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Control, Eliminate, Eradicate: What’s the difference? Q&A with Epidemiologist Sanjaya Dhakal

Global health has lots of jargon and terms that can be confusing for people who don’t speak it for a living.

Ending preventable diseases is a key focus for many in this field and one legacy of Task Force co-founder Dr. William Foege who helped lead the successful effort to rid the world of smallpox. But what does “ending” a disease look like? It begins by determining if a disease can be eradicated, eliminated, or controlled.

With a resume covering biostatistics, cancer research, Ebola outbreaks, and neglected tropical diseases (NTDs), Dr. Sanjaya Dhakal explains the jargon. Dhakal is an epidemiologist for The Task Force’s Children Without Worms (CWW) program which works to control intestinal worms, technically known as soil-transmitted helminths, a disease spread by poor sanitation that causes malnutrition and stunted growth.

Why do we have different terms and what’s the significance of their distinctions?

In the NTD community, the use of these terms and their definitions is fairly new. It wasn’t until the 1990s and early 2000s that there became universal definitions and they began to be used in public health efforts. Distinguishing between the different terms came out of an understanding that while the ideal goal is to wipe out a disease that is not necessarily achievable for every disease given differences in how a disease spreads, interventions available to address it, and its biological makeup, so there needed to be other, more realistic and common goals that countries and public health could work towards. With smallpox, for instance, it was possible to eradicate it completely – the only human virus we’ve been able to do this for – because we had an effective intervention, vaccines, and a global effort to thoroughly implement that intervention, along with other things including the scientific understanding and biological makeup of the virus, political will, funding, and social acceptance of public health efforts. We don’t have all of those pieces and tools for other diseases. Therefore, you have to determine what’s possible and which strategy makes sense in each case. Building on each other, control happens first, elimination second, and eradication is the final step, if possible.

Let’s start with the first step. What does control mean?

Control means using treatment to lower the burden of the disease in endemic areas. Burden of disease is another bit of public health jargon: it means the impact of a health problem on a given population, and can be measured using a variety of indicators such as mortality, morbidity or financial cost. And endemic areas means geographic areas where a disease is regularly found. For example, intestinal worms are endemic in Bangladesh and cause a high burden of disease. The Bangladesh Ministry of Health, my program CWW, and other partners have been working to control intestinal worms by improving water, sanitation, and hygiene practices, offering health education on the disease, and providing large-scale community treatments of intestinal worm medicine – albendazole and mebendazole – in communities where the disease is prevalent. Recently, CWW has surveyed 10 districts in Bangladesh and found that we’ve made great strides in controlling the disease burden by lowering the average prevalence of the disease from almost 80% in 2005 to 14% in the recent surveys. Most importantly, six districts are close to elimination, reducing the prevalence to below 10%.

Other NTDs such as trachoma, lymphatic filariasis, and river blindness have been controlled by similar approaches. By assessing the global burden of these diseases, the global public health community has agreed that these diseases are at least controllable – we can reduce the incidence, prevalence, and/or the conditions caused by the disease. Many of these diseases  can also be, and have been, eliminated in specific geographic regions, but eradication isn’t possible. I’ll explain that but first let me define elimination and eradication.

What does elimination mean?

Elimination means to make the disease not transmissible to other communities where the disease prevalence is almost zero. We do this through activities like improving hygiene-related infrastructure, changing human behaviors to healthier ones, and providing treatments. The term elimination is used when referring to a specific geographic area. For example, polio is eliminated in many areas of the world, but there are still some places where polio is appearing in communities, such as in Afghanistan and Pakistan where they are still working towards elimination.

In countries where CWW works to reduce intestinal worms, like Kenya, Bangladesh, and Uganda, the World Health Organization (WHO) has set the goal of elimination as a public health problem. “As a public health problem” is another bit of jargon that means reducing prevalence of STH to below 2% of the population (the specific goal can vary by disease), so it’s not completely at zero but within a margin that the country and public health community have agreed upon as feasible. In these countries, the ministries of health continue to use interventions like improving water and sanitation access and practices so that people have clean water to wash with and to drink and improved access to toilets. There is also “preventive chemotherapy” used for intestinal worms. This basically means that medicine can be provided to everyone at risk of the disease to help prevent them from getting the worms and to help them get rid of them. Although both children and women of reproductive age are at-risk groups for intestinal worms per WHO, this medicine is mostly provided through schools to children because the approach is the most cost-effective. However, select endemic countries use community clinics to provide the medicine to children not going to school and to women of reproductive age.

