RB: It goes back a long time. These cycles of infection began in the wild, where viruses were transmitted by other insects and then urbanized. "Aedes aegypti" only participates in the urban cyclewhere these viruses are already fully established, mostly dengue.

RT: How did these viruses move from the desert to urban areas?

RB: Dengue, zika, chikungunya or yellow fever were viruses found in monkeys, but spread as a result of human presence in the wild. How did the first people get it? this is variable and inaccurate data as it depends on the place.

In yellow fever, we know that transmission in the wilderness occurs through the mosquitoes of the genera Sabethes or Haemagogus, but for the wild transmission of dengue, zika, or chikungunya viruses, we do not have such exact discoveries. Already in an urban setting, all these viruses are transmitted by Aedes aegypti. ,

RT: One of the main tasks of your research team is to analyze the behavior of Aedes aegypti. What are the main discoveries of your studies?

RB: When the Aedes aegypti mosquito carries dengue fever, as a rule, has a shorter lifetime, it lays fewer eggs, but becomes more active and increases its ability to move. In contrast, a mosquito that becomes infected with Zika virus becomes slower, moves less, but lays the same eggs as an uninfected mosquito. In addition, the lower movement capacity of a mosquito infected with Zika explains why so many infections occur in the same family, as the mosquito tends to search for food within a small distance radius.

RT: How long is the life cycle of the Aedes aegypti mosquito and what mutational possibilities are observed in your research?

RB: Their lifespan varies from 15 to 20 days in their natural environment; mosquitoes breeding in the laboratory reach 45 days. The mutations that occur in these mosquitoes are of natural origin, and it takes some time until the corresponding effect occurs. In nature, there are different populations of mosquitoes that may be more or less vulnerable to viruses, depending on the phenomenon that we call “parasite-vector interaction”.

Rafaela Bruno, Head of the Insect Molecular Laboratory, Osvaldo Cruz Institute.

“The most effective is to avoid favorable breeding grounds for Aedes aegypti, that is, to avoid standing water where a mosquito can lay eggs, these eggs are almost invisible to the human eye.”

Rafaela Bruno, Head of the Insect Molecular Laboratory, Osvaldo Cruz Institute.

That is, sometimes the mosquito genotype may be incompatible with the genotype of the virus. Depending on the region of Brazil, there are different populations of mosquitoes, which is a consequence of different selective effects on the environment. In our genetic analysis, we observe that a population of a particular region may be more susceptible to a virus that circulates than another, so the frequency of infection from one area to another varies.

RT: The level of dengue epidemics is a risk factor that is more common and known in Brazil, while chikungunya is old, but less frequent, and Zika is recent, albeit threatening. What are the differences in the prevalence of these three viruses transmitted by the same mosquito?

RB: Dengue is a more dangerous virality, because there are four types of toxicity that can cause it: fever 1, fever 2, fever 3 and fever 4. That is, the one who already had the type is immunized against this particular, but if it starts to circulate another other person will be exposed to dengue again. Thus, in the case of Zika and Chikungunya, there is only one porotype, as soon as an infected person gets the vaccine forever.

RT: What caused the Zika outbreak that started in Brazil three years ago?

RB: The introduction of Zika in the country was recent. In 2015, the first cases of the disease began to occur, especially in the north-west of the country, but the first suspicions that it was Zika were detected only in October of the same year, after cases of microcephaly in children of mothers who became infected with the virus. , There is a hypothesis that the virus has arrived during the Confederations Cup; another indicates that he arrived during the rowing championship with many athletes from French Polynesia, where one of the first epidemics occurred. When Zika arrived in Brazil, no one was protected, so this caused so much chaos. It spread very quickly, and many people became infected, but today there is a tendency to a decrease in the number of cases, since many people have already been immunized.

RT: Based on your research, what are the mechanisms for fighting this type of mosquito and preventing infection?

RB: The most effective is to avoid places that promote reproduction of “Aedes aegypti”, that is, to avoid standing water, where a mosquito can lay eggs. These eggs almost invisible to the human eye and, moreover, women tend to place them in dark places. Therefore, it is most effective to avoid places that promote incubation of eggs, from the pot plate to the cap of the soda bottle.

RT: How does Brazilian public authority contribute to the prevention of the dengue epidemic?

RB: This is a joint work on the study and dissemination of information about the forms of reproduction of a mosquito to prevent its reproduction. Although public authorities are responsible for basic sanitation and garbage collection, this mosquito breeds only in clean waters. Mosquito breeding sites are found in people's homes, and from there each mosquito can move within a radius of about 300 meters. In this way, prevention is a joint responsibilityFrom public authority, research institutions and urban dwellers, the focus is now on possible dengue epidemics.

RT: Following this practice, will it be possible to destroy the dengue virus?

RB: In the short term, at least not. With joint efforts and collective efforts, we can significantly reduce the mosquito population, which is the only way to reduce the spread of dengue virus.

In addition to the information strategy for the population, there is an additional method of control, which consists in issuing modified mosquitoes. This can be done with the help of transgenic male mosquitoes, which, when crossed with wild females, produce offspring that die and cannot live. Another method is to release mosquitoes that contain bacteria called Wolbachia, which prevent the virus from reproducing inside it.

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