Survey shows higher malaria mortality in Brazil outside Amazonia

More than 6,000 cases of malaria were recorded in Brazil between 2007 and 2014 outside the Amazon. Late diagnosis and treatment may explain the high proportions of severe malaria and deaths in non-endemic areas.

By Karina Toledo  |  Agência FAPESP – According to the survey findings of Brazilian researchers published in Malaria Journal, 6,092 cases of malaria were recorded between 2007 and 2014 outside Amazonia, the only region of Brazil considered endemic for the disease.

According to the authors, only 19% of all people infected with malaria outside Amazonia are diagnosed and treated within 48 hours of symptom onset compared with 60% for cases within the region.

“This may explain the high proportion of severe malaria cases in non-endemic areas” as well as the higher mortality outside than inside the region, the article surmises.

The survey was conducted with FAPESP’s support during Camila Lorenz’s and Flávia Virginio’s PhDs. Both were supervised by Lincoln Suesdek at the Butantan Institute in São Paulo. Breno Aguiar, a researcher at the University of São Paulo’s School of Public Health (FSP-USP), also took part in the survey, which was coordinated by Francisco Chiaravalloti-Neto, also affiliated with FSP-USP.

The group used epidemiological data from the Ministry of Health’s Notifiable Diseases Information System (SINAN) and the Unified Health System’s Informatics Department (DATASUS). These databases contain details of people infected with malaria such as their gender and age, where the notification was recorded, and where they had been during the presumed contamination period.

“The study shows that although most cases occur in Amazonia, the rest of Brazil also deserves attention from health professionals because the extra-Amazonian region contains 87% of the population and also has the conditions for transmission of the disease – presence of the vector (mosquitoes of the genus Anopheles), etiological agent (parasites of the genus Plasmodium), and host (humans),” Virginio told Agência FAPESP.

According to Virginio, the clinical symptoms of the disease are often insufficient to establish a diagnosis. Moreover, they can be confused with those of dengue and other viral diseases. Parasitological tests are therefore necessary to confirm malaria cases. “It’s dangerous to confuse these diseases. The treatment is very different,” she said.

Health professionals in all states of Brazil should take the patient’s history carefully and ask for details regarding places visited recently.

“We need more and better care, in terms of doctors trained to diagnose and treat the disease, and more and better epidemiological surveillance,” she said. “Everyone focuses on the Amazon, where 99% of the cases occur, but if we neglect surveillance in the rest of the country, the problem may return to places from which it’s been eradicated.”

If diagnosis and treatment are too late, mosquitoes that bite infected patients can be contaminated by the parasite and transmit it to other local inhabitants. According to expert estimates, she said, a single untreated person with malaria can give rise to as many as 50 new cases in a week, depending on the region.

“It’s important to bear in mind that there are several species of mosquito outside Amazonia with the potential to transmit malaria,” Lorenz added. “Ongoing changes in Brazil’s landscape and climate could mean that previously harmless species start transmitting Plasmodium. This is a public health issue that needs to be investigated.”

Regional differences

Almost 90% of the cases notified during the survey period were considered imported, meaning that the patients contracted the disease during a short stay in Amazonia or outside Brazil, especially elsewhere in Latin America or in Africa or India. The remaining cases were either autochthonous, with transmission occurring locally, or the infection had been introduced, i.e. was due to blood transfusion rather than a mosquito bite.

Although imported cases predominated in all years, they peaked in 2007. Autochthonous cases peaked in 2010. The states with the highest incidence of autochthonous cases were Espírito Santo, Piauí and Paraná.

“We found that the fewest cases, both autochthonous and imported, occurred in 2014,” Lorenz said. “This reflects the measures people have taken to protect themselves even in non-endemic areas, such as using insect repellent, installing window and door screens, and not bathing during early evening and at night, when mosquitoes prefer to feed.”

Pernambuco, Alagoas, Sergipe, Minas Gerais and Rio Grande do Sul had only imported cases, although  malaria cases were notified in all states.

In the southern region, people were predominantly infected by the malarial parasite species Plasmodium vivax, whereas in the northeastern and southeastern regions, infection by Plasmodium falciparum was most frequent. In the center-west, which borders on the Amazon, cases of dual infection by both P. vivax and P. falciparum were found.

“In the extra-Amazonian regions, malaria has become a problem that mainly affects isolated subpopulations with certain social characteristics (e.g., housing types) or professional activities. Therefore, adequate education of individuals at risk and health professionals is necessary. In addition, means of rapid diagnosis should be implemented in these regions to prevent serious adverse events or deaths from malaria,” the article concludes.

The article “Spatial and temporal epidemiology of malaria in extra-Amazonian regions of Brazil” (doi: 10.1186/s12936-015-0934-6) can be read at www.malariajournal.com/content/14/1/408.