in English

The hundred years’ war

Why Brazil can’t manage to defeat Aedes aegypti

Bernardo Esteves

Translated by Flora Thomson-Deveaux

 versão em português

At seven o’clock on a Wednesday in February, a van parked in front of a supermarket on the outskirts of Piracicaba, in the interior of the state of São Paulo, waited to set off. Inside the vehicle, the space where seats would normally go was taken up almost entirely by small plastic containers covered with screens. There were over 200 of these receptacles, each containing an average of a thousand Aedes aegypti mosquitoes. Most were resting on the walls or the lids of the containers; a few buzzed around inside. There were also several mosquitoes loose inside the van. “But they’re all males, thank goodness,” observed the driver as he finished attaching a plastic tube to an opening in one of the windows.

Aedes aegypti is the species of mosquito responsible for transmitting the viruses that cause dengue, chikungunya, and Zika, among other diseases. In the past, it also served as a vector for yellow fever in urban environments; the disease was subsequently controlled within cities and only exists in rural areas in Brazil. The driver was relieved because only the female mosquitoes bite – human blood has the ingredients that they need to develop their eggs. The males generally feed on plant sap.

The hundreds of thousands of mosquitoes inside the van would soon be loosed along the streets of the neighborhood of Cecap/Eldorado, which registered the highest incidence of the disease in Piracicaba last year. Between April of 2015 and March of this year, this ritual has taken place three to five times a week, letting out around 800,000 insects per week – almost 40 million over the course of nearly a year.

As paradoxical as this may seem, the Aedes aegypti were let loose in the environment specifically to fight the diseases that they are capable of transmitting. They were born in a laboratory and come from a lineage of mosquitoes that has been genetically modified so as to make them unable to give rise to viable offspring – their progeny die in the larval phase. The aim of this mass liberation is for the transgenic males to breed with females in the environment and thus create a genealogical dead end, shrinking the local Aedes population bit by bit.

Affectionately dubbed “the good sort of Aedes,” the mosquitoes set free in Piracicaba have an English pedigree: they were developed in 2002 by the founders of the biotechnology firm Oxitec, headquartered in Oxford. The modified Aedes is the first – and, for the time being, the only – transgenic animal to be released into the wild. Before this experiment in the state of São Paulo, genetically modified mosquitoes had been released in Panama, in the Cayman Islands, and in two cities in Bahia – Juazeiro and Jacobina. The results were satisfactory: in nearly all cases, the reduction of the wild Aedes aegypti population was over 80% (in Jacobina, it was 79%). That success would be repeated in Piracicaba, according to preliminary data from Oxitec which has yet to be published in scientific literature.

When the van finally took off, the person in charge of freeing the mosquitoes was entomologist Cecília Kosmann, a 32-year-old native of the state of Santa Catarina who has worked at Oxitec’s Brazilian site in Campinas since 2014. The researcher picked up a container, took off the lid, slapped the bottom of the receptacle and tipped its contents into the plastic tube affixed to the window. Most of them flew out through the opening; some insects remained in the tube; others were dead.

Since the mosquito doesn’t tend to fly more than 100 or 200 meters, Kosmann said, the insects were to be set free every 150 meters so as to cover all the houses in the area. A tablet beeped whenever it was time to open up another container. The biologist didn’t let out any mosquitoes along stretches of the route without houses, since Aedes aegypti is a domestic insect; it lives and reproduces near to its source of food. I asked Kosmann how the mosquitoes were expected to behave once let loose in the environment. “They go into the houses,” she answered. “They know that’s where the females are.”

When I wanted to know if there was any risk of the transgenic mosquito undergoing some sort of mutation that might allow it to get around the effect of the modified gene, Kosmann said that wasn’t a concern – the strain is tested regularly, and has shown itself to be quite stable. Then her train of thought was interrupted and she started coughing and grimacing. “Agh, I swallowed a mosquito!”


Seen from outside, a genetically modified Aedes aegypti looks identical to those that Brazilian cities are currently teeming with. It’s the same little black mosquito with striped legs, white spots, and a penchant for hiding underneath tables and behind furniture. On a visit to the Oxitec factory in Campinas, I was able to certify that the bite of a “good”

Aedes is just as unpleasant as those of the regular ones. (Since it comes from a virus-free lineage and access to the production site is banned for those with fever or other symptoms, the factory females are not likely to be disease-bearing.)

The unit is able to turn out 2 million mosquitoes per week. It’s a modestly sized undertaking, enough to treat an area with 10,000 residents, which is twice the population of the Cecap/Eldorado area. The initiative arose from an agreement between Oxitec and the municipal government of Piracicaba, which put up R$150,000 (approximately $45,000) over the course of a year. Oxitec is negotiating a contract to release mosquitoes on a larger scale in downtown Piracicaba, an area with a population of 60,000, and has plans to build a larger factory in the city.

The company hopes to strike contracts with municipal and state health departments, but also with the private sector – it could be hired to treat parks or condominiums, for example. Oxitec was authorized to release mosquitoes in 2014 by the CTNBio, the National Technical Commission on Biosecurity, but awaits word from Anvisa, the National Health Surveillance Agency, in order to be able to sell them. Even with official approval, the operational costs and the logistics of the production process may wind up hobbling the large-scale use of modified Aedes.

As she emptied one container of mosquitoes after the next, Kosmann said that letting the insects loose calls for constant monitoring, lest the area be invaded once again by Aedes aegypti – which inevitably fly over from nearby areas – that can reproduce normally. “There’s no way you can keep them from infesting a place again. The mosquitoes travel on buses, cars, planes…” she said. “These here are going to Campinas with us.”

On the day that the mosquitoes were let out, I walked along the streets of Cecap/Eldorado (outside a tire shop, rainwater had pooled in the tire that served as the store’s sign) and talked to residents. Most were pleased with the release of the insects, and supported the project. With the exception of one local, they weren’t worried about having to live alongside mosquitoes manufactured in a laboratory. But many complained about the sheer numbers of Aedes in the neighborhood. “You open up the car and they rush in,” one retiree said. “They keep going up our noses,” said a housewife. “I’ve already swallowed two today,” complained a health worker.


President Dilma Rousseff declared war on Aedes aegypti on national radio and TV on February 3rd. Her tone serious, she asked for the population to mobilize in the struggle against the insect, which she didn’t refer to by its full name. “Until we develop a vaccine for the Zika virus, we need to fight the mosquito,” she proclaimed. The disease that had motivated the president’s speech was the cause of growing fear – it wasn’t well understood by scientists and seemed to have devastating consequences. Newspapers in Brazil and across the world ran photographs of the babies with pear-shaped craniums that were being born in the Northeast, the children of women who had contracted Zika during pregnancy. Rousseff, with a word of comfort to Brazilian women, launched the slogan for the campaign: “If the mosquito is never born, the Zika virus can’t live.”

