Guinea Worm: Modern efforts to eradicate an ancient parasite
This was written for a course in population health.
There are three animals whose common names start with ‘guinea’. Two of them I kept as a child, while the third is a universally despised parasitic worm targeted for planned extinction. Four decades of eradication efforts have brought the Guinea worm to the brink of extinction, from an estimated 3.5 million cases in 1986 to just 54 in 20191.
Guinea worm, dracunculus medinesis, is a parasitic nematode that begins life in stagnant water. It transits through copepod crustaceans of the genus cyclops (water fleas) which are then unknowingly ingested by humans in their drinking water2. The fleas dissolve in gastric acid, leaving the worm larvae to develop in the stomach over the next 90 days3. After using the human body as a love hotel, male worms die and leave their sweethearts to crawl through muscle tissue over the next few months4. Preferring to make her debut through the lower limbs, the lady Guinea worm (by now a meter long) releases some embryos beneath the skin5. This causes a burning, itchy allergic reaction in the form of an ulcer filled with pus and larvae, demanding attention like a quinceañera dress5. When the blister bursts and the victim rubs it with water, the worm greets the world by poking her posterior through the ulcer and releasing more embryos into the water, seeking to complete the cycle4.
Dracunculiasis is the disease caused by parasitic Guinea worm infection3. Terrible itchiness occurs as the worm makes its way to the skin; nausea, vomiting, diarrhoea and fever follow soon after it emerges6. Not only is the blister agonising, it can also lead to secondary infection, permanent disability and fatal tetanus or septicaemia6. Over the 30-60 days it takes for the worm to fully emerge, all that can be done is gradually pull it out by winding it around a stick, while debilitating pain prevents people from walking until the worm is completely removed6. Worms that remain or otherwise die inside the body can calcify, cause arthritis if they end up in joints, or paralysis if they end up in the spinal cord5,7. There is no cure or vaccination, and infection does not confer immunity3.
Since transmission depends on water availability, dracunculiasis is a seasonal condition3. In wet regions, transmission is most likely at the end of the dry season when cyclops concentration in remaining surface water is highest. Conversely, arid regions experience greater transmission during the wet season, where more surface water is available.
Seasonal onset of symptoms often coincides with harvest time, causing community-wide labour shortages to such an extent that the Dogon people of Mali call dracunculiasis “the disease of the empty granary”4. A 1989 study in the Nigerian state of Imo found dracunculiasis caused severe individual disability for about one month during the peak harvest and preparation season for rice and yam crops8. A 1988 UNICEF working paper concerning a similar region of Nigeria motivated eradication efforts by estimating a return of US$20 million in additional annual profit from rice crops alone9.
Guinea worm is more than just a detriment to agriculture. Ilegbodu’s 1986 study of 1495 Nigerian pupils found that 21% of students were infected, and those who were infected missed up to 25% of the school year – ten times more than their classmates10. Infected mothers are less able to care for their families, with a Sudanese survey finding that “children were three times more likely to be malnourished if more than half the adult [household] members had suffered from the GWD [dracunculiasis] in the previous year.”11
Ultimately, dracunculiasis is a rural disease. Rural communities are more likely to drink from unimproved water sources that harbour cyclops. They rely on their feet for transport, to tend crops, and walk to distant schools. Dracunculiasis remained a neglected disease until the 1980s, affecting people at the edge of development who were out of sight from urban hubs12. It hits poor people the hardest, perpetuating poverty.
The Guinea worm has been known since ancient times, with some records dating back 4500 years12. Historically it covered Africa, the Middle East, Pakistan, India, Brazil, Uzbekistan and the West Indies (through the African slave trade)4,13,14. Sister species of Dracunculus continue to plague animals across the planet except in the Australia-Pacific region4. The Guinea worm makes a guest appearance in the Hebrew Book of Numbers (21:4-8) as a “fiery serpent” to be set upon a pole15. The modern Western medical profession employs the Guinea worm as a mascot, to the extent that the Rod of Asclepius may have originally been a depiction of extraction by winding it around a stick16.
Russian naturalist Alexei Fedchenko was the first to identify microscopic crustaceans as the intermediate host of Guinea worm in 1870, and that drinking them serves as the infection route14. Heartthrob of helminthology Robert Leiper launched his career with an expedition to Ghana in 1905, where he confirmed Fedchenko’s results regarding Guinea worm and further developed an understanding of the parasite’s lifecycle – particularly, that the microcrustacean intermediate host must dissolve in stomach acid17,18. Another observation that would become crucial during tail-end eradication efforts over a century later, was of Guinea worm infection in both wild and domesticated animals19.
Leiper suggested simple and inexpensive control measures such as avoiding contaminated water; building water access infrastructure such as wells that prevent contamination; killing copepods during transmission season (steam was one such method); and introducing fish that would eat copepods, as he observed lack of disease where fish were living in the water source12. Leiper’s career quickly took him to loftier heights such as hookworm research, six years of tapeworm self-infection – he referred to the worm as his dining companion – and founding the Journal of Helminthology20.
Most Guinea worm intervention programs trace their methods back to Leiper’s recommendations. The USSR, in a region concerning modern-day Uzbekistan, eliminated dracunculiasis by 1931 through water management21. They also shot dogs suspected of harbouring the worm (as they did during the liquidation phase of the Chernobyl disaster – the Soviets didn’t hesitate to shoot dogs)22. In some regions, eradication has come as a coincidence. Iran treated water storage cisterns with insecticide, which eliminated dracunculiasis but not malaria as originally intended12. Through the widespread introduction of piped water and other improvements in living conditions, Saudi Arabia stopped seeing cases by the 1970s23. Global Guinea worm eradication efforts were initiated by the U.S. Centers for Disease Control and Prevention in 1980. The World Health Assembly adopted its first eradication resolution in 1986, with the Carter Center coordinating implementation with national Ministries of Health24. With no vaccine or cure, there are three varieties of intervention: health education, management of drinking water, and case management.
