Challenges for malaria elimination in Brazil

The number of cases is the lowest in 35 years, and Brazil can eradicate the disease; however, researchers see cause for concern in transmission by Plasmodium falciparum.

By Peter Moon  |  Agência FAPESP – Malaria is one of the developing world’s major public health problems, and Brazil still has the highest prevalence in the Americas, with approximately 42% of the reported malaria cases in this region. Some 144,000 cases and 41 deaths were confirmed in Brazil in 2014.

The good news is that this was the smallest number of cases in 35 years. The geographic boundary of malaria transmission has shrunk, and substantial progress has been made toward eradicating the disease in Brazil, according to the article “Challenges for malaria elimination in Brazil” published in Malaria Journal by Marcelo Urbano Ferreira of the University of São Paulo (USP) and Marcia Castro of the Harvard T.H. Chan School of Public Health. Brazil, they stress, was one of the countries that met the target included in the UN Millennium Development Goals of achieving a 75% reduction in case incidence between 2000 and 2015.

The article outlines the history of malaria in Brazil in the twentieth century, reviews key lessons learned from past and present control policies, and discusses the scientific and logistical challenges facing efforts to eradicate the disease, such as the Malaria Elimination Plan launched by Brazil’s Health Ministry in November 2015.

Marcelo Urbano Ferreira, one of the leading Brazilian experts on malaria, is a full professor and research fellow at the University of São Paulo’s Biomedical Science Institute (ICB-USP) and a member of PAHO-WHO’s Technical Advisory Group on Malaria in the Americas. He has authored more than 150 publications on malaria research, epidemiology and prevention, which have received over 3,200 citations.

Urbano Ferreira has been awarded many research grants by FAPESP over the years. In one of these projects, he developed a methodology to detect asymptomatic cases of malaria in the Amazon region, increasing the chances that infected individuals without symptoms can be diagnosed. In 2015, he co-organized the São Paulo School of Advanced Science on the Eradication of Malaria (read more at agencia.fapesp.br/22083), attended by over one hundred researchers and students from many countries.

Agência FAPESP – What is the current situation in Brazil with regard to malaria?
Marcelo Urbano Ferreira – It’s a very interesting time to think about malaria control measures, not only because the number of cases in Brazil has fallen sharply but also in light of the progress achieved in combating malaria worldwide. The UN Millennium Development Goals called for a 75% reduction in global cases between 2000 and 2015. Brazil was one of the countries that achieved this target. We still have the largest number of cases in the Americas, but our share of the total fell from 76.8% in 2000 to 42% in 2014. We’re making significant progress. The number of cases is the lowest in 35 years. The success of many malaria elimination programs, especially in Africa, is due to investment by the Bill & Melinda Gates Foundation. Bill Gates has said he wants to live to see the worldwide elimination of malaria, and the World Health Organization insists malaria can be eradicated.

Agência FAPESP – Has the UN proposed a new reduction target for the years after 2015? 
Urbano Ferreira – Yes, the UN Sustainable Development Goals call for a 90% reduction in global malaria cases by 2030 and complete elimination in 35 countries. Brazil’s Health Ministry aims to eliminate cases associated with the protozoan Plasmodium falciparum by 2030. P. falciparum transmits the most dangerous form of the disease, which is responsible for 90% of all deaths from malaria. In Brazil, this protozoan is confined to a few areas, and we have a window of opportunity that must be seized before the protozoans develop resistance to antimalarial drugs. In the case of P. falciparum, the parasites have been acquiring resistance since the 1960s, when they became resistant to chloroquine. This drug is still used to combat P. vivax, the most common form of malaria. So far, we haven’t had reports of resistant malaria cases in Brazil like those reported in the Mekong Delta in Southeast Asia, for example. That doesn’t mean such cases can’t arise. It’s now or never as far as eliminating malaria is concerned.

Agência FAPESP – How would you assess Brazil’s efforts to combat malaria in the past? 
Urbano Ferreira – Brazil was slow to pay attention to the disease. Many countries have been compiling epidemiological statistics since the 1920s, but the Brazilian government only began doing surveys – not statistics, just estimates – after World War II. That was also when the use of the insecticide DDT began, with the spraying of homes in an effort to exterminate the mosquitoes that transmit malaria, as well as the use of larvicide to eliminate breeding grounds. Brazil had 257,000 cases in 1957. Everything went well in the 1960s, so much so that this period saw the all-time low of 52,000 cases, 60% of them in the Amazon region.

Agência FAPESP – What happened then? 
Urbano Ferreira – The military government implemented policies to promote population growth and settlement in the Amazon. This was a disaster in terms of preventing and combating malaria. More than a million migrants responded to government incentives to settle in the region. The vast majority had no resistance to malaria because they came from the South and Southeast regions, where the disease had been eliminated decades earlier. They settled in areas with dense forest cover, and the number of malaria cases exploded in the 1970s and 1980s. Another reason for the outbreaks was the flood of migrants who came to the region to prospect for gold. Alluvial and placer mining continues to account for a lot of transmission. Digger camps are typically a tragedy as far as malaria is concerned. All these factors combined led to a peak in 1999, with 623,000 cases.