Two days earlier, the World Health Organization had decreed a state of global emergency due to the Zika epidemic in Latin America, a measure it had only fallen back on three times in the past, most recently in the face of Ebola in West Africa in 2014. The reason for the latest emergency is a virus known to science since 1947, baptized with the name of the forest in Uganda where it was identified. After decades of causing only sporadic cases in Africa and Asia, the Zika virus crossed the Pacific Ocean in 2013, provoking outbreaks in Polynesia and Easter Island, among other places. It came to the Americas by way of Brazil. A genetic analysis published in late March concluded that the virus has been in the country since 2013, and may have arrived during the FIFA Confederations Cup.

In Brazil, Zika found inviting conditions: an abundance of mosquitoes to serve as its vectors and a large population which had never come into contact with the virus. Much of the population is packed into cities, living in conditions that are degrading for human beings but ideal for the proliferation of Aedes aegypti. The disease has already conquered the whole of Brazil’s territory: all 27 states have reported the presence of the virus to the Ministry of Health. Moreover, the country has become ground zero in a continental epidemic: 33 countries and territories on the continent had notified the WHO of Zika transmission cases as of March 19th.

Zika generally announces its presence with mild pain, a low fever, a reddish rash and bloodshot eyes; some cases may not even cause symptoms. What keeps health authorities up at night is the wave of microcephaly cases. There are ever-stronger indications that the Zika virus is responsible for these malformations, which bear consequences for the cognitive capacity and motor skills of those affected, although scientists have not yet been able to definitively establish a causal relationship. It remains to be seen whether the virus acts alone, for example, and the circumstances that can lead to this sort of development. The virus may also be behind an increase in the incidence of Guillain-Barré syndrome, a disease that attacks the peripheral nerve system and may lead to paralysis in severe cases.

In her address, Dilma Rousseff announced that 220,000 men and women in the Brazilian Armed Forces would muster in a task force to fight the mosquito in over 400 municipalities on February 13th. Newspaper coverage documented the soldiers handing out pamphlets, inspecting plant vases and water tanks, and carrying tubes with larvae found during the inspection. The number of properties visited stood in the tens of millions. Smaller contingents of soldiers were deployed in subsequent mobilization phases, and troops remain available to municipal and state health departments should their help be requested. “In many places, doors open for the Army,” Cláudio Maierovitch, director of Communicable Disease Surveillance at the Ministry of Health. “People trust them, they’re more receptive.”

The Armed Forces had already taken part in other mobilizations in the fight against the same ubiquitous, diminutive enemy. The effort to deal with Aedes aegypti has been described in bellicose tones as far back as the anti-mosquito brigades of Oswaldo Cruz, at the turn of the 20th century. The president was not the first authority – and likely will not be the last – to launch campaigns against the mosquito. What she announced at the start of February was just another stage in a long conflict, with important battles having been won by both sides. The war itself has been going on for over a century.


Aedes aegypti belongs to the family Culicidae, a name that comes from culex, the Latin word for mosquito. It is descended from insects from the time of the dinosaurs, which may have fed on the blood of those prehistoric giants. The oldest culicid on record was found preserved in amber in Myanmar, in Southeast Asia, and was estimated to be 90 to 100 million years old, but mosquitoes may have existed far earlier. It is unclear when Aedes aegypti emerged as a species. Its birth certificate, however, was signed in the 18th century by Carl Linnaeus, the Swiss naturalist who founded modern taxonomy and first described thousands of plants and animals. Linnaeus gave the mosquito the name Culex aegypti. Before it became Aedes, the species would also be called Stegomyia fasciata. Other names proposed over time for the same mosquito say a great deal about its temperament: the aegypti has been dubbed Culex excitans, Aedes inexorabilis, and Aedes insatiabilis.

The current name for the species, in use since the 1920s, is hardly flattering – it means “the odious one of Egypt” (aedes comes from the Greek, and aegypti from Latin). “A rogue, dogged, opportunistic mosquito,” in the words of researcher Ricardo Lourenço, who studies Aedes aegypti at Fiocruz, the Oswaldo Cruz Foundation, it hails from North Africa, where it originally inhabited forests. Bit by bit, the wild mosquitoes biting primates in the jungle adapted in order to occupy the areas around human settlements, laying their eggs in water vessels and inaugurating a close-knit, long-lasting relationship with Homo sapiens.

The growing intensity of the circulation of people and goods from across the globe, in the wake of the Age of Discovery, created the ideal conditions for Aedes aegypti to see the world. The mosquito arrived in the Americas on board slave ships, sucking the blood of crew and passengers alike and reproducing in the barrels used to store potable water. Reports of outbreaks of diseases caused by Aedes, though often based on shaky diagnoses, are the best clues that we have as to the presence of the mosquito. The earliest records of yellow fever in the region date back to the 17th century.


Back when it was first identified as a potential enemy, Aedes aegypti still went by Culex. In 1881, Cuban doctor Carlos Finlay published an article entitled “The mosquito hypothetically considered as the transmitting agent of yellow fever,” in which he argued that the species, which abounded in Cuba, was transmitting one of the most feared diseases in the Americas. Finlay was unable to carry out experiments that might convince his colleagues of the hypothesis. Charging a tiny winged insect with the epidemics sweeping the continent was an original idea, one that most people found it difficult to accept.

The practice of medicine itself was undergoing important transformations at the time. With microscopes that made it possible to observe cells and microorganisms, Louis Pasteur, in France, Robert Koch, in Germany, and other researchers isolated and described miniscule beings and clarified the role that they played in causing maladies such as rabies, tuberculosis, and the plague. In the process, they changed the way that scientists understood diseases – many of them had once been attributed to miasmas, putrid emanations given off by the unwholesome environment prevalent in cities.

The same year that Finlay published his hypothesis on the role played by the mosquito in transmitting yellow fever, French entrepreneurs started work on what would be a billion-dollar project, the building of a canal in Panama so that ships could cross from the Atlantic to the Pacific. They paid dearly for not taking the precaution of controlling mosquito populations at construction sites. Deaths from malaria and yellow fever, which had been recorded even before work began, stood at over 20,000 by the end of the decade. At that point, the construction company went bankrupt and work was halted, leaving a trail of debt, court disputes, and scandals in the French press.

Yellow fever was one of the gravest threats to public health across the continent, not just in the tropics. In 1793, an epidemic in Philadelphia, then the capital of the United States, killed at least 5,000 people – around a tenth of the population – and led President George Washington to seek temporary refuge in another city.

Manifestations of the disease were horrifying for both the victims and those around them. High fevers, chills, overpowering migraines and intense muscle pain were the dire signs that an individual had been infected. As a person’s liver slowly failed, skin would grow yellow, and blood would come out of the mouth and nose. In the worst cases, the ghastly spectacle was capped off with a series of retches as the victim vomited a dark liquid caused by internal hemorrhages – a sign that his or her days were probably numbered. Illustrations in Brazilian newspapers at the time depicted yellow fever as death itself, a hooded skeleton with scythe in hand, mercilessly claiming lives.

