Rapid tests could be used to diagnose Chagas disease in resource-limited areas, according to a study led by the Barcelona Institute for Global Health (ISGlobal), a centre supported by ”la Caixa” Foundation. The results of this research, published in PLOS Neglected Tropical Diseases, show that the prevalence of Chagas in an indigenous community in Paraguay is six times higher than in the country’s capital.
Chagas disease, caused by the parasite Trypanosoma cruzi, is a serious public health problem in the Americas. Between six and seven million people suffer from the disease, which is mainly transmitted by insect vectors. Under-diagnosis is one of the main obstacles in the fight against the parasite, reflected in the fact that less than 1% of those affected receive treatment. Chagas is primarily diagnosed by serological techniques—the detection of antibodies to T. cruzi in the blood—during the chronic phase of the disease. To improve diagnostic access, Paraguayan health authorities proposed a new algorithm for resource-limited settings: a combination of rapid diagnostic tests (RDTs) followed by conventional serological tests, such as enzyme-linked immunosorbent assay (ELISA).
“In July 2023, we conducted a two-week screening campaign in the endemic community of Casanillo (an indigenous community in the Paraguayan Chaco), involving 999 people,” explains Sofía Ardiles Ruesjas, ISGlobal researcher and first author of the study. “We were able to verify the effectiveness of the combination of RDTs and serological tests compared to the standard method recommended by PAHO and WHO, which relies solely on conventional serological tests,” she adds.
The potential of rapid tests
Although they have good sensitivity and specificity, conventional serological tests require specialised personnel and equipment, which are often in short supply in endemic regions. Even when these resources are available, access to health centres can be a challenge for local people.
The use of rapid diagnostic tests offers a new approach: they are easy to use, require only a minimal sample volume (blood from a finger prick), do not require special equipment, and ensure rapid delivery of results. The algorithm validated in the study suggests using RDTs for an initial screening of at-risk individuals in endemic areas, thereby reducing the need for serological testing to confirm positive results.
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“Each participant underwent a rapid diagnostic test (RDT), and those with a positive result were confirmed using two different serological techniques (recombinant ELISA and lysate ELISA),” explains the ISGlobal researcher.
Variability in the prevalence of Chagas among communities
The study results of the study showed a seroprevalence (percentage of people with antibodies against T. cruzi) of 12.6% in the community of Casanillo, a figure significantly higher than the 2.1% estimated from blood banks in Asunción. This highlights the health inequalities between urban and rural areas.
The algorithm using rapid diagnostic tests (RDTs) showed high agreement with the standard algorithm, with a sensitivity of 94.6% and a specificity of 98.6%. These results are crucial for public health initiatives, as they validate the combined use of RDTs and conventional serology, an algorithm proposed by Paraguayan health authorities for resource-limited settings.
“The results obtained are particularly relevant in the context of a global re-evaluation of guidelines for the diagnosis and treatment of Chagas disease,” says Irene Losada, coordinator of the Chagas Initiative at ISGlobal and senior author of the study. “The adoption of RDT-based algorithms adapted to each region could improve access to diagnosis for thousands of people in remote areas,” she concludes.
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