Dracunculiasis (Guinea-worm disease) is caused by the parasitic worm Dracunculus medinensis or Guinea-worm. This worm is the largest of the tissue parasite affecting humans. The adult female, which carries about 3 million embryos, can measure 600 to 800 mm in length and 2 mm in diameter. When a person drinks contaminated water from ponds or shallow open wells, the cyclops is dissolved by the gastric acid of the stomach and the larvae are released and migrate through the intestinal wall.
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After 100 days, the male and female meet and mate. The male becomes encapsulated and dies in the tissues while the female moves down the muscle planes. After about one year of the infection, the female worm emerges, usually from the feet, releasing thousands of larvae and thus repeating the life cycle.
- Dracunculiasis is a crippling parasitic disease on the verge of eradication, with 27 human cases reported in 2020.
- From the time infection occurs, it takes between 10–14 months for the transmission cycle to complete. About this time, a mature female worm emerges from the body.
- The parasite is transmitted mostly when people drink stagnant water contaminated with parasite-infected water fleas.
- Dracunculiasis was endemic in 20 countries in the mid-1980s.
Dracunculiasis is rarely fatal, but infected people become non-functional for weeks and months. It affects people in rural, deprived, and isolated communities who depend mainly on open stagnant surface water sources such as ponds for drinking water.
Scope of the problem
During the mid-1980s an estimated 3.5 million cases of dracunculiasis occurred in 20 countries worldwide, 17 countries of which were in Africa and the 3 others in Asia. The number of reported cases fell to fewer than 10 000 cases for the first time in 2007, dropping further to 542 cases (2012). Over the past eight years, human cases have stayed at double digits (54 in 2019 and 27 human cases in 2020). These human cases were reported from four countries: Angola (1), Chad (12), Ethiopia (11), Mali (1), South Sudan (1) and Cameroon (1) – likely imported from Chad.
Transmission, life-cycle and incubation period
About a year after infection, a painful blister forms – 90% of the time on the lower leg – and one or more worms emerge accompanied by a burning sensation. To soothe the burning pain, patients often immerse the infected part of the body in water. The worm(s) then releases thousands of larvae (baby worms) into the water. These larvae reach the infective stage after being ingested by tiny crustaceans or copepods, also called water fleas.
People swallow the infected water fleas when drinking contaminated water. The water fleas are killed in the stomach, but the infective larvae are liberated. They then penetrate the wall of the intestine and migrate through the body. The fertilized female worm (which measures 60–100 cm long) migrates under the skin tissues until it reaches its exit point, usually at the lower limbs, forming a blister or swelling from which it eventually emerges. The worm takes 10–14 months to emerge after infection.
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There is no vaccine to prevent the disease, nor is there any medication to treat patients. Prevention is possible, however, and successful implementation of preventive strategies have driven the disease to the verge of eradication. Prevention strategies include:
- heightening surveillance to detect every human case and infected animal within 24 hours of worm emergence,
- preventing transmission from each worm by treatment, and regular cleaning and bandaging of affected areas of skin until the worm is completely expelled from the body;
- preventing contamination of drinking-water by preventing infected people and infected animals (dogs and cats) with emerging worms from wading into water;
- ensuring wider access to improved drinking-water supplies to prevent infection;
- filtering water from open water bodies before drinking;
- implementing vector control by using the larvicide temephos; and
- promoting health education and behavioural change.
The road to eradication
In May 1981, the Interagency Steering Committee for Cooperative Action for the International Drinking Water Supply and Sanitation Decade (1981–1990) proposed the elimination of dracunculiasis as an indicator of success of the Decade. In the same year, WHO’s decision-making body, the World Health Assembly, adopted resolution WHA 34.25, recognizing that the International Drinking Water Supply and Sanitation Decade presented an opportunity to eliminate dracunculiasis. This led to WHO and the United States Centers for Disease Control and Prevention formulating the strategy and technical guidelines for an eradication campaign.
In 1986, The Carter Center joined the battle against the disease and, in partnership with WHO and UNICEF, has since been at the forefront of eradication activities. To give it a final push, in 2011 the World Health Assembly called on all Member States where dracunculiasis is endemic to expedite the interruption of transmission and enforce nationwide surveillance to ensure eradication of dracunculiasis.
To be declared free of dracunculiasis, a country is required to have reported zero instances of transmission and maintained active surveillance for at least 3 consecutive years.
After this period, an international certification team visits the country to assess the adequacy of the surveillance system and to review records of investigations regarding rumoured cases or infected animals and subsequent actions taken.
Indicators such as access to improved drinking-water sources in infected areas are examined and assessments are conducted in villages to confirm the absence of transmission. Risks of reintroduction of the disease are also assessed. Finally, a report is submitted to the International Commission for the Certification of Dracunculiasis Eradication (ICCDE) for review.
Since 1995, the ICCDE has met 15 times and on its recommendation, WHO has certified 199 countries, territories, and areas (belonging to 187 Member States) as free of dracunculiasis.
Kenya, a formerly endemic country, was the last to attain this status in February 2018.
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WHO recommends active surveillance in a country and/or area that has recently interrupted guinea-worm disease transmission to be maintained for a minimum of 3 consecutive years. Ongoing surveillance is essential to ensure that no human cases and infected animals have been missed and to prevent reoccurrence of the disease.
As the incubation period of the worm takes 10–14 months, a single missed emerged worm could delay eradication by a year or more. Evidence of re-emergence was brought to light in Ethiopia (2008) after the national eradication programme claimed interruption of transmission, and more recently in Chad (2010) where transmission re-occurred after the country reported zero cases for almost 10 years.
A country reporting zero cases over a period of 14 consecutive months is believed to have interrupted transmission. It is then classified as being in the pre-certification stage for at least 3 years since the last indigenous case, during which intense surveillance activities must be continued. Even after certification, surveillance should be maintained until global eradication is declared.
Finding and containing the last remaining cases and infected animals are the most difficult and expensive stages of the eradication process, as these usually occur in remote, often inaccessible, rural areas.
Insecurity, with the resulting lack of access to disease-endemic areas, is a major constraint, especially in countries where cases and animal infections are still occurring.
Dracunculus medinensis infection in dogs continues to pose a challenge to the global eradication campaign particularly in Chad, Ethiopia and Mali. The phenomenon was noted in Chad in 2012, and since then several dogs with emerging worms, genetically identical to those emerging in humans, continue to be detected in the same at-risk area. In 2020, Chad reported 1508 infected dogs and 63 infected cats; Ethiopia reported three infected dogs, four infected baboons, and eight infected cats. ; Mali reported infections in nine dogs.
Transmission in animals can be interrupted through enhanced surveillance to detect all infected animals and to contain them (tethering of infected animals and pro-active tethering), provision of health education for community members and animal owners, and implementation of vigorous and comprehensive vector control interventions.