Carlos Finlay wasn’t the first to associate a mosquito to the transmission of a common tropical disease. Before him, British scientist Patrick Mason had shown in the 1870s that the house mosquito could transmit the worm responsible for filariasis. By the end of the century, mosquitoes in the genus Anopheles were singled out as vectors for malaria, the most devastating insect-borne disease, which claimed 438,000 victims in 2015 alone (attribution for the discovery is split between Ronald Ross, who took home a Nobel for the feat, and Italian scientist Giovanni Grassi). Finlay’s hypothesis was considered to have been proven in 1901, two decades after it was formulated, by an American team based in Cuba and led by the medical doctor Walter Reed.

Once the enemy had been identified, troops could be mobilized to fight it. The new theory about the origin of yellow fever led to a successful mosquito-control campaign, carried out by the American army in Cuba, which was a strategic zone in terms of Washington’s interests even back then. Captained by Major William Gorgas, the campaign consisted of hospitalizing and isolating those infected, attempting to eliminate the adult mosquito, and – in ostentatious fashion, with organized brigades – wiping out its breeding-grounds. The triumph won Gorgas an invitation to head up mosquito-fighting operations during construction on the Panama Canal, which was resumed by the Americans in 1904 and successfully completed.


American entomologist Andrew Spielman, who died in 2006, said that he was once deep in the tropical forest on a mountain in Puerto Rico when he felt a mosquito bite. Though the jungle seemed impenetrable, he concluded that there must be people living nearby. He had only to brush aside the foliage in front of him for his suspicions to be confirmed, as he spotted a handful of houses perched on a neighboring slope. “As a rule, when we encounter mosquitoes in wild places, their presence suggests that a human settlement is nearby,” he wrote in the book Mosquito: The Story of Man’s Deadliest Foe, co-authored with journalist Michael D’Antonio.

Aedes aegypti can’t survive without people close at hand. Human houses, especially in tropical and subtropical regions, provide the perfect conditions for it to proliferate: heat, water, and food. The food in this case is human blood, which is abundant in the most heavily populated communities. The mosquito’s eggs are laid close to the surface of a body of standing water, preferably clean. The eggs develop as soon as they get wet, giving rise to larvae, which look like whitish worms bobbing in the water. The larvae become pupae – twisted, floating commas – and these grow into the adults. The full cycle takes between seven and ten days.

When a female feeds on the blood of a person with dengue or Zika, she contracts the virus and becomes sick as well. “The mosquito is cast as a villain, but it’s also a victim in the process,” said Ricardo Lourenço, the Aedes expert at Fiocruz. The virus propagates when the infected female chooses a healthy person as her next target.

The strategy for fighting Aedes aegypti became clear as soon as the mosquito’s life cycle was clarified: it’s much easier to defeat an immobile enemy than a legion of winged, skittish, and starving soldiers. Hence the campaigns’ special focus on attacking the habitats where mosquitoes lay their eggs. This is no easy task: the Aedes females tend to spread their eggs across as many places as possible, maximizing the chances that some of them will survive. The eggs are resistant, and can last for months before developing.


Emílio Ribas, a medical doctor and director of the São Paulo State Sanitation Service, had heard of the experiments that pointed to Stegomyia fasciata’s role in transmitting yellow fever. He decided to replicate them in the city of São Paulo, where there had been no recent recorded cases of the disease, in the early 20th century. Rodrigues Alves, then president of the state, granted permission for Ribas to carry out experiments that seem unthinkable today and would have a hard time making it past research ethics committees.

Science historian Jaime Benchimol, a researcher at Fiocruz, tells the story of the experiments in the 1999 book Dos Micróbios aos Mosquitos: Febre Amarela e a Revolução Pasteuriana no Brasil (From Microbes to Mosquitoes: Yellow Fever and the Pasteurian Revolution in Brazil). Between 1902 and 1903, six adult men were bitten by yellow-fever-bearing mosquitoes, including Ribas himself and fellow doctor Adolfo Lutz, the director of the Bacteriological Institute in São Paulo that now bears his name. Ribas, Lutz, and a third volunteer wound up not contracting the disease, which didn’t keep them from the resolute conclusion that the mosquito was, indeed, the transmission agent. But they needed to prove that the disease could not be transmitted from one person to another in the absence of the mosquito, which led to new experiments. Benchimol writes that the test “involved three Italians who were kept in seclusion in mosquito-proofed rooms full of clothes and objects covered in the urine, vomit, and feces of yellow fever patients. They underwent this torture for ten days and then were observed for a further ten, without showing any signs of the disease.”

The greatest test of the mosquito-transmission theory was still ahead: it would come in Rio de Janeiro, where back-to-back outbreaks of yellow fever in the second half of the 19th century claimed 58,000 victims between 1850 and 1902. Urbanizing the capital and improving its sanitation were key planks in the platform of Rodrigues Alves, elected president of the Republic in 1902. As Rio mayor he named Francisco Pereira Passos, who drew up an urbanization plan for the city’s downtown inspired by the Paris of Baron Haussmann, the administrator responsible for overhauling the French capital in the 19th century. As in Europe, avenues were opened up and streets were broadened in Belle Époque Rio de Janeiro, at the cost of the demolition of hundreds of houses and buildings – in what was popularly known as the “knock-it-down” phase – and the forced removal of low-income populations.

Hygienic reforms were a key element in the transformation of the capital. A city aspiring to the title of a tropical Paris couldn’t be subject to flare-ups of plague, smallpox, syphilis, and tuberculosis. Rodrigues Alves – who had lost a daughter to yellow fever – entrusted the task to a 30-year-old public health officer little known outside medical circles. Oswaldo Gonçalves Cruz had spent three years at the Pasteur Institute in Paris and was made director-general of public health in Brazil, the equivalent to today’s Minister of Health. To carry out his plan to sanitize the capital, which focused on fighting three diseases – yellow fever, bubonic plague, and smallpox – Cruz had carte blanche from the president, with a legal framework that allowed him to enter into private residences and fall back on a special court, if necessary, that would rule on questions of public health.

Oswaldo Cruz divided up the city into districts that were covered by mosquito-killing teams, which moved around in carts: some of them went up and down the streets of Rio in search of bodies of standing water that might harbor mosquito larvae, filling reservoirs with sand and emptying out water stored in barrels. Another division set to fumigating in order to eliminate the adult insects, wafting around gases made of a mixture of sulfur and Persian powder, a natural insecticide also known as pyrethrum. Footage from the period captures the dramatic measures taken at the houses where Stegomyia mosquitoes were found: agents wrapped the entire residence in a white canvas and blocked off doors and windows before fumigating the interior, so as to keep the mosquitoes from escaping.

