Natural history and genetic diversity of Dracunculus spp.

Alec Thompson, a Microbiology major from the University of Oklahoma, worked in the lab of Dr. Michael Yablsey to increase understanding of the genetic diversity of a parasite.

Abstract: Dracunculus spp. are spiruroid nematode parasites that live in the subcutaneous tissues or abdominal cavity of mammals. The most important species is D. medinensis, the human Guinea Worm. In 1985, over 3.5 million people were infected, but due to control efforts by the Carter Center and public health agencies, there were only 22 cases in 2015. Control was primarily through the use of water filters. A related species, D. insignis, is found in various wildlife species, and rarely dogs and cats, in North America. We have been conducting studies on D. insignis as a model parasite to better understand the ecology of D. medinensis. In this study, various potential vertebrate hosts were examined to determine the host-parasite interactions and genetic diversity of Dracunculus parasites within the United States. Analysis of the preliminary results suggests that the raccoon (Procyon lotor) is the preferential host for the parasite but opossums (Didelphis virginiana) are often frequently infected. Molecular characterization was attempted to investigate the intraspecific variation between hosts and regions and also to definitively identify adult female worms which cannot be identified using morphologic characteristics. However, the PCR was problematic as low specificity was observed with the PCR primers we used. Most sequencing attempts were either host DNA or mixed products.  We did get amplicons from four worms that were parasite DNA and they were all D. insignis. Methods for better specificity and amplification and other gene targets of are currently being researched and results are pending. Finally, we conducted experimental infection trials to investigate the potential role of amphibians and fish as hosts. Several species of amphibians were exposed to copepods infected with D. insignis. Infections of 2 species of tadpoles (gray tree frog and northern cricket frog) were confirmed by necropsy. These parasites were fed to ferrets and results will take 6-8 months. Bufo tadpoles did not consume copepods. Previous studies suggested that fish did not become infected with larvae, but we investigated the possible role as a transport host. Three species of fish (tilapia, fathead minnows, and gambusia) were exposed to infected copepods and then immediately fed to ferrets. Ferrets will be tested after 6-8 months. Although results of several studies are pending, this study has provided new data on the natural history of D. insignis and intiated additional studies that may help understand the continued transmission of D. medinensis by the use of alternative hosts.

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