From Wikipedia, the free encyclopedia - View original article
|Classification and external resources|
Using a stick to remove a guinea worm from the leg of a human
|Classification and external resources|
Using a stick to remove a guinea worm from the leg of a human
Dracunculiasis, also called guinea worm disease (GWD), is an infection by the guinea worm. A person becomes infected when he drinks water that contains water fleas infected with guinea worm larvae. Initially there are no symptoms. About one year later, the person develop a painful burning feeling as the female worm forms a blister in the skin, usually on the lower limb. The worm then comes out of the skin over a few weeks. During this time it may be difficult to walk or work. It is very uncommon for the disease to cause death.
Humans are the only known animal that guinea worms infect. The worm is about one to two millimeters wide and as an adult is 60 to 100 centimeters long. Outside of humans the eggs can survive up to three weeks. They must be eaten by water fleas before this. The larva inside water fleas may survive up to four months. Thus the disease must occur each year in humans to stay in an area. A diagnosis of the disease can usually be made based on the signs and symptoms of the disease.
Prevention is by diagnosis the disease early and then preventing the person from putting the wound in drinking water. Other efforts include: improving access to clean water and otherwise filtering water if it is not clean. Filtering through a cloth is often enough. Contaminated drinking water maybe treated with a chemical called temefos to kill the larva. There is no medication or vaccine against the disease. The worm may be slowly removed over a few weeks by rolling it over a stick. The ulcers formed by the emerging worm may get infected by bacteria. Pain may continue for months after the worm has been removed.
In 2013 there was 148 cases of the disease reported. This is down from 3.5 million cases in 1986. It only exists in 4 countries in Africa down from 20 countries in the 1980s. The country most affected is South Sudan. It will likely be the first parasitic disease to be eradicated. Guinea worm disease has been known since ancient times. It is mentioned in the Egyptian medical Ebers Papyrus, dating from 1550 BC. The name dracunculiasis is come from the Latin "affliction with little dragons" while the name "guinea worm" appeared after Europeans saw the disease on the Guinea coast of West Africa in the 17th century. A species similar to guinea worms causes disease in other animals. These do not appear to infect humans.
Dracunculiasis is diagnosed by seeing the worms emerging from the lesions on the legs of infected individuals and by microscopic examinations of the larvae.
As the worm moves downwards, usually to the lower leg, through the subcutaneous tissues it leads to intense pain localized to its path of travel. The painful, burning sensation experienced by infected people has led to the disease being called "the fiery serpent". Other symptoms include fever, nausea, and vomiting. Female worms cause allergic reactions during blister formation as they migrate to the skin, causing an intense burning pain. Such allergic reactions produce rashes, nausea, diarrhea, dizziness, and localized edema. When the blister bursts, allergic reactions subside, but skin ulcers form, through which the worm can protrude. Only when the worm is removed is healing complete. Death of adult worms in joints can lead to arthritis and paralysis in the spinal cord.
Guinea worm disease is caused by drinking water contaminated by water fleas (microscopic arthropods known as copepods) that host the Dracunculus larva. Guinea worm disease used to thrive in some of the world's poorest areas, particularly those with limited or no access to clean water. In these areas, stagnant water sources may still host copepods, which can carry the larvae of the guinea worm.
Humans become infected by drinking unfiltered water containing copepods (small crustaceans) that have been infected with D. medinensis larvae. After ingestion, the copepods die and release the stage 3 larvae, which then penetrate the host's stomach or intestinal wall, and enter into the abdominal cavity and retroperitoneal space. After maturing, they mate and adult male worms die. Approximately one year after mating the fertilized females migrate in the subcutaneous tissues towards the surface of the skin causing formation of blisters on the skin, generally on the distal lower extremity (foot), which breaks open. The patients then seek to relieve the local discomfort by placing their foot in water, but when the lesion comes into contact with water, the female worm emerges and releases her stage 1 larvae. The larvae are then ingested by a copepod, and after two weeks (and two molts), the stage 3 larvae become infectious. Ingestion of the copepods is the last stage to complete the cycle.
The larvae develop for approximately two weeks inside the copepods. At this stage the larvae can cause guinea worm disease if the infected copepods are not filtered from drinking water. The male guinea worm is typically much smaller (12–29 mm or 0.47–1.14 in) than the female, which, as an adult, can grow to 2–3 feet (0.61–0.91 m) long and be as thick as a spaghetti noodle.
