Survey of Schistosomiasis in Saint Lucia: Evidence for Interruption of Transmission

Update on the Geographic Distribution of the Intermediate Host Snails of Schistosoma mansoni on St. Lucia: A Step Toward Confirming the Interruption of Transmission of Human Schistosomiasis

To provide information to guide considerations of declaring interruption of transmission of human schistosomiasis due to Schistosoma mansoni on St. Lucia, we undertook an island-wide survey in June-July 2022 to determine the presence of Biomphalaria snails, the intermediate hosts of S. mansoni, and their infection status. Snail surveys were carried out at 58 habitats to determine presence of Biomphalaria snails followed by examination of the collected snails for evidence of infection with S. mansoni. Furthermore, water samples were collected at the snail habitats and screened for presence of S. mansoni DNA using an eDNA approach. We found B. glabrata present in one habitat (Cul de Sac) where it was abundant. Specimens provisionally identified as Biomphalaria kuhniana were recovered from 10 habitats. None of the Biomphalaria specimens recovered were positive for S. mansoni. None of the eDNA water samples screened were positive for S. mansoni. Experimental exposures of both field-derived and laboratory-reared St. Lucian B. glabrata and B. kuhniana to Puerto Rican and Kenyan-derived S. mansoni strains revealed B. glabrata to be susceptible to both and B. kuhniana proved refractory from histological and snail shedding results. We conclude, given the current rarity of B. glabrata on the island and lack of evidence for the presence of S. mansoni, that transmission is unlikely to be ongoing. Coupled with negative results from recent human serological surveys, and implementation of improved sanitation and provision of safe water supplies, St. Lucia should be considered a candidate for declaration of interruption of human schistosomiasis transmission.

[Schistosomiasis, soil-transmitted helminthiases and sanitation in Latin America and the Caribbean: a systematic reviewRelación entre la prevalencia de esquistosomiasis y geohelmintiasis y las condiciones sanitarias en América Latina y el Caribe: una revisión sistemática]

Objective

To investigate the relationship between the prevalence of schistosomiasis and soil-transmitted helminthiasis with variables related to access to water, sanitation and solid waste in Latin American and Caribbean (LAC) countries.

Method

A systematic review was performed in the LILACS, PubMed, Web of Science, and SciELO databases. Studies published between 1950 and August 2021, with an ecological design and a focus on population groups (states, municipalities and/or districts), having the prevalence of infection by Schistosoma mansoni, Ancylostoma sp., Necator americanus, Ascaris lumbricoides or Trichuris trichiura as primary variable and access to water, sewage and/or solid waste as explanatory variables were included. Open access articles with full text available in English, Spanish, or Portuguese were considered. The risk of bias and the quality of the studies were assessed according to the Joanna Briggs Institute manual.

Results

Of 2 714 articles, nine were eligible, published between 1994 and 2021 and covering 22 LAC countries and 14 350 municipalities. All articles had moderate methodological quality. Environmental variables indicated an association between water supply and solid waste collection with schistosomiasis; water supply with ascariasis, trichuriasis and hookworm; and sewage with ascariasis and hookworm. Except for one article, which had regional coverage for LAC, all the others were developed in Brazil.

Conclusion

There is a clear need to expand research on the association between household and collective health conditions and parasitic diseases for all endemic countries in LAC to support environmental strategies to control these diseases.

Evaluation of the Point-of-Care Circulating Cathodic Antigen Assay for Monitoring Mass Drug Administration in a Schistosoma mansoni Control Program in Western Kenya

