in English

Malaria in her sights

A Brazilian demographer at Harvard hunts for Anopheles in Amazonia

Bernardo Esteves

Tradução de Flora Thomson-DeVeaux

 versão em português

The truck pulled over onto the shoulder of the dirt road and Marcia Castro, accompanied by a researcher and two technicians, walked up to a green house built on the shores of a small pond. Behind the building, the group set up what would be the first of a series of traps to catch mosquitoes in the rural region of Cruzeiro do Sul, in the state of Acre. The chemical compound given off by the device has a smell that attracts mosquitoes of all sorts. On that late-July afternoon, the team was interested in the vessel for the parasite that causes malaria: Anopheles darlingi, an insect smaller than the common mosquito and Aedes aegypti, which can transmit dengue, the Zika virus, chikungunya, and yellow fever. The house near the pond was ideal for capturing specimens, since the mosquito the researchers had in mind likes to lay its eggs in large bodies of still, shaded water. The females normally bite from dusk to dawn, so the trap would be left on all night.

While one technician set up the device, Marcia Castro chatted with the owner of the house. The woman’s small son, dressed in his school uniform, stood by her side. Castro asked if the boy had already had malaria. “This one here hasn’t had it for a year,” responded his mother. She hadn’t been so lucky. “I’ve had 24 malarias, vivax, falciparum, you name it. And dengue. Dengue was the worst.” She was on a first-name basis with the two main types of malaria that occur in Amazonia, which require different treatments. The disease caused by Plasmodium falciparum is a deadlier variant, but is only responsible for 11% of cases in Brazil: most are caused by Plasmodium vivax.

In the third house they visited that afternoon, the group was greeted by a woman and her teenage daughter, who looked ill. “She’s got a fever, headache, and says she’s real cold,” said the mother – on a day with temperatures in the high 80s. A municipal health agent had taken a blood sample that morning, but the results weren’t in yet. Marcílio Ferreira da Silva, one of the technicians, was sure: “It’s malaria, no doubt about it.”

The next day, at six in the morning, the researchers and technicians set off in their truck to harvest the traps they’d set the day before. At the first house, they found just two mosquitoes. “This one here is an Anopheles,” said Pablo Secato Fontoura, a biomedical scientist, examining the insect through the thin netting. “Look how beaky it is,” he went on. “When it lands, its body is slanted upwards.”

The trap at the third house – where the sick girl lived – was full of Anopheles and mosquitoes of other species. The girl hadn’t gone to school that day; she was in bed with a headache. “It’s vivax malaria,” her mother said. Castro recommended that the girl keep taking the medication they’d been given by the health agent even after her symptoms had passed. “We’re going to try and nab the mosquito that infected your daughter,” Fontoura promised.

The team took advantage of the visit to collect Anopheles larvae from behind the house, in ponds with tilapias, tambaquis, traíras, and other species of fish. Fontoura took small samples of pond water with a long-handled dipper. In a single dipperful, he found as many as six larvae. “This is how the mosquito starts,” Castro explained to the sick girl’s younger sister, who watched the entire process with a look of fierce concentration. “This one’s not going to be born now,” said Fontoura cheerfully.

Castro asked the 11-year-old if her teachers had told her about the malaria mosquito; she said they hadn’t. The researcher then explained what her group was going to try to do. “We took the mosquitoes, and now we’re taking the larvae. Then we’re going to compare them to see if the mosquitoes are the parents of the larvae.”


In 2017, Cruzeiro do Sul had the highest rate of malaria of any Brazilian municipality, with nearly 21,000 cases in a population of 87,000. Situated in far western Brazil, almost on the Peruvian border, Cruzeiro is far from alone: the disease has been growing in other communities near the Juruá Valley, such as Rodrigues Alves and Mâncio Lima. Of every five cases of malaria recorded in Brazil that year, one occurred in one of those three towns.

The houses where the researchers set up their traps in Cruzeiro do Sul are in Vila Assis Brasil, a neighborhood that was one of the biggest hotspots for malaria transmission in the municipality in 2017. A look at satellite images of the neighborhood available online quickly reveals one of the factors fueling the disease. Vila Assis Brasil is pockmarked with natural or artificial bodies of water built alongside roads and used to breed fish. Fishponds are an important element of the economy in the Valley, generating income, employment, and food. Many were created in the past decade with subsidies from the Acre state government and Sebrae, the Brazilian Micro- and Small Business Support Service. Both offered fish breeders training and technical guidance.

