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The risk of dengue fever that will occur in Brazil: What is the behavior of the Aedes aegypti mosquito?



High probability of an outbreak of dengue fever affects 500 cities in Brazil and 1,880 other cities are on standby, as indicated by the infection rate rapid survey system data by & # 39; Aedes aegypti & # 39; (LIRAa). This is a mosquito responsible for transmission of both dengue, Zika and chikungunya and, also, yellow fever in an urban context. According to the latest data from LIRAa – which analyzes the percentage of households that might be the focus of the spread of mosquitoes – cities such as Rio de Janeiro or Brasilia are among the main capital prepared for an outbreak of dengue fever. This is a recurring situation every time summer arrives, which takes place between December and March.

Dengue fever is a disease caused by the spread of a virus that is present mainly in tropical and subtropical climates. Until now, there has been no treatment for this disease and the main goal of prevention is the development of vaccines that are effective against four serotypes or types of dengue virus, according to the World Health Organization (WHO). At present, there is already commercialization of the Dengvaxia® vaccine (CYD-TDV), made by the Sanofi Pasteur laboratory, and others such as those developed by the Butantan Institute in Brazil, which was recently sold to Merck Sharp and US multinational Dohme (MSD). , or the Bio-Manguinhos Institute from the Oswaldo Cruz Foundation (Fiocruz) in collaboration with the pharmaceutical company GlaxoSmithKline (GSK).

Fiocruz is a biomedical and environmental research institute based in Rio de Janeiro since 1900, which is one of the main poles of research on the spread of dengue fever throughout the world. Rafaela Bruno, head of the Oswaldo Cruz Institute (IOC) Molecular Insect Laboratory, one of the oldest sectors of Fiocruz, investigated changes in the behavior of mosquitoes & # 39; Aedes aegypti & # 39; once infected with a virus, especially dengue fever. or zika. This biologist explained, in an interview for RT, the current risks of dengue epidemics, as well as the characteristic behavior of mosquitoes that transmit.

RT: In the current Brazilian context, what are the risks of developing a dengue epidemic?

R.B .: Once in summer, the risk of an epidemic is always close. This is because the increase in rainfall and high temperatures, typical of this season, is an excellent combination for breeding mosquitoes.

& # 39; Aedes aegypti & # 39; develops better and faster with high temperatures. Yours The egg survives for up to one year in a dry environment, and with the arrival of a more humid and warm climate, the eggs are finished developing and give rise to new mosquitoes & # 39; Aedes aegypti & # 39; transmitters of dengue and zika fever, among others.

RT: How did the increase in the number of mosquitoes affect the spread of this virus?

R.B .: & # 39; Aedes aegypti & # 39; so far this is the only known dengue sender. The more mosquitoes this type, the more likely they are to bite people who are infected and transmit the virus to other people.

Rafaela Bruno, head of the Oswaldo Cruz Institute for Insect Molecular Laboratory.

"Dengue fever continues to be one of the most dangerous viruses because it is present all year long, in the summer it is higher, but infections can occur at any time of year."

Rafaela Bruno, head of the Oswaldo Cruz Institute for Insect Molecular Laboratory.

This mosquito prefers to eat human blood, so transmission is usually given from one person to another who has this particular mosquito as a carrier. However, the virus is only transmitted when it is in the replication phase of the person, that is, with a developing disease.

RT: What are the main risks at the moment?

R.B .: At present the biggest fear is the chikungunya virus, also transmitted by & # 39; Aedes aegypti & # 39 ;. So far there has not been a strong outbreak but this year there have been a number of cases of chikungunya that were higher than in previous years. Several groups are investigating to find out why in a certain period the virus stops circulating or gives a place for others, but we don't know the specific reasons so far.

Apart from special attention with Chikungunya, dengue fever continues to be one of the most dangerous viruses because it exists throughout the year. In summer the incidence is higher, but infection can occur at any time of the year because of the four serotypes available, there is always one circulating in each region of the country.

RT: Where did the cycle of infection begin?

R.B .: This has been a long time. This infection cycle begins in the wild, where the virus is transmitted by other insects, and then spreads to the city. & # 39; Aedes aegypti & # 39; only participate in urban cycles, where the virus is fully installed, especially dengue fever.

RT: How did this virus move from the wilderness to urban areas?

R.B .: Dengue fever, zika, chikungunya or yellow fever is a virus found in monkeys, but it spreads as a result of human presence in the wild. How did the first person get it? it is variable and incorrect data because it really depends on the place.

With yellow fever we know that transmission in the wild occurs through mosquitoes from the genera & # 39; Sabethes & # 39; or & # 39; Haemagogus & # 39 ;, but for the wild transmission of the dengue, zika or chikungunya virus we do not have such an exact invention. Already in the urban context, all of these viruses are transmitted by & # 39; Aedes aegypti & # 39 ;. .