Water filtration is highly effective, as adult cyclops are about 1mm in length and can easily be filtered out with a cloth; nylon or polyester fabric becomes clogged less quickly than cotton4. Filtration cloth needs to be washed and will eventually wear out, so a continual supply is required4. Where cost is a concern, smaller amounts of cloth can be economically paired with a plastic tube to create a “straw” filter, which has the added benefit of portability for those who drink where they please, such as field workers25.
While some equipment is required, filtration is primarily about health education and behaviour change. Bernhard Bierlich’s anthropological study found that people in Northern Ghana were pragmatic and willing to try filters, but were inconvenienced by the time it took for muddy water to settle (lest the cloth become quickly clogged)26. Furthermore, the senior woman of the household was often seen to ‘own’ the filter, which meant that it might not be used if she was busy elsewhere – and that winning her cooperation would be crucial for the success of education interventions. Nevertheless, filtration came to be viewed so favourably that households in Northern Ghana do it even when Guinea worm infection isn’t their main concern27.
As a matter of behaviour change, stopping people from washing their wounds in drinking water sources also breaks the cycle of transmission. Although this message was initially considered of secondary importance to other measures, the Sudanese province of Bahr el Ghazal saw an 88% reduction of cases between 1998 and 1999 as the result of 4,304 village health education sessions promoting the message4.
Another anthropologist, William Brieger investigated folk understandings of health and attitudes toward Guinea worm disease. The Ghanaian community he studied saw the Guinea worm as a part of the body, an inevitable aspect of the human condition much like the common cold, to be endured but not cured28. It was a common affliction that caused little concern, but was attributed as a condition of one’s blood being “sweet” as opposed to “bitter”. The community did not suspect it was transmitted through drinking water, but more generally, that health and safety were conferred by one’s home and that straying too far from the protection of home was a risk factor for any aspect of health. Brieger concluded that contemporary health education efforts were over-simplistic and ought to make more of an effort to respect and incorporate existing perceptions of health28.
Provision of clean water is a major UN development goal that provides a host of benefits beyond Guinea worm eradication29. In the context of dracunculiasis, all that’s needed is to supply water from a source free of cyclops. Wells and piped water infrastructure both provide this, but must be maintained and may not be feasible to install in every tiny village or hamlet30. Improved water infrastructure needs to be convenient, as people will prefer surface water if it’s significantly closer than a well or a tap. It also needs to be ubiquitous if migratory populations are to use it, and together with filters must be used exclusively (no opportunistic sipping from puddles)4.
Chemical treatment of step wells with organic insecticides such as Temephos was successfully employed in step wells across India, Pakistan and Cameroon4. In the African context, it’s difficult to correctly estimate dosage for irregularly shaped ponds and dams, even more so with rain and evaporation4. Overall, insecticide is too labour intensive to be used widely, but did play a role in Uganda and may be useful for end-game eradication in the worm’s dwindling strongholds4,31.
Surgical removal of the worm just before it emerges has several benefits. It prevents both pain and disability from natural emergence, and the contamination of water sources. In the experience of Indian ayurvedic practitioner B. L. Sharma, patients would travel great distances for the extraction, representing a huge win for case detection and containment32. In practice, it’s difficult to widely maintain a high quality of surgical service and sterility in the field. Palliative treatments such as bandaging, controlled immersion in water that won’t be drunk later and wound management still provide enough benefit and incentive to self-report cases early4. Case containment, similar to inpatient admission for the duration of worm removal, is more expensive and of dubious effectiveness but may have a role to play during end-game eradication4.
At a high level, the Carter Center reports that case numbers have dropped 99.99% from 3.5 million in 1986, to 54 provisional cases in 20191. 17 countries have eradicated the disease, leaving only South Sudan, Mali, Chad, Ethiopia and Angola1. An estimated 80 million cases have been averted, at an estimated cost of US$432m through to 202033. This is a fantastic outcome, highlighting the strengths of a coordinated campaign between national health ministries (who are well positioned to provide appropriate, localised implementations), United Nations health and development organisations, and NGOs such as the Carter Center4. A great deal of advocacy and cat-herding has gone into the coordination effort, but there’s no evidence of opposition to eradication. Everyone hates the Guinea worm.
However, the eradication program has seen setbacks and is still not finished. Eradication target dates have been pushed back from 1995, to 2009, to 2015, and now 203033. The first two dates were overambitious targets and insufficient funding by national governments caused them to slip. The 2015 date was missed due to instability from armed conflict and newly observed infection of domestic and wild animals33. Animal transmission shouldn’t come as a surprise given the Soviet experience and Leiper’s observations from a hundred years prior, and may represent an unfortunate oversight. Long-tail eradication efforts are now targeting transmission in animals, as well as behaviours such as burying of fish entrails suspected of acting as a transmission vector for dogs2. Leiper’s suggestion of introducing predatory fish into water bodies seems to have been neglected and may prove instrumental in reducing cases in wild animals. Fitzpatrick’s 2017 estimates show that even with extra funding needed as a result of setbacks, eradication remains clearly more cost-effective than control through 203033. Eradication represents good value if it prevents enough cases before the WHO target of universal water access is met (in which case eradication comes for free)29.
The parasite’s lifecycle has proven vulnerable to a variety of inexpensive interventions – none a silver bullet, each with its own benefits and drawbacks. The Guinea worm may move easily through muscle tissue, but she is no match against an almost-impenetrable stack of ‘Swiss cheese’ interventions pitted against her31; her days are numbered.
Copyright © Mitchell Jeffrey 2024