How an Egyptian mosquito killed 10,000 people in Brazil – 05/15/2023 – Health

Popularly known as the dengue mosquito, the Aedes aegypti for more than a century he has been the most feared “public enemy” of Brazil.

The species, originally from Egypt, is responsible for transmitting the most common urban arboviruses in the country: dengue, chikungunya and zika.

Its size of less than one centimeter and its white stripes on the trunk, head and legs seem to hide its high capacity for disease transmission.

What few people know is that in the last three decades the Aedes aegypti was responsible for the deaths of 10,000 Brazilians.

A survey carried out by the Ministry of Health at the request of BBC News Brasil points out that since 1990, 10,096 Brazilians have died after being bitten by the mosquito. There were 9,186 deaths from dengue, 875 from chikungunya and 35 from zika.

Not to mention the millions of people who are infected every year by the mosquito and manage to recover.

To get an idea, in 2022 alone, 1,450,270 cases and 1,017 deaths from dengue were recorded in Brazil – a record, since deaths from the disease were officially registered.

Scientifically, the Aedes aegypti was first described in 1762, when it was named Culex aegypti — culex from ‘mosquito’ and aegypti in reference to its region of origin: Egypt.

However, in 1818, researchers noticed that the species had morphological and biological characteristics similar to those of the genus Aedes. As a result, the name became Aedes aegypti.

In Brazil, studies indicate that the arrival of the mosquito that transmits dengue, chikungunya, zika and urban yellow fever occurred between the 17th and 19th centuries, through ships that brought people from the African continent to be enslaved in Latin America.

The ability of the species’ eggs to survive up to a year without contact with water helped the mosquito from Egypt quickly find a favorable environment to reproduce on ships and then in Brazilian territory.

Tamara Nunes de Lima Camara, a researcher at the School of Public Health at the University of São Paulo (USP), points out that, despite the fact that the first official case of dengue in Brazil dates back to 1981, there is evidence that, since the beginning of the 19th century, the Aedes aegypti it was already a problem in the country.

“There are reports of disease epidemics with symptoms similar to dengue in 1916, in São Paulo (SP); and in 1923, in Niterói (RJ), but without laboratory diagnosis, only clinical. occurred in 1981, from an epidemic in the city of Boa Vista, in Roraima.”

Insulation against the mosquito

Before the first dengue case is officially confirmed, the Aedes aegypti it was already a problem in Brazil due to its ability to transmit the urban yellow fever virus.

At the time, due to lack of knowledge that the sting of the Aedes aegypti could transmit diseases many people believed that yellow fever, for example, was contracted from contact with an infected person.

It was only in the 20th century that there was a consensus that it was the vectors, including the mosquito Aedes aegyptithe main responsible for the transmission of the disease and that the fight would not be just isolating the victims, but fighting the breeding grounds of the transmitting mosquitoes.

“It was only between 1905 and 1906 that the English physician Thomas Lane Bancroft proposed in Australia that the Aedes aegypti, when infected, it could, through the bite, transmit the microorganism that causes dengue. Then, in 1908, Bancroft’s observations were confirmed by the Cuban physician Aristides Agramonte y Simoni”, explained Jorge Tibilletti de Lara, researcher in the history of sciences and health at Fiocruz.

With the discovery, a veritable “mosquito hunt” began in Brazil. Whoever was infected needed to be isolated and in the residence a wooden frame covered with mesh was installed around the bed to prevent mosquitoes from accessing the patient.

In the rest of the house, papers were pasted over all openings to keep insects out. In addition, it was common to burn pyrethrum powder, which released a vapor capable of stunning mosquitoes.

Brazil has already managed to ‘end’ with the mosquito

The quest to eliminate mosquitoes that transmit yellow fever —in the wild form, vectors are the haemagogus and the Sabethes; and in the urban form (last record in 1942), mosquitoes Aedes aegypti It is Albopictus— led Brazil to adopt a series of measures, in the first half of the 20th century, against the breeding of mosquitoes.

Land owners, for example, were punished with fines if they had vector breeding sites and even pharmacies had to report who had yellow fever or dengue fever.

The effort paid off and vectors of common diseases began to be eradicated from Brazil.

The first species was anopheles gambiaein 1940. The extermination of this mosquito, a dangerous vector of malaria, occurred before the use of the pesticide DDT (dichloro-diphenyl-trichlorethane) was used in the country.

“In 1958, the eradication of Aedes aegypti in Brazil was recognized by the Pan-American Health Organization (PAHO), after a campaign that was of great importance for inter-American cooperation in public health, but which was also marked by internal problems, such as the late adherence of the United States to the eradication program . This only occurred in 1964 and was completed in 1969 without having achieved the established goals”, pointed out Gabriel Lopes, researcher in the history of sciences and health at Fiocruz.

