Field Testing Integrated Interventions for Schistosomiasis Elimination in the People's Republic of China: Outcomes of a Multifactorial Cluster-Randomized Controlled Trial

Transmission-Blocking Vaccines against Schistosomiasis Japonica

Control of schistosomiasis japonica, endemic in Asia, including the Philippines, China, and Indonesia, is extremely challenging. Schistosoma japonicum is a highly pathogenic helminth parasite, with disease arising predominantly from an immune reaction to entrapped parasite eggs in tissues. Females of this species can generate 1000-2200 eggs per day, which is about 3- to 15-fold greater than the egg output of other schistosome species. Bovines (water buffalo and cattle) are the predominant definitive hosts and are estimated to generate up to 90% of parasite eggs released into the environment in rural endemic areas where these hosts and humans are present. Here, we highlight the necessity of developing veterinary transmission-blocking vaccines for bovines to better control the disease and review potential vaccine candidates. We also point out that the approach to producing efficacious transmission-blocking animal-based vaccines before moving on to human vaccines is crucial. This will result in effective and feasible public health outcomes in agreement with the One Health concept to achieve optimum health for people, animals, and the environment. Indeed, incorporating a veterinary-based transmission vaccine, coupled with interventions such as human mass drug administration, improved sanitation and hygiene, health education, and snail control, would be invaluable to eliminating zoonotic schistosomiasis.

A compartmental model for Schistosoma japonicum transmission dynamics in the Philippines

Schistosomiasis is a chronic and debilitating neglected tropical disease (NTD), second only to malaria as one of the most devastating parasitic diseases. Caused by a parasitic flatworm of the genus Schistosoma, infection occurs when skin comes in contact with contaminated freshwater that contains schistosome-hosting snails. The disease continues to be endemic in many regions of the Philippines, where it poses a significant public health challenge due to a lack of healthcare resources. In the Philippines, additional mammalian reservoirs for the S. japonicum parasite, especially bovines such as carabaos, also facilitate the spread of schistosomiasis. We extend existing compartment models to include human, snail, bovine, and free-living Schistosoma for a comprehensive look at the transmission dynamics of the disease. Sensitivity analysis of model parameters shows that the carabaos themselves can sustain the endemicity of schistosomiasis. Thus, we consider the control method of farming mechanization to avoid contaminated freshwater sources. We find that a reduction of contaminated water contacts by at least 77% will break the transmission cycle and eliminate the disease. However, reducing the contact by about 70% will still result in decrease of human schistosomiasis prevalence to under 1% in 15 years or less. Achieving such high reduction of contact rates could be a daunting task, especially in rural areas. Still, the potential to eliminate or at least reduce the schistosomiasis prevalence should be considered an additional benefit of mechanization efforts in the Philippines.

First bovine vaccine to prevent human schistosomiasis - a cluster randomised Phase 3 clinical trial

OBJECTIVE

Schistosomiasis is a neglected tropical parasitic disease caused by blood flukes of the genus Schistosoma. Schistosoma japonicum is zoonotic in China, the Philippines, and Indonesia, with bovines acting as major reservoirs of human infection. The primary objective of the trial was to examine the impact of a combination of human mass chemotherapy, snail control through mollusciciding, and SjCTPI bovine vaccination on the rate of human infection.

METHODS

A 5-year phase IIIa cluster randomized control trial was conducted among 18 schistosomiasis-endemic villages comprising 18,221 residents in Northern Samar, The Philippines.

RESULTS

Overall, bovine vaccination resulted in a statistically significant decrease in human infection (relative risk [RR] = 0.75; 95% confidence interval [CI] = 0.69 to 0.82) across all trial follow-ups. The best outcome of the trial was when bovine vaccination was combined with snail mollusciciding. This combination resulted in a 31% reduction (RR = 0.69; 95% CI = 0.61 to 0.78) in human infection.

CONCLUSION

This is the first trial to demonstrate the effectiveness of a bovine vaccine for schistosomiasis in reducing human schistosome infection. The trial is registered with Australian New Zealand Clinical Trials Registry (ACTRN12619001048178).

The mRNA Vaccine Technology Era and the Future Control of Parasitic Infections

Despite intensive long-term efforts, with very few exceptions, the development of effective vaccines against parasitic infections has presented considerable challenges, given the complexity of parasite life cycles, the interplay between parasites and their hosts, and their capacity to escape the host immune system and to regulate host immune responses. For many parasitic diseases, conventional vaccine platforms have generally proven ill suited, considering the complex manufacturing processes involved and the costs they incur, the inability to posttranslationally modify cloned target antigens, and the absence of long-lasting protective immunity induced by these antigens. An effective antiparasite vaccine platform is required to assess the effectiveness of novel vaccine candidates at high throughput. By exploiting the approach that has recently been used successfully to produce highly protective COVID mRNA vaccines, we anticipate a new wave of research to advance the use of mRNA vaccines to prevent parasitic infections in the near future. This article considers the characteristics that are required to develop a potent antiparasite vaccine and provides a conceptual foundation to promote the development of parasite mRNA-based vaccines. We review the recent advances and challenges encountered in developing antiparasite vaccines and evaluate the potential of developing mRNA vaccines against parasites, including those causing diseases such as malaria and schistosomiasis, against which vaccines are currently suboptimal or not yet available.

