Parasites and Microbes, Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton, Cambridgeshire, United Kingdom.
Department of Biology, Vassar College, Poughkeepsie, New York, United States of America.
PLoS Negl Trop Dis. 2020 Nov 30;14(11):e0008623. doi: 10.1371/journal.pntd.0008623. eCollection 2020 Nov.
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.
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.
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.
麦地那龙线虫（Dracunculus medinensis）曾是历史上人类的主要寄生虫之一，自古即为人知。如今，随着阻断传播的努力，麦地那龙线虫病的年发病负担已从 20 世纪 80 年代的每年数百万例感染降至 2019 年全球报告的 54 例，这种疾病已接近被消除。尽管迄今为止在消除工作方面取得了巨大成功，但还是出现了一个并发症。在过去几年中，在乍得发现了数百只感染这种以前明显人源寄生虫的狗，几乎全部在乍得。此外，人与狗的感染相对数量表明，狗目前是该国感染的主要宿主，并对维持传播起到关键作用。
为了阐明乍得麦地那龙线虫这种特殊的流行病学情况，我们对来自狗、人类和其他动物感染的线虫进行了测序和比较。我们用其他分子标记证实了以前的工作，表明所有这些线虫均为麦地那龙线虫，同一批线虫引起了这两种感染，能够证实宿主间传播的可疑性，并检测到由于消除工作而导致的种群瓶颈的迹象。乍得的线虫多样性似乎排除了在过去 10 年没有报告病例的情况下该国不存在或仅有少量线虫的可能性。
这项工作强调了在麦地那龙线虫消除运动中对人类和狗群体进行充分监测的重要性，并表明旨在阻断疾病传播的控制方案应意识到，随着病原体接近消除，可能会出现不寻常的流行病学现象。
