Strongyloidiasis and schistosomiasis: lessons from migrants' data
Authors: Humphrey D Mazigo
Journal: The Lancet Global Health (2019)

The soil-transmitted helminth Strongyloides stercolaris remains a public health concern in tropical and subtropical regions.1Schär F Trostdorf U Giardina F et al.Strongyloides stercoralis: global distribution and risk factors.PLoS Negl Trop Dis. 2013; 7: e2288Crossref PubMed Scopus (417) Google Scholar The low sensitivity of the commonly used parasitological diagnostic methods—such as the Kato-Katz technique or lesser used culture methods, including Koga Agar plate culture—has resulted into underreporting of S stercoralis infection2Bethony J Brooker S Albonico M et al.Soil-transmitted helminth infections: ascariasis, trichuriasis, and hookworm.Lancet. 2006; 367: 1521-1532Summary Full Text Full Text PDF PubMed Scopus (1586) Google Scholar and adequate information is still absent for many tropical and subtropical countries.1Schär F Trostdorf U Giardina F et al.Strongyloides stercoralis: global distribution and risk factors.PLoS Negl Trop Dis. 2013; 7: e2288Crossref PubMed Scopus (417) Google Scholar Similarly, schistosomiasis caused by Schistosoma haematobium and Schistosoma mansoni is a neglected tropical disease that mainly affects the world's poorest populations in sub-Saharan Africa.3Mazigo HD Nuwaha F Kinung'hi SM et al.Epidemiology and control of human schistosomiasis in Tanzania.Parasit Vect. 2012; 5: 274Crossref PubMed Scopus (97) Google Scholar Available epidemiological data in schistosomiasis are mainly for children (most of these data are for pre-school-age children).4Rollinson D Knopp S Levitz S et al.Time to set the agenda for schistosomiasis elimination.Acta Trop. 2013; 128: 423-440Crossref PubMed Scopus (389) Google Scholar Data for the disease are scarce among adult populations living in endemic areas. Data for specific groups, such as migrants and refugees, from regions where stongylodiasis and schistosomiasis are endemic can help to address the knowledge gaps about the prevalence of these infections in these areas, which in turn will help with clinical management and decision making for policy changes. In The Lancet Global Health,5Asundi A Beliavsky A Liu XJ et al.Prevalence of strongyloidiasis and schistosomiasis among migrants: a systematic review and meta-analysis.Lancent Glob Health. 2019; 7: e236-e248Summary Full Text Full Text PDF PubMed Scopus (68) Google Scholar Archana Asundi and colleagues report the results of a systematic review and meta-analysis of studies of the prevalence of strongyloidiasis and schistosomiasis among migrants, which adds granularity to epidemiological data since the last review was published in 2013, and helps to focus attention on a vulnerable population.1Schär F Trostdorf U Giardina F et al.Strongyloides stercoralis: global distribution and risk factors.PLoS Negl Trop Dis. 2013; 7: e2288Crossref PubMed Scopus (417) Google Scholar From the 88 included studies, they estimated a pooled seroprevalence of strongyloidiasis of 12·2% (95% CI 9·0–15·9; I2 96%) and stool-based prevalence of 1·8% (1·2–2·6; 98%). Pooled schistosomiasis seroprevalence was 18·4% (13·1–24·5; 97%) and stool-based prevalence was 0·9% (0·2–1·9; 99%). Their findings are an important reminder not to overlook infection with S stercolaris (which is the most neglected of the included parasitic infections) in control programmes for neglected tropical diseases and highlight the lack of epidemiological data for this infection in many countries.1Schär F Trostdorf U Giardina F et al.Strongyloides stercoralis: global distribution and risk factors.PLoS Negl Trop Dis. 2013; 7: e2288Crossref PubMed Scopus (417) Google Scholar The use of migrant populations served to mirror the situation of S stercolaris in endemic areas, and the use of highly sensitive diagnostic methods has previously shown very high prevalence in this group compared with that in the general population in endemic areas.1Schär F Trostdorf U Giardina F et al.Strongyloides stercoralis: global distribution and risk factors.PLoS Negl Trop Dis. 2013; 7: e2288Crossref PubMed Scopus (417) Google Scholar The highest prevalence of strongyloidiasis was in migrantsπ from east Asia and the Pacific (17·3% [95% CI 4·1–37·0]), sub-Saharan Africa (14·6% [7·1–24·2]), and Latin America and the Caribbean (11·4% [7·8–15·7]). The high seroprevalence of schistosomiasis in migrant populations, particularly those from sub-Saharan Africa (24·1% [16·4–32·7]), reflects ongoing transmission of the disease in endemic areas and provides evidence for the debate about the inclusion of adults in praziquantel mass drug administration programmes. Asundi and colleagues' findings also highlight the importance of highly sensitive diagnostic techniques for stongyloidiasis and schistosomiasis for use in epidemiological surveys and clinical practice. However, it is worthwhile noting that diagnosis of S stercolaris remains a challenge, especially in endemic areas, because of the life cycle of the parasite (females give birth to larvae, which cannot be detected with the Kato-Katz technique) and its characteristic autoinfection. In clinical practice, Asundi and colleagues emphasise the need for clinicians in non-endemic countries to consider stongyloidiasis and schistosomiasis when treating migrant groups from endemic countries. Asundi and colleagues' study included data from studies that did not focus specifically on strongyloidiasis and schistosomiasis (eg, studies that also included other infections, such as soil-transmitted helminths). Additionally, the compiled results were based on diagnostic techniques that have low sensitivity, and thus probably underestimated the true prevalence of these infections in the studied groups. Thus, studies are needed in which highly sensitive diagnostic techniques—such as circulating cathodic antigen and circulating anodic antigen tests for S mansoni and S haematobium, and Koga Agar plate culture, the Baermann method, PCR, or ELISA for S stercolaris—are used, to give a more comprehensive picture of the prevalence of these parasites in migrant populations, which would in turn help to establish the true regional and national prevalences. I declare no competing interests. Prevalence of strongyloidiasis and schistosomiasis among migrants: a systematic review and meta-analysisStrongyloidiasis affects migrants from all global regions, whereas schistosomiasis is focused in specific regions and most common among sub-Saharan African migrants. Serological prevalence estimates were several times higher than stool estimates for both parasites. These data can be used to inform screening decisions for migrants and support the use of serological screening, which is more sensitive and easier than stool testing. Full-Text PDF Open Access