Guinea Worm Eradication: Only 13 Human Cases in 2022, but Dogs Remain a Challenge

Only 13 human cases of Guinea worm disease were found worldwide in 2022, the lowest yearly total ever, and for an unprecedented six months, November 2022 to April 2023, there were none at all. But the parasite now infects far more animals than people: 686 animal infections were reported in 2022, 606 of them in Chad.

The disease

Dracunculiasis, or Guinea worm disease, is caused by the parasite Dracunculus medinensis. People catch it by drinking water containing tiny crustaceans (copepods, or water fleas) infected with its larvae, and possibly by eating undercooked fish or other aquatic animals. About a year later the worm emerges through the skin, usually of the lower leg, causing pain and disability. There is no vaccine or medicine. Eradication relies on containing cases so worms cannot contaminate water, health education, filtering water, treating it with the larvicide temephos, providing safe drinking water, cooking aquatic animals properly and burying fish guts.

The campaign

CDC began working to eradicate the disease in 1980 and in 1984 became WHO's technical monitor for the effort. In 1986, with an estimated 3.5 million cases a year in 20 African and Asian countries, the World Health Assembly called for its elimination. The Guinea Worm Eradication Program, led by The Carter Center with WHO, UNICEF and CDC, has helped health ministries ever since. WHO has certified 200 countries, areas and territories free of the disease; five countries where it remains endemic (Angola, Chad, Ethiopia, Mali and South Sudan) and Sudan have not been certified.

Since 2012, infections in animals, mostly domestic dogs, some cats, and a few baboons in Ethiopia, have become the main challenge; genetic studies confirm they carry the same parasite as people. Village volunteers under active surveillance report cases monthly; CDC's laboratory confirms specimens; and WHO certifies a country after three years of adequate nationwide surveillance with no local human or animal infections.

The numbers

Investigators found the likely source of 11 of the 13 human cases in 2022, against seven of 15 in 2021. In the first half of 2023 only one of 15 human specimens sent to CDC was confirmed, while 114 of 131 animal specimens were.

Country by country

• Chad reported seven human cases in 2022 and 606 animal infections (521 dogs, 85 cats), down from 832 in 2021; dog infections fell for the third and fourth years in a row. Transmission there is thought to come mostly from eating undercooked fish and other aquatic animals. Village surveillance covered 2,434 villages by December 2022, and rumours of possible cases rose 169% to 110,784 in early 2023. Rewards are about US$100 for a human case and US$20 for an animal; about 81% of monitored households bury fish guts; 64% and then 75% of eligible dogs were tethered; temephos reached 94% of 280 affected villages by December 2022; and 40% of villages with infections had at least one copepod-free water source, such as a borehole.
• Cameroon reported 28 infected dogs in 2022, and one human case and 56 dogs in early 2023, in villages within 3 miles (5 km) of the Chad border, probably infected in Chad, where families live on both sides and take their dogs.
• Angola, which first found cases in 2018, detected seven infected dogs in 2022 and 32 in early 2023, all in one province, and began tethering dogs and using temephos in 2023; it offers about US$450 for a report.
• Ethiopia reported one human case, two baboons and one dog in 2022, and none in early 2023, almost all in the Gog district of Gambella, the only place infected baboons have been found. Trapping of roughly 555 baboons since 2018 and examination of dead ones found 20 infected in 2013–2021 and two in 2022. About 1,900 dogs and cats are tethered, water sources are treated monthly, and satellite imagery from Maxar Technologies has helped find new water sources to treat since 2022.
• Mali had no human cases from January 2022 to June 2023, but 41 infected animals in 2022, many in Mopti Region, partly cut off by civil unrest. It watches 2,216 villages and introduced dog tethering in 2021, extended to puppies in 2023.
• South Sudan reported five human cases in 2022 and none since, with only two infected dogs ever recorded. Mobile cattle herders and sporadic insecurity make surveillance hard; 2,044 villages are under watch, and with security it could soon reach zero cases.

Dogs: the main challenge

From January 2022 to June 2023, Chad accounted for 835 of the world's 1,017 infections, and dogs for 893 of them, mostly along the Chari River, in a pattern of many infected dogs and few people unique to Chad. Worldwide, dog infections fell 24% from 2021 to 2022; a small rise in early 2023 reflected new surveillance in Angola and Cameroon. Proactive tethering of dogs in at-risk villages, pioneered by Ethiopia in 2018, has proven effective and spread to Chad (2020), Mali (2022), Cameroon (2022) and Angola (2023), and research is under way on new interventions.

What remains

Leaders of seven current or former endemic countries, the United Arab Emirates, The Carter Center and WHO renewed their commitment at a Guinea Worm Summit in Abu Dhabi in March 2022. A human case in the Central African Republic, near dog infections in Chad, shows the risk of spread across borders. In Mali, a Peace-Health Initiative with local leaders works to reduce insecurity in affected districts.

Infections may be undercounted where they are undiscovered, hidden or out of reach because of insecurity, though cash rewards, widely known, and trained local surveillance help. With just 13 human cases in 2022, eradication appears close; the biggest obstacles are infections in dogs and civil unrest and insecurity in parts of Mali and South Sudan.

Sources

• Hopkins DR, Weiss AJ, Yerian S, Sapp SGH, Cama VA. "Progress Toward Eradication of Dracunculiasis — Worldwide, January 2022–June 2023," MMWR. https://www.cdc.gov/mmwr/volumes/72/wr/mm7245a4.htm