The WHO guidelines for monitoring and evaluating Schistosoma mansoni control programs are based on the Kato-Katz (KK) fecal examination method; however, there are limitations to its use, particularly in low prevalence areas. The point-of-care urine circulating cathodic antigen (POC-CCA) assay has emerged as a useful tool for mapping schistosomiasis prevalence, but its use in monitoring and evaluating control programs has not been evaluated. Before POC-CCA can be used for these programs, it must be determined how previous guidance based on the KK method can be translated to the POC-CCA assay; furthermore, its performance in different endemicity settings must be evaluated. Urine and stool specimens were collected from students attending public primary schools in western Kenya before mass treatment with praziquantel at baseline (51 schools), year 1 (45 schools), year 2 (34 schools), and year 3 (20 schools). Prevalence and infection intensity were determined by the KK method and POC-CCA assay. Changes in prevalence and intensity were compared within the strata of schools grouped according to the baseline prevalence determined by the KK method (0-10%, > 10-20%, > 20%). The prevalence determined by the POC-CCA assay was higher than that determined by the KK method at all time points for all strata. The prevalence determined by the KK method decreased from baseline to 2 and 3 years, as did infection intensity (with one exception). A corresponding decrease was not always replicated by the POC-CCA assay results. The POC-CCA assay did not perform as expected, and the concordance of results of the two tests was poor. Furthermore, there are emerging concerns regarding the specificity of the POC-CCA assay. Therefore, it is impossible to translate historical data and programmatic guidelines based on the KK method results to the POC-CCA assay.

Evaluation, Validation, and Recognition of the Point-of-Care Circulating Cathodic Antigen, Urine-Based Assay for Mapping Schistosoma mansoni Infections

Efforts to control Schistosoma mansoni infection depend on the ability of programs to effectively detect and quantify infection levels and adjust programmatic approaches based on these levels and program goals. One of the three major objectives of the Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) has been to develop and/or evaluate tools that would assist Neglected Tropical Disease program managers in accomplishing this fundamental task. The advent of a widely available point-of-care (POC) assay to detect schistosome circulating cathodic antigen (CCA) in urine with a rapid diagnostic test (the POC-CCA) in 2008 led SCORE and others to conduct multiple evaluations of this assay, comparing it with the Kato–Katz (KK) stool microscopy assay—the standard used for more than 45 years. This article describes multiple SCORE-funded studies comparing the POC-CCA and KK assays, the pros and cons of these assays, the use of the POC-CCA assay for mapping of S. mansoni infections in areas across the spectrum of prevalence levels, and the validation and recognition that the POC-CCA, although not infallible, is a highly useful tool to detect low-intensity infections in low-to-moderate prevalence areas. Such an assay is critical, as control programs succeed in driving down prevalence and intensity and seek to either maintain control or move to elimination of transmission of S. mansoni.

Fast and reliable easy-to-use diagnostics for eliminating bilharzia in young children and mothers: An introduction to the freeBILy project

Schistosoma antigen detection tests have a large potential for schistosomiasis control programs due to their ability to detect active and ongoing Schistosoma infections, their much higher sensitivity compared to microscopical methods, and the possibility to use non-invasive urine samples. Pregnant women and young children could especially benefit from affordable and easy-to-use antigen tests as inclusion of these vulnerable groups in mass drug administration campaigns will always require higher justification hurdles, especially in low to middle endemic regions with a higher proportion of individuals who are not infected and thus unnecessarily exposed to praziquantel. The overall objective of the 'fast and reliable easy-to-use diagnostics for eliminating bilharzia in young children and mothers' (freeBILy, www.freeBILy.eu) project is to thoroughly evaluate the point-of-care circulating cathodic antigen (POC-CCA) and the up-converting phosphor reporter particle, lateral flow circulating anodic antigen (UCP-LF CAA) urine strip tests to diagnose Schistosoma infections in pregnant women and young children and to assess their potential as a schistosomiasis control tool in test-and-treat strategies. The freeBILy project will generate valuable, evidence-based findings on improved tools and test-and-treat strategies to reduce the burden of schistosomiasis in pregnant women and young children.

