Study is investigating factors that influence the transmission of Chagas disease in Northeast Brazil
Brazilian and French researchers have studied specimens of the vector insect captured in Brazil that recorded an outbreak of the disease and have observed a high prevalence of infection by T. cruzi; two species of rodents were identified as potential reservoirs of the parasite.
Maria Fernanda Ziegler, from Lyon | Agencia FAPESP – Chagas disease is considered one of the biggest public health problems in Latin America. According to data from the not-for-profit organization Drugs for Neglected Diseases initiative (DNDi), around 6 million infected people live in the region, spread over 21 countries. Only 10% of them are diagnosed and only 1% receives treatment.
In Brazil, the Ministry of Health estimates that there are at least 1 million people infected by the Trypanosoma cruzi protozoan – the cause of the disease, which when it becomes chronic can lead to death from heart failure. More than 90% of cases are concentrated in the North and Northeast regions.
With the aim of understanding the elements involved in the chain of transmission of Chagas disease in the Brazilian semi-arid region, researchers at the State University of Campinas (Unicamp) conducted a field study in the municipality of Marcelino Vieira in Rio Grande do Norte, where, in 2015, there was an outbreak possibly caused by oral transmission. Three deaths and 18 cases were recorded, all related to the consumption of sugarcane juice, according to the patients.
The research received support from FAPESP and was presented during the FAPESP Week France symposium.
“In the Brazilian semi-arid region, especially where outbreaks occur, there needs to be a more accurate understanding about the elements involved in the ecoepidemiological chain, since the risk of infection may be changing. Socioeconomic, behavioral, and climatic factors may have a crucial influence on the biology of the vector species and parasites,” said Carlos Eduardo de Almeida, a professor at the Institute of Biology of Unicamp and coordinator of the project.
The bug of the Triatoma brasiliensis species – popularly known as “barbeiro” – is the main vector of Chagas disease in the region studied. In collaboration with French scientists from the Centre Nacional de Recherche Scientifique (CNRS), Almeida has been working on sequencing the genome and on studying the transcriptome (set of expressed genes) of specimens of T. brasiliensis captured in the location of the outbreak.
By analyzing genetic markers of the single nucleotide polymorphism (SNP) type, the group is developing genetic population studies to understand the speciation and adaptation processes in this group of insects. The work has be carried out within the scope of the São Paulo Excellence Chair Program (SPEC ).
The analyses indicate that the homes in Marcelino Vieira were invaded by wild and domestic populations of T. brasiliensis, both with a high prevalence of infection by T. cruzi. The scenario, according to Almeida, is conducive to the occurrence of new outbreaks.
“These insects aren’t born infected by the parasite. They generally get contaminated by biting some animal and, thus, become apt for transmitting the disease to humans,” he explained.
Data from the research reveal that 52% of the wild “barbeiros” captured and 71% of the domestic insects were infected by the protozoan. The high prevalence of the infection in the wild specimens and the occurrence of two different parasitic lineages are factors that, according to the researcher’s assessment, threaten the efforts to control the disease.
The study also showed that 68% of the 202 insects analyzed using molecular techniques had fed on the blood of Brazilian guinea pigs (Galea spixii) and rock cavies (Kerodon rupestris). This finding indicates the rodents as possible reservoirs of T. Cruzi – a role that was previously only attributed to opossums (Didelphis). The results were published in PLOS Neglected Tropical Diseases.
Using ecological modeling studies, the researchers identified the environments that favor rodent infestations near human settlements. “This knowledge enables us to outline a strategy for controlling Chagas disease similar to that used against dengue: avoiding the formation of breeding grounds for the vector insect and the reservoir rodents, such as piles of wood and bricks,” said Almeida.
The scientists now intend to carry out blood tests among the population of Rio Grande do Norte to measure the real size of the outbreak. However, one of the discoveries of the research may prove to be a complicating factor.
The group found, for the first time in nature, specimens of T. brasiliensis infected by Tripanosoma rangeli parasites. “This protozoan isn’t pathogenic and, therefore, isn’t a threat to human health. However, it can cause cross reactions and false-positive results in blood tests for the detection of Chagas disease,” he said.
This, according to the researcher, could make evaluating the prevalence of the human population infected by T. cruzi difficult, which is crucial information for the development of public policies.
The FAPESP Week France symposium was held between November 21st and 27th, thanks to a partnership between FAPESP and the universities of Lyon and Paris, both in France. Read other news about the event at www.fapesp.br/week2019/france.