Schistosomiasis The Blood Worm – It’s in Our Blood

In the Philippines, water flows through every vein of society, shaping the landscapes, traditions, and lives of its people. From the rice paddies that sustain communities to the shimmering rivers where children play, freshwater is more than a resource — it is the lifeblood of Filipino culture from the coast to the highest mountain. The connection to water is deeply rooted in the daily rhythms of human life: from the carabao ploughing through flooded fields, farmers planting rice with methodical, synchronized precision, and indigenous groups who gather by streams for rituals passed down through generations. Water is both fundamental sustenance and spirit.

Yet within these vital waterways lies an invisible peril. The same waters that nourish life can also harbour the parasitic helminth responsible for schistosomiasis, Schistosoma japonicum. This disease, transmitted through contact with contaminated freshwater, infiltrates one’s body by penetrating the skin to settle into a life inside the veins of its host. For many Filipinos, especially those whose lives are tied to agriculture and water, schistosomiasis is an ever-present threat, one that intertwines with their way of life in ways that are proving impossible to untangle.

A Hidden Threat in Plain Sight

Schistosomiasis is caused by a blood fluke, predominantly by 3 Schistosoma species, namely Schistosoma mansoni, Schistosoma haematobium and Schistosoma japonicum. It is the second most common parasitic infection after Malaria with the main countries being impacted residing in Africa, South America, China and south east Asia. According to the World Health Organization there is estimated to be over 250 million people living across the 78 endemic countries who require preventive treatment1.  In the Philippines, an estimated 12 out of the 117 million people live in endemic areas(2). National prevalence, as reported by a 2012 national survey, is at a little under 5%. However, local studies reveal a starkly different picture, with rates varying from 4.7% to as high as 90%(3) in some infected communities. This disparity reflects the focal nature of the disease, which depends on the presence of specific freshwater conditions and its intermediate host, the nondescript freshwater snail Oncomelania hupensis. This focal nature adds the concern that there is a large potential for underestimating the impact of this disease. This disease doesn’t impact everyone evenly but specific communities drastically.

For communities in endemic regions, the risk of infection is inseparable from their daily routines. Schistosoma japonicum eggs are dispersed through infected stool getting into the water systems, whether that is from animals or humans. Farmers working in the rice paddies, children crossing streams on their way to school, and people collecting water for household use are all vulnerable to exposure and therefore infection. The carabao, a revered symbol of rural life and living tractor, is also a significant reservoir of the parasite, releasing up to 2 million eggs into water sources daily by their stool according to International Journal of One Health4, further complicating efforts to control its spread. In this delicate balance between tradition and survival, schistosomiasis has become more than a health issue; it is a challenge to the very fabric of Filipino culture.

The Burden of Disease

Schistosomiasis, on the surface, can appear symptomless. The impact isn’t instantaneous but manifests over time, slowly degrading one’s health and casting a chronic shadow over those it affects. The WHO estimates a global fatality rate of 11,792 per year(1), but this figure fails to capture the true burden of the disease and the WHO admits this needs to be revisited. Its slow degradation of internal organs often disables rather than kills. The parasite’s eggs, released into the host’s bloodstream by the hundreds or thousands daily, become trapped in tissues, triggering inflammatory responses that can lead to severe complications, including liver scarring, cirrhosis, and even liver cancer. In rare cases, eggs migrate to the brain, causing seizures, paralysis, or death.

For children, even low-intensity infections can result in anaemia, nutrient deficiencies, and delayed cognitive development, hindering their growth and prospects. As Professor Amaya Bustinduy of the Schistosomiasis Clinical Research Group at the London School of Hygiene & Tropical Medicine explains, “You have to look at this as a life-course disease. It’s not just about things that happen at a specific age; there are nuances at every stage. I always like to start at birth because exposure at that time matters. If you arrest everything early and start intensive treatment, you can prevent manifestations later, even before adolescence.”

