Control and Elimination of Human Schistosomiasis
Summary of Recommendations
- Prevalence of infection is defined as the percentage of individuals of all agesin a population targeted for treatment who are infected with any species ofSchistosoma. The strategy of preventive chemotherapy does not differ bySchistosoma species.
- The prevalence threshold of 10% is based on estimation by parasitologicalmicroscopy, using duplicate Kato–Katz smears from one stool sample for intestinalschistosomiasis, predominantly S. mansoni and S. japonicum, and single 10 mLurine filtration for urogenital schistosomiasis due to S. haematobium.
- The point-of-care circulating cathodic antigen test can be used to determineprevalence of S. mansoni; 30% prevalence by this test is to be consideredequivalent to 10% prevalence by the Kato–Katz technique.
- Routine monitoring for effective coverage and evaluation of the impact of theintervention (using repeat population-based surveys conducted after five roundsof preventive chemotherapy, or more frequently with a mid-term evaluation afterthree rounds) should be integral parts of preventive chemotherapy programmes,to help inform the decision on changing the strategy and continuing or stoppingthe programme.
- Expanded preventive chemotherapy programmes pose a greater theoretical riskto the development of drug resistance. Evidence of the potential emergence ofreduced praziquantel efficacy in response to increased drug use is rarely reported;thus, continued vigilance to monitor drug efficacy over time through efficacysurveys is imperative to detect any emergence of drug resistance.
- Routine monitoring for safety of the intervention should also be an integral part ofpreventive chemotherapy programmes.
- Preventive chemotherapy in preschool-aged children (pre-SAC) is appropriatefor those aged ≥ 2 years. Younger children, aged < 2 years, may be consideredfor treatment on an individual clinical basis. The medication for children aged <2 years should be an oral disintegrating tablet formulation (under development)that is easily administered, disintegrates in the mouth and, ideally, has a sweettaste and smell; if paediatric formulations are not available, praziquantel crushedin soft food may be used for individual case treatment only.
- Available evidence does not differentiate approaches to infection with thedifferent species of Schistosoma.
- The 10% prevalence threshold for intervention will expand eligibility for preventivechemotherapy programmes and necessitate a larger global supply of praziquantelthan that currently available via donation schemes (estimated at 300 milliontablets annually at the time of publication of this guideline).
- Community mapping of the epidemiology of schistosomiasis can reduce the needfor praziquantel, as treatment can be better targeted to communities and at-riskregions.
- Ensuring high coverage is essential for preventive chemotherapy and may requireincentivization of local community drug distributors.
- Public health awareness campaigns are necessary to ensure high coverage inpreventive chemotherapy programmes and to address concerns about adverseevents from medication.
- Close epidemiological monitoring (sentinel sites surveys or mid-term evaluationevery 3 years) should be established to monitor Schistosoma spp. prevalence,especially in settings in which the prevalence was previously ≥ 10% or with ahistory of preventive chemotherapy with praziquantel if reducing the frequency ofpreventive chemotherapy with praziquantel.
- Lack of an appropriate response should be defined as a less than one-thirdrelative reduction in prevalence comparing the baseline prevalence surveyand a repeat prevalence survey completed after 2 years of annual preventivechemotherapy. The intervening period should include a minimum of tworounds of preventive chemotherapy to all at-risk groups at adequate treatmentcoverage (≥ 75%). The relative reduction in prevalence can be estimated asfollows: [(prevalence at baseline − prevalence at year 3)/(prevalence at baseline)].Alternative definitions could consider absolute changes in prevalence of infection,or changes in average intensity of infection (defined as egg concentrations instool or urine).
- The timing of prevalence surveys should consider the seasonality of transmissionto ensure that prevalence is measured at the same point in each seasonaltransmission cycle.
- Communities suspected to be “persistent hot spots” or of high endemicity(defined as areas with baseline prevalence ≥ 50% in school-aged children (SAC)are encouraged to conduct early prevalence surveys (after two annual roundsof preventive chemotherapy) to inform any decision on the use of biannualtreatment.
- Biannual preventive chemotherapy should be prioritized in areas of higherprevalence (defined as areas with baseline prevalence ≥ 50% in SAC andpersistent hot spot settings already achieving high levels of coverage of annualpreventive chemotherapy without appropriate response. In settings of moderateprevalence (defined as areas with prevalence 10–49% in SAC), annual treatmentmay be sufficient.
- Routine monitoring for effective treatment coverage should be an integralpart of preventive chemotherapy programmes, with attention to ensuring thatannual treatment achieves high coverage (≥ 75%) before any decision to move tobiannual treatment.
- There is currently a lack of evidence to inform recommendations on the durationof biannual treatment. As an interim measure, 3 consecutive years of biannualpreventive chemotherapy is suggested, followed by implementation of an impactsurvey to assess if it should be continued or reduced in frequency.