What does eradication mean?

Eradication means reduction of the disease to zero globally with no more risk of the disease coming back, thanks to consistent interventions. Smallpox is the beacon that many disease efforts look to as proof that it can be done. Due to a concerted vaccination campaign between the 1960s and 1980s people stopped getting and dying from smallpox. Now, there are zero cases around the world. Once it was declared eradicated by the WHO in 1980, it was no longer necessary to use interventions like mass vaccination to prevent the disease. While goals have been set for other diseases like polio to be eradicated, it is a term carefully and sparingly used because of the immense difficulty and time it takes to completely wipe a disease out.

Is it possible to eradicate a disease like intestinal worms?

Science is not advanced enough at this moment to help us eradicate intestinal worms, which is the case with many diseases. First, we have not invented sophisticated enough testing tools to detect cases. In addition, the environment and animals allow these types of parasitic worms to continue thriving and therefore continue infecting humans. In order to make eradication a goal for this disease, we would need to invent better testing tools and have public health programs that are built on effective coordination between the human health sector, animal health sector, and environmental health sector – commonly referred to as One Health. We’re making progress towards this but are still too far to be able to say we can eradicate intestinal worms.

What are the different challenges associated with each of the three goals?

The challenges really depend on the communities where disease control, elimination, or eradication activities are being conducted. With NTDs in particular, these diseases are so intertwined with society that it’s not so much what the goal is – control, elimination, or eradication – that presents different challenges but more about what’s happening in the community. For example, medicine is provided at schools for intestinal worms, but if a community is far from the nearest school and children from that community attend infrequently because of transportation or household responsibilities then they won’t have access to the regular treatment needed to prevent infections and therefore will be more at risk. It takes sound science and epidemiology as well as analyzing human behavior and environmental factors to design an effective program.

It’s a balance though and should be looked at as sequential steps. For example, it is practical to think about elimination after you are controlling the disease. Once it is eliminated, and you have advanced science, the disease may be eradicated. Control, elimination, and eradication programs must be tailored to the specific community they are serving, but we’ve also learned over the years that there are similarities across geographic areas, diseases, and types of activities. The Task Force’s Health Campaign Effectiveness Coalition is working on this with partners from various disease programs such as malaria control, lymphatic filariasis elimination, and polio eradication. By identifying the synergies that do exist, we’ll be able to make public health more efficient at achieving control and elimination, and hopefully getting them all to eradication status.

What inspired you to work on NTDs?

After I graduated with my first Masters degree in Statistics in Nepal, I started teaching biostatistics in a medical school in Nepal during which time I completed a fellowship in Norway on international health. That gave me a completely different perspective on looking at health issues. From there I did a stint in Honolulu working on cancer research and then realized I needed to study more and thus joined the PhD program at the University of Pittsburgh. After my PhD, I eventually joined the U.S. Centers for Disease Control and Prevention’s Epidemic Intelligence Service (EIS) – a two-year hands-on applied epidemiology training program – and that was a big sun in my career. It is kind of an accumulative effort –  my education, experiences such as the fellowship in Norway, doing Ebola or H1N1 outbreak responses with EIS, working with the WHO in refugee camps in Bangladesh have all been building blocks to where I am now. When I first started at The Task Force and CWW, I really didn’t know much about NTDs and I wasn’t sure it was going to be quite as exciting as working on infectious diseases like Ebola or H1N1 but I soon realized that these are diseases where I could have a huge impact. As the name indicates, there aren’t the mass amounts of resources that flashier diseases get and they truly are neglected in many ways but also diseases we can wipe out. So I’ve come to love what I’m learning from my peers in the NTD community and find that sharing what I know has a major impact.

Header photo: Dhakal with NTD partners in Kenya. Photo courtesy of Children Without Worms.

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