Guinea Worm Eradication in Ethiopia Predicted Close at Hand

Daniel M. Keller, PhD

July 09, 2012

July 9, 2012 (Bangkok, Thailand) — Although it missed its 2009 target date for eradication, Ethiopia has made great strides in the past 2 decades toward eliminating guinea worm infection.

However, Gole Yembo, MPH, from the field epidemiology and laboratory training program at Addis Ababa University in Ethiopia, told delegates here at the 15th International Congress on Infectious Diseases that constant vigilance is needed to prevent the reestablishment of the disease because of missed cases.

Guinea worm disease is transmitted in drinking water containing "water fleas" (copepods) that harbor the larvae of Dracunculus medinensis, a nematode that develops in the subcutaneous tissue of mammals. The adult worm (60 to 100 cm) eventually emerges through a blister on the skin, causing a painful burning sensation. It is removed using mechanical extraction. Secondary bacterial infection of the site is not uncommon.

The disease inflicts disability and social and financial burdens on affected communities. Because there is no medication or vaccine to eliminate guinea worm, control of the disease depends on not ingesting contaminated water, treating water sources with larvicides, and preventing people with emerging adult worms from entering water sources used for drinking so that adult female worms do not release more larvae into the water.

Since a global campaign to eliminate the disease was begun in 1986, the number of cases has decreased from 3.5 million to 1058 in 2011. TThe 2009 target date for eradication has passed, but obviously, significant progress has been made. Disease transmission is currently limited to 4 countries in Africa — South Sudan, Mali, Chad, and Ethiopia, Yembo reported.

Disease Remains Endemic in Ethiopia After 17-Year Campaign

Ethiopia has had a program of active surveillance and intervention since 1994. At that time, guinea worm disease affected 7 districts in 2 states in the southwestern part of the country.

Because surveillance is necessary to detect and contain all cases, and therefore stop transmission, the researchers analyzed Ministry of Health surveillance data from 1994 to 2011 to better understand the epidemiology of the disease, follow the progress of eradication, and determine what impediments were slowing eradication. Of the 3521 cases (196 per year), they found that 2.7% were imported from South Sudan. Equal numbers of males and females were affected.

Although there is year-round transmission of guinea worm, the incidence in the study period peaked from April to July (when 2488 of 3521 cases were reported). The incidence rate decreased from 2.34 cases per 100,000 in 1994 to 0.01 cases per 100,000 in 2011. In 1994, there was only a 37% rate of case containment (463 of 1252 cases); by 2011, the rate was 88% (7 of 8 cases). During that period, the number of villages with endemic guinea worm disease decreased from 99 to 5.

For a case to be considered contained, it had to be detected before the emergence of the worm through the skin.

Disease-Control Measures

The greatest decrease in cases occurred in the first 6 years of the eradication program. In 1994, after water filters were introduced, health-education sessions were conducted, and cases were contained, disease incidence decreased from 1252 cases in 1994 to 514 cases the next year. After targeting the water supply and providing cash rewards for the identification of cases in 1996, the number of cases decreased to 371. However, that number rose a bit in 1997. Using vector control and a containment center, the number dropped to 59 in 2000, and has remained below that level in all subsequent years.

The trend in the number of villages reporting cases followed a similar pattern — from 2 states with larger areas of focus to 1 state with a much smaller area of focus.

In 2008/09, there was an outbreak of 41 cases, with about 61% of those in females. Four of the cases were imported. Yembo said that local transmission resumed, and guinea worm disease in Ethiopia again became endemic. An unusually high number of cases occurred in 2010, and only returned to yearly single digits in 2011.

In summary, Yembo said that Ethiopia has reported fewer than 50 cases each year since 2001, although low-level transmission remains uncontrolled. Cases now come from the remotest villages, which are inaccessible during seasons of heavy rain. In addition, periodic political instability results in migrants, especially from South Sudan, coming into Ethiopia, which "presents a challenge for eradication" of guinea worm, he said. In addition to the outbreak in Ethiopia in 2008, Chad experienced an outbreak in 2010.

Therefore, Yembo warned that after 10 years of interruption of the disease, "the disease came back... This [highlights] the corresponding need for vigilance to prevent restarting local transmission due to missed cases or incompletely controlled cases. Although the number of imported cases and transmission have decreased significantly, the struggle toward total elimination of the disease remains a challenge."

Despite the challenge, session moderator Teshome Gebre, PhD, regional representative for Africa on the Task Force for Global Health, International Trachoma Initiative, in Addis Ababa, told Medscape Medical News that he is optimistic that guinea worm transmission can be stopped. Dr.Gebreformerly worked on guinea worm eradication, but was not involved in the study or in recent phases ofthe guinea worm eradication program.

"I think it's an eradicable disease, definitely, because earlier on we had about 21 countries that were endemic over the years," he said. Three were in Asia, leaving 18 African countries with endemic guinea worm disease; that number has now been reduced to 4.

Dr. Gebre said that after 20 straight months of no cases in Ethiopia, the disease returned in 2008. "But now, things look very well under control, and I believe in the coming 1 or 2 years, Ethiopia will be free from guinea worm disease. Also, South Sudan, especially, is really doing very well," he said. "I believe very soon we'll get rid of guinea worm from that part of the world, and eventually from all over Africa."

He said the original target date for Ethiopia to be free of transmission was December 1995, but conflicts, wars, and political instability in endemic countries and regions delayed the program. "We believe it's just delayed, not denied. Definitely eradication will be achieved; it's more evident now than ever before," Dr. Gebre said.

According to Dr. Gebre, President Jimmy Carter has been a leading force in the eradication program. "Without his leadership, without his active involvement in this program, I believe this wouldn't have been achieved," he said.

Dr. Gebre also credits a host of international partners, such as UNICEF, the US Centers for Disease Control and Prevention, the World Health Organization, and other nongovernmental organizations. "Guinea worm sets an example" for how international partners can collaborate to eliminate other neglected tropical diseases, Dr. Gebre explained.

He cautioned that once the disease is considered eradicated, surveillance must continue uninterrupted. "But the difference is whether it is active or passive surveillance," he said. Active surveillance involves people going from house to house and from village to village in search of active cases when cases have been reported in an area. If no cases have been reported, health workers will stay vigilant for any case that shows up in the clinic. This passive surveillance usually continues for 36 consecutive months after the last case, Dr. Gebre said. After 36 months without a case, an area can be certified as free of guinea worm transmission.

Mr. Yembo and Dr. Gebre have disclosed no relevant financial relationships.

15th International Congress on Infectious Diseases (ICID): Abstract 21.001. Presented June 15, 2012.