Systematic review of applied mathematical models for the control of Schistosoma japonicum

BACKGROUND

Schistosoma japonicum remains endemic in China and the Philippines. Substantial progress has been made in the control of Japonicum in both China and the Philippines. China is reaching elimination thanks to a concerted effort of control strategies. Mathematical modelling has been a key tool in the design of control strategies, in place of expensive randomised-controlled trials. We conducted a systematic review to investigate mathematical models of Japonicum control strategies in China and the Philippines.

METHODS

We conducted a systematic review on July 5, 2020, in four electronic bibliographic databases - PubMed, Web of Science, SCOPUS and Embase. Articles were screened for relevance and for meeting the inclusion criteria. Data extracted included authors, year of publication, year of data collection, setting and ecological context, objectives, control strategies, main findings, the form and content of the model including its background, type, representation of population dynamics, heterogeneity of hosts, simulation period, source of parameters, model validation and sensitivity analysis. Results After screening, 19 eligible papers were included in the systematic review. Seventeen considered control strategies in China and two in the Philippines. Two frameworks were identified; the mean-worm burden framework and the prevalence-based framework, the latter of which increasingly common. Most models considered human and bovine definitive hosts. There were mixed additional elements included in the models, such as alternative definitive hosts and the role of seasonality and weather. Models generally agreed upon the need for an integrated control strategy rather than reliance on mass drug administration alone to sustain reductions in prevalence.

CONCLUSIONS

Mathematical modelling of Japonicum has converged from multiple approaches to modelling using the prevalence-based framework with human and bovine definitive hosts and find integrated control strategies to be most effective. Further research could investigate the role of other definitive hosts and model the effect of seasonal fluctuations in transmission.

Public Health Policy Pillars for the Sustainable Elimination of Zoonotic Schistosomiasis

Schistosomiasis is a parasitic disease acquired through contact with contaminated freshwater. The definitive hosts are terrestrial mammals, including humans, with some Schistosoma species crossing the animal-human boundary through zoonotic transmission. An estimated 12 million people live at risk of zoonotic schistosomiasis caused by Schistosoma japonicum and Schistosoma mekongi, largely in the World Health Organization’s Western Pacific Region and in Indonesia. Mathematical models have played a vital role in our understanding of the biology, transmission, and impact of intervention strategies, however, these have mostly focused on non-zoonotic Schistosoma species. Whilst these non-zoonotic-based models capture some aspects of zoonotic schistosomiasis transmission dynamics, the commonly-used frameworks are yet to adequately capture the complex epi-ecology of multi-host zoonotic transmission. However, overcoming these knowledge gaps goes beyond transmission dynamics modelling. To improve model utility and enhance zoonotic schistosomiasis control programmes, we highlight three pillars that we believe are vital to sustainable interventions at the implementation (community) and policy-level, and discuss the pillars in the context of a One-Health approach, recognising the interconnection between humans, animals and their shared environment. These pillars are: (1) human and animal epi-ecological understanding; (2) economic considerations (such as treatment costs and animal losses); and (3) sociological understanding, including inter- and intra-human and animal interactions. These pillars must be built on a strong foundation of trust, support and commitment of stakeholders and involved institutions.

The Search for a Schistosomiasis Vaccine: Australia's Contribution

Schistosomiasis, a neglected tropical disease caused by parasitic flatworms of the genus Schistosoma, results in considerable human morbidity in sub-Saharan Africa, in particular, but also parts of the Middle East, South America, and Southeast Asia. The anti-schistosome drug praziquantel is efficacious and safe against the adult parasites of all Schistosoma species infecting humans; however, it does not prevent reinfection and the development of drug resistance is a constant concern. The need to develop an effective vaccine is of great importance if the health of many in the developing world is to be improved. Indeed, vaccination, in combination with other public health measures, can provide an invaluable tool to achieve lasting control, leading to schistosomiasis elimination. Australia has played a leading role in schistosomiasis vaccine research over many years and this review presents an overview of some of the significant contributions made by Australian scientists in this important area.