The mata-mosquito brigades, as they were known, brought protests from citizens who felt that their privacy was invaded. Among them was Senator Barata Ribeiro, who made it known that he would bar any agent from entering his house. “Water tanks in private residences may be sealed up, but mine is the exception,” he declared on the floor of the Senate. “I shall never allow ignorant pedantry to overstep the bounds of my authority as head of household.” Despite popular resistance, the campaign would be a victorious battle in the war against Aedes: yellow fever deaths, which had come to nearly 600 in 1903, fell to zero six years later. Cruz took on the stature of a national hero. The institute under his command, located in a neo-Moorish castle that he had built in the suburb of Manguinhos, was rebaptized with his name and became one of the most important biomedical research centers in Latin America.

The violent campaign was victorious, and the mosquito was exterminated from the capital. In reference to the eradication of Aedes in early 20th-century Rio de Janeiro, historian Jaime Benchimol put the insect’s defeat into surprising perspective. “Oswaldo Cruz’s campaign was developed in a city with fewer than a million inhabitants, and the main affected areas were the central region and its immediate outskirts,” he pointed out in an interview in the library at his house in Rio. Benchimol emphasized the fact that the mosquito, while wiped out in the capital, remained untouched in the rest of the country. “The federal, oligarchical structure of the First Republic made a nationwide initiative unfeasible,” he explained. “It was inefficient to control the disease in an urban center when it was endemic in other regions of the country. Sooner or later, that urban center would inevitably be reinfested, as was indeed the case with Rio.”


In the late 1910s, the fight against Aedes aegypti took on a national scale and gained a partner in the Rockefeller Foundation, a recently created American philanthropic organization which began pouring considerable sums into the effort to address public health problems in developing countries. One of its first goals was to eliminate the mosquito in the Americas. Acting in several parts of Brazil and prioritizing an attack on larvae, as opposed to the use of insecticides to destroy adult insects, the Americans helped to contain the transmission of urban yellow fever in the country. In 1926, President Artur Bernardes announced that the disease had been eradicated from the Brazilian coast, and 61 Aedes aegypti combat centers were closed nationwide, according to historian Rodrigo César da Silva Magalhães, who investigated the campaigns to stamp out Aedes aegypti in his PhD dissertation.

The consequences of this lapse in control would emerge two years later, with the merciless return of yellow fever to the nation’s capital after two decades of epidemiological calm. The 1928 outbreak in Rio de Janeiro infected hundreds and left a trail of 436 corpses. The disease, which in years past had sailed into the city on ships, had probably come from the countryside this time – perhaps brought by someone who had contracted wild-type yellow fever. The condition was also recorded in dozens of cities in the state of Rio, as well as in Bahia, Recife, and Belém. Over the decade, outbreaks in the Northeast would be attributed to soldiers who had penetrated deep into the backcountry to fight the Prestes Column, rebel forces seeking to foment a popular uprising against the prevailing political oligarchy.

This is when the most important figure in Brazil’s second victory in the war against Aedes aegypti comes onstage: American public health specialist Frederick Lowe Soper. Brought in to head up the Rockefeller Foundation’s Rio office, Soper would become a towering figure in the history of public health work in the 20th century. In addition to fighting Aedes in the Americas, Soper took on – and defeated – Anopheles in Sicily and Egypt. When he docked in Rio to take on the job, however, he was still building a reputation; he had worked on hookworm disease, malaria, and yellow fever in Paraguay and other South American countries.

In the photo included in Ventures in World Health, a book of Soper’s memoirs edited and published after his death by John Duffy, the epidemiologist gazes soberly out at the camera from behind a pair of round glasses and a short mustache that only covers the middle of his upper lip. He was known for his reserve, and wrote an autobiography so impersonal that certain passages stand out by virtue of how little they employ the pronoun “I.” Even so, Soper left a record of his relationships with Brazilian authorities and friction with the local culture – he grew impatient with postal service delays, an unannounced visit from a colleague, and with the diversion of traffic so that President Washington Luís might convalesce in peace at a nearby hospital.

The fundamentals of Soper’s plan of attack on the mosquito hadn’t changed since Oswaldo Cruz’s time. True, he did swap out fumigations for long spray pumps and the use of fish that fed on mosquito larvae in water tanks and other reservoirs. But the difference that Soper made may stem in large part from the draconian discipline that he imposed on the campaign. In a plan based on painstakingly detailed protocol, the houses and streets to be covered by the brigades were numbered and the tasks in each agent’s work plan were rigorously timed. The American would accept nothing short of perfection from his employees. Tardiness was punished with salary cuts, and employees who came in from the sweltering heat with their shirts crisp and dry were fired. Once in the thick of the American campaign against the mosquito, a munitions deposit in Niterói exploded, as Malcolm Gladwell wrote in a profile of Soper for The New Yorker. Upon hearing that the building had blown up just as one of his men was scheduled to be inspecting it, Soper sent a telegram with his condolences to the widow. The next day, however, the man in question showed up for work – and was promptly fired.

The results weren’t long in arriving. By the late 1930s, Aedes aegypti had been eliminated from six states and the Federal District. Successful parallel initiatives were being carried out all across the continent.

As with Oswaldo Cruz decades before, Soper was backed up by an institutional apparatus that allowed him to carry out a top-down campaign, this time across the country. Getúlio Vargas, who installed a dictatorial regime known as the Estado Novo in 1937, was a powerful ally, issuing decrees that allowed Soper’s men to enter homes to inspect for larvae and adult mosquitoes. “The Rockefeller Foundation had a very efficient structure, and thanks to extremely specific historical circumstances, it was able to operate outside the normal bounds of State action,” said Jaime Benchimol, the yellow fever historian at Fiocruz. “Today, things are infinitely more complex.”


In the early 1940s, Fred Soper gained an important ally in his fight against disease vectors: a chemical compound called dichlorodiphenyltrichloroethane, a white powder better known by the initials DDT. Swiss chemist Paul Müller was testing out the compound’s efficacy on another front when he observed that it was spectacularly good at killing insects. That wasn’t all: this insecticide also kept on working days after it was applied. DDT would be used in massive quantities in agriculture, and came to be seen as a panacea in medical entomology. Müller won a Nobel Prize in 1948, before the environmental and health-related consequences of his discovery came to light in the early 1960s.

Soper embraced DDT like no other public health official. Pesticide was the backbone of his malaria-controlling campaigns in Europe and Africa. In Brazil, it helped to put the final nail in the coffin of what was left of Aedes aegypti – by the time the compound was incorporated into Soper’s arsenal, the mosquito was thought to be completely eliminated in the North, South, and Center-West regions. It was only a matter of time before the insect would be wiped out entirely. A breeding ground eliminated in 1955 in the municipality of Santa Teresinha, in rural Bahia, was considered the last refuge for Aedes aegypti in the country. The war seemed to have come to an end.

