12 diciembre, 2021

Dracunculiasis — Guinea Worm Disease — Is Close to Eradication. But Will We Ever Reach the Finish Line?

When in 1988 former US President Jimmy Carter toured Denchira and Elevanyo, two villages near Accra, Ghana, he noticed a young woman who appeared to be cradling a baby. Carter approached her for a chat, but was stopped in his tracks by a disquieting sight.

“It was not a baby. It was her right breast, which was about a foot long, and it had a guinea worm coming out of its nipple,” Carter later recalled. During his tour of Ghana that year, Carter saw hundreds of people affected by the guinea worm, an infection known as dracunculiasis — a disease caused by the nematode parasite Dracunculus medinensis. It’s a condition that can cause fever, severe pain, and even permanent damage to affected limbs.

In the late 1980s the country reported as many as 180,000 cases of guinea worm disease per year. Across the globe, that number was a staggering 3.5 million. However, by 2020, the world was down to just 27 cases, all of them in Africa.

This enormous reduction in prevalence is a direct effect of campaigns by endemic countries assisted by organizations such as the Centers for Disease Control and Prevention, the World Health Organization (WHO), and the Carter Center (a not-for-profit founded in 1982 by Jimmy Carter), which have strived since the 1980s to eradicate dracunculiasis, hoping to make it the second human disease purposefully wiped off the face of Earth. (Smallpox was the first.)

Dr David Molyneux

“That’s an extraordinary public health achievement,” said David Molyneux, parasitologist at the Liverpool School of Tropical Medicine, in an interview with Medscape Medical News. Yet the eradication goal, currently set for 2030, seems unlikely to be met. What’s more, some experts argue that chasing eradication may be altogether a misguided idea.

Humanity has known dracunculiasis for millennia. Well-preserved specimens of Dracunculus medinensis were discovered in Egyptian mummies, while some researchers claim that the Old Testament’s “fiery serpents” that descended upon the Israelites near the Red Sea were in fact guinea worms, as the parasite was endemic to the area in the past. Even the serpent coiled around the staff of Asclepius, the god of medicine, might have been a guinea worm, according to some historians.

This would make sense considering how the disease is treated. When an adult worm emerges through the skin, a painful and crippling occurrence, it is wound up around a stick or a piece of gauze, a little at a time, to slowly draw it out of the skin. As the worm can be over 3 feet long, this procedure may take weeks. What you end up with is a stick with a long, snake-like animal coiled around it. Asclepius’s staff.

The first step in the infection is when a person drinks water contaminated with copepods, or water fleas, which contain the larvae of Dracunculus medinensis. Next, the larvae are freed in the stomach and start migrating through the body, looking to mate. The fertilized female worm is the one that causes the debilitating symptoms.

Adam Weiss, MPH

About a year after the initial infection, the pregnant female worm looks for exit points from the body, usually through legs or feet, ready to release new larvae. If the unlucky sufferer steps into a pond or a river, the immature larvae escape into the water, where they are eaten by water fleas. “People are fetching water to drink, and they walk into the water thinking they can get cleaner water not along the edge,” said Adam Weiss, director of the Carter Center’s Guinea Worm Eradication Program, in an interview with Medscape. The vicious cycle begins anew.

Dracunculiasis may not be a killer disease, but it is painful and disabling. A study on school attendance in Nigeria showed that in 1995, when guinea worm infection prevalence among schoolchildren was as high as 27.7%, it was responsible for almost all school absences. As the result of the infection, children were seen wandering and sitting around the village helplessly. If it was the parents who got infected, children stayed out of school to help around the home. The dracunculiasis’ impact on work and earning capacity is so profound, in fact, that in Mali the infliction is known as “the disease of the empty granary.”

When in 1986 the Carter Center took the reins of the global dracunculiasis eradication campaign, India was the only country with a national program to get rid of the disease. Yet, once other nations joined the struggle, the results rapidly became visible. By 1993, the American Journal of Tropical Medicine and Hygiene published a paper titled, “Dracunculiasis Eradication: Beginning of the End.” The cases plummeted from 3.5 million in 1986 to 221,000 in 1993 and 32,000 in 2003, then to a mere 22 cases in 2015. What worked was a combination of surveillance, education campaigns, safe water provision, and treating potentially contaminated water with a chemical called Abate, a potent larvicide.

Today, many endemic countries, from Chad and Ethiopia to Mali and South Sudan, follow similar procedures. First and foremost is the supply of clean drinking water. However, Weiss says, this is not a “silver bullet, given how people live.” Those who are semi-nomadic or otherwise take care of livestock often fetch water outside of the village, from ponds or rivers. This is why dracunculiasis eradication programs include handing out portable water filters, which can be worn around the neck.

But if you don’t know why you should filter water, in all likelihood you won’t do it — cloth filters distributed for home water purification sometimes ended up as decorations or sewn into wedding dresses. That’s why education is key, too. Poster campaigns, comic books, radio broadcasts, instructions by volunteers, even t-shirts with health messages slowly but surely did change behaviors.

Cash rewards for reporting cases of dracunculiasis, which can be as high as $100, also work well to boost surveillance systems. Once a case is identified, patients may be moved to a containment center, both to treat the wound and to prevent patients from spreading the disease. Local water sources, meanwhile, may be sprayed with Abate.

1995 was the first year set as a target date for the eradication of dracunculiasis. Yet the goal wasn’t met — even though the total number of cases did decline by 97%. Next goals followed: 2009, 2020, and now, finally, 2030. For well over a decade now the world has been down to a trickle of cases per year, but the numbers don’t seem to want to budge lower. Weiss calls it a “limbo period” — we are almost there, but not quite. The final push, it seems, may be the one that’s the most difficult, especially now that we have two further complications: increasing conflicts in some endemic areas and zoonotic transmission.

According to WHO, in places like the Democratic Republic of the Congo, Mali, South Sudan, and Sudan, insecurity “hinders eradication efforts.” Not only does this insecurity make it difficult for health workers to reach endemic areas, but wars and violence also displace people, pushing those infected with guinea worm to walk far distances in search of safety, and spreading the disease during their travels. Case containment and contact tracing become challenging. A recent study by Molyneux and his colleagues showed that in the 3 years since 2018, conflicts in the endemic areas have increased dramatically.

And then there are the animals. Up until 2012, eradication of guinea worm seemed fairly simple, at least from a biological perspective: stop infected humans from contaminating drinking water and the parasites won’t be able to continue their life cycle. But in 2012, news came from Chad that a significant number of local dogs were found infected with the Dracunculus medinensis parasite, the very same one that attacks humans. In 2020, close to 1600 dogs were reported to be infected with guinea worm, most of them in Chad. This left scientists scratching their heads: dracunculiasis was supposed to be a purely human infliction. How were the dogs getting infected? Did the parasite jump to a new species because we were so efficient at eliminating it from humans?

Créditos: Comité científico Covid

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