Agência FAPESP – What was done to turn the situation around? 
Urbano Ferreira – The number of cases began trending down after that peak, especially those due to P. falciparum. The number of cases caused by P. vivax took longer to fall: they have been trending down since 2005. Why did the former start falling first? Because they’re easier to treat than cases due to P. vivax. If they’re treated early on, during the clinical stage of the disease, when the patient has a high fever and shaking chills, P. falciparum is eliminated before it reaches the transmission stage, when the patient feels better but the protozoan remains in the blood. All it needs is for the person to be bitten by a mosquito. The disease is then transmitted to the mosquito, and the cycle of infection proceeds. It’s different in the case of P. vivax. Although it’s a milder form of malaria, the patient enters the transmission phase while the symptoms are at their strongest. There are also cases where the parasite remains dormant in the liver only to reappear months or years later in a relapse of the disease. To address this situation, in the 1990s, the Brazilian government introduced a major policy of epidemiological surveillance, early diagnosis, treatment and prevention. Because DDT was banned in 2009 in Brazil and can no longer be used, other methods have to be deployed to combat the vectors, such as the distribution of insecticide-treated bed nets funded by the World Bank. All of these effective steps reduced the number of cases from 615,000 in 2000, with 243 deaths, to 142,000 in 2014, with 41 deaths.

Agência FAPESP – What are the main challenges to malaria control in Brazil? 
Urbano Ferreira – They haven’t changed much. The biggest challenge is still the size of the country: in other words, logistical complexity, huge distances, and the isolation of hundreds of communities in the Amazon, where malaria is endemic. The best way to tackle these challenges is by redoubling epidemiological surveillance and vector control, while at the same time bearing in mind that the parasites may well develop resistance to drugs. A study covering the Guianas (Guyana, Suriname and French Guiana), not yet confirmed, suggests there may be cases in the region that are resistant to treatment with derivatives of artemisinin. This is cause for concern, since the entire border area between the Guianas, Venezuela and Brazil is full of gold-mining camps, mostly on the other side of the border, where the majority – 15,000 – are Brazilian. When the gold runs out, these Brazilians return to Brazil and may go back home, taking the disease with them.

Agência FAPESP – The other challenge is diagnosis? 
Urbano Ferreira – That’s right. For every sick person, there are large numbers of asymptomatic individuals, between five and ten. They’re infected, but they have no symptoms of the disease. The parasite is in their blood, and they may be asymptomatic for months, becoming chronic patients and transmitting malarial parasites to mosquitoes. The most common method for confirming cases of malaria is microscopic analysis. However, these people may have a low density of protozoans in their blood, so they aren’t diagnosed. We’ve now begun using more sensitive laboratory techniques, including molecular techniques such as PCR [polymerase chain reaction].

Agência FAPESP – Where is the situation most worrying? 
Urbano Ferreira – Not among gold miners anymore, although alluvial and placer mining areas remain important transmission hotspots, especially along the border. The area most affected by malaria in Brazil today is the Juruá River valley in western Acre, where 120,000 people live in four municipalities. In 2014, they accounted for a third of Brazil’s malaria cases, and 46% or 8,000 cases were caused by P. falciparum.

Agência FAPESP – Why is the problem so serious in that area? 
Urbano Ferreira – The reason for so many cases to be concentrated in a single region is the development of fish farming in the Amazon. The government offers incentives to freshwater fish farmers, and many rural proprietors have built tanks to breed fish. The edges of these tanks aren’t kept clear, so they become full of weeds and grasses that serve as breeding grounds for mosquito larvae. There are also tanks that are abandoned after the owners give up fish farming and likewise become breeding grounds for the vectors. People can’t be forced to stop fish farming, which is a subsistence activity, so the action to be evaluated [jointly with the Health Ministry] is the application of biological larvicide to the tanks while requiring that their owners keep the edges free of weeds. This larvicide harms neither the fish nor the people who eat them, while being lethal to larvae.

Agência FAPESP – Do you think it will be possible to achieve the target of a 75% reduction in cases by 2030? 
Urbano Ferreira – I confess I was more optimistic at the start of 2016, when we finished writing the article published in Malaria Journal. But PEC 55, the constitutional amendment to freeze federal government spending for 20 years, could make Brazil lose decades of progress in combating malaria. The result could be a catastrophe our grandchildren will study one day at school. But if everything continues to run smoothly, if we have consistent and stable public policies, then yes, I do think we could achieve the 75% reduction target and eventually eradicate the disease. If we control the disease in the Juruá Valley, the number of cases of P. falciparum in Brazil could fall by half. The risk is that Brazil will follow the example set by countries that failed to meet the Millennium Development Goal for lack of investment, like Peru, which in the last three years has seen malaria cases rebound, and Venezuela, where there’s an alarming number of cases because of the economic crisis there.

The article “Challenges for malaria elimination in Brazil” by Marcelo U. Ferreira and Marcia C. Castro (doi: 10.1186/s12936-016-1335-1) can be read at: malariajournal.biomedcentral.com/articles/10.1186/s12936-016-1335-1.