by Rebecca Mandt
We usually think of extinction of a species as a bad thing. But what if that species is directly causing human suffering or death on a global scale? The ultimate goal of disease eradication efforts is to target an infectious disease by completely removing the pathogen from the human population, thereby reducing the number of cases to zero worldwide, generally leading to the extinction of the microorganism. Most people in the US have heard of the campaigns to eradicate smallpox, measles and polio. So far, smallpox is the only disease that has been successfully eradicated from all countries. While much progress has been made in decreasing the numbers of measles and polio cases worldwide, another disease that you may never have heard of–Dracunculiasis– is currently on the brink of global eradication, and will likely reach the finish line first [1,2,3].
Dracunculiasis, better known as Guinea worm disease, is a debilitating parasitic disease prevalent mainly in Africa. The Guinea worm eradication campaign began in 1986, with a formal resolution by the World Health Assembly. The Carter Center took the lead on these efforts, spearheading the global Guinea Worm Eradication Program (GWEP), which works closely with the Ministries of Health in countries where Guinea worm disease is common to build local, national and international partnerships . In 1986, there were over 3.5 million estimated cases of Guinea worm disease across 20 countries. By 2014, this number had been reduced to 126 cases in just four remaining countries (Figure 1). As of just last month, provisional data suggests that the number of Guinea worm cases that occurred in the year 2015 is…twenty! [5,6]. If you haven’t been paying attention to this little parasite, now is the time, because if everything goes as planned and progress continues, the Guinea worm will very soon be gone from this earth, forever. We doubt anyone will miss it!
So what is Guinea Worm Disease, anyway?
Guinea worm disease is caused by the roundworm Dracunculus medinensis. Dracunculiasis, the Latin name for the disease, translates to “affliction with little dragons”. The lifecycle of D. medinensis is summarized in Figure 2. Humans are the definitive host, which means that we are the host in which the parasite reaches maturity and reproduces sexually. People contract the parasite by drinking water containing infected copepods, or ‘water fleas’. After ingestion, the copepods die and release the larvae, which burrow into the host’s stomach and intestinal wall. The larvae make a home for themselves in the abdominal and thoracic cavities, growing and developing into sexually mature, male and female worms. Once the worms mate, the males die, but the females continue to grow, reaching lengths of nearly forty inches! The fertilized female also migrates towards the surface of the skin. Eventually, she pierces through the skin, causing a hot, painful blister. This blistering occurs 10-14 months after the initial transmission, and is generally the first sign that a person is infected. The pain of the blister induces the host to seek relief by soaking the affected body part in water, which triggers the female worm to emerge and release hundreds of thousands of her larvae. The larvae are then taken up by water fleas, and the life cycle begins again [7,8].
While Guinea worm disease is not generally fatal, it is excruciatingly painful. A swollen ulcer forms, followed by a blister at the site of emergence. The worm can be removed manually, but only a few centimeters at a time, so the patient must endure this process for several weeks. Secondary bacterial infection is common, which can contribute to the pain and inflammation, occasionally leading to more serious complications. The disease is also seasonal, with the worms generally emerging at the peak of the harvest season; this means that a large proportion of a village’s population could be incapacitated at once, thus posing a significant economic burden [8,9].
The pursuit of extinction: what makes a disease eradicable?
Not every disease is eradicable. Biological, technical and political factors all play a role in determining if eradication is feasible. From a biological perspective, Guinea worm disease is a good candidate. Humans are essential for the life cycle of D. medinensis, and there is no significant animal reservoir, meaning there is no other species which the Guinea worm can infect long-term. Thus, if we can interrupt transmission in humans, we can end the disease. Guinea worm disease is also easy to diagnose, and transmission requires the presence of symptoms, making it possible to identify and contain infected individuals to prevent them from contaminating community water supplies. One challenge of Guinea worm disease is the parasite’s long incubation period, which delays the impact of control measures and makes it impossible to diagnose at the time of infection [2,3].