These impacts are compounded by co-infections with other intestinal helminths, such as hookworm, Ascaris, or Trichuris, which are also highly endemic in schistosomiasis-affected regions. Professor Bustinduy highlights a critical aspect of children’s recovery, noting, “There’s a window period for catch-up growth that we’ve seen in children—not just for schistosomiasis but for any insult.” This means that early and effective interventions not only reduce immediate harm but also offer a crucial opportunity to reverse some of the damage and improve long-term outcomes.

Professor Bustinduy further emphasizes the overlooked effects on children: “Now we know there’s anaemia, and not just one type of anaemia. Of course, anaemia has a snowballing effect on cognition, aerobic capacity, and development. There’s also growth retardation.” These deficiencies have a cascading effect on cognitive development, aerobic capacity, and physical growth. “The body prioritises vital functions and arrests non-vital ones like growth,” she explains, a process that may seem minor but has profound consequences. Economic studies have linked stunting and low height to reduced productivity in adulthood, placing children from schisto-endemic regions at a lifelong disadvantage.

This underscores the importance of addressing schistosomiasis not as a disease confined to a single stage of life but as a pervasive, cumulative condition. Without early and sustained treatment, the burden of schistosomiasis becomes a lifelong struggle, compounding the challenges faced by individuals and communities alike.

The economic impact is equally devastating. Schistosomiasis saps the strength of those who rely on physical labour, reducing productivity and deepening cycles of poverty. Dr Mario Jiz who heads the Department of Immunology at the Philippines Department of Health states “Farmers or adults experience fatigue, weakness, and chronic infections, which directly affect their livelihood. If they can't farm for the day, they won't be able to provide for their needs. These communities are subsistence farmers, so what they earn for the day is what they have for the day”. While there is official mass drug administration of praziquantel to treat communities for Schistosomiasis these are often not implemented due to shortages of treatment or financial resources devoted to the program. There is also sometimes poor compliance, treatment with praziquantel can make one sick for a short period afterwards – and for what? I have to take a day off work to be treated for a disease I can’t see I have? As Dr Jiz states, “The major problem is compliance, mostly because mass drug administration requires people to take a drug, and people do not like this drug at all. They hate it because it smells bad and makes them sick due to side effects.” Families already struggling to scrape by must bear the added burden of medical costs and lost income relating to the impact of this disease. This creates a ripple effect that undermines entire communities. The disease not only weakens the body but also threatens the social and economic structures that support life in rural areas – without rice farming these people would not survive. “It's ironic that these communities accept schisto as just a way of life, that it's normal to have schisto infection simply because they’re so used to it. For several generations, like three or four generations already, they’ve seen everybody getting schisto, and it's just normal for them. But we know that this should not be the status quo because of the implications for their health, long-term survival, and disabilities. Right now, what we’re hoping to push for is advocacy that infection equals disease. You don’t have to wait for overt symptoms to emerge. Once you know that someone is infected, you have to act quickly before the damage becomes irreversible.”

Not only is this threat limited to endemic areas already struggling with this infestation but there remain uninfected areas of rice farming there the environmental condition are set for this disease to spread, and it has. New foci of infection have been discovered in the north of the country where previously schistosomiasis was thought not to be a threat. The increasing ability of people and resources to travel is adding to this threat of disease spread. Snail species have been introduced to the rice paddies before from other parts of the country too, the Golden Apple Snail or ‘Golden Kohul’ to increase income from passive protein production but is now labelled a pest. Would it take much to introduce an infected O. hupensis?

Cultural Vulnerabilities and Indigenous Communities

The cultural significance of water in the Philippines makes the threat of schistosomiasis particularly poignant. For indigenous groups, whose traditions and livelihoods are deeply connected to their environment, the disease represents an existential risk. Rituals performed at waterways, communal bathing practices, and reliance on natural water sources for agriculture and sustenance all increase the likelihood of exposure and therefore infection.

These practices are not merely habits or adopted farming techniques but are integral to the identity and cohesion of these communities. The loss of these traditions, whether through the measures taken to control it, would be a profound cultural blow. The challenge lies in balancing the need for health interventions with the preservation of cultural heritage, ensuring that the fight against schistosomiasis does not come at the cost of erasing the very traditions it seeks to protect.

