Mapping Out a Plan
By Cicely Krebill, Biochemistry, 2019
Soil transmitted helminth infections (STH) are easily treated parasite infections, yet the World Health Organization (WHO) estimates that more than 880 million children are still in need of treatment. Although most infections are relatively asymptomatic, STH has been linked to impaired cognitive and physical development in children. It tends to be found in areas that lack clean water and sanitation, as STH is passed through the eggs found in feces of infected individuals. To combat its spread, WHO and other organizations like it have implemented Mass Drug Administrations (MDAs) to populations where STH is prevalent, and have also encouraged good water and hygiene practices.
One such program is run in the Philippines, a country in which STH is endemic. The Philippines Integrated Helminth Control Program has existed since 2006, and has resources for mass targeting and deworming; however, their resources are not extensive. With so many people affected, the real challenges are figuring out how to best prevent the parasite from spreading and how to treat the population.
In the past, large-scale surveys were conducted to predict areas of high prevalence in order to estimate the number of people in need of treatment in a given area. Unfortunately, these types of surveys are hard to sustain and fund, which makes data collection significantly less accessible to developing countries. Doctor Richard Wamai, Assistant Professor of African American Studies and Co-Leader of the Integrated Initiative for Global Health at Northeastern University, says that in countries where large surveys aren’t an option, “usually people do localized surveys and extrapolate a modeling base. They look at population size [and] areas in which the transmission is happening and extrapolate based on risk of transmission and patterns of risk in a population.”
A typical predictive map includes estimated people in need of treatment as well as predicted areas of high prevalence; however, this isn’t all the information needed to build a successful parasite control program. When doing parasite control, “you have to consider the epidemiological prevalence of the disease, the species itself, and the infectivity rate for the species,” Wamai notes. Wamai also believes the environment should also be considered as “[it] has a role in the sustainability of the vector”.
“You have to consider the epidemiological prevalence of the disease, the species itself, and the affectivity rate for the species.”
A recent study published in the Public Library of Science looked to create a new strategy to prioritize regions for treatment. Its development is the first model-based predictive prevalence map based out of the Philippines, in which specific species of STH, as well as the relationships between environmental factors, were considered when developing the maps. To determine the relative prevalence in the area of the specific types of STH, the researchers collected data by taking samples from the populations that are considered to be at greater risk, such as children and farmers who tend to interact more frequently with the parasite’s environment. They also took data on the physical environment, such as rainfall and temperature, which also impacts the parasite’s development. This data was used to create maps that can be used to determine where a greater emphasis on treatment and prevention needs to be placed.
This study suggests that there is significant spatial variation in STH infection prevalence, and that a spatially targeted approach to intervention is necessary. Although predictive maps may fail to illustrate some important factors that influence global health, like access to sanitation, this study is a step in the right direction to developing better treatment approaches. It shows that prior research is a necessary component in developing successful global health programs. As Wamai puts it, “[s]cience and research have to always establish the evidence, and then communicate the results to the policymakers who are the decision makers.”
PLOS Neglected Tropical Diseases (2015). DOI: 10.1371/journal.pntd.0003915.