Population genomic evidence that human and animal infections in Africa come from the same populations of Dracunculus medinensis

Abstract

Background Guinea worm–Dracunculus medinensis–was historically one of the major parasites of humans and has been known since antiquity. Now, Guinea worm is on the brink of eradication, as efforts to interrupt transmission have reduced the annual burden of disease from millions of infections per year in the 1980s to only 54 human cases reported globally in 2019. Despite the enormous success of eradication efforts to date, one complication has arisen. Over the last few years, hundreds of dogs have been found infected with this previously apparently anthroponotic parasite, almost all in Chad. Moreover, the relative numbers of infections in humans and dogs suggests that dogs are currently the principal reservoir on infection and key to maintaining transmission in that country. Principal findings In an effort to shed light on this peculiar epidemiology of Guinea worm in Chad, we have sequenced and compared the genomes of worms from dog, human and other animal infections. Confirming previous work with other molecular markers, we show that all of these worms are D. medinensis, and that the same population of worms are causing both infections, can confirm the suspected transmission between host species and detect signs of a population bottleneck due to the eradication efforts. The diversity of worms in Chad appears to exclude the possibility that there were no, or very few, worms present in the country during a 10-year absence of reported cases. Conclusions This work reinforces the importance of adequate surveillance of both human and dog populations in the Guinea worm eradication campaign and suggests that control programs aiming to interrupt disease transmission should stay aware of the possible emergence of unusual epidemiology as pathogens approach elimination.

Surveillance of Human Guinea Worm in Chad, 2010–2018

“…Cameroon was also certified to be free of Guinea worm in 2007, but, regretfully, four canine cases and one feline case were reported in 2020, in addition to a human case that was likely infected in Chad. 38,39 In response, active surveillance has been initiated in communities on both sides of the Chad-Cameroon border, along with application of Abate to water sources, tethering of dogs, purchasing and destroying fish guts, and health messaging campaigns. 38 Dracunculus medinensis infection occurs in a range of hosts in Chad, including humans and domestic dogs and cats, 13 and evidence from population genetics and genomics shows that worms emerging from these hosts are indeed the same population.…”

New global targets for NTDs in the WHO roadmap 2021–2030

“…Dracunculiasis is, in theory, not far from eradication, with only 54 human cases reported in 4 countries in 2019 and 24 cases reported until end of November 2020 [ 12 ]. However, the recent finding of a genetically identical Guinea worm population, which infect both human and dogs, seems to rise complications in this public health effort [ 13 ].…”

Specialty Grand Challenge: Embracing the Need for Research and Innovation as Fundamental Enablers for Programmatic Progress for All Neglected Tropical Diseases

“…One of only two NTDs targeted for eradication, the programme has encountered an entirely unexpected challenge in the "last mile". The parasite so frustratingly close to being eradicated from humans appears to have expanded into zoonotic animal reservoirs including, dogs, cats and baboons, with genomic analysis supporting a common origin of animal and human parasite populations (7). This together with the extreme challenges of surveillance in countries blighted by civil unrest and insecurity and the strict criteria for eradication demanded by the International Commission for the Certification of Dracunculus Eradication, questions whether Guinea worm eradication is still achievable and further re-enforces the need for research and innovation right up until the end.…”