When ponds are abandoned or maintenance lapses, the plants that grow around them shade the water and create the ideal environment for the malaria mosquito to procreate. “The vegetation at the water’s edge needs to be cut back, or it’ll create an important niche for larval development,” says Rio-based biologist Izabel Cristina dos Reis, a researcher at Fiocruz looking into the importance of these reservoirs in the malarial transmission process.

Marcia Castro, 54, is a native of Rio de Janeiro with wavy black hair and thick eyebrows behind thin-framed rectangular glasses. She studied statistics before turning her graduate studies to demography; since 2006, she has taught at Harvard University.

Since the late 1990s, Castro has used demographic tools to understand how malaria and other communicable diseases affect the lives of populations in developing countries – in addition to multiple projects in Brazil, she has taken part in initiatives in Tanzania and Ghana. Her work draws on statistical models, satellite images, and field research to understand how these diseases spread.

Castro spent a week in Cruzeiro do Sul, in July of 2018, as one of the coordinators of a research project on malaria in the Juruá Valley, developed with colleagues from the University of São Paulo (USP). The fieldwork is led by Pablo Secato Fontoura, 38, a malaria researcher with curly hair and a slight beard who has lived in Cruzeiro do Sul since 2017. Fontoura is a native of Américo de Campos, in the north of the state of São Paulo, and is a postgraduate fellow at USP.

Over the course of a year, he and the technicians on the project collected around 33,000 Anopheles larvae from the 170 fishponds monitored in the project, as well as hundreds of adult mosquitoes. The material was sent to a laboratory at USP, where genetic tests will be able to say whether the mosquitoes around the houses are from the same lineage as the larvae found in the fishponds. Fontoura also interviewed the approximately 2,000 inhabitants of Vila Assis Brasil and took blood samples from around 1,800 of them. The samples also went to São Paulo, where they’ll be submitted to a molecular malarial detection process that can track asymptomatic cases not identified in tests done on-site, with microscopes.

Fontoura’s work up until this point was all to prepare for an offensive that began in November 2018: applying a product to kill mosquito larvae to the fishponds, preventing the insects from becoming winged adults, which are more difficult to eliminate.

In the 1970s, entomologist Joel Margalit discovered that toxins secreted by the bacteria Bacillus thuringiensis can destroy the intestinal walls of the larvae of Anopheles and other mosquitoes, without harming fish or human beings. These compounds, generally combined with substances produced by another bacteria, Lysinibacillus sphaericus, became the basis for the most widely used larvicides in the world.

In an Amazonian environment, Anopheles breeding sites tend to be spread far and wide and are difficult to access, making larvicide an inefficient tool. That’s why public health authorities prioritize rapid diagnosis and immediate treatment of patients to curb the disease. Once properly medicated, infected humans no longer transmit the parasite that causes malaria, even if they are bitten again – thus interrupting the chain of transmission. Larvicide can, however, be an effective weapon in Cruzeiro do Sul, where researchers know where the mosquito lays its eggs.

The product used in the Juruá Valley was donated by its American producer, Valent BioSciences, which had collaborated on a previous study conducted by Marcia Castro. The first installment arrived at the port of Santos in July of last year and was taken by truck to Cruzeiro do Sul, where it arrived in October. This was a load of 160 forty-pound bags of larvicide, a total of nearly 3 tons – enough for six months of work.

Late last year, in the thick of the rainy season, the larvicide applications began in the Juruá Valley. A month later, Fontoura reported that the intervention was having an effect. “We’re seeing a significant reduction in the number of larvae in some ponds.” Even so, he’d have to finish applying the product – a process that will last through November of 2019 – to calculate the size of that reduction more precisely. This experiment aims to show that fishponds are the main breeding sites for Anopheles in Vila Assis Brasil, and that larvicide is an effective tool in halting malaria transmission. If the group’s hypothesis is correct, Castro hopes that the product will be adopted by the national malaria-fighting campaign for use in regions with many fishponds. “I can only find meaning in the work that I do if I’m able to change something in public health policy,” she said.


In September 2015, the television host Pedro Bial contracted malaria while visiting a region of Atlantic forest on the northern coast of São Paulo. While this was an extreme outlier, since 99.7% of reported cases of malaria come from Amazonia, Bial’s illness was news. “This disease only makes the headlines when a guy like him gets it,” complained Castro in one of her conversations with piauí. “But behind Pedro Bial, you’ve got all these people for whom malaria is a routine.” Lending a voice to the “invisible” population affected by this and other common diseases in developing countries was one of the reasons that led Castro to research them – she also studies dengue, the Zika virus, leishmaniasis, tuberculosis, and other neglected diseases.