It was the trigger for Brazil to register cases of dengue again in 1967.

From yellow fever to dengue

When the Aedes aegypti became a problem again, in the 1970s, Brazil no longer had the same characteristics as in the 1900s.

The rural exodus that made Brazilians move from the countryside to the cities stimulated disorderly urban growth, the lack of basic sanitation and, concomitantly, the accelerated reproduction of the species.

“Dengue, as we know it today, spread throughout Latin America from the 1980s onwards, affecting 25 countries and expanding rapidly through the most populated cities. The return and spread of the mosquito Aedes aegypti, which intensified at the end of the 1970s, was fundamental to this process. The permanence of this mosquito in poorly sanitized urban regions ensured the circulation of unprecedented epidemics in the 21st century, such as the cases of zika and chikungunya”, pointed out Gabriel.

Another explanation is linked to the life cycle of the Aedes aegypti. Its rapid reproduction with eggs capable of staying up to a year in a dry environment to produce larvae are pointed out as reasons why the vector continues to be feared.

“Mosquitoes have a holometabolous life cycle, that is, with complete metamorphosis. The cycle has the stages of egg, larva, pupa and adult. The eggs are very resistant to dissection and the embryo can remain viable for up to a year without contact with the water”, explained Tamara.

Deadliest animal on the planet

Contrary to what many people imagine, mosquitoes are the deadliest animals on the planet.

Data from the World Health Organization (WHO) indicate that about 725 thousand people die every year from diseases transmitted by them.

That’s because, unlike many other dangerous creatures, mosquitoes can be found in virtually all parts of the world without being noticed.

In case of Aedes aegypti, for dengue transmission to occur, the vector must be infected. This is because, at the same time that it bites to suck blood, the Aedes expels infected saliva and transmits the disease to humans.

In addition, the infected person, when entering the acute phase of dengue and being bitten by another mosquito, will contaminate it, starting the virus transmission cycle again.

“Today, we know that even the eggs of the infected female are also born with the virus”, emphasized Lívia Vinhal, arbovirus surveillance coordinator at the Ministry of Health.

disease vectors

Jorge Tibilletti de Lara, researcher in the history of science and health at Fiocruz, explains the transmission of many of the viruses related to aedes aegypti it comes from the blood.

“These viruses replicate in the mosquito’s stomach. At the same time, human blood, the preferred food for the females of the species, increases the mosquitoes’ skills and the rate of virus reproduction.”

In addition, the fact that mosquitoes feed several times in a sneaky way, by the ankles, increases the chances of transmission. This is because people often cannot see the insect in contact with their skin in time.

“O aedes aegypti it is not the only mosquito that transmits pathogens to humans, but it fulfills very well several criteria that corroborate its role as a transmitter of diseases: it uses humans as a source of blood supply; and lives in close association with humans in a wide geographic distribution”, pointed out Jorge.

That is, unlike other mosquitoes that live more in forest areas, the aedes aegypti adapted well to the urban environment. As a result, it has greater contact with humans than other vectors on the planet, gaining a leading role in transmitting diseases.

“Popular cities without adequate sanitation, when hit by the rains, produce very good conditions for the proliferation of the aedes aegypti in Brazil. In general, urban regions that have worse conditions related to garbage disposal, drainage and unfinished or precarious works can produce very productive breeding grounds for the vector”, said Gabriel.

How to fight the aedes aegypti

Researchers heard by BBC News Brasil say that Brazil will hardly be able to eradicate the aedes aegyptias it did 70 years ago.

“Today, the vector is highly domiciled. What we are currently talking about is reducing the vector infestation and consequently the transmission of viruses”, said Livia Vinhal, arboviruses surveillance coordinator at the Ministry of Health.

According to WHO, dengue is considered endemic in at least one hundred countries, covering the Americas, Africa, Middle East, Asia and Pacific Islands.

Currently, the great hope is related to the positive results of vaccines against severe forms of dengue – the most common disease transmitted by the aedes aegypti in Brazil.

However, Alda Maria da Cruz, director of the communicable diseases department at the Health and Environment Surveillance Secretariat of the Ministry of Health, points out that, with or without a vaccine, the best way to avoid dengue, chikungunya and zika remains to end the breeding grounds of aedes aegypti.

“The population often believes that fogging is one of the most effective measures to combat Aedes aegypti, but we use it when all the control opportunities are no longer working. What is highly effective in combating the vector is avoiding standing water. So we really need everyone’s collaboration.”