A Point Source Outbreak of Dracunculus Medinensis Affecting Both Humans and Dogs -- Chad, 2019

Background: Guinea worm is on the verge of eradication, with a 99.9% reduction in cases since the mid-1980s. Most cases now occur Chad. On April 19, 2019, a 19-year-old woman presented with a Guinea worm in Salamat Region, Chad, an area where the disease had not been previously reported. Methods: We conducted a field investigation including household case searches and informal group interviews. Four mitochondrial genes and 22 nuclear microsatellite markers were used to assess relatedness of worms associated with the outbreak in comparison with other worms from elsewhere in Chad. Findings: We identified 22 human cases and 2 canine cases. Most human case-patients were from three villages in Salamat, but one case-patient was detected nearly 400km away in Sarh city. All case-patients reported a history of consuming fish and unfiltered water. Community members recalled a dog in 2018 with a Guinea worm-like infection (undetected by the surveillance system) that could have been the source of water contamination that ultimately seeded the 2019 outbreak. Worms associated with this outbreak were genetically similar and shared the same maternal lineage. Interpretation: Molecular epidemiologic results suggested a point-source outbreak that originated from a single female Guinea worm, rather than newly identified sustained local transmission. The unusually long 147-day duration of this outbreaks suggests the possible involvement of a paratenic host. This outbreak affected both humans and dogs, illustrating the importance of prevention and control of Guinea worm in dogs as a continued focus for eradication efforts. Funding: The Carter Center. Declaration of Interest: None to declare Ethical Approval: Approval for this analysis was granted by the Chad Ministry of Public Health (MOPH), and a non-research determination was granted by the delegated authority at the U.S. Centers for Disease Control and Prevention (CDC). Investigation methods employed are a part of routine outbreak response protocols as defined by the Chad Guinea Worm Eradication Program (CGWEP, which is a part of the MOPH).