Anopheles – which has been the target of interventions directed by Castro in Amazonia and Africa – is among her fiercest adversaries. “It’s two steps ahead of researchers, and always finds a way to dodge our blows,” she says. “When you think you’ve got a read on it, it changes its behavior.”

After Homo sapiens itself, no other animal kills as many humans as the mosquito. The dozens of Anopheles species that transmit malaria took the lives of 435,000 people across the world in 2017, most of them children under the age of 5. The species are adapted to multiple sorts of environments and spread across the planet, mainly in tropical and subtropical regions. In Africa, which sees 93% of fatal cases, the main species are Anopheles gambiae and Anopheles funestus; in Amazonia, the most common variety is Anopheles darlingi. Close to half the world’s population lives in areas that put them at risk of contracting malaria.

Anopheles is one of humanity’s oldest scourges. The malaria it transmitted inspired the figure of a Roman goddess (Febris, the protector of those stricken by the disease), probably took down both popes and monarchs alike, including Alexander the Great, and helped keep Genghis Khan’s army at bay, as Andrew Spielman and Michael D’Antonio write in Mosquito: The Story of Man’s Deadliest Foe.

The late 19th-century discovery that malaria was transmitted by a mosquito led to outright campaigns against the insect, which managed to wipe out the disease in many formerly endemic territories. Even so, malaria kept on rolling through poor and developing countries. By the end of the 20th century, it was killing nearly a million people every year, even with effective medication and a good understanding of how the disease is transmitted.

Malaria was endemic in most of Brazil through the end of the last century. In the early 1940s, the annual number of infections stood in the millions, with some 80,000 deaths per year. But over the course of that decade and the one that followed it, the government was able to eliminate most cases of malaria outside Amazonia, thanks to vector-fighting campaigns armed with a recently discovered pesticide, DDT (dichlorodiphenyltrichloroethane). Thanks to these campaigns, in 1961 Brazil would see the lowest number of cases of malaria in its history: 36,900.

The disease stayed alive in Amazonia, however, where fighting it was a thornier task. The situation became even more serious after the military dictatorship launched a National Integration Plan designed to encourage occupation of sparsely populated areas of Amazonia, mainly helping to relocate victims of severe droughts in the Northeast. With the stated goal of giving “land without men to men without land,” highways were blazed and large swathes of forest were clear-cut to make way for agricultural settlements, mining camps and cattle farms, supported by generous tax incentives. The newly shorn edges of the forest were ideal environments for Anopheles, which could now nourish itself with the blood of new settlers never before exposed to the malaria parasite. The population of Amazonia tripled in under four decades, and malaria followed on its heels. In 1970, Brazil saw 52,000 cases of the disease; ten years later, that number had risen to 170,000; by 1985, there were nearly 400,000. The peak – just shy of 633,000 cases – came in 1999, when Castro was in the second year of her PhD program.


Marcia Caldas de Castro was raised in the Tijuca neighborhood of Rio de Janeiro. Her father, who left Portugal to avoid the draft, co-owned multiple gas stations in Rio, worked as a car salesman, and is currently retired. Her mother is a homemaker. Castro and her older brother were the first in their family to go to college. She got her bachelor’s degree in statistics from the State University of Rio de Janeiro (UERJ) and her master’s in demography from Cedeplar, a research institute affiliated with the Federal University of Minas Gerais (UFMG).

In Minas Gerais, she met Burton Singer, an American mathematician who was researching infectious diseases at Princeton University and working alongside Diana Sawyer, Castro’s advisor at Cedeplar. Since the late 1980s, Singer and Sawyer had studied malaria transmission in an agricultural settlement in the state of Rondônia, which, in 1986, was responsible for 43% of Brazil’s reported malarial cases. But their research had been in a rut for years: the pair couldn’t find a pattern in the data they’d been collecting.

Singer encouraged Castro to apply to the PhD program at Princeton and be his advisee, proposing that she attack precisely this stubborn problem. Castro picked up the gauntlet. In 1999, she went to Amazonia for the first time, visiting Rondônia’s capital, Porto Velho, and the settlement of Machadinho d’Oeste, which had been created and supported by the government in the early 1980s. From then on, Amazonia would never leave her; she returns to do fieldwork on a near-yearly basis to this day.

