Schistosomiasis is an infectious disease caused by helminth parasites of the genus Schistosoma. Worldwide, an estimated 250 million people are infected with these parasites with the majority of cases occurring in sub-Saharan Africa. Within Asia, three species of Schistosoma cause disease. Schistosoma japonicum is the most prevalent, followed by S. mekongi and S. malayensis. All three species are zoonotic, which causes concern for their control, as successful elimination not only requires management of the human definitive host, but also the animal reservoir hosts. With regard to Asian schistosomiasis, most of the published research has focused on S. japonicum with comparatively little attention paid to S. mekongi and even less focus on S. malayensis. In this review, we examine the three Asian schistosomes and their current status in their endemic countries: Cambodia, Lao People's Democratic Republic, Myanmar, and Thailand (S. mekongi); Malaysia (S. malayensis); and Indonesia, People's Republic of China, and the Philippines (S. japonicum). Prospects for control that could potentially lead to elimination are highlighted as these can inform researchers and disease control managers in other schistosomiasis-endemic areas, particularly in Africa and the Americas.

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Asian schistosomiasis: current status and prospects for control leading to elimination

Intestinal schistosomiasis was not considered endemic in Lake Malawi until November 2017 when populations of Biomphalaria pfeifferi were first reported; in May 2018, emergence of intestinal schistosomiasis was confirmed. This emergence was in spite of ongoing control of urogenital schistosomiasis by preventive chemotherapy. Our current study sought to ascertain whether intestinal schistosomiasis is transitioning from emergence to outbreak, to judge if stepped-up control interventions are needed. During late-May 2019, three cross-sectional surveys of primary school children for schistosomiasis were conducted using a combination of rapid diagnostic tests, parasitological examinations and applied morbidity-markers; 1) schistosomiasis dynamics were assessed at Samama (n = 80) and Mchoka (n = 80) schools, where Schistosoma mansoni was first reported, 2) occurrence of S. mansoni was investigated at two non-sampled schools, Mangochi Orphan Education and Training (MOET) (n = 60) and Koche (n = 60) schools, where B. pfeifferi was nearby, and 3) rapid mapping of schistosomiasis, and B. pfeifferi, conducted across a further 8 shoreline schools (n = 240). After data collection, univariate analyses and Chi-square testing were performed, followed by binary logistic regression using generalized linear models, to investigate epidemiological associations. In total, 520 children from 12 lakeshore primary schools were examined, mean prevalence of S. mansoni by ‘positive’ urine circulating cathodic antigen (CCA)-dipsticks was 31.5% (95% confidence interval [CI]: 27.5–35.5). Upon comparisons of infection prevalence in May 2018, significant increases at Samama (relative risk [RR] = 1.7, 95% CI: 1.4–2.2) and Mchoka (RR = 2.7, 95% CI: 1.7–4.3) schools were observed. Intestinal schistosomiasis was confirmed at MOET (18.3%) and Koche (35.0%) schools, and in all rapid mapping schools, ranging from 10.0 to 56.7%. Several populations of B. pfeifferi were confirmed, with two new eastern shoreline locations noted. Mean prevalence of urogenital schistosomiasis was 24.0% (95% CI: 20.3–27.7). We notify that intestinal schistosomiasis, once considered non-endemic in Lake Malawi, is now transitioning from emergence to outbreak. Once control interventions can resume after coronavirus disease 2019 (COVID-19) suspensions, we recommend stepped-up preventive chemotherapy, with increased community-access to treatments, alongside renewed efforts in appropriate environmental control.

