MORBID pilot study

Identifying meaningful and measurable targets for the control of schistosomiasis-related morbidity in Africa

The Morbidity Operational Research for Bilharziasis Implementation Decisions (MORBID) pilot study in Kenya and Malawi aims to identify meaningful and measurable targets for detecting the control of schistosomiasis-related morbidity in Africa as a tool to guide programmatic decisions for country programs.

The MORBID project will contribute to the way progress against schistosomiasis is measured globally and is a collaboration between Unlimit Health, the US Centers for Disease Control, Centre for Health, Agriculture and Development Research & Consulting, Malawi and the Kenya Medical and Research Institute, funded by USAID.

The World Health Organization has now recognised the need to ‘Define indicator for measuring morbidity’ as the primary critical action in the new 2021 – 30 NTD roadmap. This project will provide evidence to define this indicator and contribute to the way we measure progress in schistosomiasis (SCH) globally.

MORBID pilot study objectives

The study seeks to find out the following:

1. The infection levels of schistosomiasis below which there is little or no detectable schistosomiasis morbidity.
2. Identify the markers of morbidity for Schistosoma mansoni and S. haematobium infections that are readily measurable.
3. Inform control programmes on the optimal species-specific morbidity that schistosomiasis control programmes should be aiming at.

Measuring and sustaining public health gains

There has been great progress in the scaling up of schistosomiasis control programs with widespread MDA in numerous African countries. However, the answers to questions about how long to continue MDA and when the control of morbidity has been achieved are less clear.

Ensuring a robust framework is in place to measure and achieve control of schistosomiasis morbidity is crucial for programmes to ensure that public health gains are sustained. Following this milestone, some countries may look to transition to interruption of transmission through the scale-up of other interventions – snail control, water and sanitation, and behaviour change. Having a clear first phase of a framework for control is a priority for country control programmes.

Definitions and targets for morbidity control

The current goals for controlling schistosomiasis morbidity are based on reducing prevalence of heavy infection in selected populations, primarily school-aged children. At lower than 1% prevalence of high intensity infection, schistosomiasis is considered eliminated as a public health problem which is the WHO NTD Road map target for 2030.

This was a reasonable target when initially defined, as the relationship between the cut-offs for heavy, moderate and low intensity infections (the number of worms an individual has) and morbidity was poorly understood. Our understanding of what constitutes schistosomiasis-associated morbidity has expanded in recent years. Hence, the WHO identifying the critical need to ‘Define an indicator for measuring morbidity’ for schistosomiasis.

Evidence-based targets for morbidity control will support more effective use of the donated drug, praziquantel, and will help to maximise programmes’ public health impact.

Evidence based targets for morbidity control will support more effective use of the donated drug, praziquantel, and will help to maximise programmes’ public health impact.

Different species, different morbidities?

There are different species of schistosome infections, for example S. mansoni and S. haematobium and whilst schistosomiasis presents with a range of morbidities, some of these are common to infection with either species (e.g., anaemia and impaired growth), whilst some are species specific (e.g. hepatomegaly in S. mansoni infections, and hydronephrosis and bladder cancer in S. haematobium infections).

Therefore, morbidity control will likely require species-specific targets for S. mansoni and S. haematobium.

Morbidity can be expressed differently in different age groups, with less severe, more reversible symptoms occurring more frequently in children and more severe, less reversible pathologies occurring in adults with a long history of infection.

This project will assess age-appropriate morbidity targets in preschool aged children, school aged children, and adults separately.