During a NASA-sponsored course in California, Castro found the key to interpret the data that had stymied her advisors. She learned how to use satellite images and spatial analysis techniques to understand the dynamics driving disease transmission, and these tools would become a hallmark of her work. When she used them to analyze the data from Machadinho d’Oeste, she understood why Singer and Sawyer had been frustrated. Where they saw a labyrinth of data, Castro could, after dividing the region into smaller subsections, see a pattern. “Malarial transmission in settlements had an extremely significant spatial element that wasn’t being modeled in the analysis,” she explained. Castro discovered that variables such as vegetation, the type of agriculture being practiced in a given place, or the altitude of the land all influenced the likelihood that a given individual would contract the disease.

In an interview over Skype, Singer – now age 80, retired from Princeton but still active as a visiting professor at the University of Florida – said that his advisee did pioneering work by using spatial analysis to understand the dynamics of malaria in Amazonia, and emphasized the fact that she combined that data with the results collected from fieldwork and ethnographic studies. “In most analysis of malaria transmission in other parts of the world you almost never see analysis that involves that level of ecological detail. She really brought all the ecological details into it, which clarified that they were absolutely essential to understand the whole process.”

Castro started out in the exact sciences, became a specialist in a field related to the humanities, and now tackles public health problems. As she sees it, the issues at hand can only be dealt with by way of a multidisciplinary approach that weighs both environmental factors and the socioeconomic characteristics of the affected population.  “It’s complicated as hell,” she said ruefully. “But if it were easy, someone else would already have done it.”


The start of this century saw a steep drop in the number of cases of malaria in Brazil. In 2005, the country saw 606,000 cases; by 2016, that number had fallen nearly fivefold, to 129,000, the lowest level since 1970. The decline was chalked up in part to government action: a malaria-fighting program brought investments in training for local agents and expanded a rapid diagnostic network, helping to slow the advance of the disease. The trend was also fed by policies that cut Amazonian deforestation by 83% between 2004 and 2014.

For its continued success in fighting malaria, in 2015 Brazil was honored by the Pan-American Health Organization (PAHO). The Ministry of Health, riding this optimistic wave, launched a plan to eliminate the lethal variant of the disease – caused by Plasmodium falciparum – within fifteen years. But the project would wither when faced with the malaria numbers for 2017: 194,000 cases, 50% more than the year before. In 2017, 35 people died of malaria in Brazil, a number that has held steady for the past few years.

Brazil wasn’t alone in seeing fresh advances of the disease: after years of slumping numbers at the turn of this century, malaria has been regaining ground across the world since 2015. According to the World Health Organization, there were 219 million cases of malaria in 2017, 2 million more than the year before. The disease has become more prevalent in ten out of the eleven most affected countries – all of them in Africa, which sees 91% of the world’s cases.

In Latin America, the country with the direst situation is Venezuela, given its current political and economic predicament. There, the number of infections tripled in a three-year period, swelling to 411,000 cases in 2017 alone. Venezuelan immigration, some of it to Brazil via Roraima, boosts the parasite’s chances of spreading across the continent. Brazil and Nicaragua were the other two Latin American countries to see an uptick in malaria. Elsewhere, the tide is going out: last year Paraguay was declared malaria-free by the WHO, and Argentina hopes to attain the same status soon.

Certain country-specific factors contributed to the rise of malaria in Brazil. As the number of cases fell on a yearly basis, the disease lost visibility and prestige, dropping off the Ministry of Health’s list of priorities. Governmental energies were turned towards fighting seemingly more urgent public health challenges, such as the epidemics of Zika virus, dengue, and chikungunya that erupted in multiple cities in 2015-16.

In November of 2016, then-Minister of Health Ricardo Barros announced the fusion of the agency’s malaria-fighting program with the sector dedicated to addressing diseases transmitted by Aedes aegypti. Marcia Castro sees this as a serious mistake. “The decision betrayed a profound lack of knowledge about work that has to be done in the field,” she argued. “The vector is different, the breeding sites are different, the interventions are different, and the educational part is different.”

Cássio Peterka, an epidemiologist speaking on behalf of the Ministry of Health in an interview over the phone, denied that the move in any way hurt malarial control. As the coordinator of the unified program, he said that while efforts to fight malaria and Aedes-transmitted diseases are now under the same supervision, they maintain separate teams. “They’re two robust, independent, complementary programs.” Peterka did admit that, at an administrative level, malaria wound up taking a back seat. “When the number of cases of a disease goes down, it becomes less of a priority, and others will take up that space.”