Schistosomiasis with a Focus on Africa

Schistosomiasis is a common neglected tropical disease of impoverished people and livestock in many developing countries in tropical Africa, the Middle East, Asia, and Latin America. Substantial progress has been made in controlling schistosomiasis in some African countries, but the disease still prevails in most parts of sub-Saharan Africa with an estimated 800 million people at risk of infection. Current control strategies rely primarily on treatment with praziquantel, as no vaccine is available; however, treatment alone does not prevent reinfection. There has been emphasis on the use of integrated approaches in the control and elimination of the disease in recent years with the development of health infrastructure and health education. However, there is a need to evaluate the present status of African schistosomiasis, primarily caused by Schistosoma mansoni and S. haematobium, and the factors affecting the disease as the basis for developing more effective control and elimination strategies in the future. This review provides an historical perspective of schistosomiasis in Africa and discusses the current status of control efforts in those countries where the disease is endemic.

Experimental Infection of the Biomphalaria glabrata Vector Snail by Schistosoma mansoni Parasites Drives Snail Microbiota Dysbiosis

Host-parasite interaction can result in a strong alteration of the host-associated microbiota. This dysbiosis can affect the fitness of the host; can modify pathogen interaction and the outcome of diseases. Biomphalaria glabrata is the snail intermediate host of the trematode Schistosoma mansoni, the agent of human schistosomiasis, causing hundreds of thousands of deaths every year. Here, we present the first study of the snail bacterial microbiota in response to Schistosoma infection. We examined the interplay between B. glabrata, S. mansoni and host microbiota. Snails were infected and the microbiota composition was analysed by 16S rDNA amplicon sequencing approach. We demonstrated that the microbial composition of water did not affect the microbiota composition. Then, we characterised the Biomphalaria bacterial microbiota at the individual scale in both naive and infected snails. Sympatric and allopatric strains of parasites were used for infections and re-infections to analyse the modification or dysbiosis of snail microbiota in different host-parasite co-evolutionary contexts. Concomitantly, using RNAseq, we investigated the link between bacterial microbiota dysbiosis and snail anti-microbial peptide immune response. This work paves the way for a better understanding of snail/schistosome interaction and should have critical consequences in terms of snail control strategies for fighting schistosomiasis disease in the field.

Current Status of Schistosomiasis Control and Prospects for Elimination in the Dongting Lake Region of the People's Republic of China

Schistosomiasis japonica is an ancient parasitic disease that has severely impacted human health causing a substantial disease burden not only to the Chinese people but also residents of other countries such as the Philippines, Indonesia and, before the 1970s, Japan. Since the founding of the new People's Republic of China (P. R. China), effective control strategies have been implemented with the result that the prevalence of schistosomiasis japonica has decreased markedly in the past 70 years. Historically, the Dongting Lake region in Hunan province is recognised as one of the most highly endemic for schistosomiasis in the P.R. China. The area is characterized by vast marshlands outside the lake embankments and, until recently, the presence of large numbers of domestic animals such as bovines, goats and sheep that can act as reservoir hosts for Schistosoma japonicum. Considerable social, economic and environmental changes have expanded the Oncomelania hupensis hupensis intermediate snail host areas in the Dongting lake region increasing the potential for both the emergence of new hot spots for schistosomiasis transmission, and for its re-emergence in areas where infection is currently under control. In this paper, we review the history, the current endemic status of schistosomiasis and the control strategies in operation in the Dongting Lake region. We also explore epidemiological factors contributing to S. japonicum transmission and highlight key research findings from studies undertaken on schistosomiasis mainly in Hunan but also other endemic Chinese provinces over the past 10 years. We also consider the implications of these research findings on current and future approaches that can lead to the sustainable integrated control and final elimination of schistosomiasis from the P. R. China and other countries in the region where this unyielding disease persists.

Schistosomiasis-from immunopathology to vaccines

Schistosomiasis (bilharzia) is a neglected tropical disease caused by trematode worms of the genus Schistosoma. The transmission cycle involves human (or other mammalian) water contact with surface water contaminated by faeces or urine, as well as specific freshwater snails acting as intermediate hosts. The main disease-causing species are S. haematobium, S. mansoni and S. japonicum. According to the World Health Organisation, over 250 million people are infected worldwide, leading to considerable morbidity and the estimated loss of 1.9 million disability-adjusted life years (DALYs), a likely underestimated figure. Schistosomiasis is characterised by focal epidemiology and an over-dispersed population distribution, with higher infection rates in children. Complex immune mechanisms lead to the slow acquisition of immune resistance, but innate factors also play a part. Acute schistosomiasis, a feverish syndrome, is most evident in travellers following a primary infection. Chronic schistosomiasis affects mainly individuals with long-standing infections residing in poor rural areas. Immunopathological reactions against schistosome eggs trapped in host tissues lead to inflammatory and obstructive disease in the urinary system (S. haematobium) or intestinal disease, hepatosplenic inflammation and liver fibrosis (S. mansoni and S. japonicum). An effective drug—praziquantel—is available for treatment but, despite intensive efforts, no schistosomiasis vaccines have yet been accepted for public use. In this review, we briefly introduce the schistosome parasites and the immunopathogenic manifestations resulting from schistosomiasis. We then explore aspects of the immunology and host-parasite interplay in schistosome infections paying special attention to the current status of schistosomiasis vaccine development highlighting the advancement of a new controlled human challenge infection model for testing schistosomiasis vaccines.