The political support for an eradication initiative is as important as the biological and technical feasibility. Several international bodies, developed-country governments, and NGOs have provided financial support and resources throughout the eradication campaign. The figurehead for these international efforts is Jimmy Carter, who first witnessed the devastating effects of Guinea worm disease during a trip to Ghana in the late 1980s . This visit inspired him to make the eradication of Guinea worm disease a major goal of the Carter Center foundation. Carter has remained personally involved in Guinea worm eradication efforts. He was also instrumental in securing support of the heads of state of endemic countries . In September of this year, the 91-year-old former president stated, “I would like the last Guinea worm to die before I do”.
However, the greatest responsibility for eradication efforts falls upon the governments and healthcare workers in endemic countries. The strategies for eradication must be implemented at the local level, and the success of these programs really depends on the commitment of the community and individuals. Because of the enormous efforts required, political instability can also severely hamper eradication efforts. The four countries in which Guinea worm is still endemic are South Sudan, Chad, Mali and Ethiopia. South Sudan in particular has faced challenges due to political instability. In spite of this, the country has made tremendous strides. D. medinensis prevalence in South Sudan decreased by 86% from 2008 to 2012, and in the past 12 months, the country reported only four cases of Guinea worm disease .
How to slay tiny dragons: The tools of the current eradication campaign
For the smallpox, polio and measles campaigns, we’ve had one powerful tool at our disposal: vaccines. In the case of Guinea worm disease, no vaccine or therapeutics are available. Amazingly, this has not hindered the progress of eradication. Several tools and strategies have been used to target Guinea worm disease at various stages of the parasite’s life cycle (see figure 2 and figure 3). Cases of Guinea worm disease were initially detected by community based surveillance and active house-to-house searches. Now, with very few cases present in each country, rewards are offered to any individual who can notify health care officials of a new case [13,6]. Following detection, a Guinea worm case must be properly contained. Successful containment means ensuring that the patient does not enter and contaminate any water source, and that they receive proper treatment including bandaging of the wounds and complete removal of the worm. Detection and case management thus prevent further transmission of the parasite . Access to safe drinking water is another key step in blocking transmission. A simple solution is to filter water through a nylon membrane, which effectively removes the infected water fleas. People can even use pipes with nylon filters at the end, through which they can drink water as from a straw . The fleas can also be targeted by chemically treating the ponds where they live. However, the quantity of chemicals and labor needed for this type of intervention can be prohibitively expensive for some communities .
Health education is a vital component of all of these efforts. Education interventions aim to teach community members to recognize how Guinea worm is transmitted, to protect themselves from getting the disease, and to prevent the disease from spreading by not entering sources of drinking water if they are infected .
The final mile is always the hardest
Towards the end of an eradication campaign, the resources needed to find and treat each case increases. This is because in the initial stages, when there are many people infected, finding and treating cases is relatively easy. However, for a goal of complete eradication, every single case matters and must be accounted for. Thus, the few final cases that arise towards the end of the campaign must be actively hunted down through intensified surveillance efforts  .
Global eradication of a disease thus requires an extensive, coordinated and sustained effort; however, the potential benefits are immense, as once a disease is eradicated, it no longer poses a health and economic burden to society. Further, if a disease is truly eradicated, there is no risk of it reemerging. In contrast, even if a country has worked hard to eliminate a disease within its borders, as long as the pathogen still exists in other regions, there is always a risk that the disease can reenter the population. For example, although measles was eliminated in the United States in 2000, it is still common in many countries. Thus, cases still occur when travelers (either American or foreign) contract measles outside of the country and then come to the US, bringing the disease with them .
The progress that has been made towards the eradication of Guinea worm disease is truly remarkable, and the end of Guinea worm is now in sight. However, it is important not to celebrate too early. The momentum of the previous decades must be maintained as we move towards the finish line. In disease eradication efforts, the last mile is always the hardest. It is important to remember the lasting benefits that can be claimed from ridding the world of this parasite for good–as well as the danger of losing the progress that has been made if the task at hand is not completed .
If you would like to continue following the exciting saga of the Guinea worm eradication campaign, visit http://www.cartercenter.org/health/guinea_worm/case-totals.html for monthly updates and country reports.
Rebecca Mandt is a first year Ph.D. student in the Biological Sciences in Public Health program at the Harvard TH Chan School of Public Health. She is interested in a broad spectrum of infectious disease research.
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