Canine Guinea Worm Infection Sparks Global Concern

June 27, 2018
Amanda Carrozza

Amanda Carrozza is a freelance writer and editor in New Jersey.

Once believed to be on the verge of global eradication, Guinea worms have infected hundreds of dogs in Chad.

Although rarely talked about today, in the 1980s the world was faced with a parasitic epidemic: Guinea worms were infecting 3.5 million people per year in 21 countries. By the middle of the decade, the problem became so prevalent that the Carter Center—a nonprofit founded by former President Jimmy Carter—joined forces with the Centers for Disease Control and Prevention (CDC) to formally target Guinea worm for global eradication. And the work paid off.

After decades of focused attention, the number of infected people dropped to just 30 in 2017 and was confined to 2 countries—Chad and Ethiopia. With such a drastic decrease in incidence, many experts, including the CDC and President Carter, were confident that eradication was within reach. It would have been only the second human disease in history, after smallpox, to be eradicated.

And then in 2012, the worms inexplicably began developing in dogs in Chad.

“An animal reservoir is the kiss of death for eradication,” Mark L. Eberhard, PhD, a CDC parasitologist, said.

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Caused by the parasite Dracunculus medinensis, the worms are transmitted to people who drink water infested with fleas that have eaten infected larvae. Once ingested, the larvae burrow through the host’s intestine and into the layer of tissue beneath the skin, where they mate. Although the male Guinea worm dies, the female worm can remain in the body for a year and grow to be 3 to 5 feet long. Eventually, the worms form a blister that erupts through the skin of the arms, legs, or chest.

Although rarely fatal, the infection is extremely painful and there is no treatment or vaccine to prevent it. Becoming infected does not grant immunity against future infections either. In fact, a host could become infected with multiple worms at once or within the same short time period.

Now faced with a spreading infection among dogs in Chad, scientists are at a loss for how so many dogs have become infected in recent years. By 2017, more than 750 canine cases had been reported. Although dogs cannot infect people directly, the worms from dogs can be carried into the ponds from which people drink.

Until scientists have a better grasp on the scope of the problem and how dogs are becoming infected, an attempt has been made to curb the spread of the worms by paying villagers to tether their infected dogs until all worms have been expressed. The reward of $20, plus a stout chain with two locks, is distributed at ceremonies held in weekly roadside markets to increase attention about the program. This incentive, coupled with the way people in Chad are taught to handle fish and infected dogs, has had some effect. In April 2017, the CDC stated that 37% fewer infections in dogs were reported in the first quarter. This marked the first time since 2012 that canine infections had experienced a decrease.