Looking to confirm the kill, Brazil summoned an international commission to carry out tests proving that the country was no longer host to the mosquito. The group selected 102 municipalities in the states of Bahia, Paraíba, Pernambuco, and Rio Grande do Norte, where the infestation had hung on the longest. After three years of inspections with no sign of the insect, the battle was declared to have been won. “After a long and arduous campaign, the time has come for Brazil to declare itself free of Aedes aegypti,” read the report that the country presented in 1958 at the 15th Pan American Sanitary Conference, in Puerto Rico. Other countries announced similar success stories at the same conference. In the end, the Pan American Health Organization declared that Belize, Bolivia, Brazil, Ecuador, French Guyana, Nicaragua, Panama, Paraguay, Peru, Uruguay, and the Canal Zone were all Aedes aegypti-free.

“But did they really eradicate it?” Rodrigo Magalhães, a historian of the mosquito-fighting campaigns, wondered aloud in a pointed tone. Magalhães is a Rio native who sports a short beard, earrings in both ears, and glasses with striped arms that recall the legs of an Aedes aegypti. There was nothing to guarantee that isolated populations couldn’t evade the brigades’ control and keep on reproducing in isolated havens.

That wasn’t what happened, according to Magalhães. The historian says he is convinced that the mosquito was indeed eliminated across Brazil at that point. He pointed to the conclusions of a 2014 study that examined the genetic diversity of the Aedes aegypti now present in the country. The results suggest that there were two separate waves of colonization, come from Venezuela and the Caribbean, respectively – two areas that were never declared absent of Aedes during the eradication campaigns of the 1950s. This, the authors conclude, fits with the hypothesis of a genuine extermination. “If that weren’t the case, there would be other mosquito varieties that had survived from the period. And there aren’t,” Magalhães argued. “They did a thorough job.”


In the wake of the eradication campaigns, Aedes aegypti was down but not out. The clusters remaining in the countries that had been unable to eliminate it would serve as a launch pad for the mosquito to take back the continent.  Ironically, the United States, having led the fight against the insect, would also play an important role in its resurgence in the Americas. Since yellow fever wasn’t a public health emergency in the States, the American government did not immediately join the campaign to eliminate Aedes. The 1960s would bring a national initiative to wipe out the mosquito, but by then it was too late. Mosquito-fighting campaigns ran up against funding problems, difficulties posed by the country’s federal system of governance, and the fact that health agents couldn’t walk into citizens’ homes.

His country’s failure to join the push to eradicate the mosquito was one of Fred Soper’s greatest disappointments. He attributed Aedes aegypti’s return to the continent to the carelessness of the United States. Rodrigo Magalhães pointed to the path taken by the reinfestation reports: “First Mexico announces in 1965 that the mosquito is back in its territory; in 1966, a few Central American countries do the same; Colombia comes in 1967; and then it’s Brazil’s turn in the same year.” The mosquito was spotted back in the country by a researcher in Belém, in his own house, near the city’s port. Magalhães has no doubts as to the route taken in this fresh conquest. “It’s a straight line. That mosquito’s coming from the United States.”

Magalhães believes that Brazil could have kept the mosquito from coming back if the country hadn’t let its guard down. An effective yellow fever vaccine had been available since the 1930s, and Aedes seemed like a lesser threat. Bit by bit, the mosquito-fighting infrastructure built up since the start of the century began to be dismantled. It began under Juscelino Kubitschek’s administration in the 1950s, Magalhães explained; finally, Castello Branco, the first general to govern the country after the 1964 coup d’état, eliminated what was left of the national yellow fever task force.


On April 2nd, 1986, lab tests were carried out to determine the nature of a disease afflicting patients in Nova Iguaçu, in the greater metropolitan area of Rio de Janeiro. They were incapacitated by high fevers, intense headaches, and severe joint pain. The tests showed that they had dengue, caused by a virus of Asian origin not often seen in that part of the world. There had been reports of dengue in Brazil since the 19th century, but the cases confirmed in Rio de Janeiro were the first in decades. This wasn’t exactly a surprise; in recent years the disease had left a trail of destruction in Central America and the Caribbean, and a 1981 epidemic in Cuba had seen 344,000 cases. Dengue arrived in Brazil in late 1981, via the state of Roraima, which was ground zero for an outbreak with over 11,000 cases. Some 33,500 cases were reported in Rio in 1986. At the time, some attributed the start of the epidemic to the arrival of a circus come from Amazonia, which set up camp in Nova Iguaçu.

The virus and the disease were new to Brazilians, but the vector was that old acquaintance Aedes aegypti.  The microorganism found a metropolitan region which had been reinfested by Aedes at least a decade earlier and a population highly susceptible to the virus, most living in conditions favorable to the reproduction of the mosquito. This wasn’t for a lack of warning: a report in the Folha de S. Paulo published at the time showed that the Ministry of Health had shelved an action plan, drawn up at the start of the decade, designed to contain the mosquito in Rio de Janeiro. By late 1985, on the eve of summer, 27 neighborhoods in Rio had a building infestation rate of over 5%, considered alarming by epidemiologists. The mosquito was back in at least 14 Brazilian states.

Port cities like Rio, Santos, and Salvador showed high infestation levels. Aedes aegypti might have returned by sea, perhaps in ships laden with tires, which the mosquitoes love to use as breeding grounds. Infectious disease specialist Artur Timerman, president of the Brazilian Society of Dengue and Arboviruses, likes to define dengue as an “urban disease” – as it figures in the subtitle of a landmark book on the topic that he released in 2012, co-authored with two colleagues. The doctor noted that the mosquito benefited from vast demographic changes in Brazil over the second half of the last century – in 1950, nearly 2/3 of Brazilians lived in rural zones, while by 2000, four out of five could be found in cities. “And we know how that urbanization was carried out,” Timerman went on. People clustered together in cities where the soil was sealed off with asphalt and concrete, “without the slightest infrastructure in terms of basic sanitation, water, or trash collection.”

The correlation isn’t hard to trace. Trash littered around houses contains a plethora of plastic and Styrofoam packaging, which can instantly become mosquito breeding grounds when it rains. If there are water shortages, people are forced to store it inside their houses, in reservoirs that provide the conditions for the mosquito to procreate. It’s no coincidence that the state of São Paulo, which saw supply problems in the first half of 2015 during a severe water crisis, had 733,000 cases of dengue last year – almost half of those recorded in the country as a whole.

The numbers on basic sanitation in Brazil are on Timerman’s side. A diagnosis published by the Ministry of Cities in February showed that 35 million Brazilians still have no access to treated water, and that just 57.6% of the urban population is hooked up to the sewage system. If the rural population is taken into account, sewage coverage falls below 50%, leaving Brazil behind countries like Venezuela, Bolivia, and Peru.

