Dengue,Zika,andChikungunya

"Aedes Aegypt" - Beth Thunder - 2015

When it was first scientifically described, in 1762, no one imagined that the Aedes aegypti - a small mosquito of African origin - would become world-renowned as one of the greatest vectors of disease transmission in tropical and subtropical regions.

The first step in this globalization process was taken back in the 16th century with the great voyages of navigation. And, as could not fail to happen, Rio de Janeiro fell into the mosquito's route and was hit by outbreaks of yellow fever – a disease transmitted by the Aedes aegypti – between the 19th and 20th centuries.

Image description: The image is a black-and-white photograph. In the upper part, a group of people in formal attire are observing an insect depicted through a graphic drawing. Below, two individuals are kneeling, examining a complex device connected to barrels labeled "MOSQUITO." In the background, other visitors are walking through the exhibition.

Already by the late 20th century, in the 1980s, Rio experienced the epidemic face of yet another disease spread by mosquitoes: dengue fever. Between 1986 and 1991, the new plague was reported 113 thousand times in the city of Rio de Janeiro. Initially mistaken for typhoid fever, the epidemic caused symptoms already well known to Rio residents: high fever, muscle pain, and skin blotches, lasting on average 7 to 10 days. At the time, older Rio residents nicknamed the mosquito responsible for the outbreak “Lacerdinha”: besides being a clear reference to the former governor of Guanabara, the name had become popular in the 1960s, when Rio's streets were infested by a mosquito of another species.

Image description: The image is a confidential document from the National Information Service, Central Agency, dated July 11, 1986. It is in black and white and features an organized structure with elements such as date, subject, origin, and distribution. The subject deals with the evolution of the dengue epidemic and its combat by the country's health agencies. The document contains information about the first cases of the disease in April 1986, symptoms, and transmission by the Aedes aegypti mosquito.

The vector-control campaigns involved the "fumacê" fumigation truck passing through the streets and the elimination of breeding sites scattered across the city: debris, open water tanks, gutters, old tires... From plant pots to abandoned swimming pools, anything that accumulated water deserved attention. Especially in the summer, when temperatures are higher and make the environment even more conducive to the mosquito's development.

Image description: The image is a photograph of an open area, possibly a sambadrome, with a number of people wearing yellow protective gear, including coveralls, boots, and gas masks. They are arranged in two rows, some holding equipment. In the background, there are bleachers and an arched bridge. The sky is partly cloudy, and the horizon shows a distant city.

Prevention showed results but never managed to permanently eliminate the Aedes aegypti. Meanwhile, the virus transmitted through the mosquito's bite grew more sophisticated: back in the 1990s, the population fearfully watched the emergence of the hemorrhagic strain of dengue, more aggressive and deadly. From then on, Rio de Janeiro – one of the main hotspots of dengue in Brazil – began living with four serotypes of the virus. While there is no difference in severity between the types of the disease, recurring contamination by distinct variants of the virus leads to a worsening of symptoms.

And with each new Rio summer came the discouraging prospect of a record epidemic. Notable were the years 1986, 1991, 2002, 2008, 2011, 2012, and 2013. In 2002, for example, 146 thousand cases of dengue fever were counted – about 2% of that year's population. More recently, between late 2023 and early 2024, a new surge in cases left Rio's hospitals overcrowded. The city recorded as many as 2.6 thousand infected patients per day, and over the twelve epidemic weeks, at least five deaths were recorded. Rio saw the resurgence of dengue types 3 and 4, which had not been recorded in 5 and 15 years, respectively.

The novelty (and hope) came in the form of the dengue vaccine, approved by Anvisa in March 2023 and included in the National Immunization Program (PNI) in January 2024. With this, Brazil became the first country in the world to offer dengue vaccination through its public health system.

Image description: The image is a black-and-white map representing the evolution of the dengue epidemic and its control in different neighborhoods of a city. The spatial layout begins on the left with the most distant neighborhoods and moves rightward, showing completed and ongoing areas. On the left are the neighborhoods marked in gray, where insecticide application is still being carried out by Sucam. In the areas marked with diagonal lines, the fight against the Aedes aegypti mosquito has already been completed. The map presents numbered and labeled neighborhoods, highlighting the progression of the fight against dengue in each location.

If dengue wasn't reason enough for controlling the Aedes aegypti, starting in 2015 two other diseases transmitted by the mosquito's bite came onto Rio residents' radar: zika and chikungunya. Zika is a virus from the same family as dengue and was discovered in 1947, in Uganda; the second one, in turn, was first identified in Tanzania, in 1952. Although they present almost the same symptoms as dengue – with mild clinical presentation and a low fatality rate –, it was soon noticed that zika virus infections were associated with the development of neurological complications, such as Guillain-Barré syndrome – an autoimmune disease that causes progressive muscle weakness. Furthermore, the zika virus ended up becoming feared for another sad consequence: infected pregnant women began showing a high probability of fetuses developing microcephaly.

At the height of the 2016 epidemic, Rio was preparing to host the 31st edition of the Olympics. Amid expectations of high tourist traffic in the city, a group of more than 100 international doctors and scientists sent an open letter to the World Health Organization (WHO) requesting the postponement or cancellation of the Games. Within a matter of days, they said, the Zika epidemic could become a serious pandemic. At the time, the WHO saw no reason to postpone or cancel the event but, in a statement, reinforced the recommendation that pregnant women should not come to Rio.

The 2016 Olympic Games took place and, indeed, Rio did not become an exporting hub for tropical diseases. However, the outbreaks of dengue, zika, and chikungunya ended up becoming part of the city's everyday life. Between 2018 and 2019, for example, Rio's city government recorded a 298% increase in chikungunya cases. The spread of Aedes aegypti became as certain as the Rio summer.

In light of this, Fundação Oswaldo Cruz (Fiocruz) began conducting the activities of the World Mosquito Program (WMP) in Brazil, an international initiative that brings together 11 countries around operations aimed at mitigating the transmission of these so-called "arboviruses" (viruses transmitted by mosquitoes). And the method developed by the program ended up becoming known as the "good Aedes aegypti". It involves inoculating the bug with an intracellular microorganism called Wolbachia, which prevents the development of the dengue, zika, chikungunya, and yellow fever viruses. After the mosquitoes with Wolbachia are released into the environment, they reproduce with the others and help create a generation free of viruses.

Image description: This is a black-and-white image, possibly an electron micrograph of cells. The image shows several cellular structures, with central nuclei and other round shapes distributed throughout the image. On the right, there is a light area with an arrow pointing to a specific structure.

And it seems the initiative has been effective. Between March 2019 and June 2020, the Rio city government recorded an almost 90% drop in the number of chikungunya, zika, and dengue cases. Either way, you can't be too careful. Despite the modernization of preventive resources, the risk of new epidemics transmitted by the Aedes mosquito still looms on the horizon. That's why the good old elimination of the mosquito's breeding grounds remains the most effective prevention: #DontLeaveStandingWater #FightAedes.