Today we will examine a case study of a waterborne parasite: Dracunculus medinensis, (a.k.a. Guinea Worm). Wednesday we will conclude with a discussion of efforts to eradicate this disease. (More)
Guinea Worm Disease (Introduction)
Guinea worm disease is a debilitating and painful infection caused by a large nematode (roundworm), Dracunculus medinensis. It begins with a blister, usually on the leg. Around the time of its eruption, the person may experience itching, fever, swelling and burning sensations. Infected persons try to relieve the pain by immersing the infected part in water, usually open water sources such as ponds and shallow wells. This stimulates the worm to emerge and release thousands of larvae into the water. The larva is ingested by a water flea (cyclops), where it develops and becomes infective in two weeks. When a person drinks the water, the cyclops is dissolved by the acidity of the stomach, and the larva is activated and penetrates the gut wall. It develops and migrates through the subcutaneous tissue. After about one year, a blister forms and the mature worm, 1m long, tries to emerge, thus repeating the life cycle.
For persons living in remote areas with no access to medical care, healing of the ulcers can take several weeks. This can be further complicated by bacterial infection, stiff joints, arthritis and even permanent debilitating contractures of the limbs. People in endemic villages are incapacitated during peak agricultural activities. This can seriously affect their agricultural production and the availability of food in the household, and consequently the nutritional status of their family members, particularly young children.
The story of Guinea Worm Disease demonstrates many of the issues discussed so far in the Evening Focus series on Water Security. Previously we have discussed the importance of clean water sources, effective sanitation and good cultural practices. Public health is highly dependent upon these for control of parasites such as Dracunculus medinensis. The parasite’s existence throughout human history is a direct result of failures in these three areas. Its near eradication is a story of how changes in these key areas can greatly improve human health and quality of life.
Guinea Worm Disease is a disease of poverty. It afflicts people in parts of the world where access to clean water and good sanitation is not available. It afflicts people who depend upon marginal water supplies from stagnant sources for drinking water. It requires that the water not be sanitized. Boiling water before drinking it, filtering it with a fine cloth mesh, or treatment of the water with chemicals is sufficient to prevent infection. These practices are difficult for people who live in the most poverty stricken parts of the world. Fuel to boil water before consumption is often difficult or impossible to acquire in sufficient quantities to prevent infection. Access to the chemicals needed to sanitize water require access to distribution networks and money to acquire them. Without foreign aid, people in these regions of the world would never be free of the disease.
The guinea worm is one of the best historically documented human parasites, with tales of its behaviour reaching as far back as the 2nd century BC in accounts penned by Greek chroniclers. It is also mentioned in the Egyptian medical Ebers Papyrus, dating from 1550 BC. The name dracunculiasis is derived from the Latin “affliction with little dragons”. While the common name “guinea worm” appeared after Europeans saw the disease on the Guinea coast of West Africa in the 17th century.
People become infected with Guinea worm by drinking stagnant water that contains copepods (tiny “water fleas”) that carry Guinea worm larvae (immature forms of the worm). These larvae are eaten by the copepods that live in these stagnant water sources. The larvae need about 2 weeks to mature inside the copepods before they can infect humans. Unsafe stagnant water includes ponds, pools in drying riverbeds, and shallow uncovered wells. Anyone who drinks from contaminated water sources can become infected. GWD is not normally caught from drinking flowing water (rivers and streams)
GWD transmission has a seasonal pattern. In dry regions, people generally get infected during the rainy season, when stagnant surface water is available. In wet regions, people generally get infected during the dry season, when surface water is drying up and becoming stagnant.
The risk for disease varies by sex, age, profession, and ethnicity. These differences reflect how and where people get their drinking water in different areas and countries. In general, about the same number of men and women get infected. GWD occurs in all age groups but it is more common among young adults 15–45 years old. This may be because of the type of work done by people this age. Farmers, herders, and those fetching drinking water for the household can become infected more often. It is thought they are more likely to drink contaminated stagnant water while away from home. In certain areas, GWD affects some ethnic groups more than others.
The greatest risk for GWD is having GWD the year before. People do not become immune to infection. Many people in affected villages suffer from GWD year after year. This is probably because the same water sources are repeatedly contaminated and conditions that support the spread of disease have not changed. It might also be related to some biological factor of the person that increases susceptibility. Not everyone drinking from the same contaminated water supply will become infected. A few people seem to keep getting infected while others drinking the same water do not.
Life cycle of a parasite
The parasitic lifecycle of Dracunculus medinensis depends then upon poor sanitation. People reintroduce the parasite back into the environment by bathing areas where the worm has erupted from the skin in the same water that people drink. Without this crucial human activity, the parasite can be eradicated in only a few years.
Treatment of Guinea Worm Disease is a painful, manual process that can take many days. It involves wrapping the roundworm around a small stick or piece of gauze and gradually pulling on the worm until it is removed. The process recommended by the CDC is as follows:
First, each day the affected body part is immersed in a container of water to encourage more of the worm to come out. To prevent contamination, the infected person is not allowed to enter drinking water sources. Next, the wound is cleaned. Then, gentle traction is applied to the worm to slowly pull it out. Pulling stops when resistance is met to avoid breaking the worm. Because the worm can be as long as one meter in length, full extraction can take several days to weeks. The worm is then wrapped around a rolled piece of gauze or a stick to maintain some tension on the worm and encourage more of the worm to emerge. This also prevents the worm from slipping back inside. Afterwards, topical antibiotics are applied to the wound to prevent secondary bacterial infections. The affected body part is then bandaged with fresh gauze to protect the site. Medicines, such as aspirin or ibuprofen, are given to help ease the pain of this process and reduce inflammation. These steps are repeated every day until the whole worm is successfully pulled out.
The method of extracting guinea worm by twisting the worm around a stickmay have inspired the rod of Asclepius, a symbol of medicine since Ancient Greek times which portrays a snake winding around a staff.
Wednesday we will conclude with a discussion of efforts to eradicate Guinea Worm Disease.
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