In addition to this urban disarray, the mosquito took advantage of authorities’ lack of preparation, which was heavily criticized by the press during the 1986 epidemic. A documentary recorded the protest in which residents of Nova Iguaçu blocked the highway between Rio and Petrópolis, calling for measures to be taken to fight dengue. In an editorial published in 1987 in the Rio publication Cadernos de Saúde Pública, infectious disease specialist Keyla Marzochi compared the means used by Brazilian authorities with those brought to bear on the Cuban epidemic in 1981. In Rio, the relevant agency (SUCAM, the Office for Ministry of Health Campaigns) had fewer than 3,000 agents in the field, as opposed to the 15,000 mobilized in Cuba; Rio had 16 insecticide-spraying trucks, with another 60 insecticide sprayers that could be strapped to agents’ backs; in Cuba, those numbers were 215 and 3,961, respectively. The Cuban epidemic was over in five months.


The Aedes aegypti infestation has only grown since 1986. The graph showing the number of dengue cases per year shows that the mosquito has come back for good: there are significant spikes in 1991, 1998, 2002, 2008, 2010, and 2013. Last year saw the worst dengue epidemic in Brazil’s history, with over 1.6 million cases.

The past two years have also seen the rise of another disease transmitted by Aedes aegypti: chikungunya, a virus that causes a febrile illness with symptoms similar to those of dengue, characterized by pain that is more intense and which can last for years (the name, of Swahili origin, means “that which bends up”). Over the past year, nearly 27,000 suspected cases of chikungunya were reported, with three deaths. The virus arrived in the Americas in 2013, and was reported in Brazil by the next year. The number of cases on the continent has passed the 1-million mark.

In a phone interview with Antônio Nardi, the Secretary of Health Surveillance at the Ministry of Health, I asked him if the record-setting dengue epidemic of 2015 was a sign that authorities had acted with less than due diligence. Nardi hemmed and hawed as to how much the government was to blame. “Often, even due diligence on the part of public authorities isn’t enough to avoid a negative outcome,” he replied. He believes that accountability should be split between the government and its citizens. “We can use all the technology at our disposal, but if we don’t see real behavioral change across the board, it will be extremely difficult.”

This appeal to individual action is a key element in campaigns against the mosquito, and is, in fact, indispensable if the goal is to defeat it. “Our house visits proved that 80% or more of all breeding grounds are inside residences,” said Nardi, a dental surgeon who served as health secretary in the city of Maringá for nine years before going to the Ministry of Health. The total manpower mustered to fight Aedes comprises some 46,500 endemic disease control agents and 266,200 state and municipal community health agents. According to the secretary, the real work is done during the winter, when mosquito populations fall, as the population is instructed to act and sweeps are carried out in search of larvae. “There is a permanent staff on retainer,” he said.


In 1962, American biologist Rachel Carson published Silent Spring, a book denouncing the impact of pesticide use on nature. Carson presented evidence that DDT had brought about a decline in bird populations in areas of the United States, and raised suspicions that the chemical might be behind diseases affecting the workers who produced it. She also called attention to the danger of the emergence of pesticide-resistant insects, which had become evident in the wake of systematic use of DDT since the 1940s.

Carson’s book is considered a landmark in the emergence of the environmental movement. The author died two years after the book was released, too soon to see the creation of the Environmental Protection Agency in the United States, which banned the use of the insecticide in 1972. Other countries gradually adopted similar measures. In Brazil, DDT stopped being used in agriculture in 1985, and it has not been a part of public health campaigns since 1998. Today it is only produced in India, for the sole purpose of insect control.

The resistance that Carson wrote of is the fate of all insecticides. It’s not hard to understand why: if there is a mosquito population in which one or more individuals have a mutation that protects them from the insecticide, those few will be the only survivors of a chemical attack – and will pass the resistant gene on to their offspring. Over time, only the mosquitoes that are immune to the effect of the pesticide will be left.

DDT alternatives have been developed in the wake of the global ban. Most of them act on insects’ nervous systems, killing them by overloading the animals’ neurons and muscles. All of them will inevitably cease to function one day. When resistance emerges, a new compound is introduced and the cycle begins again.

Since 1999, Brazil has monitored Aedes aegypti’s resistance to insecticides through a network set up by the Ministry of Health. In 2000, the group observed that the compounds then in use were no longer working, and recommended that a new class of insecticides be put into action. “We thought that we’d get another 15 or 20 years, problem-free, but two or three years later we started to see resistance,” said Denise Valle, a biologist at Fiocruz who specializes in vector control.

Valle – a talkative researcher with curly black hair – opened up a reference book on dengue, published in 2015, which she edited. She pointed to a table of the insecticides recommended by the WHO for killing adult insects: of the five compounds listed, she said, four belong to the same class and no longer have any effect. Brazilian mosquitoes developed immunity to them at the start of the last decade, in record time, and use was stopped in 2009. “Only Malathion was left,” said Valle, referring to the only pesticide currently being used to kill mosquitoes. Sooner or later, Malathion will become useless in turn. “If we start in on heavy usage, we’re going to lose it quickly, and then there’ll be nothing to do,” she said, before adding that the development of a new insecticide can take decades.

In 2011, Jornal Nacional, the most popular nightly news show in the country, covered a campaign in which the municipal government in Foz do Iguaçu handed out 80,000 bottles of insecticide to residents – an “excellent example that the rest of Brazil can follow,” news anchor William Bonner noted approvingly. In the piece, one homemaker is seen spraying preventive puffs of pesticide around her house. Denise Valle brought up the episode in order to emphasize that the indiscriminate use of such compounds actually helps to accelerate the emergence of resistant mosquitoes. Insecticides, she said, give people a false sense of security, which is often reflected in increasingly lax larvae control measures. Many complain that the fumacês – spray trucks – don’t come around as often as they once did, but their use is only recommended when attempting to control epidemics, and not as a preventative measure. Private companies that provide unregulated insecticide sweeps also play a part in the resistance problem. In the gated community where Valle lives, in the Rio neighborhood of Jacarepaguá, residents ignored her protests and pay a company to spray insecticide around the complex twice a day.


Brazil beat the mosquito on more than one occasion, only to see it reconquer territory – and transmit new diseases. The logical conclusion that researchers came to was that they needed new weapons. The current fight against Aedes maintains some of the methods and practices of the eradication campaigns of the 20th century, but also includes solutions brought over from biotechnology. In the conventional war, the aim was to keep the mosquito from being born – via the elimination of breeding grounds, eggs, and larvae – or keep it from passing on the virus – with the use of insecticides on the winged adults. Today, new weapons make it possible to block Aedes on another front, interfering directly in its ability to reproduce.

Oxitec’s transgenic mosquitoes are an example of the attempt to control Aedes’ reproductive capacity. Another alternative is a technique developed decades ago, with the same aim, which has seen a resurgence: exposing mosquitoes to nuclear radiation so that they become sterile, thus reducing the wild population. The method has been in use since at least the 1950s to sterilize flies and agricultural pests. In recent years, the scientific literature has seen ever more successful reports of the use of the technique to control mosquito populations.