Peterka pointed out that the execution of malaria-fighting initiatives is decentralized. “The diagnostic network and microscopists are managed by municipalities. There’s no use saying that I’m going to do something if we’re not on the same page.” The Ministry of Health’s main role in combating the disease is to ensure that strategic supplies – medicine, pesticides, and rapid diagnostic tests – make it to states and municipal governments. Last year, the Ministry set aside R$10.3 million (shy of $3 million) for malaria-fighting initiatives in priority areas – 35 cities where 80% of all cases are reported. These initiatives included handing out 245,000 diagnostic kits and 300,000 mosquito nets saturated with long-lasting pesticides in the areas affected by the disease, as well as visits by teams from the ministry to guide local agents and administrators.

The plan from 2015 to eliminate malaria altogether is still in effect, despite the recent explosion in cases. But the window of viability is a narrow one, in specialists’ eyes. “Resistance to the treatment currently used in Brazil for falciparum malaria is right around the bend,” said Peterka – there have been reports of resistant parasites in other Latin American countries. “If we can’t finish the disease off before resistant strains make their way here, we’ll have a much bigger problem.”


By seven o’clock in the morning on a Friday in July 2018, things were already bustling at the large white house where entomological inspection services in Cruzeiro do Sul are headquartered. Agents outfitted in the long-sleeved blue shirts of the municipal health department were getting ready to head out on their malaria-fighting missions. The city has 184 community health agents who visit homes, do rapid diagnostic tests on individuals with symptoms of malaria, and provide medication to those with confirmed diagnoses. They’re directed by Muana Araújo, a 30-year-old biologist born and raised in Cruzeiro do Sul, who’s been working at the health department since 2014.

She told piauí that the agents have nine trucks and 26 motorcycles. Cases of malaria are registered at 52 notification posts scattered across the community, which has a total area five times the size of the city of São Paulo. “One place is twelve hours away from here by boat, but in that community we’ve got a person who’s been trained to do rapid diagnosis and break the transmission chain,” explained Araújo. “Certain places are hard to reach, but the national health care system is for everyone, including those people. So we go out there and take care of them.”

When asked last July about why the city had seen the most cases of malaria in 2017, Araújo said that the peak had passed: cases slumped in 2018, and would probably come in at under the last year’s total. Indeed, by the end of 2018, Cruzeiro do Sul had seen nearly 13,000 cases of malaria, 39% less than the year before. This meant that São Gabriel da Cachoeira, in the state of Amazonas, took first place in the national rankings and pushed Cruzeiro do Sul down to second.

Araújo pointed out that Cruzeiro do Sul was the last city in Brazil to take charge of malarial control at the municipal level, which only happened in June of 2017. “The last time vectors were controlled along the riverbanks was twelve years ago.” The drop in reported cases may be attributed to the effort to make health agents ever more present in the community. “With vector-transmitted diseases, you work today to see results in six months,” explained Araújo. She, like Marcia Castro, criticized the disease’s low profile. “On TV, you’ll see tons of campaigns about dengue, Zika virus, and chikungunya, but nothing about malaria.”

There’s no lack of obstacles to her work. Araújo reported that locals have gotten used to malaria – since they know there’s a treatment, many people would prefer to catch malaria than the flu. “But malaria causes real damage to your organism, it’s not just any old disease.” Apart from all of that, there’s a new enemy to face alongside it: the growing violence in the state of Acre, which had the second-highest per capita homicide rate in Brazil in 2017. Criminal factions have settled in Cruzeiro do Sul to control drugs arriving from Peru, and have kept health agents from freely accessing certain territories. Araújo once received a call from the traffickers warning her to remove her teams from a given area. “When it comes to that, you leave.”


The rise in malaria in Brazil wasn’t the only bad news from recent health indicators. In 2016, the infant mortality rate went up for the first time in 26 years, which the Ministry of Health attributed to the Zika virus epidemic and the ongoing economic crisis. Maternal mortality and chronic malnutrition also went up. Equally worrisome is the slide in child vaccination rates – in 2017, the percentage of immunized children was at its lowest in 16 years. These conditions can pave the way for the return of polio; vaccine coverage against the disease, which had remained above 95%, fell to just 77% in two years’ time. This has already happened with measles. In 2016, the Pan American Health Organization declared Brazil free of the disease; but the virus, brought in by Venezuelan refugees, began circulating again and found fertile ground, given low vaccination rates. By early December of 2018, the Ministry of Health had recorded over 10,000 cases of measles that year, and the disease had claimed twelve victims.