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An outbreak of intestinal schistosomiasis, alongside increasing urogenital schistosomiasis prevalence, in primary school children on the shoreline of Lake Malawi, Mangochi District, Malawi

Schistosomiasis causes significant levels of morbidity and mortality in many geographical regions of the world. The disease is caused by infections with parasitic blood flukes known as schistosomes. The control of schistosomiasis over the last several decades has been centered on the mass drug administration (MDA) of praziquantel (PZQ), which is the only drug currently available for treatment. Despite the concerted efforts of MDA programs, the prevalence and transmission of schistosomiasis has remained largely unchecked due to the fact that PZQ is ineffective against juvenile schistosomes, does not prevent re-infection and the emergence of PZQ-resistant parasites. In addition, other measures such as the water, sanitation and hygiene programs and snail intermediate hosts control have had little to no impact. These drawbacks indicate that the current control strategies are severely inadequate at interrupting transmission and therefore, implementation of other control strategies are required. Ideally, an efficient vaccine is what is needed for long term protection thereby eliminating the current efforts of repeated mass drug administration. However, the general consensus in the field is that the integration of a viable vaccine with MDA and other control measures offer the best chance of achieving the goal of schistosomiasis elimination. This review focuses on the present status of schistosomiasis vaccine candidates in different phases of human clinical trials and provide some insight into future vaccine discovery and design.

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Schistosomiasis vaccine development: update on human clinical trials

More than half of the world’s population lives in places endemic for soil-transmitted helminths (STHs), and an estimated 1.45 billion people are infected [1,2]. In 2017, the global burden of STH infection (Ascaris lumbricoides, hookworm, and Trichuris trichiura) was estimated at 1.9 million disability-adjusted life years (DALYs) [3]. Moderate and heavy infection intensity and chronic STH infection are associated with anemia, malnutrition, educational loss, and cognitive deficits, but recent systematic reviews and meta-analyses produced conflicting results on the impact of preventive chemotherapy (PC) [4–6].

The Soil-Transmitted Helminthiasis Advisory Committee (hereafter called “the Committee”) is a group of independent experts with a broad range of expertise. It is convened annually by Children Without Worms (CWW), an organization whose purpose is to utilize available evidence to identify best practices and opportunities for the prevention and control of STH infection [7]. On November 1 and 2, 2017, the Committee met in Baltimore, Maryland, United States of America, in order to discuss the critical need to develop a data-driven guide to the STH endgame on late-stage program functioning, processes, and surveillance. The focus was on research and field experiences from countries approaching the “elimination of STH infection as a public health problem” after consecutive years of PC and countries that are now considering scaling down their PC frequency but may be concerned about infection rebound. Emphasis was placed on interim recommendations for monitoring and decision-making for national program managers desiring to achieve the World Health Organization (WHO) goal of eliminating STH infection as a public health problem by 2020, particularly related to STH infections in risk groups other than school-age children (SAC), namely preschool-age children (PSAC) and women of reproductive age (WRA) [8]. The following is the Committee’s recommendations stemming from the Baltimore meeting in November 2017. It complements and updates the publication derived by the Committee’s meeting a year earlier in Basel, Switzerland [7], and was instrumental in shaping the agenda for the October 2018 meeting, convened jointly by CWW and WHO, with recommendations to be reported elsewhere.

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Challenges and opportunities for control and elimination of soil-transmitted helminth infection beyond 2020.

https://cyberleninka.org/article/n/840819.pdf

Tailoring Water, Sanitation, and Hygiene (WASH) Targets for Soil-Transmitted Helminthiasis and Schistosomiasis Control

Integration of water, sanitation and hygiene for the control of neglected tropical diseases: a review of progress and the way forward

Collaborating to develop joint water, sanitation and hygiene (WASH) and neglected tropical disease (NTD) sector monitoring: an expert consultation.

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Geordie Woods

Papers

Tailoring Water, Sanitation, and Hygiene (WASH) Targets for Soil-Transmitted Helminthiasis and Schistosomiasis Control

Integration of water, sanitation and hygiene for the control of neglected tropical diseases: a review of progress and the way forward

Collaborating to develop joint water, sanitation and hygiene (WASH) and neglected tropical disease (NTD) sector monitoring: an expert consultation.

Recognising the potential of neglected tropical disease programmes as a platform for pandemic preparedness: the Ascend experience