At the Department of Nuclear Energy at the Federal University of Pernambuco, in Recife, there is a room with a machine that has been used to sterilize Aedes aegypti pupae. Imported from Canada, the grey apparatus looks something like a rocket. Inside it, a cobalt source exposes male mosquito pupae to gamma radiation for 48 seconds. The dose has to be strong enough to neutralize their sperm, but not so strong that it jeopardizes their performance. “With larger doses, the pupae may never transform into the winged phase, or generate an adult that can compete adequately,” explained physicist Edvane Borges, who coordinates mosquito irradiation.

Since late last year, Borges and a student have irradiated around 3,000 Aedes aegypti pupae per week, to be set free on an isolated beach in Fernando de Noronha. She hopes that field results produce efficacy similar to that seen in tests in controlled environments. Samples from eggs taken at places where the sterile males had been released showed that 70% of them were not viable. Borges interrupted the interview to kill a mosquito that was flying close to her head. “That’s a Culex,” she assured me, cleaning her hands with a tissue, not bothering to examine the insect on the floor.


Two thousand kilometers from the campus of the Federal University of Pernambuco lies the modest neighborhood of Tubiacanga, in Rio de Janeiro. Squeezed into a corner of the Ilha do Governador, behind the international airport, it consists of no more than 800 houses spread along a handful of streets. There is only one access road, flanked by forest on both sides, snaking around the edge of a runway. With dogs wandering around the streets and people sitting in doorways, watching the day go by, the community doesn’t give the impression of being just ten minutes from the heavy traffic of Avenida Brasil, one of the city’s major arteries.

This isolation was one of the characteristics that made Tubiacanga an ideal candidate to host an experiment carried out by researchers at Fiocruz. Between August of last year and January of this year, 300,000 laboratory-born Aedes aegypti were released there. This was a dry run for a new bioweapon to fight mosquito-borne diseases.

The Aedes released in Tubiacanga act like a troop of Trojan horses. In their cells, they bear a bacteria – Wolbachia pipientis – that can impede the replication of the dengue virus, and possibly Zika as well. When they breed with the naturally occurring mosquito population, they will slowly transmit Wolbachia to their offspring, creating a population of dengue- and Zika-immune insects that can halt disease transmission at that site. That, at least, is what the architects behind the experiment hope.

The first Aedes aegypti to be contaminated with Wolbachia and released in Tubiacanga have already died. Now, researchers must determine whether they did indeed mate with native mosquitoes and produce bacteria-bearing progeny. To do so, the group set traps at 30 houses and commercial establishments in Tubiacanga. Once a week, a team goes into the field to collect the ensnared insects.

In an inspection on a Wednesday in March, at a modest house surrounded by an orange-painted wall, the team received a warm welcome from the diminutive homemaker. Four mosquitoes were flying around inside the tulle bag that a technician took out of a trap on a corner of the woman’s porch – now it had to be seen whether they were Aedes aegypti or house mosquitoes, Culex quinquefasciatus. The booty can vary significantly. That morning, the team had picked up five dead mosquitoes – probably starved to death – on the roof of a house, and a single live specimen at a nearby restaurant. The mosquitoes were taken to Fiocruz and euthanized by freezing. From there, they were sent for analysis at a laboratory at the René Rachou Research Center, a Fiocruz unit in the city of Belo Horizonte.

The recipient for the mosquitoes was Luciano Moreira, an agronomist from São Paulo specializing in insect control. Early last month, he presented a project in a talk to an audience of colleagues. “Wolbachia is a bacteria naturally found in 60% of all insects worldwide,” he said, as he projected photos of examples. “Culex is one of them, as is Aedes albopictus,” said Moreira, referring to a cousin of the aegypti that can also transmit dengue and Zika. “But, for reasons unknown to us, Aedes aegypti does not contain Wolbachia,” he went on.

Moreira first crossed paths with the bacteria in 2008, when he went to Australia for a postdoctoral fellowship. There he worked with Scott O’Neil, an entomologist who had been working for years on the idea of infecting Aedes aegypti with Wolbachia pipientis, and had finally found a way to do so in the lab. Moreira took part in the experiment that showed that the bacteria kept the virus from multiplying, a result that took the group by surprise – they expected the bacteria to simply diminish Aedes’ lifespan, as it had with fruit flies. The Brazilian researcher is the first author listed on the article detailing the discovery, published in the journal Cell in 2009.

Back in Brazil, he became the local coordinator on an international project that sought to use mosquitoes with Wolbachia to reduce the impact of dengue in the world (the initiative had an illustrious team of backers, headed up by the Bill and Melinda Gates Foundation). Aedes with the bacteria were being set loose in Vietnam, Indonesia, and Colombia. In Brazil, in addition to the Tubiacanga experiment, mosquitoes were set free in the neighborhood of Jurujuba, in Niterói. In an interview at Fiocruz’s Rio headquarters, Moreira said that the preliminary results from week-to-week monitoring, which remain unpublished in the scientific literature, are promising: “80% of the mosquitoes we’ve collected are positive.”


While Wolbachia is a bioweapon targeting the transmission of the viruses carried by Aedes, the chemical war remains an important battlefront. This is the line of attack taken at the laboratory of Pedro Lagerblad, a researcher at the Federal University of Rio de Janeiro who defines himself as a gastroenterologist for mosquitoes and kissing bugs. “My focus is what goes on in those guys’ intestines,” he told me when I met up with him at his workbench. Lagerblad studies mosquitoes’ digestive process in search of an Achilles heel that can be attacked. “What’s extremely singular and specific to the life of a blood-sucking critter?” he asked. “The adaptations that allowed it to feed itself that way.” That’s precisely what he’s after. His group has shown that the mosquito lets its immunological guard down in order to digest the toxic components of blood, and that this can favor infection by the virus. The discovery is at the root of a compound that is toxic to mosquitoes, and which he plans to patent.

Lagerblad believes that the arsenal for fighting Aedes aegypti has to be diversified. “We have a variety of tools to deal with the mosquito, and all of them are kind of ham-fisted,” he said. The solution is to combine a number of them on a case-by-case basis. “None of them is a magic bullet that can fix the problem.” An attack on multiple fronts is also the tack preferred by the WHO, which recently recommended that countries both reinforce conventional methods for combating Aedes and carry out tests with recently developed weaponry at the same time, such as transgenic mosquitoes, irradiated ones, and those with Wolbachia.


In the case of the Zika epidemic, none of the new techniques will eliminate the virus if Aedes aegypti isn’t its only vector. Researchers know that Aedes albopictus, a cousin of aegypti that lives in semi-urban zones, with more vegetation nearby, can also transmit the viruses for dengue and Zika. And what if house mosquitoes, which are far more numerous than Aedes, had a hand in things as well?

Biologist Constância Ayres raised this possibility at an event in early March, in Recife, where scientists, doctors, and public health officials got together to discuss the Zika epidemic. Ayres analyzed the studies indicating that Aedes aegypti was the vector for Zika and found that none of them presented extremely convincing evidence. “The incrimination of Aedes as the vector is very shaky,” she concluded.

