University of São Paulo: Mapping shows the areas of greatest malaria transmission in Mâncio Lima (Acre)

Research by the Institute of Biomedical Sciences (ICB) at USP reveals the demography of malaria transmission in Mâncio Lima, in Alto Juruá, Acre, one of the regions in the country with the highest incidence of the disease.

According to the study by sociologist Igor Cavallini Johansen, the most exposed population is the one with more mobility among residents and moves from the city to the rural area, a distance of up to 20 kilometers from the urban center. They are mainly men, of working age (between 16 and 60 years), are among the poorest of the population, without a formal job and move to work in activities related to agriculture. By making maps of the region, showing where these people moved the most and where the locations with the most records of malaria cases were, the researchers realized that the two maps “talked about”.

In terms of public policies, this mapping is very important, as the research manages to show exactly where the most sensitive areas for the transmission of the disease are, says Cavallini in an interview with Jornal da USP . The study also shows the urban aspect of malaria in the region.

The article Human mobility and urban malaria risk in the main transmission hotspot of Amazonian Brazil describes the study and was published in November 2020 in the scientific journal PLoS ONE .

The research was carried out between 2018 and 2020 under the guidance of Professor Marcelo Urbano Ferreira, from the ICB, who is developing a series of research in the region within the Thematic Project: Scientific bases for the elimination of residual malaria in the Brazilian Amazon , by the Foundation for Support to Survey of the State of São Paulo (Fapesp). In 2018, Jornal da USP published the special report No Acre, USP researches malaria and the health of mothers and their babies , which describes the project’s activities.

Malaria is an infectious disease caused by the protozoa Plasmodium vivax and Plasmodium falciparum (in the studied region, vivax cases prevail). It is transmitted by infected females of the Anopheles mosquito . They get infected by biting someone with malaria at a certain stage of the disease. Then, when biting another person, they inject the parasite into the bloodstream, infecting the person and starting a new cycle of disease. The correct treatment, based on medicines available in the Unified Health System (SUS), interrupts this cycle.

In his postdoctoral research, Cavallini made periodic visits to Mâncio Lima, along with the thematic project team, to collect data and interview residents. Between the questions, it was important for him to know where the person spent the night, since Anopheles has two peaks of activity: dusk and dawn. About two thousand residents were accompanied.

Igor Cavallini explains that 99% of malaria cases in Brazil occur in the Amazon region, with the vast majority of transmissions taking place in rural areas, but in Mâncio Lima malaria is also urban. The analysis carried out by the researcher associates mobility to cases of the disease from two aspects.

The first are the residents who go to the countryside to work. They may own a small property or work for others near the city. These residents travel to the workplace and return daily or stay there for a few days or even weeks, depending on the type of activity they perform. The other aspect is the rural residents who, faced with the symptoms of malaria, go to the city to diagnose and obtain medication. In the first case, the person is infected during this stay in the countryside. In the second, she is infected and may end up transmitting the disease when she goes to the city in search of care and treatment, considering that the malaria vector is also present in the city’s urban area.

In Mâncio Lima and in the region, both in urban and rural areas, there are a series of tanks used for raising fish, the result of a public policy implemented in the State of Acre, in the early 2000s, to transform fish farming in a source of income for the residents. However, over the years, many tanks were abandoned and became an ideal breeding ground for Anopheles .

“Many tanks were abandoned but remain there. When this tank is not taken care of, there is vegetation on the edges and shadows, it is in this environment that Anopheles lays its eggs. It needs still water and shade – and that’s not lacking in these tanks. On the other hand, if a tank is properly maintained, it poses no risk of contributing to the reproduction of the malaria vector”, explains Cavallini.

Another point that helps in the occurrence of urban malaria is the city’s geography. Mâncio Lima is a city that has a linear shape, it extends around Avenida Japiim, which practically cuts through the entire urban area. This elongated formation allows a considerable part of the city to be very close to an area of ​​primary vegetation, dense forest – an environment that Anopheles likes to use to protect itself and rest after biting a person. In addition to the fish farming tanks mentioned, this is another factor that makes it easier for the mosquito to be found in virtually every urban area of ​​the city, says the researcher.

In addition, there are several igarapés (small streams of water) that cut through the city and, at certain points, are naturally or artificially barred, creating an adequate environment for the reproduction of the malaria vector.

“On the one hand, the opening of ponds for raising fish has created a large number of breeding sites for anophelines on the outskirts of Amazonian cities. On the other hand, city dwellers often move into rural locations with high transmission, where they can become infected. Thus, we have mosquitoes and parasites present on the outskirts of cities, potentially spreading to more densely populated areas. These are elements that promote outbreaks of malaria in urban areas”, highlights professor Marcelo Urbano Ferreira.



Professor Marcelo Urbano Ferreira, from the Institute of Biomedical Sciences at USP and coordinator of the research project in Acre, comments that this picture of urban malaria found in Mâncio Lima can be reproduced in other urban centers in the Amazon, including large cities such as Manaus and Porto Velho. “On the one hand, the opening of ponds for raising fish has created a large number of breeding sites for anophelines on the outskirts of Amazonian cities. On the other hand, city dwellers often move into rural locations with high transmission, where they can become infected. Thus, we have mosquitoes and parasites present on the outskirts of cities, potentially spreading to more densely populated areas. These are elements that promote outbreaks of malaria in urban areas.”


Other elements make the situation even more complex: asymptomatic and subpatent malaria. In asymptomatic patients, the person has no symptoms (fever, chills, sweating), but, if bitten, can transmit the parasite. Subpatent malaria is that case in which there are so few parasites in the bloodstream that the more conventional test used to detect the disease, called microscopy, fails to make a successful diagnosis. However, as with asymptomatic malaria, if the mosquito bites a person with subpatent malaria, the vector can become infected and transmit the disease to other people.


The researcher points out that, since the beginning of the research, the team from the municipality’s malaria control program helped him to match the names of the places mentioned by the residents with the official names of the places. The sociologist says that when the research was ready, he made a summary pointing out the main findings and sent it to the team. “They had very interesting questions for our work, suggestions on how to improve, and we have this feedback all the time, it’s a joint and very important work”, he highlights.

Finally, Cavallini points out that, at the end of the research, cases of malaria in the region were decreasing and highlights the role of the Institute of Biomedical Sciences in this, despite not being the main objective of the project. Every six months, a large number of residents are interviewed and tested for malaria and, when positive, receive medication. With that, the disease cycle is interrupted. The researcher also highlights the role of public policies in reducing cases, both through the work carried out by the malaria control team in the municipality, as well as through receiving funds directly from the Ministry of Health.

However, the researcher warns of an increase in the number of cases of falciparum malaria in the region, which could indicate a problem in the way of diagnosing the disease. This is because in vivax malaria , as soon as a person is infected, he can start transmitting, even if he has no symptoms. In falciparum it is different, the person only starts transmitting a few days after the infection starts. When the diagnosis is made, treatment stops the infection even before transmission. “If falciparum cases are increasing, it means that the diagnosis needs to be carried out more efficiently”, he concludes.

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