Once inside the body, the copepod is digested, but not the guinea worm larvae sheltered inside. These larvae find their way to the body cavity where the female mates with a male guinea worm. This takes place approximately three months after infection. The male worm dies after mating and is absorbed.
About a year after the infection has begun, the worm makes a blister in the human host's skin—usually on the leg or foot. Within 72 hours the blister ruptures, exposing one end of the emergent worm. This blister causes a very painful burning sensation as the worm emerges. Infected persons often immerse the affected limb in water to relieve the burning sensation. Once the blister or open sore is submerged in water, the adult female releases hundreds of thousands of guinea worm larvae, contaminating the water supply.
During the next few days, the female worm can release more larvae whenever it comes in contact with water as it extends its posterior end through the hole in the host's skin. These larvae contaminate the water supply and are eaten by copepods, repeating the life-cycle of the disease. Infected copepods can live in the water for up to 4 months. Infection does not create immunity, so people can repeatedly experience guinea worm disease throughout their lives.
In drier areas just south of the Sahara desert, cases of the disease often emerge during the rainy season, which for many agricultural communities is also the planting or harvesting season. Elsewhere, the emerging worms are more prevalent during the dry season, when ponds and lakes are smaller and copepods are thus more concentrated in them. Guinea worm disease outbreaks can cause serious disruption to local food supplies and school attendance.
Guinea worm disease can be transmitted only by drinking contaminated water, and can be completely prevented through two relatively simple measures:
1. Prevent people from drinking contaminated water containing the Cyclops copepod (water flea), which can be seen in clear water as swimming white specks.
2. Prevent people with emerging Guinea worms from entering water sources used for drinking.
The global campaign to eradicate Guinea worm disease began at the U.S. Centers for Disease Control and Prevention (CDC) in 1980. In 1986, former U.S. President Jimmy Carter and his not-for-profit organization, The Carter Center, began leading the global campaign, in conjunction with CDC, UNICEF, and WHO. At that time India, Pakistan, Yemen and 17 countries in Africa were endemic for this disease and reported a total of 3.5 million cases per year.
Carter made a personal visit to a Guinea worm endemic village in 1988. He said: "Encountering those victims first-hand, particularly the teenagers and small children, propelled me and Rosalynn to step up the Carter Center's efforts to eradicate Guinea worm disease."
President Carter also recruited two African former heads of state to the battle against Guinea worm disease. Then-former head of state of Mali, General Amadou Toumani Toure (since elected President of Mali) has been a strong advocate of Guinea worm eradication in Mali and all other French-speaking African endemic countries since 1992. Since 1999, former Nigerian head of state General (Dr.) Yakubu Gowan has played a similar role in Nigeria, which at the eradication campaign's start had more cases than any other country.
Since humans are the principal host for Guinea worm, and there is no evidence that D. medinensis has ever been reintroduced to humans in any formerly endemic country as the result of non-human infections, the disease can be controlled by identifying all cases and modifying human behavior to prevent it from recurring. Once all human cases are eliminated, the disease cycle will be broken, resulting in its eradication.
In 1991, the World Health Assembly (WHA) agreed that Guinea worm disease should be eradicated. At this time there were 400,000 cases reported each year. The Carter Center has continued to lead the eradication efforts, primarily through its Guinea Worm Eradication Program. Other major actors in the eradication of Guinea worm disease include: World Health Organization, U.S. Centers for Disease Control and Prevention, Bill & Melinda Gates Foundation, and UNICEF, but the global coalition now includes dozens of other donors, nongovernmental organizations, and institutions, most especially the ministries of health of the affected countries themselves.
In December 2008, The Carter Center announced new financial support totaling US$55 million from the Bill & Melinda Gates Foundation and the United Kingdom Department for International Development. The funds will help address the higher cost of identifying and reporting the last cases of Guinea worm disease. According to The Carter Center, surveillance of countries, including the smallest communities in the most remote areas, needs to be intensified to prevent outbreaks and setbacks. In the case of Guinea worm disease, which has a one-year incubation period, there is a very high cost of maintaining a broad and sensitive monitoring system and providing a rapid response when necessary.