RT: One of the main goals of your research group is behavior analysis & # 39; Aedes aegypti & # 39 ;. What are the main findings of your study?

R.B .: When mosquitoes & # 39; Aedes aegypti & # 39; carrying dengue usually has a shorter life time, it places fewer eggs but becomes more active and increases its ability to move. Conversely, mosquitoes that contract the Zika virus become slower, move less but place the same eggs as non-infected mosquitoes. In addition, lower displacement capacity in mosquitoes infected with Zika explains why so many cases of infection occur in the same family, because mosquitoes tend to look for food within a small radius of distance.

RT: How long is the life cycle of mosquitoes & # 39; Aedes aegypti & # 39; and what are the possible mutations observed in your research?

R.B .: Their life expectancy varies between 15 and 20 days in a natural environment, mosquitoes bred in the laboratory reach up to 45 days. This mutation that occurs in mosquitoes comes from nature and takes a long time until some relevant effects occur. In nature there are different mosquito populations that can be more or less susceptible to viruses depending on the phenomenon we call "parasitic-vector interactions".

Rafaela Bruno, head of the Oswaldo Cruz Institute for Insect Molecular Laboratory.

"The most effective thing is to avoid places that are favorable for reproduction" Aedes aegypti ", that is, to avoid stagnant water where mosquitoes can lay eggs, these eggs are practically invisible to the human eye".

Rafaela Bruno, head of the Oswaldo Cruz Institute for Insect Molecular Laboratory.

That is, sometimes the mosquito genotype may not be compatible with the viral genotype. Depending on the region of Brazil, there are different mosquito populations, as a result of selective pressure that is different from the environment. In our genetic analysis, we observe that populations of a particular region may be more susceptible to circulating viruses than others, so the incidence of infection from one region to another varies.

RT: The rate of dengue epidemic is a more present and well-known risk factor in Brazil, while chikungunya is old but less frequent and Zika has recently, though threatening. What variations in the third occurrence of this virus are transmitted by the same mosquito?

R.B .: Dengue fever is a more dangerous virus because there are four sorotypes that can cause it: dengue fever 1, dengue fever 2, dengue fever 3 and dengue fever 4. Namely, those who already have the sorotype immunized against that specific, but if another sorotype starts circulating the person will get back to dengue fever. In the case of Zika and Chikungunya there is only one sorotype, therefore, after the infected person is immunized forever.

RT: What are the factors that caused the Brazilian Zika outbreak to start living about three years ago?

R.B .: Zika's introduction in the country recently. In 2015 the first cases were observed, especially in the northwest of the country, but the first suspicion that it was Zika was only found in October of that year, after a microcephaly case in infants of mothers who had contracted the virus. . There is a hypothesis that the virus comes during the Confederations Cup; others pointed out that he arrived at rowing championships with many competitors from French Polynesia, where one of the first outbreaks occurred. When Zika arrived in Brazil, no one was protected, which is why it caused great chaos. The spread is very fast and many people are infected, but now the trend is the number of cases is decreasing because many people have been immunized.

RT: Based on your research, what is the mechanism to combat this mosquito species and prevent infection?

R.B .: The most effective way is to avoid places that are conducive to reproduction Aedes aegypti, that is, to avoid stagnant water where mosquitoes can lay eggs. These eggs practically invisible to the human eye and, in addition, females tend to place it in a dark place. Therefore, avoiding conducive places for egg incubation, from a plate of saucers to soda bottle caps, is the most efficient.

RT: How do Brazilian public forces participate in preventing dengue epidemics?

R.B .: This is a joint work of research and information about reproductive forms of mosquitoes to prevent them from reproducing. Although public authorities are responsible for basic sanitation and garbage collection, these mosquitoes only reproduce in clean water. There are breeding grounds for mosquitoes that occur inside people's homes and, from there, each mosquito can move within a radius of about 300 meters. Therefore, prevention is a shared responsibility, public power, research institutions and city residents, the current main focus of the possibility of dengue fever epidemic.

RT: Following these practices, will it be possible to eradicate the dengue virus?

R.B .: In the short term, at least, no. By working together and our collective efforts can greatly reduce the mosquito population, which is the only way to reduce the spread of the dengue virus.

In addition to information strategies for the population, there is a complementary battle method consisting of releasing modified mosquitoes. This can be done with transgenic male mosquitoes which when crossing with wild females give rise to offspring that die, which do not succeed in living. Another technique is to release the bacteria that contains bacteria called & # 39; Wolbachia & # 39; which prevents the virus from multiplying in it.

Luna Gámez

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