In these declining indicators, specialists saw signs of the dismantling of Brazil’s public healthcare system. In an article published last July in the British medical journal The Lancet, researchers from Brazil, England, and the United States recalled that in 2017, the federal government – then under Michel Temer – failed to spend the minimum amount on health care stipulated by the Constitution. “Brazil’s government is backing away from the core principles of universal health care,” the authors wrote, “despite it being a constitutional right.”

In another 2018 article, this one published in the British journal BMJ Global Health, Marcia Castro and four colleagues warned of the risk posed to Brazil’s national health system by the economic recession. As they saw it, austerity measures taken since 2015 – especially the cap on public spending for the next two decades, as determined by a constitutional amendment – may spark a full-blown public health crisis and roll back the progress made by the national system since its creation in 1988. “Continuing these austerity policies may lead to a major decline in health indicators as a whole,” said Adriano Massuda, 39, a physician and public health scholar who was the lead author on the article.

At the Brazilian Society of Tropical Medicine’s annual conference, held last September in Olinda, Jarbas Barbosa, the adjunct director of the PAHO, gave a broad view of how communicable diseases are gaining new strength on the continent. In a conversation after his talk, Barbosa said that the climbing indicators, while driven by specific factors in each case, should be a warning to public health administrators. “Even diseases that have tended to decline can bounce back,” he said. “We have to keep health services functioning and ensure that people can access them. Our task will never be done.”

Castro gave two talks at the conference in Olinda. During both, she talked about the recent Zika virus epidemic, another disease that she is currently studying. In an article written in 2018 along with four collaborators, she showed how it has affected the birth rate in Brazil: 119,000 fewer children were born than would have been expected between September 2015 and December 2016, the height of the outbreak. Castro reminded those in attendance that the Zika virus has also fallen out of the headlines, but the children that contracted it are still suffering the consequences, as are their families. “The epidemic produced a generation of children with congenital Zika syndrome, both reflecting and exacerbating Brazil’s inequalities,” she said.


The struggle against malaria in the Juruá Valley was inspired by a similar initiative that Castro had helped lead a decade earlier, in Tanzania. The project was designed to take on the disease in Dar es Salaam, the most populous city in the country, which had 2.7 million inhabitants then (today it has 4.3 million) and offered a very different array of challenges from those Castro had faced in Amazonia – starting with the fact that this was an urban environment. “It was a different context, with a different vector and a different dominant strain of the disease,” she recalled. “I thought I knew a lot about malaria, and then I got there and found I didn’t know a thing.”

Dar es Salaam was an ideal candidate for the use of larvicide, which the WHO recommends for areas where mosquito breeding sites follow the 3 Fs – where they are “few, fixed, and findable.” The project included mapping breeding sites, collecting blood samples, and interviewing the affected population – tactics later adopted in Acre. It also called for training the local population to help fight the problem; Castro helped to train over 300 people to carry out the tasks involved in the plan.

The project lasted from 2004 and 2008, and showed that the number of individuals who contracted malaria in areas treated with larvicide was 21% lower than in untreated areas, a rate that Castro considers quite satisfactory. “Larvicide was seen as a secondary tool in controlling malaria,” she observed. “But our work showed that it can be effective in urban areas with easy access to breeding sites.”

Just like the drainage canals in Dar es Salaam, mosquito breeding sites in the fish ponds of Cruzeiro do Sul were fixed and findable, and hence potential targets for biolarvicide. “Larval control isn’t a panacea or a silver bullet, and it only works in very specific contexts,” observed Marcelo Urbano Ferreira, one of the coordinators of the USP-Harvard partnership in the Juruá Valley.

Ferreira, 54, is a São Paulo native and researcher at USP, where he’s been studying malaria since 1990. In an interview during the tropical medicine conference in Olinda, he indicated that the main malarial foci have shifted to western Amazonia, reaching Acre. “These are areas which are being deforested and occupied for the first time right now,” he said. “In regions of Rondônia, southern Pará and northern Mato Grosso, where malaria was historically endemic, there’s practically no forest left, hence no environmental conditions for malaria to be transmitted.”

Ferreira added that the malaria which has been expanding into urban and peri-urban areas in the Juruá Valley is a novelty for researchers. “We were more used to dealing with ordinary malaria in agricultural settlements on the edge of the forest.” Ferreira emphasized the threat posed by Cruzeiro do Sul: as a relatively large community connected to the rest of the country by commercial flights, it could become a trampoline for the parasite that causes the disease. “Urban malaria is explosive, and the potential for it to spread is enormous.”

