Date of Award:

1967

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Ecology

Advisor/Chair:

Datus M. Hammond

Abstract

A study of the conccidia of the Uinta ground squirrel, Spermophilus (Citellus) armatus, was undertaken to determine the incidence of coccidia in a population of these ground squirrels, the life cycle and pathogenicity of the coccidia, and the host specificity of certain of the species of coccidia found in this and five other species of ground squirrels (S. richardsoni, S. variegatus, S. lateralis, S. columbianus, and S. beecheyi).

Uinta ground squirrels were live trapped and their feces examined to determine the incidence of coccidian infection. Specimens of S. armatus were maintained in the laboratory and given a pure inoculum of Eimeria callospermophili, E. larimerensis, or E. bilamellata. The animals were then killed at 12 to 24 hour intervals, and tissues were prepared by routine histological methods for microscopical examination.

Oocysts of these three species of coccidia from other species of ground squirrels caused patent infections in S. armatus. Spermophilus richardsoni could not be infected with E. larimerensis or E. bilamellata. The incidence of infection in each of the three species of coccidia was similar in adult and juvenile animals. Eimeria bilamellata had the lowest incidence of the three species, and was the only one that caused immunity or was pathogenic in experimental infections. Eimeria callospermophili was recovered from five of the six species of ground squirrels examined and from the prairie dog, Cynomys leucurus. This is evidently the first time that a specis of Eimeria has been found in two rodent genera. Eimeria larimerensis, a species previously reported from prairie dogs, was found in S. armatus.

Endogenous stages of E. callospermophili were located above the host cell nuclei of epithelial cells on the villi of the small intestine. Two asexual stages preceded the sexual stages, and oocysts were first discharged five days after inoculation. The life cycle of E. larimerensis was similar to that of E. callospermophili, except that greater numbers of merozoites were produced during schizogony and the endogenous stages were located below the host cell nuclei. Developing macrogametes of these two species differed in that those of E. callospermophili contained basophilic plastic granules that later assumed eosinophilic properties. The plastic granules of E larimerensis were eosinophilic throughout the development of the macrogamets. Microgametocytes of E. callospermophili had a simple type of development, in which the microgametes were formed around the periphery of the gametocyte; the microgametes of E. larimerensis developed around internal formative areas of the gametocyte as well as peripherally.

The asexual development of E. bilamellata was determined only in part. Mature schizonts were present on the seventh day after inoculation, and gametogenesis began at this time; oocysts were first discharged on the tenth day after inoculation. Eimeria bilamellata differed from the other two species in that gametocytes developed in epithelial cells, which became displaced, finally being located deep in the lamina propria of the mucosa. Macrogametes contained both basophilic and eosinophilic plastic granules. Microgametogony was more complex than in the other two species, and the microgametocytes were much larger, producing thousands of gametes.

Excysted sporozoites of the three species of coccidia differed in morphology and staining properties. The sporozoites of E. callospermophili and E. E. larimerensis had unusually large posterior refractile bodies. Eimeria callospermophili was also unusal in that no PAS positive material was found in the sporozoites.

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