The Seville Lab
The Seville Lab
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Since the mid-1980s I have been periodically live-trapping and collecting fecal samples from a variety of sciurid rodents endemic to Wyoming to monitor the occurrence of intestinal parasitic protozoans. Previously I've documented (Seville and Stanton, 1993) that ground squirrels (Spermophilus spp.), prairie dogs (Cynomys spp.) and marmots (Marmota spp.) are commonly infected with a suite of "coccidian" species (Apicomplexa: Eimeriidae) throughout Wyoming and the world (Wilber et al., 1998). To date eimerian species identified from sciurid rodents in Wyoming include Eimeria beecheyi, E. cynomysis (syn. E. bilamellata), E. callospermophili, E. morainensis, E. lateralis, and E. spermophili (Seville and Williams, 1989; Seville et al., 1992; Stanton et al., 1992; Seville and Stanton, 1993; Seville, 1997). The protozoan phylum Apicomplexa Levine, 1970, comprises a large and heterogenous assemblage of obligate, intracellular parasites, many of which are of medical and veterinary importance. The suborder Eimeriorina Leger, 1911, is the largest subgroup in the phylum and contains species collectively referred to as the coccidia. Levine and Ivens (1990) list 473 species of coccidia identified from rodent hosts, of which 372 are Eimeria spp. Schneider, 1881 (Family Eimeriidae, Minchin, 1903). Members of this genus are directly transmitted between hosts and infections are self-limiting. Infections begin when a susceptible host ingests a sporulated oocyst. In the small intestine of a suitable host, sporozoites are released from the oocyst; these enter epithelial cells and then undergo asexual reproduction (merogony) to produce meronts. The meronts rupture from the cell to infect additional cells, thus producing additional meronts. The number of asexual generations varies among eimerian species. Eventually merozoites enter epithelial cells and produce either micro- or macrogametes (gamogony). Microgametes exit the host cell and enter cells where macrogametes are located and fertilization occurs resulting in production of the oocyst. The oocyst breaks out of the host cell and passes out of the host animal in its feces. Typically, oocysts are passed in an undeveloped state and require several days in the external environment to develop (sporulate) to the infective state. Classification of species in the genus Eimeria involves recovery of oocysts passed in the feces of an infected host and is based on measurements and descriptions of structural features of the sporulated oocyst. Unfortunately, identification and classification is difficult because eimerians are rather morphologically conservative. In 1998 Wilber et al. reviewed all published descriptions of eimerians from rodents in the Marmotini Tribe and found that many of the species descriptions were invalid and that several previous authors erroneously assumed that Eimeria spp. of this host group were highly host specific. Based upon a re-analysis of published morphologic species descriptions we reduced the number of named eimerian species in the Marmotini from 40 to 26 (Wilber et al., 1998). Recently Barta et al. (1997) and Hnida (1998) developed techniques for isolating and amplifying eimerian DNA for diagnosis, sequencing, and developing molecular phylogenies. These advances have the potential to resolve a number of questions regarding taxonomy and systematics of this parasite group and for testing hypotheses regarding the evolution of this parasite-host complex. In light of the above, my current work focuses on three objectives: 1.) systematically sampling sciurid rodent populations in central Wyoming to determine eimerian species presence/absence and seasonal host population and parasite prevalence patterns; 2.) comparing parasite species and seasonal dynamics in central Wyoming to other populations and other hosts in other geographic locations; 3) adding molecular approaches to our research program to test recently proposed taxonomic revisions of Wilber et al. (1998), examine phylogenetic relationships, and test hypotheses regarding parasite-host coevolution.
1999 field crew: Clint (MS candidate in 2004-05), Shawnna at the thermal cycler; Don, Lori, April, Christine, and Janet in the field. This work has been supported with funds provided by the University of Wyoming/ Casper College Center and a grant from the University of Wyoming/ NSF-EPSCoR Community College Grant Program.
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This page compiled by R. Scott Seville , last update on 01/04/05 |