The communities where this disease flourishes are those communities that rely on the rice farming the most. Rice is their predominant food source accounting for 38% of agriculture; an energy supply they can’t live without. Without alternative jobs to bring in money, they are forced to continue farming, and the methods relied upon by the subsistence farmer include using carabao as living tractors and barefoot planting of the rice which exposes one’s skin to Schistosoma japonicum. Wellies just don’t cut it in the rice paddy.

Progress and Challenges in Control Efforts

Efforts to combat schistosomiasis in the Philippines have been ongoing for decades. The Department of Health has implemented mass drug administration programs, distributing praziquantel to school-age children and at-risk populations. Community education initiatives, improved water, sanitation, and hygiene (known as WASH) facilities, and veterinary management of animal reservoirs have also been key components of control strategies.

Innovative approaches have been explored, such as mechanized farming to reduce reliance on carabao and therefore limit transmission. These measures have yielded significant progress, reduced mortality rates and bringing national prevalence below the WHO threshold of 5%. A level considered a benchmark for reducing mortality associated with the infection. However, the focal nature of the disease means that localised hotspots persist, often in remote or marginalized areas where access to healthcare and resources is limited.

Diagnostics remain a critical bottleneck in the fight against schistosomiasis. Dr Mario Jiz has been working on improving interventions to stop the spread of Schistosomiasis tells us "Interestingly, the people who have Schisto don't even know that they have Schisto because there are no overt symptoms of the infection. Without screening and testing, people don't really know that they have the infection. And if you don't know that you have an infection, then there's really nothing much you can do in terms of treatment and other interventions." The current WHO gold standard is the Kato-Katz technique, a method that uses a microscope to count eggs in a stool sample. However, it is labour-intensive and less sensitive in low-intensity infections, categorised by low egg counts in stool implying fewer adult worms infecting the host. While advanced methods like PCR offer greater accuracy, their cost and complexity make them impractical and even impossible for large-scale use in endemic regions. The development of affordable, point-of-care diagnostic tools is essential to accurately map prevalence and monitor the impact of interventions. There is progress here too, in an African species of Schistosomiasis, Schistosoma mansoni, a cheap point of care diagnostic is being rolled out to diagnose, displaying improved sensitivity over Kato Katz and a lower labour requirement. It tests for a protein called the circulating cathodic antigen which is shed from adult worms and excreted through the blood. Unfortunately, this method is proving unreliable in the Philippines with Schistosoma japonicum and more research is required.

The Role of Science

Large open-source datasets including satellite imagery, water sources and climate data are becoming publicly available online for scientists to use for modelling infectious diseases and this has been implemented in schistosomiasis. As Dr. Hope Simpson from the London Applied & Spatial Epidemiology Research Group at the London School of Hygiene & Tropical Medicine explains, “Geostatistical modelling has emerged as a powerful tool for understanding and combating infectious diseases including schistosomiasis. It allows us to make predictions across space using data from a limited number of locations, which is useful for targeted public health measures.”

In the context of schistosomiasis, this is particularly valuable as control efforts often rely on distributing treatments via mass drug admininstration to areas at risk. Dr. Simpson continues, “It’s not feasible to collect data from the entire population of a country, so instead we measure prevalence in a relatively small number of communities and use this to make predictions. Intuitively, prevalence in an unsampled village is likely to be similar to that in a nearby village—we call this the spatial effect.” In the Philippines, studies have highlighted factors such as proximity to infested waterways, rainfall patterns, and the presence of animal reservoirs as key determinants of risk.

Dr. Simpson also emphasizes the growing importance of environmental data, noting, “The recent explosion in the availability of satellite data means these factors and many others can be represented at fine scales across the world. Geostatistical models incorporate spatial and covariate effects, allowing us to estimate prevalence between sampled locations. This means we can identify hotspots of risk and focus control measures on these areas, ensuring that medicines reach those most in need and avoiding unnecessary treatment.” By leveraging such innovative methods, public health efforts can maximize their impact, ensuring resources are directed where they are most urgently needed.