On 30 January 2012 the WHO meeting at the Royal College of Physicians in London launched the most ambitious and largest coalition health project ever, known as London Declaration on Neglected Tropical Diseases which aims to end/control dracunculiasis by 2020, among other diseases. This project was declared under the official support of all major pharmaceutical companies, the Bill & Melinda Gates Foundation, the governments of the United States, United Kingdom DFID and United Arab Emirates and the World Bank.
The eradication of Guinea worm disease has faced several challenges:
One of the most significant challenges facing Guinea worm eradication has been the civil war in southern Sudan, which was largely inaccessible to health workers due to violence. To address some of the humanitarian needs in southern Sudan, in 1995, the longest ceasefire in the history of the war was achieved through negotiations by Jimmy Carter. Commonly called the "Guinea worm cease-fire," both warring parties agreed to halt hostilities for nearly six months to allow public health officials to begin Guinea worm eradication programming, among other interventions.
Public health officials cite the formal end of the war in 2005 as a turning point in Guinea worm eradication because it has allowed health care workers greater access to southern Sudan's endemic areas. One remaining area in West Africa outside of Ghana remains challenging to ending Guinea worm: northern Mali, where Tuareg rebels have made some affected areas unsafe for health workers.
One of the greater challenges in eradicating dracunculiasis has been and will continue to be in South Sudan (formerly southern Sudan), particularly political uncertainty in the country with national elections in 2009 and the referendum on the status of southern Sudan in 2011 resulting in South Sudan's independence. Sporadic insecurity or widespread civil conflict could at any time ignite, thwarting eradication efforts. The remaining endemic communities in South Sudan are remote, poor and devoid of infrastructure, presenting significant hurdles for effective delivery of interventions against disease. Moreover, residents in these communities are nomadic, moving seasonally with cattle in pursuit of water and pasture, making it very difficult to know where and when transmission occurred. The peak transmission season coincides with the rainy season, hampering travel by public health workers.
In the 1980s, former U.S. President Jimmy Carter persuaded President Zia al-Haq of Pakistan to accept the proposal of the eradication program, and by 1993, Pakistan was free of the disease. Key to the effort was, according to Carter, the work of "village volunteers" who educated people about the need to filter drinking water. Other countries followed, and by 2004, the worm was eradicated in Asia.
Eradication in Sudan had proven to be difficult, and although Carter had brought about a six-month armistice in 1995—the "Guinea worm ceasefire"—to allow volunteers enter the region in safety, but endemic sections remain.
Ghana is winning the battle against the Guinea worm disease, recording a zero infection rate in the month of November 2009. In the year 2008, 501 new cases were recorded, against 3,357 cases in 2007, representing about an 85% reduction. A number of interventions in the previous two years had been pursued, including monitoring dams and other sources of drinking water in endemic communities to ensure infected people did not contaminate the water sources. Additionally, filters and other water treatment equipment were provided at both water pumping sites and homes to treat water before drinking. This is all due to the efforts of the National Guinea Worm Eradication Program, funded by the WHO, UNICEF, the Japanese International Cooperation Agency, and the European Union.
Guinea worm disease has been eradicated from India. Rajasthan was severely affected by dracunculiasis, especially southern Rajasthan (Dungarpur, Banswara and Udaipur districts), and was hyperendemic about two decades ago. The alarming status of the guinea worm led to the launching of the SWACH project by the government in 1986. This project assured proper sanitation and supply of clean and hygienic potable water to the residents of endemic areas and, as expected, it was a huge success. Owing to the success of the SWACH project, a decade later, the State Government declared Rajasthan rid of Dracunculus. But, every species struggles for its existence, and so did Dracunculus. In 2002 and 2003, two cases of dracunculiasis were reported from Dungarpur and Banswara districts.
There is no vaccine or medicine to treat or prevent Guinea worm disease. Once a Guinea worm begins emerging, the first step is to do a controlled submersion of the affected area in a bucket of water. This causes the worm to discharge many of its larva, making it less infectious. The water is then discarded on the ground far away from any water source. Submersion results in subjective relief of the burning sensation and makes subsequent extraction of the worm easier. To extract the worm, a person must wrap the live worm around a piece of gauze or a stick. The process can be long, taking anywhere from hours to a week. Gently massaging the area around the blister can help loosen the worm up a bit. This is nearly the same treatment that is noted in the famous ancient Egyptian medical text, the Ebers papyrus from 1550 BC. Some people have said that extracting a Guinea worm feels like the afflicted area is on fire. However, if the infection is identified before an ulcer forms, the worm can also be surgically removed by a trained doctor in a medical facility.