Just as with Castro, Ferreira began his Amazonian fieldwork in Rondônia, at USP’s research base in the state capital, Porto Velho (the university still has a presence in the state, in Monte Negro). As the dynamics of malaria in Amazonia changed, he changed his research base. He spent twelve years studying malaria in settlements in Acrelândia, eastern Acre, where he and his wife – a fellow USP researcher – went so far as to buy a house. In 2010, Ferreira decided to pull up stakes and go to the Juruá Valley, on the other side of the state, where he felt that his work would be more useful. There, he set up a lab at the Federal University of Acre’s Cruzeiro do Sul campus, which serves as a base of operations for researchers from multiple institutions who have come to study malaria in the region.

Castro and Ferreira, the demographer and the parasitologist, have worked together since 2011. The project they’re heading up in the Juruá Valley is supported by both the National Institutes of Health (NIH) and the São Paulo Research Foundation (FAPESP). Their specialties complement one another. Ferreira wields the tools of molecular biology to understand the identity of parasites and mosquitoes, and Castro uses spatial analysis and statistical tools to analyze the epidemic. “What I do, he doesn’t do, and vice-versa. The work is really enriched by it,” she said.


In April 2018, Marcia Castro’s department announced that she had been made a full professor of demography at Harvard’s School of Public Health. Founded in 1913, the school is one of the world’s most prestigious institutions in the field; since 2014 it has borne the name of T.H. Chan, the father of a generous alumnus.  Castro was the first woman in the history of the Department of Global Health and Population, created over a half-century ago, to obtain tenure.

Hired as an assistant professor in 2006, Castro set up shop in a two-bedroom apartment in Brookline, a 25-minute walk from the School of Public Health. Before then, she’d worked for two years at the Department of Geography at the University of South Carolina. She had applied to the position at Harvard with a degree of apprehension. For all the university’s prestige, researchers at the School of Medicine and the School of Public Health are granted annual salaries that only cover part of the year; funding for the rest has to come from research projects supported by public or private institutions. That goes for tenured professors as well. “I’m still writing grant proposals like crazy,” said Castro. “You’re always just keeping your head above water.” Her recent promotion has brought a comfortable salary with it, but she prefers not to reveal the exact sum.

The promotion was celebrated on a September night in a posh hall in Harvard’s School of Medicine. After a reception, students, colleagues, and professors took turns at the microphone, paying tribute to Castro. Speaking on behalf of her fellow professors, Jennifer Leaning said that she was “absolutely elated” that the department had finally given tenure to a woman. “There’s going to be a different feeling in department meetings.”

Notable attendees included the public health physician and researcher Richard Cash, a senior lecturer in Castro’s department. At 77, with a full white beard and a bald head, he is best known for having led the first clinical tests that proved the efficacy of oral rehydration therapy, an innovation that prevented the deaths of tens of millions of children. In a brief, heartily applauded speech, he praised Castro’s ability to practice good science and steer clear of “bullshit.”

In addition to her research, Castro teaches demography and a class on spatial statistical analysis that she created to teach her specialty. A rigorous professor, she updates her syllabi every year and tends to include articles of somewhat suspect quality in order to encourage her students to read critically. In 2018, the student body voted to recognize her for excellence in teaching – the closest that Harvard’s School of Public Health gets to something like “teacher of the year.” Along with the honor, Castro received $10,000.

Castro’s students and former students who took to the microphone on the day of the reception portrayed her as a generous, exacting, and dynamic professor. One of them recalled a classmate who’d been on the verge of a nervous breakdown before going into an advising meeting with Castro, and who left her office beaming. Another remembered that the woman of the evening was a Star Wars fan, and dubbed her “Master Yoda come to life.”

Tenure wasn’t the only academic surprise that 2018 had in store for Castro. In December, it was announced that, as of January, she would become department head – an unusual responsibility for a newly minted full professor. Castro is now in a position to influence the work culture at her institution; among the initiatives she has in mind is to instate a code of ethics. On the other hand, her administrative tasks will take up part of her research time. “Life will get even crazier,” she said, a few weeks before her new responsibilities kicked in.


