Schistosomiasis
significantly impacts the economy and poses a public health burden. In 2021,
the worldwide disability-adjusted life year (DALY) for schistosomiasis was
1.863 million, with the Philippines accounting for 22,300 DALYs, WHO reported.
Infected individuals in Leyte lose 45.4 productive days per year, which was reduced
to four days after treatment. In 2013, the economic losses of 1,415
hospitalized cases were estimated to be around PHP13 million (USD306,726.25). [
Southeast Asian J.
Trop. Med. Public Health. 2006;37:26–32]
Tabilin
et al.’s comprehensive review in January 2025 examined the epidemiology of
schistosomiasis in the country, analyzed the different factors that influence
its distribution and transmission, and provided an overview of the current
control program. [
Trop Med Infect Dis. 2025 Jan 21;10(2):29. Doi:
10.3390/tropicalmed10020029]
Transmission dynamics
In Tabilin et al.'s review,
environmental, socioeconomic, and biological factors influence transmission. The
year-round rainfall in many endemic areas in the Philippines, they noted, allows
year-round transmission, and vegetation provides moisture and shade for snails.
The snail that is its intermediate host,
Oncomelania hupensis quadrasi, lives in shallow,
slow-moving freshwater wetlands, and agricultural lands such as rice fields and
irrigation canals have become common habitats.
While
dogs were initially considered primary hosts, they noted that carabaos (water
buffaloes) are also major contributors to environmental contamination, with
infected bovines releasing tens to hundreds of thousands of parasite eggs with
their stool per individual per day. For example, in Northern Samar, water
buffaloes were reported to have an 80 percent prevalence, releasing an
estimated 352,500 eggs per gram of stool.
Humans,
the authors said, are exposed through agricultural activities, domestic chores,
and recreation in contaminated waters, and contribute significantly to
transmission, with children aged ten to 14 years old being the most affected.
Biological factors such as age-dependent immune response and post-pubertal
hormonal influences, they said, play a role in susceptibility. Socioeconomic
factors and individual behavior are also said to affect transmission, with low
socioeconomic status and poverty being highly predictive of infection; poor
nutrition among children increases susceptibility to schistosomiasis, while the
lack of hygiene and sanitation infrastructure contributes to the persistence
and spread of the disease.
Current control programs and challenges
Tabilin
et al. cited the National Schistosomiasis Control and Elimination Program
(NSCEP), a comprehensive initiative created to eliminate schistosomiasis by
2025. This strategy, they said, recognizes the interconnectedness of human,
animal, and environmental health, and leverages a multi-sectoral partnership to
achieve its objectives. The strategy encompasses several key components: (1) preventative
chemotherapy to reduce the risk of infection in vulnerable populations; (2) treatment
and management of animals that can act as reservoirs for the parasite,
including the establishment of testing sites and training of provincial and
municipal veterinarians and livestock technicians; and (3) environmental controls
aimed at improving sanitation and water quality to diminish the habitats
conducive to the parasite's life cycle.
This
program also emphasizes health education to raise awareness about
schistosomiasis, its transmission, and prevention methods, empowering
communities to adopt healthier practices. It also involves monitoring and
tracking schistosomiasis cases to quickly identify outbreaks and evaluate the
effectiveness of interventions. The NSCEP is supported by a substantial budget
of PHP5.6 billion (approximately USD100.7 million), reflecting a strong
financial commitment to the cause. The program's success relies on the
collaboration of various government agencies and non-government organizations,
highlighting the importance of coordinated efforts across different sectors to
eliminate schistosomiasis.
However,
the reviewers said the program faces significant challenges: Mass Drug
Administration (MDA), a part of the preventative chemotherapy component,
yielded abysmal nationwide coverage, annually failing to reach the department’s
target of greater than
85 percent due to MDA fatigue, fear of adverse drug reactions, religious
beliefs, and the unappealing taste and size of the drug. Testing capacity and
competency also remain limited due to staff shortages in the health units. The
COVID-19 pandemic also disrupted the delivery of health services and
interventions.
Future directions
While
the goal of complete schistosomiasis interruption of transmission by 2025 is
ambitious, Tabilin et al. observed that is unlikely to be achieved in the
foreseeable future. They identified integrated control efforts targeting
different aspects of the disease, as well as the mechanization of agriculture,
vaccination of carabaos, and improved diagnostics as promising strategies for
disease elimination, ie, the replacement of water buffaloes with mechanized
farming equipment in China demonstrated a significant reduction in
schistosomiasis prevalence in both humans and bovines, highlighting the
potential of this approach. In the Philippines, where carabaos are still widely
used in agriculture, promoting a shift towards mechanized farming, they said,
could mirror this success, offering the additional benefit of alleviating
poverty in farming communities. Furthermore, they said the development and
deployment of a carabao vaccine would directly target a key animal reservoir of
the parasite, potentially reducing environmental contamination.
According
to Tabilin et al., improved diagnostics are also critical, particularly in
areas with low-intensity infections, such as the more sensitive and specific
molecular- and antibody-based point-of-care tests, being developed and could
enhance surveillance and case management.
Finally,
they mentioned progress in schistosome transcriptomics, proteomics, immunomics,
and mRNA vaccine technology, which should accelerate vaccine discovery and
testing, making the reality of a publicly available licensed vaccine closer
than ever. Advances in these fields, they said, pave the way for the
identification of potential vaccine targets and the development of effective
vaccine candidates, which would be a powerful tool in the fight against
schistosomiasis.
Schistosomiasis
remains a significant public health and economic burden in the Philippines. The
authors recommend integrated, holistic, and multi-sectoral control efforts.
Economic reforms towards equitable progress and development across the
Philippines, they added, are necessary to eradicate schistosomiasis and lift
endemic communities from poverty. Ultimately, Tabilin et al. said the success
of these control programs relies on the households in these endemic communities
as the main drivers and grassroots actors in these interventions.
