17 July 2018
This is part of a series of posts from our own Shane Hanlon’s disease ecology class that he’s currently teaching at the University of Pittsburgh Pymatuning Laboratory of Ecology. Students were asked to write popular science posts about (mostly) wildlife diseases. Check out all the posts here.
By Elizabeth Morris
The end of the guinea worm’s life cycle looks like a scene from a horror movie: a thin, slimy creature emerging from lesions on the legs of the infected. The worm must be spun around a small stick to be pulled out 1-3 cm a day. This process can last for weeks, as guinea worms are around 70-120 cm in length. Even though the worm will be killed when it is pulled out, thousands of its offspring will burst from the lesion along with it, and will continue the horrifying life cycle over again if the blistering skin bursts in water. This often happens, as the people and other animals that are infected with guinea worm seek out cool water sources to ease the burning pain of a worm emerging through their skin.
The terror that accompanies guinea worm was noticed by former president Jimmy Carter and his foundation for global health (along with the WHO and the CDC) in the 1980’s. His mission was to make the guinea worm the first parasite to ever be eradicated and his approach was simple: deliver water-filter straws to people in countries that were affected by the disease and provide better care in treatment. This magic bullet was not accepted immediately, as locals who lived in areas of high prevalence of guinea worm did not believe that the parasite was in the water they were drinking, instead they thought that the worm lived naturally in their blood, as it had been virulent since Biblical times and nearly everyone would get it once during their lifetime. Luckily, this resistance did not persist and the cases of guinea worm dropped from 3.5 million in 21 countries in 1986 to only 30 in 2017, half in Chad and half in Ethiopia.
Although these statistics point towards global eradication of guinea worm, a new challenge to wiping out the parasite has emerged: dogs. Dogs are not treated the same way in Africa as they are in the United States. Instead of keeping dogs in their homes, the dogs stay outside as guardians of households and are fed scraps such as fish guts and frogs. Frogs are not regularly consumed in Chad, but children and people with mental illnesses sometimes consume them. They do not fully cook these frogs, so the worms inside of them are not killed, and are trophically passed on to their next host. The entire life cycle of guinea worm relies on tropic transmission, as tadpoles eat the worm larvae present in the ponds they are living in.
The next step to guinea worm eradication now involves dogs. News reports from NPR in 2016 and the New York Times in 2018 both mentioned that nationwide culling of dogs has been considered. The culling of animals has been proven an effective strategy for clearing disease in cases such as Avian Flu and Mad Cow Disease, but culling dogs is not as receptive of a strategy as culling poultry or livestock. Although dogs have little economic value in terms of buying and selling, the protection they provide to homes and crop fields is invaluable. Another issue with culling is that it would pull funding from the Carter Center, as it’s Western donors do not want to be involved with the mass killing of man’s best friend. Other strategies must be considered before the progress made on guinea worm eradications begins to move in reverse. The Carter Center suggested that families tie up their dogs, but this would not fully prevent others from feeding them. Perhaps focusing on the frogs would be the most effective strategy, as they are not an economic resource to the people of Chad or Ethiopia. With the major vector of guinea worm transmission removed, the control of the disease would possibly be more manageable, although ecological impacts of the amphibians should be assessed before making any dramatic steps forwards