A systematic review of Schistosoma intercalatum: an obscure causative agent of human schistosomiasis

BackgroundHuman schistosomiasis caused by Schistosoma intercalatum is poorly understood compared to other species of public health importance, such as S. haematobium, S. mansoni, and S. japonicum. The restricted distribution of S. intercalatum in Africa, its perceived low virulence, and poor understanding of its pathological consequences are possible reasons for this neglect. However, schistosomiasis as a public health problem cannot be eradicated without adequate knowledge of existing species of schistosomes and the biological interactions between them, their hosts, and the environment. Current information on S. intercalatum is often confused with the previous S. intercalatum (Lower Guinea strain) which has now been described as S. guineensis n. sp. The S. intercalatum (Zaire strain) with known foci only in Democratic Republic of the Congo (DRC) is now recognized as the true S. intercalatum species. Investigators not conversant with the present status of both species still get confused in understanding the literature hence this review. It is essential to discuss available knowledge on S. intercalatum and highlight gaps that are critical for deepening our understanding of the parasite in the DRC. MethodsThus, we systematically review existing available literature on S. intercalatum obtained from PubMed Central, Web of Science, Embase, and Scopus databases according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Relevant publications were screened and publications reporting S. intercalatum from other than the DRC were excluded. Eligible studies on the epidemiology and biology of S. intercalatum were reviewed. ResultsBased on 38 publications that met our inclusion criteria, we confirm that S. intercalatum is the most neglected among Schistosoma species responsible for human schistosomiasis. We discuss our synthesis of the available information in the context of the distribution, biology, pathology, and genetics of S. intercalatum. Also highlighted are outstanding questions on S. intercalatum population genomics, hybridization with other Schistosoma species, snail vector host, zoonotic epidemiology, and pathology. ConclusionThe review calls for a rekindling of research interest in the parasite and the need to answer fundamental questions that can deepen our understanding of the parasite epidemiology, disease ecology, and environmental interactions to help in control strategies and elimination.