Although Guinea worm disease is usually not fatal, the wound where the worm emerges could develop a secondary bacterial infection such as tetanus, which may be life-threatening—a concern in endemic areas where there is typically limited or no access to health care. Analgesics can be used to help reduce swelling and pain and antibiotic ointments can help prevent secondary infections at the wound site. At least in the Northern region of Ghana, the Guinea worm team found that antibiotic ointment on the wound site caused the wound to heal too well and too quickly making it more difficult to extract the worm and more likely that pulling would break the worm. The local team preferred to use something called "Tamale oil" (after the regional capital) which lubricated the worm and aided its extraction. As a practical matter, many patients were also given prophylactic oral antibiotics.
It is of great importance not to break the worm when pulling it out. Broken worms have a tendency to putrefy or petrify. Putrefaction leads to the skin sloughing off around the worm. Petrification is a problem if the worm is in a joint or wrapped around a vein or other important area.
In 1986, there were an estimated 3.5 million cases of Guinea worm in 20 endemic nations in Asia and Africa. Ghana alone reported 180,000 cases in 1989. The number of cases has since been reduced by more than 99.98% to 542 in 2012—in the four remaining endemic nations of Africa: South Sudan, Chad, Mali and Ethiopia. This is the lowest number of cases since the eradication campaign began. As of 2010, however, the WHO predicted it will be "a few years yet" before eradication is achieved, on the basis that it took 6–12 years for the countries that have so far eliminated Guinea worm transmission to do so after reporting a similar number of cases to that reported in southern Sudan (now South Sudan) in 2009.
The World Health Organization is the international body that certifies whether a disease has been eliminated from a country or eradicated from the world. The Carter Center also reports the status of the Guinea worm eradication program by country.
Endemic countries must report to the International Commission for the Certification of Dracunculiasis Eradication and document the absence of indigenous cases of Guinea worm disease for at least three consecutive years to be certified as Guinea worm-free by the World Health Organization.
The results of this certification scheme have been remarkable: by 2007, Benin, Burkina Faso, Chad, Côte d'Ivoire, Kenya, Mauritania, Togo, and Uganda had stopped transmission, and Cameroon, Central African Republic, India, Pakistan, Senegal, Yemen were WHO certified.
At the end of 2012, South Sudan, Mali, Ethiopia and Chad still had endemic transmission. The major focus is South Sudan (independent after 2011, formerly the southern region of Sudan), which reported 96% of all cases in 2012.
Sudan increased its efforts at eradication from 2005 when the Comprehensive Peace Agreement was signed, ending a more than two-decade long civil war. 2006 saw an increase to 15,539 cases of Guinea Worm disease, from 5,569 cases in 2005, as a result of reporting from endemic areas that were no longer war-torn. The Southern Sudan Guinea Worm Eradication Program (SSGWEP) has deployed over 28,000 village volunteers, supervisors and other health staff to work on the program full-time. The SSGWEP was able to slash the number of cases reported in 2006 by 63% to 5,815 cases in 2007. Since 2011, at the time that South Sudan became independent, its northern neighbor Sudan had reported no endemic cases of dracunculiasis .
Four of Mali's regions—(Kayes, Koulikoro, Ségou, and Sikasso)—have eliminated dracunculiasis, while the disease is still endemic in the country's other four regions (Gao, Kidal, Mopti, and Timbuktu). Late detection of two outbreaks, due to inadequate surveillance resulted in a meager 36% containment rate in Mali in 2007. 2008 and 2009 were more successful, however, with containment rates of 85% and 73% respectively. The civil war prevented accurate information from being gathered in northern Mali in 2012.
Prior to March 2008, there had been no cases reported in Ethiopia since June 2006.
Before 2010, Chad had not reported any indigenous cases of guinea worm in over 10 years.