The contribution of domestic animals to the transmission of schistosomiasis japonica in the Lindu Subdistrict of the Central Sulawesi Province, Indonesia

Background and Aim:

Schistosomiasis is endemic in Indonesia and is found in three remote areas in Central Sulawesi Province. Non-human mammals serve as reservoir hosts, meaning the disease is zoonotic. The previous schistosomiasis studies in animals from the Lindu Subdistrict did not determine which domestic animal species can serve as the primary source of transmission. No animals have been treated in Indonesia to control the disease; therefore, the parasite’s life cycle is not blocked entirely. This study aimed to determine the prevalence and identify the risk factors associated with, Schistosoma japonicum infection in animals, and identify animals’ relative contributions to S. japonicum transmission in the Lindu Subdistrict.

Materials and Methods:

A cross-sectional survey of S. japonicum infected animals was conducted in five villages of the Lindu Subdistrict. Fecal samples were collected from 134 selected animals (13 cattle, 26 buffaloes, 28 horses, 59 pigs, and 8 dogs). S. japonicum infection and infection intensity were determined using the Danish Bilharziasis Laboratory method. Environmental contamination with schistosome eggs was measured. The data were analyzed using a Chi-square test.

Results:

The overall prevalence of schistosomiasis was 32.9%, with the prevalence of infection in each species of animal at 61.5% in cattle, 42.3% in buffaloes, 25.0% in horses, 35.6% in pigs, and 12.5% in dogs. Free-range pigs were 8.667 times more likely to have S. japonicum infection than pigs kept in cages. Buffaloes, cattle, and horses were the primary sources of S. japonicum egg contamination, with relative transmission indices of 59.15%, 22.80%, and 10.61%, respectively.

Conclusion:

Bovines and horses are the main contributors to schistosomiasis transmission in the Lindu Subdistrict. In conjunction with other schistosomiasis control programs, the government should treat infected animals living within endemic areas where there are high infection rates of S. japonicum.

From inspiration to translation: Closing the gap between research and control of helminth zoonoses in Southeast Asia

Poverty magnifies limitations resulting from traditional biases and environmental risks in endemic areas. Any approach towards disease control needs to recognise that socially embedded vulnerabilities can be as powerful as externally imposed infections. Important for RNAS was networking across borders, not just on schistosomiasis but on the whole spectrum of endemic helminthiases, and this bore fruit in the form of the expansion of RNAS into the 'Regional Network on Asian Schistosomiasis and other Helminth Zoonoses (RNAS⁺)', which focuses on technical standardization, supporting the growth of research capacity and the further development of networking. Administration is lean and largely virtual with the focus on connecting members via the Internet, providing databases and administrative back-up. The strategy emphasizes ways and means to alleviate the spectre of disease and poverty from the endemic areas through boosting research on target diseases and supporting collaboration between basic and operational research on the one hand and control/elimination activities on the other. RNAS⁺ also benefits from continuing input from outside research institutions in areas outside Southeast Asia. This paper is aiming to identify the priority actions to close the gap between researcher and policy makers.

Schistosomiasis Elimination: Beginning of the End or a Continued March on a Trodden Path

In spite of spectacular progress towards the goal of elimination of schistosomiasis, particularly in China but also in other areas, research gaps and outstanding issues remain. Although expectations of achieving elimination of this disease have never been greater, all constraints have not been swept aside. Indeed, there are some formidable obstacles, such as insufficient amounts of drugs to treat everybody and still limited use of high-sensitive diagnostic techniques, both for the definitive and the intermediate hosts, which indicate that prevalence is considerably underrated in well-controlled areas. Elimination will be difficult to achieve without a broad approach, including a stronger focus on transmission, better diagnostics and the establishment of a reliable survey system activating a rapid response when called for. Importantly, awareness of the crucial importance of transmission has been revived resulting in renewed interest in snail control together with more emphasis on health education and sanitation. The papers collected in this special issue entitled ‘Prospects for Schistosomiasis Elimination’ reflect these issues and we are particularly pleased to note that some also discuss the crucial question when to declare a country free of schistosomiasis and present techniques that together create an approach that can show unequivocally when interruption of transmission has been achieved.