Dracunculiasis

Dracunculiasis, more commonly known as Guinea worm disease (GWD), is an infection caused by the parasite Dracunculus medinensis. The parasite is alternately known in English as "Guinea worm", "Medina worm", and finally "fiery serpent" which reflects the Latin root word Dracunculus meaning "little dragon".

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Life cycle

  The female Dracunculus worm emerges through the skin of its human host one to two years after infection. Often, persons with emergent worms enter sources of drinking water and unwittingly allow the worm to release larvae into the water. These larvae are ingested by microscopic fresh-water arthropods known as copepods ("water fleas", especially of the genus Cyclops). Inside the copepods, the larvae develop into the infective stage in 10–14 days. In turn, humans may then become infected by drinking water containing infected copepods.

Once inside the body, the stomach acid digests the water flea, but not the guinea worm larvae sheltered inside. These larvae find their way to the small intestine, and then pass into the body cavity. During the next 10–14 months, the female copulates with a male guinea worm. The small male (1.2–2.9 centimeters, 0.5-1.1 inches, long) dies and is absorbed into the larger female. The female develops into its full length of 60–100 centimeters (2–3 feet) long and a narrow width similar to that of a cooked spaghetti noodle. Having mated, the adult female is packed with thousands of tiny larvae. The worm migrates to the area of the body from which it will emerge, which, in more than 90% of all cases, is on one of the lower limbs.

A blister develops on the skin at the site where the worm will emerge. This blister causes a very painful burning sensation, and, within 24 to 72 hours of its appearance, will rupture, exposing one end of the emergent worm. To relieve the burning sensation, infected persons often immerse the affected limb in water. When the blister, which shortly becomes an ulcer or open sore, is submerged in water, the adult female releases a milky white liquid, containing hundreds of thousands of guinea worm larvae, into the water. Over the next several days, the female worm is capable of releasing more larvae whenever it comes in contact with water. These larvae contaminate the water supply and are eaten by copepods, thereby repeating the lifecycle of the disease, as described above.

Treatment

The most common practice to treat dracunculiasis involves wrapping the worm around a stick. This treatment has been employed for millennia and may have inspired the Rod of Asclepius^[1] which historically has symbolized the medical profession. As the adult worm first begins to emerge from the patient's skin, it is wrapped or wound around a stick, then further wound by a few centimeters per day. Considering a full-grown worm can measure up to a meter in length, this slow process can take many days or even weeks, but it is required to avoid breakage and leaving behind a portion of the worm. Breaking the worm will not cause the death of the individual; however, having a portion of the dead worm remain within the host's body increases the risk of infection, and can trigger immune responses resulting in pain and swelling. In many countries, a broken worm is immediately removed surgically. The worm also can be excised surgically from the very beginning, where such facilities are available.

Metronidazole or thiabendazole (in adults) is usually adjunctive to stick therapy and somewhat facilitates the extraction process. However, one study found that antihelminthic therapy was associated with aberrant migration of worms, resulting in infection in areas other than the lower extremity. Therefore, such medications should be used with caution.

If history or examination findings lead to suspicion of dranunculiasis, consultation is warranted with an infectious disease specialist for involvement in management and follow-up care. This also allows for initiation of epidemiologic protocol if the patient presents in a non-endemic country.

Complications

Dracunculiasis in itself is not lethal, and the overall mortality rate due to secondary infections is quite low. Even without primary treatment the prognosis is generally good as long as a secondary infection of the worm's exit site, which may lead to sepsis, is prevented or treated. Common morbidity include cellulitis or the formation of an abscess as well as pain from the worm exit site. Permanent scarring or deformity of the lower extremity may also occur. Another common and more chronic complication is encapsulation of the adult worm, which occurs when the calcified remains of the worm persist in the extremity of the patient. This can result in chronic pain and intermittent swelling of the extremity.^[2]

Eradication efforts

The Dracunculiasis Eradication Program (DEP), an effort to eradicate the disease from the world, has been funded by charities such as the Carter Center and the Bill & Melinda Gates Foundation. As a result of its efforts, as of 2005 Asia has been completely free of dracunculiasis, and in 9 of the 20 countries where dracunculiasis eradication began transmission has been interrupted. Five of the countries where the disease is still endemic saw fewer than 50 cases each in 2004. DEP has set a goal of global eradication by 2009.^[3]

Worldwide, there were about 3.5 million cases reported in 1986^[4], over 30,000 cases in 2003^[5], and only about 16,000 cases in 2004.^[3]

Dracunculiasis now occurs only in 12 countries in sub-Saharan Africa. Transmission of the disease is most common in very remote rural villages and in areas visited by nomadic groups. In the 2nd century BC, the Greek writer Agatharchides described this affliction as being endemic amongst certain nomads in what is now Sudan and along the Red Sea (fragments preserved in Photius, Bibliotheca Cod. 250.59, 453b; and Plutarch, Quaestiones Convivales 8.9.16).