- Biannual treatment programmes will require a larger global supply of praziquantelthan that currently available via donation schemes (estimated at 300 milliontablets annually at the time of publication of this guideline).
- Biannual treatment programmes should have administrations spaced out equallythroughout the year (approximately 6 months between treatments).
- Pregnancy status should be assessed by discretely questioning the individualherself. If she is uncertain, a negative urine-based pregnancy test can berequested before the treatment is administered.
- The medicine for children aged < 2 years should be an oral formulation (currentlyunder development) that is easily administered, disintegrates in the mouth and,ideally, has a sweet taste and smell; if paediatric formulations are not available,praziquantel crushed in soft food may be used for individual case treatment only.
- WASH interventions are expected to provide modest benefits in limitingSchistosoma transmission, but these benefits extend also to reducing risk formultiple infectious diseases.
- Behavioural change interventions should be implemented from the start of anypreventive chemotherapy programme.
- Coordination and joint planning between programmes for control ofschistosomiasis and WASH are essential. Inclusion of WASH in the schistosomiasisstrategy will require mapping and sharing of epidemiological informationalongside WASH coverage to ensure prioritization of water and sanitation servicesto areas that are endemic for schistosomiasis.
- Similarly, schistosomiasis education and health programme delivery shouldinclude inputs to WASH programme design, collaboration on behavioural changeinterventions and integration of behavioural change promotion.
- Where persistent hot spots of transmission emerge during the course ofpreventive chemotherapy campaigns, control of intermediate host snailpopulations should be prioritized especially if the programme is already achievinghigh levels of treatment coverage.
- Co-implementation of snail control with mass treatment campaigns is expectedto hasten achievement of WHO goals for morbidity control and elimination as apublic health problem.
- Snail control will be essential to ultimately eliminate local transmission, incombination with WASH interventions.
- Sensitization and public health awareness campaigns will be necessary to ensurehigh acceptance of snail control interventions.
- Development of snail control programmes will require a larger and less expensiveglobal supply of molluscicides.
- Skilled and dedicated snail control workers will be essential to the success of snailcontrol initiatives.
- Deworming should be delivered together with promotion of health and hygieneto reduce transmission by encouraging healthy behaviours such as properdisposal of faeces.
- Testing for Schistosoma infection in humans with a diagnostic that has highsensitivity and specificity. This may require the use of a two-step diagnostic processstarting with a high sensitivity test confirmed with a second, high specificity test.
- Testing for Schistosoma infection in snails with a diagnostic that has high sensitivityand specificity. This may require the use of a two-step diagnostic process startingwith a high sensitivity test confirmed with a second, high specificity test.
- Testing for Schistosoma infection in non-human mammalian hosts, as applicable,with a diagnostic that has high sensitivity and specificity. This may require the useof a two-step diagnostic process starting with a high sensitivity test confirmed witha second, high specificity test.
- The eventual predictive performance of the sampling of humans, snailsand non-human mammalian hosts to identify settings that have eliminatedtransmission will depend upon the sampling strategy, with decisions on samplesize, geographical zone and timespan for sampling.
- Future work could consider a two-step verification of Schistosoma infection statusin humans with a first highly sensitive test (for example, serology) and a secondconfirmatory highly specific test (for example, miracidia hatching test).
- Sampling and diagnostic tools in snail populations and in non-human mammalianhosts should be considered when interruption of transmission is the publichealth goal and is suspected based on recent epidemiological surveys in humanpopulations.
- The magnitude of the contribution of non-human mammalian hosts totransmission of schistosomiasis remains understudied, especially for species otherthan S. japonicum.
Control and Elimination of Human Schistosomiasis
February 14, 2022
Country of Publication
The specific objectives are to provide guidance on:
- prevalence thresholds, target age groups and frequency of preventive chemotherapy for schistosomiasis;
- establishment of water, sanitation and hygiene (WASH) and snail control activities to support control and elimination of schistosomiasis;
- use of diagnostic tests in humans in low transmission areas and for moving to, and evaluating the interruption of transmission of schistosomiasis;
- tools for the assessment of Schistosoma spp. infection in snail hosts;
- diagnostic tests for the assessment of schistosomiasis infection in animal reservoirs of infection
Target Provider Population
Policy-makers, national NTD control programmes and national NTD task forces in health ministries, regional programme review groups and implementation partners
Adolescent, Adult, Child, Infant, Older adult
Health Care Settings
Ambulatory, Hospital, Outpatient
Healthcare business administration, nurse, nurse practitioner, physician, physician assistant
Diagnosis, Assessment and screening, Treatment, Management, Prevention
D012552 - Schistosomiasis