Why does the Aedes aegypti mosquito transmit so many diseases?

Why does the Aedes aegypti mosquito transmit so many diseases?

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Resistant and adaptable, the species is at the center of the current Zika epidemic, as well as being a vector of contagion of dengue, chikungunya and yellow fever and other rarer diseases.

In the world, it is called the yellow fever mosquito. In Brazil, it is known as the Dengue Mosquito - and more recently also Zika and Chikungunya.

Considered one of the most widespread mosquito species on the planet by the European Agency for Disease Prevention and Control (ECDC), the Aedes aegypti - name meaning "hateful of Egypt" - has been fought in the country since the beginning of the last century.

From the mid-1990s, with the classification of dengue as an endemic disease, began to be annually in evidence. This occurs mainly with the arrival of summer, when the higher intensity of rainfall favors its reproduction.

Aedes aegypti, which transmits dengue and chikungunya, can also transmit the zika virus.

Now a new warning sign comes from the Zika epidemic, a disease with dengue-like symptoms that has been ongoing since mid-year.

It has been confirmed by the federal government that the Zika virus is linked to a malformation in the brains of babies, microcephaly, which has had at least 1,248 cases this year in 311 municipalities in 14 states, most of them in the Northeast.

Mosquitoes Aedes aegypti, dengue transmitter.

O Aedes aegypti It was also at the center of an outbreak of chikungunya fever that occurred in the country last year, when this virus arrived in Brazil and spread with the help of the mosquito.

And although yellow fever was considered eradicated from Brazilian urban areas in 1942, cases of contamination were confirmed in cities of Goiás and Amapá in 2014.

"O Aedes aegypti it is also linked to rarer illnesses of the flavivirus group, "said Felipe Pizza, an infectologist at Albert Einstein Hospital.

"Among the contamination agents, this mosquito is the one that has the ability to transmit the widest variety of diseases."

Some factors contribute to making the Aedes aegypti such an efficient agent for transmitting these viruses. Among them are, according to experts heard by BBC Brazil, their ability to adapt and their proximity to man.

Appeared in Africa in wild places, the mosquito arrived in the Americas in ships at the time of colonization. Over the years, it has found in the urban environment an ideal space for its proliferation.

"He specializes in sharing space with man," says Fabiano Carvalho, entomologist and researcher at Fiocruz Minas.

"The mosquito prefers clean water to lay its eggs, and any object or place is a breeding ground. Even in an orange peel or bottle cap, if there is a minimum of standing water, its eggs develop."

But the lack of clean water does not prevent the Aedes aegypti reproduce yourself. Scientific studies have shown that, in this case, the female can lay her eggs in water with greater presence of organic matter.

Eggs can also remain inert in dry places for up to a year, and upon contact with water they develop rapidly - over an average of seven days.

"Other vectors don't have this ability to withstand the environment," says Albert Einstein's Pizza. "That's why it's present almost worldwide, except in places where it's very cold."

One aspect that also favors reproduction is the fact that the female lays an average of one hundred eggs at a time, but does not do so in one place. Instead, it distributes them across different points.

"When we try to exterminate it, there is a great chance that one of these places goes unnoticed," says Carvalho.

It is also a flexible mosquito in its eating habits. O Aedes aegypti It is usually daytime: it prefers to go for blood in the morning or late afternoon, avoiding the hottest times of the day.

"But he is opportunistic. If he has not been able to feed during the day, he will sting at night. This is not the case with the mosquito, which is nocturnal and will only be when the sun begins to set," says biologist Denise. Valle, researcher at the flavivirus molecular biology laboratory of the Oswaldo Cruz Institute (IOC / Fiocruz).

In addition, the mosquito usually targets mammals, especially humans. As the European agency explains, even in the presence of other animals it "feeds preferentially on people".

Because it is an urban mosquito that stays in constant contact with man, is very adaptable and has a special appetite for human blood, the insect has become an efficient vector for disease transmission.

"Every living being seeks a way to proliferate, and with viruses is no different. In these cases, they can be transmitted by other vectors, but they are not as effective," says Erico Arruda, president of the Brazilian Society of Infectious Diseases. "They (viruses) succeeded in Aedes aegypti and in the way this mosquito evolved a very good symbiosis relationship. "

To be able to infect a person, the virus must be present in the insect's saliva. Valle, from IOC / FioCruz, explains that in the case of dengue, for example, after Aedes aegypti poking someone who is infected, the virus takes about ten days to be present in your saliva.

"Few mosquitoes live longer than ten days. But the less energy it needs to spend to feed and lay eggs, the longer it lives," says Valle. "Thus, the urban settlement, with many breeding sites and many targets to bite, makes the mosquito live longer, favoring the process of infection."

The biologist also points out that it is a particularly dangerous mosquito: "When it bites, if the person moves, it tries to escape and bite someone else. If it is infected with a virus, it will transmit it to several people."

Exterminating it is also difficult. According to the United States Center for Disease Prevention and Control, the Aedes aegypti It is "very resilient", which causes "its population to return to its original state quickly after natural or human intervention".

In Brazil, it was eradicated twice in the last century. In the 1950s, Brazilian epidemiologist Oswaldo Cruz led an intense campaign against him in combating yellow fever. In 1958, the World Health Organization declared the country free from Aedes aegypti.

But as it had not occurred in neighboring countries, the mosquito was detected again in the late 1960s. It was eradicated again in 1973 - and returned once again three years later. "Today we no longer talk about eradication. We know that this is not possible," says Valle, from IOC / Fiocruz.

"The country is very large and has many entrances to the mosquito. There are also many more people living in cities, and the movement of people around the world with globalization has greatly increased. The human and financial resources to wipe it out would be enormous."

A common way to fight the mosquito, to disperse a cloud of insecticide - a technique popularly known as "smoke" - is not very effective because the chemical has to enter a spiral located under the wing. Therefore, the insect must be flying, which is difficult because it is a species that is mostly resting.

"Most of the time, this is throwing money away and breeding tougher mosquitoes. Today, it takes 20 to 30 years to develop an insecticide, and within two years it loses its effectiveness because of abuse," says Valle. "And the chemicals used to control larvae are not available to the population."

Carvalho, from Fiocruz Minas, also points out that 80% of the breeding sites are found in homes, and that prevent and exterminate outbreaks of Aedes aegypti it's not easy. "When we have an epidemic, it is simpler to get the support of the population, but outside this period, it is more complex to make people aware of the issue," says the entomologist. "For all that, I find it very complicated to talk about eradication. Maybe the best word is control."

A new approach has been tested in Bahia and São Paulo. Transgenic males of the Aedes aegypti They are released into the wild and, when crossed with common females, generate larvae that die before reaching adulthood, which over time reduces the mosquito population in a given area.

Responsible for tests carried out since May in Piracicaba, state of São Paulo, the company Oxitec said that the results are being analyzed by its technical team and that there is no prediction of when they will be released.

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