The Morphology of Trichomonas ovis from the Cecum of Domestic Sheep

Abstract

Trichomonas ovis (Robertson, 1932) Morgan, 1946 was found in the ceca of 12 out of 16 domestic sheep in Illinois and Utah and was cultivated readily at 37 C in Diamond's medium, CPLM medium and bovine cecal extract medium. It was studied by phase-contrast microscopy and after fixation with osmium tetroxide or Bouin's or Hollande's fixatives and staining with Giemsa, Heidenhain's iron hematoxylin, or silver impregnation. It was piriform, 6 to 9 by 4 to 8 A with a mean of 7 by 6 ,u, with an anterior nucleus, with a prominent pelta at the anterior end, with a slender, hyaline axostyle which protruded a mean of 5 , beyond the body and gradually tapered to a point, without a chromatic ring at the point of exit of the axostyle, with 4 anterior flagella of unequal length averaging 14, 11, 9, and 7 u, respectively, with a prominent undulating membrane which extended from three-fourths to the full length of the body and usually had two to three undulations, with a posterior, free flagellum extending beyond the undulating membrane, with a prominent costa and several irregular rows of paracostal granules, with an ovoid or club-shaped parabasal body averaging 2 by 1 a and containing an intensely chromophilic body, and with a parabasal filament. This is the only species of enteric trichomonad of sheep or cattle which has been described in detail following study by modern techniques. Robertson (1932) described a trichomonad which he observed in the gut in one of 86 sheep in England. He said that this trichomonad possessed only two anterior flagella and therefore proposed the name Ditrichomonas ovis for it. Since that time there appears to have been no further investigation of this parasite or of any other trichomonad from sheep. In 1958, Dr. Krishna N. Mehra of the College of Veterinary Medicine, University of Illinois, Urbana, Illinois, isolated a strain of cecal trichomonad from a domestic sheep (Ovis aries). This strain, labeled 0, has been used since that time in connection with experiments on the survival of various trichomonad species during extended frozen storage. This strain possessed four anterior flagella and also differed in other morphological aspects, such as body size and prominence of the undulating memReceived for publication 15 March 1962. * This investigation was supported in part by a research grant (E790C) from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, and in part from a Utah State University Research Fellowship, Utah State University, Logan, Utah. t Present address: Department of Zoology, Utah State University, Logan, Utah. brane, from the trichomonad described previously by Robertson. Four other strains which were subsequently isolated from sheep during 1961 (one from a sheep raised in Illinois, one from a sheep shipped to Illinois from Texas, and two from sheep killed in Logan, Utah) all appeared identical with strain 0 when observed with the phase-contrast microscope. Because of the obvious differences from the trichomonad described by Robertson as Ditrichomonas ovis, it was decided to make a detailed study of the morphology of these cecal trichomonads. MATERIALS AND METHODS All observations reported in this paper were made on trichomonads of strain O. Cultures were grown at 37 C in Diamond's (1957) medium without agar or phosphate buffer, in Johnson and Trussell's (1943) CPLM medium, and in bovine cecal extract medium (Jensen, 1961), which was a modification of the cecal extract medium used by Hibler et al. (1960) in their investigation of porcine trichomonads. A Zeiss photomicroscope was used for both phase-contrast and bright-field observations. Morphological studies were based upon observations of living trichomonads, of specimens fixed for one minute in the vapors of 2% osmium tetroxide solution, and of specimens stained with Giemsa's stain