In Ghana, after a decade of frustration and stagnation, in 2006 a decisive turnaround was achieved. Multiple changes can be attributed to the improved containment and lower incidence of dracunculiasis: better supervision and accountability, active oversight of patients daily by paid staff, and an intensified public awareness campaign. After Jimmy Carter's visit to Ghana in August 2006, the government of Ghana declared Guinea worm disease to be a public health emergency. The overall rate of contained cases has increased in Ghana from 60% in 2005, to 75% in 2006, 84% in 2007, 85% in 2008, 93% in 2009, and 100% in 2010.
to March 2014
Ghana appears to have eradicated guinea worm. In August 2011, their public health officials reported that Ghana was free of reported cases for over 14 months. While promising, given the incubation period, it will be some time before the WHO certifies Ghana as free of this disease.
To the end of June 2011 the number of cases were: Chad 2 cases; Ethiopia 6 cases; Mali 3 cases: and South Sudan 806 cases. After South Sudan separated from Northern Sudan, Northern Sudan has been free of guinea worm disease for several years and it has been certified free of this disease by the WHO.
To the end of August 2011 the number of cases reported were: Chad 7 cases; Ethiopia 8 cases; Mali 9 cases: and South Sudan 944 cases. These occurred in 440 villages. One possible case has been reported from India: investigation into this is ongoing. India has been certified free since 2000 and it is suspected that this possible case may be an imported case. The majority of cases (78% of 944 total) in South Sudan were in Kapoeta East County, (561 cases), and Kapoeta North County, (146 cases). These adjacent counties are in the state of Eastern Equatoria. Aside from 2 cases imported from South Sudan, no cases were reported in Ethiopia in July and August from the single focus (Gog District) from which all cases in the last few years have been found. Although transmission in Ethiopia may have been interrupted, official confirmation will not be forthcoming for several months.
Up to September 2011 the number of uncontained cases were: South Sudan—241; Chad—6; Mali—6; Ethiopia—1. Of the 70 counties in South Sudan, 56 (80%) are considered free of dracunculiasis.
The total number of reported cases in 2011 was 1060. Of these 1030 were: South Sudan 1030. Mali 12; Chad 10; and Ethiopia 8. The cases in Chad were part of an outbreak that was originally identified in 2010 as part of a pre-certification process. Chad had not reported any cases between 2001 and 2009. Two of the cases in Ethiopia were imported from South Sudan.
According to the WHO the number of reported cases of dracunculiasis has continued to drop to 143 cases between 1 January and 30 April 2012 compared with 382 cases during the same period in 2011. South Sudan alone reported 142 cases, or 99% of the global total, and Ethiopia reported 1 case.
The July 16 report from the WHO Collaborating Center for Research, Training and Eradication of Dracunculiasis states that the number of reported cases between 1 January and 30 June 2012 has dropped to 391 from 807 cases in the same period in 2011—a 52% improvement. By country the number of reported cases are South Sudan 387, Ethiopia 2, Mali 1 and Chad 1. In the same period of 2011 the number of reported cases were South Sudan 794, Ethiopia 8, Mali 3 and Chad 2.
The September 12 report from the WHO Collaborating Center for Research, Training and Eradication of Dracunculiasis states that the number of reported cases between 1 January and 31 August 2012 has dropped to 484 from 944 cases in the same period in 2011—a 49% improvement. By country the number of reported cases are South Sudan 494, Ethiopia 3, Mali 4 and Chad 7. In the same period of 2011 the number of reported cases were South Sudan 944, Ethiopia 6, Mali 9 and Chad 8. However, since March 2012, Mali’s Guinea Worm Eradication Program workers have had limited access to the rebel–held regions in northern Mali, and are not able to investigate cases there. Médecins du Monde have reported rumours of a further 5 unconfirmed cases in northern Mali since March.
The October 18 report from the WHO Collaborating Center for Research, Training and Eradication of Dracunculiasis states that the number of reported cases between 1 January and 30 September 2012 has dropped to 521 from 1004 cases in the same period in 2011—a 48% improvement. By country the number of reported cases are South Sudan 502, Ethiopia 3, Mali 7 and Chad 9. In the same period of 2011 the number of reported cases were South Sudan 980, Ethiopia 6, Mali 10 and Chad 8. Again, Mali’s Guinea Worm Eradication Program workers have limited access to northern Mali, and are not able to investigate or confirm all cases there.
The provisional figures for all of 2012 are: total 542; South Sudan 521; Chad 10; Mali 7; and Ethiopia 4. This is a 49% improvement of the total compared to 2011.
