High schistosomiasis-related mortality in Northeast Brazil: trends and spatial patterns

Helminth community of Nectomys squamipes naturally infected by Schistosoma mansoni in an endemic area in Brazil: A comparison of 22 years apart

The municipality of Sumidouro in the state of Rio de Janeiro, southeastern Brazil, is considered an area with low endemicity of Schistosoma mansoni. In this municipality, the wild water rat Nectomys squamipes is a wild reservoir of S. mansoni. A helminth community survey was carried out on N. squamipes populations in Sumidouro from 1997 to 1999. In the present study, we compared the helminth fauna and the helminth community structure of N. squamipes with a recent survey after a 22-year time interval, considering that the prevalence of S. mansoni infection in humans remained stable and that the area showed the same environmental characteristics. Seventy-three host specimens of N. squamipes collected between 1997 and 1999 and 21 specimens collected in 2021 were analyzed in this study. Seven helminth species were found in each collection period. The nematode Syphacia evaginata was recorded for the first time in N. squamipes in 2021. Syphacia venteli was the most abundant species in both periods and the most prevalent in 2021. During the period from 1997 to 1999, the most prevalent species was Hassalstrongylus epsilon. Significant differences in prevalence and abundance in relation to host sex were observed only for S. mansoni in 1997-1999. Significant differences in the abundance of the helminth species over time were observed only in Physaloptera bispiculata. Hassalstrongylus epsilon, S. venteli and S. mansoni were the dominant species in both periods. Litomosoides chagasfilhoi, Echinostoma paraensei paraensei and P. bispiculata became dominant, codominant and subordinate, respectively, over time. In conclusion, the helminth community of N. squamipes remained stable, with similar species richness, prevalence and abundance values and low beta-diversity over time. The occurrence of S. mansoni in the water rat has remained stable for decades, highlighting its importance for schistosomiasis control.

Laboratory and field validation of the recombinase polymerase amplification assay targeting the Schistosoma mansoni mitochondrial minisatellite region (SmMIT-RPA) for snail xenomonitoring for schistosomiasis

Improvements in diagnostics for schistosomiasis in both humans and snail hosts are priorities to be able to reach the World Health Organization (WHO) goal of eliminating the disease as a public health problem by 2030. In this context, molecular isothermal amplification tests, such as Recombinase Polymerase Amplification (RPA), are promising for use in endemic areas at the point-of-need for their accuracy, robustness, simplicity, and time-effectiveness. The developed recombinase polymerase amplification assay targeting the Schistosoma mansoni mitochondrial minisatellite region (SmMIT-RPA) was used to detect S. mansoni DNA from both laboratory and field Biomphalaria snails. Laboratory snails were experimentally infected and used at one, seven, and 28 days post-exposure (dpe) to 10 S. mansoni miracidia to provide samples in the early pre-patent infection stage. Field samples of Biomphalaria spp. were collected from the Mucuri Valley and Jequitinhonha Valley regions in the state of Minas Gerais, Brazil, which are endemic for S. mansoni. The sensitivity and specificity of the SmMIT-RPA assay were analysed and compared with existing loop-mediated isothermal amplification (LAMP), PCR-based methods, parasitological examination of the snails, and nucleotide sequencing. The SmMIT-RPA assay was able to detect S. mansoni DNA in the experimentally infected Biomphalaria glabrata as early as one dpe to 10 miracidia. It also detected S. mansoni infections (55.5% prevalence) in the field samples with the highest accuracy (100% sensitivity and specificity) compared with the other molecular tests used as the reference. Results from this study indicate that the SmMIT-RPA assay is a good alternative test to be used for snail xenomonitoring of S. mansoni due to its high sensitivity, accuracy, and the possibility of detecting early pre-patent infection. Its simplicity and portability also make it a suitable methodology in low-resource settings.

Assessment of the accuracy of 11 different diagnostic tests for the detection of Schistosomiasis mansoni in individuals from a Brazilian area of low endemicity using latent class analysis

Background

Schistosomiasis is a parasitic disease associated with poverty. It is estimated that 7.1 million people are infected with Schistosoma mansoni in Latin America, with 95% of them living in Brazil. Accurate diagnosis and timely treatment are important measures to control and eliminate schistosomiasis, but diagnostic improvements are needed to detect infections, especially in areas of low endemicity.

Methodology

This research aimed to evaluate the performance of 11 diagnostic tests using latent class analysis (LCA). A cross-sectional survey was undertaken in a low endemicity area of the municipality of Malacacheta, Minas Gerais, Brazil. Feces, urine, and blood samples were collected from 400 residents older than 6 years of age, who had not been treated with praziquantel in the 12 months previous to the collection of their samples. The collected samples were examined using parasitological (Helm Test® kit Kato-Katz), nucleic acid amplification tests -NAATs (PCR, qPCR and LAMP on urine; PCR-ELISA, qPCR and LAMP on stool), and immunological (POC-CCA, the commercial anti-Schistosoma mansoni IgG ELISA kit from Euroimmun, and two in-house ELISA assays using either the recombinant antigen PPE or the synthetic peptide Smp150390.1) tests.

Results

The positivity rate of the 11 tests evaluated ranged from 5% (qPCR on urine) to 40.8% (commercial ELISA kit). The estimated prevalence of schistosomiasis was 12% (95% CI: 9-15%) according to the LCA. Among all tests assessed, the commercial ELISA kit had the highest estimated sensitivity (100%), while the Kato-Katz had the highest estimated specificity (99%). Based on the accuracy measures observed, we proposed three 2-step diagnostic approaches for the active search of infected people in endemic settings. The approaches proposed consist of combinations of commercial ELISA kit and NAATs tests performed on stool. All the approaches had higher sensitivity and specificity than the mean values observed for the 11 tests (70.4 and 89.5%, respectively).

Conclusion

We showed that it is possible to achieve high specificity and sensitivity rates with lower costs by combining serological and NAATs tests, which would assist in the decision-making process for appropriate allocation of public funding aiming to achieve the WHO target of eliminating schistosomiasis as a public health problem by 2030.