Adults from Kisumu, Kenya have robust γδ T cell responses to Schistosoma mansoni, which are modulated by tuberculosis

Schistosoma mansoni (SM) is a parasitic helminth that infects over 200 million people and causes severe morbidity. It undergoes a multi-stage life cycle in human hosts and as such stimulates a stage-specific immune response. The human T cell response to SM is complex and varies throughout the life cycle of SM. Relative to the wealth of information regarding the immune response to SM eggs, little is known about the immune response to the adult worm. In addition, while a great deal of research has uncovered mechanisms by which co-infection with helminths modulates immunity to other pathogens, there is a paucity of data on the effect of pathogens on immunity to helminths. As such, we sought to characterize the breadth of the T cell response to SM and determine whether co-infection with Mycobacterium tuberculosis (Mtb) modifies SM-specific T cell responses in a cohort of HIV-uninfected adults in Kisumu, Kenya. SM-infected individuals were categorized into three groups by Mtb infection status: active TB (TB), Interferon-γ Release Assay positive (IGRA+), and Interferon-γ Release Assay negative (IGRA-). U.S. adults that were seronegative for SM antibodies served as naïve controls. We utilized flow cytometry to characterize the T cell repertoire to SM egg and worm antigens. We found that T cells had significantly higher proliferation and cytokine production in response to worm antigen than to egg antigen. The T cell response to SM was dominated by γδ T cells that produced TNFα and IFNγ. Furthermore, we found that in individuals infected with Mtb, γδ T cells proliferated less in response to SM worm antigens and had higher IL-4 production compared to naïve controls. Together these data demonstrate that γδ T cells respond robustly to SM worm antigens and that Mtb infection modifies the γδ T cell response to SM.

Schistosomiasis, a disease caused by parasitic helminths including Schistosoma mansoni (SM), affects hundreds of millions of people globally. SM undergoes a complex life cycle within humans resulting in adult worm pairs that release eggs into the circulatory system. The human immune response to SM, especially to adult worms, is not well characterized. In addition, the impact of co-infections, which are common in SM endemic regions, on the immune response to SM is unknown. In this study, we first sought to characterize the T cell response to different stages of the SM life cycle. We next evaluated whether T cell responses to SM were altered in the setting of co-infection with Mycobacterium tuberculosis, the bacteria that causes tuberculosis. We determined that human T cell responses to SM adult worm antigen are more robust than to SM egg antigen. This response is dominated by a non-classical T cell subset of γδ T cells producing IFNγ and TNFα. Lastly, we found that the ability of γδ T cells to proliferate in response to SM worm was lower in individuals with tuberculosis compared to naïve controls. This study provides novel insights into the immune response to SM and how tuberculosis may impair SM immunity.

Identification of Schistosoma mansoni Infection in a Nonhuman Primate from St. Kitts More than 50 Years after Interruption of Human Transmission

Transmission of Schistosoma mansoni was interrupted on St. Kitts, a Caribbean island, in the 1950s. With no reported cases since that time and most Biomphalaria spp. snail populations eliminated based on surveys in the 1970s, S. mansoni has been considered eliminated on St. Kitts. In 2019, S. mansoni eggs were found in an African green monkey (Chlorocebus aethiops sabaeus) that originated from St. Kitts. Nonhuman primate (NHP) infections have been considered incidental to human infections, with infections in NHPs resolving with the elimination of S. mansoni in the human population. An NHP with S. mansoni infection suggests that the NHP may be able to maintain a reservoir sylvatic cycle. Alternatively, S. mansoni transmission was not eliminated or S. mansoni has been reintroduced to St. Kitts. The occurrence of an infected NHP from St. Kitts supports the need for continuous monitoring in areas where S. mansoni is considered eliminated.

Schistosoma mansoni Vector Snails in Antigua and Montserrat, with Snail-Related Considerations Pertinent to a Declaration of Elimination of Human Schistosomiasis

