Historically referred to as “little dragons”, this week’s NTD is Guinea worm disease. Guinea worm is caused by a parasitic worm that causes severe pain and blisters in those it infects. It is a disease that has been around for as long as time. Mummies from ancient Egypt have been discovered to carry the worms and in the Book of Numbers, the “fiery serpents” infecting the Israelites is believed to have been Guinea worms [1]. Muslim pilgrims participating in the hajj suffered from infections on the way to Medina, giving the infectious disease its Latin name, Dracunculus medinensis, or “Little dragon of Medina” [1]. Even more fascinating, many believe that the symbol of medicine, snakes coiled around a staff, represents the ancient treatment for the disease documented on the Ebers papyrus from approximately 1500 BC that is still utilized today [1, 2].
Guinea worm disease is caused by the ingestion of contaminated water containing microscopic water fleas called copepods that carry the Guinea worm larvae [3]. It is typically contracted from drinking stagnant water from a pond or water source. Once digested, the larvae are released in the digestive tract and enter the body cavity, where the larvae develop into adult worms that can reach two to three feet in length over a period of 10 to 14 months [3]. When the female worm is ready to release larvae, it moves to the surface of the skin and creates a painful blister, often on the leg or foot [3]. Most often, once the blister forms, people submerge the blister in water, as it greatly relieves the burning pain. However, doing so signals the worm to release larvae into the water source, thus contaminating the water supply and perpetuating their life cycle [3]. Whenever the worm comes in contact with water, the female worm can release millions of immature larvae [3]. Humans typically are infected with one worm, but they can be infected with multiple worms at the same time if there is a higher prevalence of the parasite in their local area [4].
Treatment for Guinea worm disease is not comfortable. With no preventative vaccine or drug to treat the disease, the only option is to take a small stick or gauze and slowly pull the worm out of the wound [3]. It can only be pulled out a few centimeters a day to avoid tearing of the worm, so the process typically takes a few weeks to remove the worm completely [3]. Antibiotic ointment is typically applied to the wound to prevent secondary bacterial infection, which is very common in rural regions of Africa where there is limited access to healthcare and sanitation[3].
Infection with Guinea worm disease can be debilitating. This often means they are unable to work due to the pain caused by the worm, leaving their families to struggle, thus continuing a cycle of poverty. The Center for Disease Control (CDC), in association with organizations like the Carter Center and World Health Organization (WHO), have worked tirelessly to educate those most at risk and have provided tools for filtering drinking water to drastically reduce the incidence of Guinea worm disease. In 1986, 20 countries globally had a combined 3.5 million cases a year and 120 million people were at risk for the disease [5]. Due to eradication and elimination efforts, there were only 25 new cases worldwide in 2016, coming from Chad, Ethiopia and South Sudan [5]. In March 2016, 198 countries, territories and areas representing WHO Member States were declared free from Guinea worm disease transmission [5]. It is expected that Guinea worm disease will be the first disease to be eradicated using core public health practices, including surveillance, case containment and simple interventions, without the use of vaccines or medicines [5]. The eradication campaign has prevented at least 80 million cases of Guinea worm disease since its inception [6].
Disease elimination and eradication can be incredibly complex and time-consuming, requiring a multidisciplinary approach to stop the spread of disease. To understand this process, we must first understand basic epidemiologic principles. Elimination refers to incidence of a disease or infections associated to a disease being reduced to zero in a specific geographic region [7]. For example, poliomyelitis has been eliminated in the United States, however, you can still find cases around the globe. Eradication refers to the permanent global reduction of a specific disease agent to zero [7]. The only infectious disease that has been completely eradicated is smallpox, which was declared to be eradicated in 1980 after an extensive campaign led by the World Health Organization [8].
There are many biologic and technical characteristics of infectious diseases that make them more or less likely to reach eradication [7]. However, these factors can be boiled down to three simple traits: there is an effective treatment for the disease; there are tools that are both appropriately specific and sensitive to detect disease; and humans are essential for the infectious agent to complete its life cycle and are the only reservoir for it [7]. Simply put, if humans are the only species to carry the disease, it is much more feasible to eradicate. The ultimate goal of public health is disease elimination and eradication, which requires directed efforts of the public health community and government organizations in order to effectively prevent and treat disease to avoid transmission.
Seven diseases are currently targeted by the International Task Force for Disease Eradication, including Guinea worm, lymphatic filariasis, measles, mumps, rubella, poliomyelitis and cysticercosis [9]. However, now that Guinea worm infections in both domestic and wild dogs have been confirmed, the possibility that it can be truly eradicated is no longer certain, putting thirty-two years of dedicated efforts at risk [10]. Last year, over 800 cases of Guinea worm occurred in dogs along the Chari River, compared to thirty human cases in 2017 [10]. It is still unclear how the dogs are contracting the larvae, though the CDC does not suspect that it is from drinking water [3]. One hypothesis is that the dogs are eating aquatic animals, like frogs or fish, that have consumed copepods that carry the Guinea worm larvae [3]. Luckily, there is no sign of dog to human transmission yet, but the dogs can transmit the parasitic worm to water sources, where humans are most susceptible to contracting the parasite [10].
With this new knowledge that humans are not the only species at risk for infection of Guinea worm, the eradication process has become more challenging. However, this has not deterred public health officials from taking every step necessary to contain the infections and prevent the spread to humans. Infections in dogs have been a bump in the road, but the public health community has and will remain steadfast in their efforts to make sure those most at risk are cared for.
Sources:
[1] http://phenomena.nationalgeographic.com/2013/01/24/the-guinea-worm-a-fond-obituary/
[2] https://www.florenceinferno.com/rod-of-asclepius-and-caduceus-symbols/
[3] https://www.cdc.gov/parasites/guineaworm/gen_info/faqs.html
[4] https://www.cartercenter.org/news/documents/doc1308.html
[5] https://www.cdc.gov/parasites/guineaworm/gwep.html
[6] https://www.cartercenter.org/health/guinea_worm/index.html
[7] https://www.cdc.gov/mmwr/preview/mmwrhtml/su48a7.htm
[8] http://www.who.int/csr/disease/smallpox/en/
[10] https://www.nytimes.com/2018/06/18/health/guinea-worms-dogs-chad.html