In 2004 the three most endemic countries—i.e. Ghana, Sudan, and Nigeria—reported 7,275; 7,266; and 495 cases of GWD respectively. Other endemic countries reporting cases of GWD in 2004 were: Benin (3 cases), Burkina Faso (60 cases), Côte d'Ivoire (21 cases), Ethiopia (17 cases), Mali (357 cases), Mauritania (13 cases), Niger (293 cases), and Togo (278 cases). Kenya (7 cases) and Uganda (4 cases) reported incidences imported from Sudan.

Transmission of GWD no longer occurs in several African countries, including Kenya, Senegal, Cameroon, Chad, and Central African Republic. No locally acquired cases of disease have been reported in these countries in the last year or more. The World Health Organization has certified 180 countries free of transmission of Dracunculiasis, including five formerly endemic countries: Pakistan (in 1996), India (in 2000), Senegal (in 2004), Yemen (in 2004), Cameroon (in 2007), and the Central African Republic (in 2007).^[6][7]

In 2006, 25,217 cases were reported. 20,582 were from southern Sudan; this increase in the number of reported cases from 2005 (5,569) reflects better reporting from southern Sudan's eradication program. Ghana reported a total of 4,136 cases. The 8 other endemic countries reported a total of 499 cases: Burkina Faso, 5; Côte d'Ivoire, 5; Ethiopia, 3; Mali, 329; Niger, 110; Nigeria, 16; Togo, 29; Uganda, 2 (imported). Benin, Chad, Kenya, Mauritania, and Uganda are in the precertification stage, and Cameroon and the Central African Republic were certified Dracunculiasis free.^[8]

Practical concerns

  The significance of an infection reported in a country considered free of dracunculiasis depends on the species of the parasite. Occasionally, a species which normally infects animals such as D. insignis may infect a human. Such zoonotic cases are considered atypical, and are not a cause for concern. Infection by D. medinensis in a location considered GWD-free is of great concern to the eradication effort. Therefore, the ability to distinguish between the human parasite, D. medinensis, and other Dracunculus species is important. This may be done by examination of the victim's travel history and by DNA fingerprinting of the worm itself.^[9]

Prevention

Because GWD can only be transmitted via drinking contaminated water, educating people to follow these simple control measures can completely prevent illness and eliminate transmission of the disease:

• Drink only water from underground sources free from contamination, such as a borehole or hand-dug wells.
• Prevent persons with an open Guinea Worm ulcer from entering ponds and wells used for drinking water.
• Always filter drinking water, using a cloth filter or better yet a nylon mesh filter, to remove the water fleas.
• Additionally, unsafe sources of drinking water can be treated with an approved larvicide such as Abate, that kills water fleas, and communities can be provided with new safe sources of drinking water, or have existing dysfunctional ones repaired.

See also

• Infectious disease in the 20th century
• List of infectious diseases
• Parasites
• Tropical disease

References

1. ^ Zimmer, Carl (2000). Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures.. New York, NY: Touchstone, 2. ISBN 074320011X. 
2. ^ http://www.emedicine.com/ped/topic616.htm
3. ^ ^{a b} Hopkins, Donald R.. "Dracunculiasis Eradication: The Final Inch". American Journal of Tropical Medicine and Hygiene 73 (4): pp. 669-675coauthors = et al.. Retrieved on 2007-02-28.
4. ^ Morbidity and Mortality Weekly Report. Carter Center (28 October). Retrieved on 2007-02-28.
5. ^ Dracunculiasis Fact Sheet. United States Centers for Disease Control and Prevention (CDC) (September 30). Retrieved on 2007-02-28.
6. ^ World moves closer to eradicating ancient worm disease. World Health Organization (2007-03-27). Retrieved on 2007-06-17.
7. ^ Weekly epidemiological record, No. 19, 2007, 82, 161–168 (pdf). World Health Organization (2007-05-11). Retrieved on 2007-06-17.
8. ^ Weekly epidemiological record, No. 16, 2007, 82, 133–140 (pdf). World Health Organization (2007-04-20). Retrieved on 2007-06-17.
9. ^ Bimi, L.; et al. (2005). "Differentiating Dracunculus medinensis from D. insignis, by the sequence analysis of the 18S rRNA gene" (PDF). Annals of Tropical Medicine and Parasitology 99 (5): 511-517. Retrieved on 2007-02-27.