In recent years, environmental DNA (eDNA) testing has further enhanced the capabilities of spatial epidemiology. This method involves detecting genetic material shed by Schistosoma japonicum or its intermediate snail hosts directly from water samples. eDNA testing offers a non-invasive and highly sensitive approach to monitoring transmission hotspots, even in areas where traditional surveillance methods may struggle to detect low-intensity infections. This method means one can test the environment and not just the people and offers the ability to survey far greater areas with smaller teams. When combined with geospatial mapping, eDNA testing provides a dynamic and cost-effective means of pinpointing at-risk areas, enabling more precise interventions.

These insights have practical implications for public health strategies, enabling the deployment of resources where they are needed most. However, more granular data is needed to understand risk at the household level, particularly in highly endemic areas. eDNA testing could play a pivotal role here as well, offering a scalable tool for monitoring transmission risks across small-scale water bodies used by individual communities. Such information could inform tailored interventions that address the specific needs and vulnerabilities of these populations while optimizing resource allocation.

A Call to Action

There has been major steps forward since it was first described over a century ago but still so far to go. It is a reminder that health is not just a medical issue that can be treated with a pill but deeply intertwined with culture, economy, and personal identity. The fight against this disease’s eradication demands a holistic approach that goes beyond medicine, addressing the underlying social and environmental factors that sustain its transmission. Professor Julius Hafalla, a Filipino scientist from the London School of Hygiene & Tropical Medicine who has been working on neglected tropical disease in his home country for the last 25 years, reflects “I’ve seen how these illnesses affect families who already face many challenges. Children miss school, and parents lose their livelihoods due to diseases that are preventable and treatable. These conditions create a cycle of poverty and poor health, leaving communities vulnerable.”

Efforts to control schistosomiasis must prioritize the voices and needs of affected communities, ensuring that interventions are culturally sensitive and sustainable. Public health campaigns must be coupled with investments in infrastructure, education, and research to break the cycle of infection and poverty. At the same time, the cultural heritage of these communities must be preserved, recognizing that their connection to water, rice farming and their land is not only a risk factor but also a source of strength and identity. Professor Hafalla highlights this, “Growing up in the Philippines, I’ve always admired the resilience of our people. As a scientist, I feel a duty to help break this cycle. By improving our understanding of these diseases and enhancing prevention, diagnosis, and treatment, we can build healthier communities and create opportunities for marginalized areas to thrive.”

As the Philippines strives toward the WHO goal of interrupting schistosomiasis transmission by 2030, it stands at a crossroads. Moving forwards requires large investment of time, intellect and money. It requires a commitment from those at the highest of the political pyramid to ensure continued access to treatment and investment in research but also equally those living and working in the fields to implement the interventions they have been educated about.

1.           World Health Organisation. Schistosomiasis Fact Sheet. https://www.who.int/news-room/fact-sheets/detail/schistosomiasis (2021).

2.           Leonardo, L. et al. A national baseline prevalence survey of schistosomiasis in the philippines using stratified two-step systematic cluster sampling design. J Trop Med 2012, (2012).

3.           Gordon, C. A. et al. Real-time PCR Demonstrates High Prevalence of Schistosoma japonicum in the Philippines: Implications for Surveillance and Control. PLoS Negl Trop Dis 9, (2015).

4.           Tenorio, J. C. B. & Molina, E. C. Schistosoma japonicum infections in cattle and water buffaloes of farming communities of Koronadal City, Philippines. Int J One Health 6, 28–33 (2020).

5.           A. W. Cheever, J. G. Macedonia, J. E. Mosimann & E. A. Cheever. Kinetics Of Egg Production And Egg Excretion By Schistosoma Mansoni And S. Japonicum In Mice Infected With A Single Pair Of Worms. American Journal Of Tropical Medicine And Hygiene (1994).