Investigations leading to a WHO-validated declaration of elimination of schistosomiasis transmission are contemplated for several countries, including Caribbean island nations. With assistance from the Pan American Health Organization, we undertook freshwater snail surveys in two such nations, Antigua and Barbuda, and Montserrat in September and October 2017. Historically, the transmission of Schistosoma mansoni supported by the Neotropical vector snail Biomphalaria glabrata occurred in both countries. Transmission on the islands is thought to have been interrupted by the treatment of infected people, improved sanitation, introduction of competitor snails, and on Montserrat with the eruption of the Soufrière volcano which decimated known B. glabrata habitats. Guided by the available literature and local expertise, we found Biomphalaria snails in seven of 15 and one of 14 localities on Antigua and Montserrat, respectively, most of which were identified anatomically and molecularly as Biomphalaria kuhniana. Two localities on Antigua harbored B. glabrata, but no schistosome infections in snails were found. For snail-related aspects of validation of elimination, there are needs to undertake basic local training in medical malacology, be guided by historical literature and recent human schistosomiasis surveys, improve and validate sampling protocols for aquatic habitats, enlist local expertise to efficiently find potential transmission sites, use both anatomical and molecular identifications of schistosomes or putative vector snail species found, if possible determine the susceptibility of recovered Biomphalaria spp. to S. mansoni, publish survey results, and provide museum vouchers of collected snails and parasites as part of the historical record.

Circulating Anodic Antigen (CAA): A Highly Sensitive Diagnostic Biomarker to Detect Active Schistosoma Infections-Improvement and Use during SCORE

The Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) was funded in 2008 to conduct research that would support country schistosomiasis control programs. As schistosomiasis prevalence decreases in many places and elimination is increasingly within reach, a sensitive and specific test to detect infection with Schistosoma mansoni and Schistosoma haematobium has become a pressing need. After obtaining broad input, SCORE supported Leiden University Medical Center (LUMC) to modify the serum-based antigen assay for use with urine, simplify the assay, and improve its sensitivity. The urine assay eventually contributed to several of the larger SCORE studies. For example, in Zanzibar, we demonstrated that urine filtration, the standard parasite egg detection diagnostic test for S. haematobium, greatly underestimated prevalence in low-prevalence settings. In Burundi and Rwanda, the circulating anodic antigen (CAA) assay provided critical information about the limitations of the stool-based Kato-Katz parasite egg-detection assay for S. mansoni in low-prevalence settings. Other SCORE-supported CAA work demonstrated that frozen, banked urine specimens yielded similar results to fresh ones; pooling of specimens may be a useful, cost-effective approach for surveillance in some settings; and the assay can be performed in local laboratories equipped with adequate centrifuge capacity. These improvements in the assay continue to be of use to researchers around the world. However, additional work will be needed if widespread dissemination of the CAA assay is to occur, for example, by building capacity in places besides LUMC and commercialization of the assay. Here, we review the evolution of the CAA assay format during the SCORE period with emphasis on urine-based applications.

Fifteen Years of Sm-p80-Based Vaccine Trials in Nonhuman Primates: Antibodies From Vaccinated Baboons Confer Protection in vivo and in vitro From Schistosoma mansoni and Identification of Putative Correlative Markers of Protection

Recent advances in systems biology have shifted vaccine development from a largely trial-and-error approach to an approach that promote rational design through the search for immune signatures and predictive correlates of protection. These advances will doubtlessly accelerate the development of a vaccine for schistosomiasis, a neglected tropical disease that currently affects over 250 million people. For over 15 years and with contributions of over 120 people, we have endeavored to test and optimize Sm-p80-based vaccines in the non-human primate model of schistosomiasis. Using RNA-sequencing on eight different Sm-p80-based vaccine strategies, we sought to elucidate immune signatures correlated with experimental protective efficacy. Furthermore, we aimed to explore the role of antibodies through in vivo passive transfer of IgG obtained from immunized baboons and in vitro killing of schistosomula using Sm-p80-specific antibodies. We report that passive transfer of IgG from Sm-p80-immunized baboons led to significant worm burden reduction, egg reduction in liver, and reduced egg hatching percentages from tissues in mice compared to controls. In addition, we observed that sera from Sm-p80-immunized baboons were able to kill a significant percent of schistosomula and that this effect was complement-dependent. While we did not find a universal signature of immunity, the large datasets generated by this study will serve as a substantial resource for further efforts to develop vaccine or therapeutics for schistosomiasis.