A systematic literature review of schistosomiasis in urban and peri-urban settings

Abstract

Background Schistosomiasis is a parasitic disease caused by trematode worms of the genus Schistosoma and belongs to the neglected tropical diseases. The disease has been reported in 78 countries, with around 290.8 million people in need of treatment in 2018. Schistosomiasis is predominantly considered a rural disease with a subsequent focus of research and control activities in rural settings. Over the past decades, occurrence and even expansion of schistosomiasis foci in peri-urban and urban settings have increasingly been observed. Rural–urban migration in low- and middle-income countries and subsequent rapid and unplanned urbanization are thought to explain these observations. Fifty-five percent (55%) of the world population is already estimated to live in urban areas, with a projected increase to 68% by 2050. In light of rapid urbanization and the efforts to control morbidity and ultimately achieve elimination of schistosomiasis, it is important to deepen our understanding of the occurrence, prevalence, and transmission of schistosomiasis in urban and peri-urban settings. A systematic literature review looking at urban and peri-urban schistosomiasis was therefore carried out as a first step to address the research and mapping gap. Methodology Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a systematic computer-aided literature review was carried out using PubMed, ScienceDirect, and the World Health Organization Database in November 2019, which was updated in March 2020. Only papers for which at least the abstract was available in English were used. Relevant publications were screened, duplicates were removed, guidelines for eligibility were applied, and eligible studies were reviewed. Studies looking at human Schistosoma infections, prevalence, and intensity of infection in urban and peri-urban settings were included as well as those focusing on the intermediate host snails. Principal findings A total of 248 publications met the inclusion criteria. The selected studies confirm that schistosomiasis is prevalent in peri-urban and urban areas in the countries assessed. Earlier studies report higher prevalence levels in urban settings compared to data extracted from more recent publications, yet the challenge of migration, rapid uncontrolled urbanization, and resulting poor living conditions highlight the potential for continuous or even newly established transmission to take place. Conclusions The review indicates that schistosomiasis has long existed in urban and peri-urban areas and remains a public health problem. There is, however, a challenge of comparability of settings due to the lack of a clear definition of what constitutes urban and peri-urban. There is a pressing need for improved monitoring of schistosomiasis in urban communities and consideration of treatment strategies.

Cryptic population structure and transmission dynamics uncovered for Schistosoma mansoni populations by genetic analyses

“…Schistosomiasis persists throughout the world and is now spreading from rural to urban areas despite control efforts, including successful treatment using the drug praziquantel 6 , 19 . Methods to detect the sources of recurring infections and the spread of new infections are of paramount importance, and genetic analysis has become prominent in the epidemiological toolbox 9 .…”

“…Schistosomiasis is most common in rural communities. However, migration of people from the countryside to cities has resulted in presence and transmission of schistosomaisis in urban environments 5 , 6 .…”

Emerging and Re-emerging Vector-Borne Infectious Diseases and the Challenges for Control: A Review

“…Influxes of rural to urban in poor and average-income nations coupled with fast and unplanned urbanization appear to such phenomena (86). More recent study reported that schistosomiasis, being common in urban and urban peripheries, was a significant menace to the public health (87).…”

Stage-specific miRNAs regulate gene expression associated with growth, development and parasite-host interaction during the intra-mammalian migration of the zoonotic helminth parasite Fasciola hepatica

“…Soil-transmitted intestinal nematodes such as hookworms ( Ancylostoma duodenale and Necator americanus ), Trichuris trichiura and Ascaris lumbricoides infect over two billion people worldwide [ 13 ] while flatworms like Schistosoma spp. cause ~200 million infections per year [ 14 ]. Recent studies have shown that miRNAs are essential not only for the development of parasites within their hosts but for regulation of the complex interactions between them [ 15 – 17 ].…”