Deworming for Schistosomiasis

The World Health Organization (WHO) recommends that all at-risk groups receive anthelminthic treatment for schistosomiasis with praziquantel—a safe and low-cost medicine—in areas of endemic schistosomiasis infection. While it is still possible to become infected, the treatment minimizes the progression of the disease (WHO 2016). At-risk groups include preschool-age children, starting at 12 months of age; and school-age children and adults, including pregnant and lactating women. In addition, individuals—such as fishermen and farmers—who must work near or in infested water are at an increased risk of schistosomiasis.

According to WHO, treatment should be given periodically, based on the level of infection, and as often as once a year in areas with high transmission. In highly endemic areas, anthelminthic treatment is recommended for the entire community, including pregnant women (WHO 2016). WHO’s prevalence categories are used to recommend the frequency of deworming; prevalence is based on school-age children because data for this population group is most often available, but treatment applies to all populations (see Table 2).

Many countries with endemic schistosomiasis, at certain intervals, administer praziquantel in schools. They have also integrated schistosomiasis treatment into broader deworming efforts for hookworm, onchocerciasis, and other initiatives (King 2011). The medicines, widely administered to everyone in the high-risk groups, can be given without prior diagnosis and, often, by non-medical personnel.

Table 2: Prevalence Levels for Treatment of Schistosomiasis

Source: Crompton and WHO 2006

Measurement and data sources

Population-based surveys typically report the percentage of children 6–59 months who were given deworming medication in the six months preceding the survey, as well as the percentage of women with a live birth in the two to five years before the survey who were given deworming medication during their most recent pregnancy. In post-event coverage surveys, coverage is the percentage of the eligible population who received deworming medication during the last campaign. These surveys usually take place within a few weeks of the campaign, and interviewers will show participants the provided medications to ensure accurate recall.

Surveys that collect information related to deworming coverage include—

• Demographic and Health Surveys
• Multiple Indicator Cluster Surveys
• National Micronutrient Surveys
• Post-event coverage surveys
• Knowledge, Practice, and Coverage Surveys
• other research or evaluation activities.

In addition, health monitoring information systems may include coverage estimates of deworming activities, both from mass treatment events, as well as routine treatment. In the case of campaign-based distribution, these data often come from tally sheets completed during mass drug administration, which are compared against the total target population to obtain coverage estimates.

Most implementers who conduct deworming campaigns for schistosomiasis—often the government or specific organizations—will have detailed reports on distribution. You may be able to access up-to-date coverage information from these sources and use this information to cross-reference survey data.

Methodological issues

• Generally, tally sheets and other administrative data may overestimate deworming coverage compared to post-event coverage survey data; therefore, it is preferable to use post-event coverage data.
• Recall bias in these routine population-based surveys may result in lower coverage estimates compared to post-event surveys.
• Consider the regularity of deworming campaigns, as well as the timing of data collection, to assess coverage in population-based surveys and other sources, including health monitoring information systems and post-event coverage surveys. Discrepancies may be noted between these sources, based on whether information was collected prior to or following a deworming campaign. In other words, coverage estimates from population-based surveys may be affected by the time interval between the survey and the mass antihelminthic treatment, especially when estimates are compared between years.
• While WHO recommends anthelminthic treatment for children starting at 12 months, many population-based surveys collect information about deworming coverage in children younger than 12 months. It is best to exclude these younger children in the overall assessment of deworming coverage, especially if a country policy is aligned with WHO’s recommendation of starting deworming at 12 months.
• While looking for information on this topic, remember that most data on deworming refers to both treatment for schistosomiasis and soil-transmitted helminths.