The Anatomy of Tetratrichomonas didelphidis (Hegner and Ratcliffe, 1927) comb. n. from the Opossum

Abstract

Tetratrichomonas didelphidis (Hegner and Ratcliffe, 1927) comb. n. was found in the cecum and colon in 20 of 24 opossums (Didelphis marsupialis) in Illinois. The organisms grew best in Stuart's leptospira medium at 29 C. The trichomonads were piriform, 7 I long by 4 u wide; with four anterior flagella of unequal length averaging 17, 14, 10, and 8 4,, respectively. The slender hyaline axostyle extended 4 /u posteriorly and had an inconspicuous capitulum. A discoid parabasal body with an intensely argentophilic central granule, a long slender parabasal filament, a narrow pelta, a prominent costa, and a pronounced undulating membrane extending full length of the body and continuing as a long posterior free flagellum were present. Hegner and Ratcliffe (1927) first described Trichomonas didelphidis from the intestine of an opossum shipped to them from Ohio by Dr. Justin Andrews. Three other new species were also described, namely, Trichomonas cynomysi from the intestine of the prairie dog, Trichomonas felistomae from the mouth of the cat, and Trichomonas macacovaginae from the vagina of the rhesus monkey. Because of the slight variation in size and description and, especially, the striking similarity of the schematic illustrations of forms from the opossum, cat, and monkey, it is difficult to ascertain from the literature whether morphologic differences exist among these parasites. Additional information on the detailed anatomy of these flagellates with the aid of modern staining procedures would be helpful in determining the taxonomic and morphologic relationship of these forms to trichomonads from other hosts. To our knowledge, no subsequent reports on the occurrence or anatomy of trichomonads from the opossum exist. Because of the frequency with which trichomonads were detected in opossums used in research at the College of Veterinary Medicine, University of Illinois, it was decided to make a detailed morphologic study of these parasites. MATERIALS AND METHOD Opossums used in various research projects at the College were routinely examined at necropsy for the presence of trichomonads in the stomach, small intestine, cecum, and colon. Most of the Received for publication 29 March 1965. * This research was supported in part by research grants U. S. Public Health Service Communicable Disease Center 00037 and NIH CC-00070. animals had been captured as adults in southern Illinois, although a few were raised in captivity as littermates after females with pouched young had been obtained. In addition to the necropsy examinations, fecal samples taken periodically from caged opossums were also examined for trichomonads. When abundant organisms were detected, a small amount of the intestinal content or fecal material was inoculated into Diamond's (1957) medium without agar or phosphate buffer, Fletcher's (1928), Stuart's (1946), or Ellinghausen's and McCullough's (1965) leptospira media, or opossum cecal extract medium. The last was a modification of the cecal extract medium used by Hibler et al. (1960) and Jensen and Hammond (1964) in their investigations of porcine and bovine trichomonads. All these media were tested at 20, 25, 29, 35, and 37 C. Because of the results obtained, cultures were routinely maintained only in Stuart's medium and at 29 C. In order to secure additional infornmation on the body temperature of opossums, daily rectal temperatures were determined on eight caged adult opossums for a period of 10 days during the first part of August 1964 and on 5 days during the middle of September 1964. These measurements were made with a thermistor rectal probe and a battery-powered telethermometer. Extreme caution was used to minimize excitement of the animals. Microscopic observations of the trichomonads were made under a Zeiss photomicroscope with apochromatic objectives. Living organisms from freshly obtained material or from culture, and specimens fixed in 2% osmium tetroxide vapors were studied under phase-contrast. Stained specimens fixed in methanol, Schaudinn's fluid, Bouin's or Hollande's fixatives, and stained with Giemsa stain, Heidenhain's iron hematoxylin, or protargol (Pfaltz and Bauer, control number 6990, and ltablissements Roques Paris, control numbers 789 and 2304) were examined with the bright-field microscope. In order to make a comparison with the mensural data given by Hegner and Ratcliffe (1927), measurements of length and width were taken on 50 specimens fixed in Schaudinn's fluid and stained