Ayres – an insect geneticist who works for Fiocruz in Pernambuco – infected both species, Aedes and Culex, with the Zika virus in her laboratory. “After seven days, we were able to detect the presence of the Zika virus with a high viral load in Culex’s salivary glands,” she announced to her colleagues, while underscoring that these were “quite preliminary” results a ways from publication. She also emphasized that detecting the virus in the laboratory wasn’t enough evidence to incriminate Culex, and that the species’ ability to transmit the virus would also have to be studied in the field. I asked the specialists on the same panel as Ayres to react to the results she had presented. Her fellow speakers agreed that field observations would be needed. “We can’t yet conclude that Culex is a Zika vector,” said one of them, agronomist Luciano Moreira, who would later speak about his work with Wolbachia.

Another line of attack is the development of vaccines that make the population immune to mosquito-borne diseases. The race for a dengue vaccine has slogged on for decades. The first formula to be approved for commercial use, produced by French company Sanofi Pasteur, was first green-lighted in Brazil this year. But its protection is less than ideal: in clinical tests, it provides a 60% reduction in the risk that an immunized adult will develop the disease if infected by the virus. Its efficacy falls even further when tested on children.

There are other dengue vaccines in various stages of development across the world, one of them at the Butantan Institute in São Paulo, in the third phase of clinical studies, the last before approval. In a phone interview, Jorge Kalil, the doctor who directs the Institute, estimated development costs for the vaccine at around R$600 million (or $185 million), of which R$200 million (approximately $60 million) were paid for by the U.S. National Institutes of Health. Butantan is also one of the research centers that has thrown itself into the race to find a vaccine for Zika. Kalil said that the institute’s approach will build on the know-how accrued during the development of the dengue vaccine, since the two viruses have much in common. But he warned that good news will not be soon in coming. “It’s hard to make a vaccine for use on humans in under three years,” he said.

Vaccines, in any case, don’t fight epidemics. Nor do they address the proliferation of other viruses that may also be transmitted by Aedes aegypti and haven’t become public health problems yet. Most of these microorganisms emerge in wild environments, and would remain there if humans didn’t invade their territory. The quick spread of a disease across the globe is not improbable in a world where human comings and goings are ever more intense. “Aedes is a wide-open road,” said Atila Iamarino, a virologist who studied at the University of São Paulo, where he specialized in the molecular evolution of the virus. “Sooner or later, something much worse than Zika is going to come around.”

Some of the viruses that can infect Aedes aegypti – there are dozens of them – are being investigated by the team run by virologist Paolo Zanotto, at USP, which Iamarino was a part of. I asked Zanotto if his group was looking at other Aedes-borne viruses that might start circulating in Brazilian territory. “We’ve paid attention to barkedji, kedougou, the Rift Valley fever virus, and lineage 2 of the West Nile Virus,” the scholar reported. “It’s a massive list. The question is which one will be next.”

Even the fact that he’d been studying the Zika virus since the start of the previous decade didn’t equip Zanotto to predict the 2015 epidemic, which he feels somewhat guilty about. “We have to be prepared. It’s extremely important that we look at all these other candidates and start to study them to have diagnostic tests ready,” he said.


American ant specialist Edward Osborne Wilson, age 86, is the most prominent name in sociobiology, the scientific discipline that seeks to explain the social behavior of living beings in evolutionary terms. He has also made a name for himself thanks to his unconditional defense of biodiversity and the fights he has picked with not a few colleagues. In the 2006 book The Creation: An Appeal to Save Life on Earth, Wilson wrote that “it would be a serious mistake to let even one species out of the millions on Earth go extinct.” He made exceptions, however, for lice and for a relative of Aedes’. “I’d not mourn the passing of mosquitoes of the Anopheles gambiae complex of Africa,” he went on, in reference to the mosquito that transmits malaria. “Keep their DNA for future research and let them go.  Let us not be conservation absolutists when it comes to creatures specialized to feed on human beings.”

Some insects are fundamental for maintaining life on Earth. The pollination of a variety of plant species by bees, beetles, butterflies, moths, and many others has been a central link in plant reproduction for at least 100 million years. The elimination of any one of these species could have far-reaching consequences. But nobody would shed a tear over Aedes aegypti if it went extinct. “The environmental impact of the removal of the mosquito from a city is zero,” argued biochemist Margareth Capurro, who develops transgenic mosquito strains in her laboratory at USP, at the event on Zika in Recife. “It’s not a unique or exclusive part of any food chain. No gecko is going to die because you killed Aedes aegypti.”

Eradicating the mosquito – nipping it in the bud, in a more floral figure of speech – is an aim that, while achieved in the past, now seems unattainable. When Oswaldo Cruz and Fred Soper led successful campaigns against Aedes, cities were smaller, less densely populated, and the soil there was more permeable; people didn’t move around as much as they do today; and trash was mainly organic (global plastic production went from 15 million tons in 1964 to 311 million tons in 2014).

Cláudio Maierovitch, head of Communicable Disease Surveillance at the Ministry of Health, told me that the naturalization of dengue, which has been in Brazil for three decades, also led to society’s letting its guard down. “I get the impression that people started seeing dengue as something normal. Over the course of 30 years it became familiar, and it became a part of people’s lives.”

I asked Jaime Benchimol, of Fiocruz, what we might learn from the successful campaigns helmed by Oswaldo Cruz and Fred Soper – the only major battles that Brazil won in the long war on Aedes aegypti. Benchimol believes that mosquito-fighting campaigns should return to the professionalism and organizational efficiency of those historical examples. “Despite a legitimate critical vision of the arrogance implicit in vertical campaigns, the context calls for somewhat centralizing measures,” he affirmed. “The mosquito is a tenacious enemy. In situations like these, the common good inevitably stands above certain private interests.” But Benchimol doesn’t think that a victorious thrust against Aedes is likely to emerge now, with the dismantling of the public healthcare system, the growth of urban violence, and, above all, widespread institutional crises. “I think it would be very difficult for a campaign of this sort to be resuscitated with a political structure like the one we have today, which is totally dominated by immediate local interests, bargaining, and the basest sort of clientelistic criteria.”

In 1995, a majority of the public health specialists at a conference on the spread of Aedes aegypti recognized the challenges of Brazil’s new urban reality, but recommended that the country implement a new mosquito-elimination program in any case. Today, the prevailing vision has changed. None of the specialists consulted by piauí considered eradication a feasible goal. Nor is it among the government’s targets. “If you’re talking about eradicating a disease transmitted by a vector as versatile as Aedes aegypti in this day and age, that’s absolutely baseless,” Antônio Nardi at the Ministry of Health told me. “We have to talk about control.”

Indifferent to the mobilization of enemy troops, Aedes aegypti continues to gain ground. The number of dengue cases reported in Brazil by February 27th of this year was over 396,000 – a 97% increase over the same period of 2015, which had already set a record number of notifications of the disease in the country.

Bernardo Esteves

Repórter da piauí desde 2010, é autor do livro Domingo É Dia de Ciência, da Azougue Editorial

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