Guinea worm disease eradication: a moving target

Abstract

Deadlines for the eradication of Guinea worm disease have come and gone without success. The first deadline was set in 1991, when the World Health Assembly adopted a resolution calling for the eradication of the disease, which is caused by the nematode Dracunculus medinensis, within 4 years. This target was not met, so a second 2009 deadline was set; this too was not met. After an additional failed deadline in 2015, a new date of eradication has been scheduled for 2020. However, data from the US Centers for Disease Control and Prevention (CDC) and the Carter Center, a US-based global health non-governmental organisation, puts even this new target in question. The reasons for the past and present failures are multi-faceted and have important ramifications for other disease eradication ambitions. Eradication, defined by WHO as “the permanent reduction to zero of the worldwide incidence of infection caused by a specific pathogen established in a human or animal population, as a result of deliberate efforts, with no more risk of reintroduction”, has thus far only been achieved with smallpox and rinderpest, a disease of cattle and related ungulates. Guinea worm disease is a debilitating condition, in which infected people experience burning sensations, oedema, and ulcers until the worm migrates and emerges from the body, often through the feet. To alleviate the painful sensation, people often seek relief in local waterbodies, which completes the parasite's lifecycle. Key to understanding whether eradication of a disease is possible are comprehensive scientific and epidemiological data and whether there is an important zoonotic reservoir of the disease. At the outset of the Guinea worm disease eradication programme, when former US President Jimmy Carter became involved in 1986, the global annual incidence was estimated to be 3·5 million cases. The numerous partners who have since contributed to the campaign include WHO, UNICEF, CDC, the Bill & Melinda Gates Foundation, private philanthropists, industry, and several bilateral donors—with astonishing success. The eradication programme employed a variety of simple but effective public health methods designed to prevent people ingesting the intermediate water flea host, which included the improvement of water sources, water filtration with different types of cloth or filament filters, health education to inform people how the infection is acquired and how it can be prevented, vector control by killing water fleas, case management, and containment by rolling the adult worm gradually from the body using a stick or match. Additionally, active surveillance to promptly report and contain new cases was put in place. At the end of 2018, just 28 cases in humans globally had been reported in the previous 12 months: 17 cases in Chad, ten in South Sudan, and one in Angola. The Angolan case was notable because it was the first to ever be reported in the country. A second Angolan case was confirmed and reported to WHO in January, 2019. The source of the two Angolan cases remains unclear: they are not connected and are some 2000 km from known endemic areas. In Chad, despite the absence of reported cases in humans for 10 years, the disease was found again in 2011, leading to the revelation that dogs carried Guinea worm. Intense research by teams from the Carter Center and the CDC, in work with the Chadian Ministry of Health, showed the potential existence of a new lifecycle involving paratenic (frogs) and transport (small fish) hosts, which could explain the infections in dogs. The full implications for the eradication programme have now begun to be appreciated. In Chad, thought to be the largest source of Guinea worm disease, dogs have emerged as an important reservoir. In a setting where upwards of 56 000 domestic dogs have been documented in villages along the Chari River, where most of the canine infections occur, the practical scale of interrupting vector transmission in a new host strikes home. In Ethiopia, where Guinea worm disease has been detected in dogs and cats, an infection in a baboon has created new necessary avenues for disease surveillance by experts. As surveillance and detection continue to evolve to track the changing epidemiology, additional challenges stymie the goal of eradicating Guinea worm disease. In most settings where the parasite circulates, ongoing or sporadic conflict and considerable migration facilitate transmission and challenge surveillance. Still, progress has been remarkable using simple but effective public health methods. The employment of these measures must continue. Eradication of Guinea worm disease is a noble goal, but the added challenges and complexities now facing the programme suggest that this aim is, at best, many years away. At worst, it is simply a pipe dream.