Marcia Castro also directs an intensive course that her university sponsors in Brazil, in partnership with local institutions. The class is taught in a different city every year, and has already been through Fortaleza, Salvador, Rio de Janeiro, and São Paulo. Every January, fifteen Harvard students and fifteen Brazilian students of diverse backgrounds are selected for a three-week run of talks, field visits, and collaborative work. The students are split into groups to analyze local public health issues; now and then, the results inspire master’s theses or doctoral dissertations.

The idea, Castro says, is to introduce students to the practical problems of the discipline. “Nobody can learn about public health in a nice, comfortable classroom in Boston,” she said. “We want to let students see what works and doesn’t work, what’s innovative, what’s terrible, all the politics involved, everything.” She’s taken students to Vidigal, a favela in Rio de Janeiro, and to the Cracolândia [Crackland] area of São Paulo. “The class shows students things you can’t find in textbooks or classrooms,” said infectious disease specialist Aluísio Segurado, of the USP School of Medicine, who worked with Castro to organize two editions of the January course in São Paulo.

This year, the course was held in Curitiba from January 7th to 24th. A few students visited an NGO that tests people in at-risk groups for HIV; others went to the port city of Paranaguá, a site ripe for all sorts of diseases. Castro took the class to the Pastoral da Criança – in her words, “an organization that saved children’s lives before the creation of the national health system, providing oral rehydration.” The closing session included a conversation with Richard Cash, who addressed the students via Skype from the United States.

Castro threw wide Harvard’s doors to Brazilian students and colleagues who head to Cambridge for graduate work or for stints as visiting scholars. It’s a two-way street: she sends plenty of her own students to study in Brazil. Recent visitors to Harvard include Antonio Silva Lima Neto, 49, a Fortaleza native with whom she’s collaborated in recent years. Lima Neto is a physician specializing in epidemiology and collective health, and is also the manager of the Epidemiological Surveillance Division of the Fortaleza Municipal Health Secretariat. In August of 2018, he arrived in Boston for a one-year post-doctoral fellowship at the School of Public Health.

Working alongside Castro, Lima Neto has studied the transmission patterns of dengue in Fortaleza, using georeferenced data for each case, which has made for a window onto the inequalities between multiple regions of Ceará’s capital. In December of 2018, both researchers, along with five other authors, published an article in the journal PLoS Neglected Tropical Diseases. The group’s work showed that, in years without dengue epidemics (which are generally concentrated in the rainy season), dengue cases are spread out over the other months. That’s why surveillance has to be kept up all year long, even during the dry season. These findings, arrived at through a partnership with Fortaleza’s Municipal Health Secretariat, prompted the government to change the guidelines for its agents.

The study also showed that the most violent neighborhoods in Fortaleza also had the highest rates of dengue. Castro explained that drug traffickers keep health agents from accessing certain areas, which undercuts mosquito control. The researchers had seen a similar trend in other studies. “Diseases are superimposed in the same areas,” said Lima Neto. “The individuals at a higher risk for being murdered are the same individuals who are at greater risk of acquiring tuberculosis or having a child with congenital syphilis,” he went on, noting that the same pattern has been observed in other major cities.


Late last November, the federal government announced the annual deforestation rate for Amazonia. The forest lost 7,900 square kilometers, the most devastation in a decade. The calculation covered August 2017 to July 2018, thus leaving out the start of the presidential campaign, when chainsaws roared in response to the anti-environmentalist speeches of then-candidate Jair Bolsonaro. Preliminary figures indicate that, throughout the campaign, from August to October, deforestation went up by 49% in comparison to the same period the previous year.

“If this trend isn’t slowed down or turned around, the negative consequences won’t just affect the environment,” predicted Castro. “They’ll affect health, too. You’ll see an impact on malaria, Chagas’ disease, and diseases transmitted by Aedes, which are already making their way into Amazonia.” She pointed out that malaria is closely associated with deforestation, and that removal of vegetation followed by disorganized settlements is a recipe to foment the reproduction of Anopheles. “We’ve seen this before, and we know how the story goes.”

The most recent data on malaria in Brazil, as informed by the Ministry of Health before this edition went to press, cover January to November 2018: over 179,000 cases were reported in that time, an increase of 1.6% over the same period in the previous year. Preliminary numbers do not include December, which is one of the most critical months for malaria in the Juruá Valley and other Amazonian regions. Even so, in comparison with the ministry’s 2018 target of 109,000 cases, the figure was 64% higher than it should have been.

Bernardo Esteves

Repórter da piauí desde 2010, é autor do livro Domingo é dia de ciência, da Azougue Editorial

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