The wild world of Guinea Worms: A review of the genus Dracunculus in wildlife

Abstract

Nematodes are an extremely diverse and speciose group of parasites. Adult dracunculoid nematodes (Superfamily Dracunculoidea) occur in the tissues and serous cavities of mammals, fish, reptiles, amphibians and birds. Of the dracunculid group, perhaps best known is Dracunculus medinensis, the human Guinea Worm. Considerable work has been done on D. medinensis; however recent infections in peri-domestic dogs and the finding of naturally-infected paratenic hosts (previously unreported for D. medinensis) indicate we still have much to learn about these parasites. Furthermore, among eight species in the Old World and six species in the New World there is a lack of general life history knowledge as well as questions on species occurrence, host diversity, and transmission dynamics. Herein, we provide a comprehensive review of the genus Dracunculus, in order of a theoretical evolutionary progression from reptilian to mammalian hosts. Species descriptions, where available, are provided but also show where gaps occur in our knowledge of various species. Additionally, many first reports of Dracunculus spp. were done prior to the development and use of molecular tools. This is especially important for this group of parasites as speciation based on morphology is only applicable to males of the genus, and males, given their size, are notoriously difficult to recover from definitive hosts. Therefore, we also discuss current molecular tools used in the investigation of this group of parasites. Given recent host-switching events, the dracunculids are of increasing importance and require further work to expand our understanding of this genus.

Dracunculus Species in Meso-Mammals from Georgia, United States, and Implications for the Guinea Worm Eradication Program in Chad, Africa

“…Dracunculus infections have been documented in a variety of hosts from multiple regions of North America; however, identification in most studies was limited to the morphology of female worms, which cannot be reliably identified to species without genetic characterization. Although male worms are morphologically distinguishable, they are rarely detected (Cleveland et al, 2018). The only previous study that examined the host range of D. insignis (confirmed by sequence analysis) was conducted in Canada and found that D. insignis recovered from raccoons, mink, fishers (Martes pennanti), and river otters had minimal sequence divergence among hosts, supporting the hypothesis that D. insignis is a host generalist (Elsasser et al, 2009).…”

“…Dracunculus insignis has been well documented in raccoons across a wide geographic area of North America Beverly-Burton, 1974, 1977;Cleveland et al, 2018); however, detailed investigation into the range of susceptible wildlife, associated phylogenetic relationships, and the role of paratenic and transport hosts in the transmission cycle at endemic locations had yet to be investigated. Our study supports the role of raccoons as the most common definitive host for D. insignis (Crichton and Beverly-Burton, 1974) but also indicates the potential involvement of opossums in supporting sylvatic transmission.…”

“…Adult females were classified as Dracunculus sp. based on general characteristics such as location in the definitive host, size, morphology, and the presence of larvae (Anderson, 2000;Cleveland et al, 2018).…”

Dogs and the classic route of Guinea Worm transmission: an evaluation of copepod ingestion

“…If numbers of copepods ingested under natural conditions is similar to our experimental data, numerous drinking events from contaminated water bodies may be necessary for Dracunculus transmission to occur. It is important to note the prevalence of infected copepods in a contaminated pond is poorly understood but is presumed to be relatively low based on past studies (range of 0.5-33.3%, average of 5.2%) [15][16][17] . Also, because both a female and male worm are required to complete the life cycle, and copepods infected with more than one Dracunculus L3 are likely to die 18 , multiple infected copepods must be ingested.…”

“…In conclusion, despite our small sample size, our data indicate that dogs can ingest relatively few copepods while drinking, but there are still many factors to investigate to determine the primary transmission route(s) of D. medinensis in the remaining GWD-endemic countries. Other possibilities include ingestion of amphibian paratenic hosts or fish transport hosts 2,[4][5][6]15 . Currently, there are many interventions in place to minimize transmission risk including: tethering of infected dogs, treatment of potentially contaminated water bodies with Abate ® , and the burning or burial of fish entrails, but dog infections continue to occur suggesting that improved adherence to interventions or new interventions are necessary to interrupt transmission.…”