Dracunculus insignis

Cleveland, Christopher A., Garrett, Kayla B., Cozad, Rebecca A., Williams, Brianna M., Murray, Maureen H. & Yabsley, Michael J., 2018, The wild world of Guinea Worms: A review of the genus Dracunculus in wildlife, International Journal for Parasitology: Parasites and Wildlife 7 (3), pp. 289-300 : 295-296

4.1.2. Natural infections of D. insignis in wildlife

4.1.2.1. Infections in wild raccoons. Raccoons are the most common host for D. insignis ( Cheatum and Cook, 1948; Long, 2003). Although the classic transmission route for D. medinensis is the ingestion of copepods infected with L 3 in drinking water, it has been suggested that this is unlikely to be the primary route for D. insignis among raccoons (Muller, 1971; Crichton and Beverley-Burton, 1977). Instead, transmission via consumption of an amphibian paratenic host or fish transport host containing D. insignis L3 seems more likely, although this has not been evaluated beyond showing the capability of transmission ( Fig. 1 ) ( Crichton and Beverley-Burton, 1977; Andersen, 2000).

Most reports of D. insignis in raccoons have been based on detection of adult females which cannot be identified to species ( Fig. 2 ); thus, these infections cannot be definitively said to have been with D. insignis . To date, however, no other Dracunculus sp. has been detected in raccoons (either by identification of males or genetic characterization) ( Chitwood, 1950; Crichton and Beverley-Burton, 1975; Elsasser et al., 2009). Infections have been noted in raccoons in numerous states in the United States (primarily East of Texas / South Dakota line) and in Ontario province, Canada ( Table 2). The prevalence of infections in raccoons from Ontario, Canada, where a good proportion of surveillance work has been conducted, was 69% (154/223) (Crichton and Beverly-Burton, 1974). In the southeastern United States at a site with endemic D. insignis transmission in raccoons, a prevalence of 36% (35/98) has been detected (Cleveland and Yabsley, unpublished data).

Several studies have noted a marked seasonality in the prevalence of infection and stage of development of D. insignis . The highest prevalence has been reported in the spring (April–June) at multiple locations throughout the United States (Texas, New Hampshire, Tennessee, and Kentucky) and Canada (Ontario). However, the lower prevalence noted in other seasons may be related to the lack of detection of males and immature females, as female worms in the fall are mostly in the subcutaneous tissues of the abdomen or thorax and are small and immature ( Chandler, 1942a; Siegler, 1946; Crichton and Beverly-Burton, 1974; Crichton and Beverley-Burton, 1977; Diters and Ryan, 1980; Smith et al., 1985). A study of D. insignis in raccoons at a site in the southeastern United States with endemic transmission found that naturally-infected individuals sampled in February–March had gravid females subcutaneously or had post emergence scarification, indicating a late winter to early spring emergence (Cleveland and Yabsley, unpublished data).

4.1.2.2. Infections in other wild species. In addition to raccoons, infections with parasites presumed to be D. insignis have been reported in multiple wild carnivore species (e.g., skunks ( Mephitis spp. ), coyotes ( Canis latrans ), foxes ( Vulpes spp. )), Virginia opossums ( Didelphis virginiana ), and rarely rodents (i.e., muskrat ( Ondatra zibethicus ) and North American beaver ( Castor canadensis )) ( Table 2). Except for a study in Ontario Canada, none of the worms detected in these other wild species have been confirmed to species by examination of males or through molecular confirmation. In Ontario, fisher ( Martes pennanti ), mink ( Neovison vison ), and North American river otter ( Lontra canadensis ) have been confirmed as hosts for D. insignis through molecular characterization ( Elsasser et al., 2009). This lack of species confirmation may be important for species that are known to harbor more than one Dracunculus sp. (e.g., river otters), are hosts for other subcutaneous filarid worms (e.g., Filaria taxidae in mustelids and raccoons), or unusual hosts (e.g., rodents, none of which were infected with mature larvigerous females so may be dead-end hosts) ( Gibson and McKiel, 1972; McKown et al., 1995).

Figures

Fig. 1. Life-cycle of Dracunculus insignis in wildlife and domestic dogs. Arrows in red represent transmission from (A) definitive hosts to intermediate hosts (Cyclopoid copepods) and (B) transmission to definitive hosts via consumption of intermediate hosts. Arrows in blue represent (C) transmission from intermediate hosts to paratenic and transport hosts (amphibains and fish) via consumption of infected copepods and (D) transmission to definitive hosts via consumption of paratenic/transport hosts. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2. Dracunculus insignis infection in definitive host raccoon (Procyon lotor) and intermediate host (Cyclopoid copepod): (A) lesion from emergence of gravid female D. insignis (marked by arrow); (B) in situ photograph of patent D. insignis infection in forelimb of raccoon; (C) first-stage larvae (L1) of D. insignis (0.596–0.857 mm); (D) thirdstage larvae (L3) of D. insignis (0.434–0.605 mm) with trilobed tail, a distinguishing morphologic characteristic; (E) a copepod infected with D. insignis (L3s marked with arrow).