Up to the end of March, six cases have been reported, all in South Sudan, compared to 61 cases in 2012 in the same period—a 90% reduction in cases. The February WHO report goes on to say after recording no new cases in January "This is not the end of Guinea worm disease—there will be cases later in 2013—but we can see the end from here." The report also compares the 521 cases in South Sudan in 2012 (out of 542 globally) with Ghana's 501 cases in 2008, and says it took 18 more months to subsequently eliminate dracunculiasis from Ghana, with the last case in May 2010.
By 22 April, three cases have been confirmed in Chad. After 10 years without any reported cases the reporting of 10 cases in each of 2010, 2011 and 2012 is a very unusual pattern. There are concerns that surveillance vigilance has decreased, and renewed efforts are being made to increase monitoring. This includes coordinating monitoring with its neighbors Nigeria and Cameroon.
By the end of May, 67 cases had been reported—55 in South Sudan, 4 in Chad, 3 in Mali and 5 in Ethiopia.
By the end of June, 89 cases have been reported—74 in South Sudan, 5 in Chad, 4 in Mali and 6 in Ethiopia. No further cases have been reported to 2 July. In the same period of 2012, 391 cases were reported—all but 4 from South Sudan—a 77% reduction.
By the end of August, 115 cases have been reported—97 in South Sudan, 8 in Chad, 4 in Mali and 6 in Ethiopia. In the same period of 2012, 484 cases were reported—a 76% improvement. Sixty five of these cases were confined. Chad failed to contain 1 case; both Ethiopia and Mali failed to contain 3; the other uncontained cases were in South Sudan.
By the end of September, 128 cases have been reported—108 in South Sudan, 9 in Chad, 5 in Mali and 6 in Ethiopia. In the same period of 2012, 520 cases were reported—a 75% improvement.
By the end of November, 144 cases have been reported—115 in South Sudan, 11 in Chad, 11 in Mali and 7 in Ethiopia. In the same period of 2012, 540 cases were reported—a 72% improvement.
The preliminary complete year figures for 2013 are 148: 113 in South Sudan, 14 in Chad, 11 in Mali and 7 in Ethiopia and 3 (none yet confirmed) in Sudan. In 2012 542 cases were reported—a 73% improvement. Due to civil insecurity in South Sudan monitoring was suspended in parts of the country on 15 December - however, as no new cases were reported since October, it seems likely that the 113 figure for South Sudan is correct, but still very provisional.
As of 28 February 2014 three cases of dracunculiasis have been detected (two in Chad and one in South Sudan).
The pain caused by the worm's emergence—which typically occurs during planting and harvesting seasons—prevents many people from working or attending school for as long as three months. In heavily burdened agricultural villages fewer people are able to tend their fields or livestock, resulting in food shortages and lower earnings. A study in southeastern Nigeria, for example, found that rice farmers in a small area lost US$20 million in just one year due to outbreaks of Guinea worm disease.
Dracunculiasis has been a recognized disease for thousands of years:
The Russian scientist Alexei Pavlovich Fedchenko (1844–1873) during the 1860s while living in Samarkand was provided with a number of specimens of the worm by a local doctor which he kept in water. While examining the worms Fedchenko noted the presence of water fleas with embryos of the guinea worm within them.
In modern times, the first to describe dracunculiasis and its pathogenesis was the Bulgarian physician Hristo Stambolski, during his exile in Yemen (1877–1878). His theory was that the cause was infected water which people were drinking.
In 1984, the World Health Organization (WHO) asked the Centers for Disease Control and Prevention (CDC) to spearhead the effort of its eradication, an effort that was further supported by the Carter Center. Major progress has been made; in 1985, 3.5 million cases were still reported annually, but by 2008, the number had dropped to 5,000. This number further dropped to 1060 in 2011 and a mere 5 cases reported in the first few months of 2012.
Dracunculiasis once plagued a wide band of tropical countries in Africa and Asia. Its Latin name, Dracunculus medinensis ("little dragon from Medina"), derives from its one-time high incidence in the city of Medina, and its common name, Guinea worm, is due to a similar past high incidence along the Guinea coast of West Africa; both of these locations are now free of Guinea worm. In the 18th century, Swedish naturalist Carl Linnaeus identified D. medinensis in merchants who traded along the Gulf of Guinea (West African Coast), hence the name Guinea worm.