Synonym: Tritrichomonas suis pro parte.
Common Name: Medium-sized pig cecal trichomonad.
Location: Cecum, colon.
Geographic Distribution: This species has been recognized so far only in North America, but presumably occurs thruout the world.
Prevalence: Hibler et al. (1960) found T. rotunda in the ceca of 10.5% of 496 pigs in Utah.
Morphology: This species was described in detail by Hibler et al. (1960) and by Buttrey (1956); the latter referred to it as "T. suis-like". T. rotunda is typically broadly piriform, and only occasionally ovoid or ellipsoidal. It measures 7 to 11 by 5 to 7 u with a mean of 9.0 by 5.8 u. Hibler et al. saw no cytostome. Cytoplasmic inclusions were frequently present. The 3 anterior flagella are about equal in length, being 10 to 17 u long with a mean of 14.9 u, and terminate in a knob or spatulate structure. The blepharoplast appears to consist of a single granule. The undulating membrane is relatively low. It and the costa extend about 1/2 to 2/3 of the length of the body according to Hibler et al. (the full length of the body, according to Buttrey), and its undulation pattern varies from smooth to tightly telescoped or coiled waves (with 3 to 5 indistinct folds, according to Buttrey). The accessory filament impregnates heavily with silver. The posterior free flagellum is generally shorter than the body. The axostyle is a narrow, straight, non-hyaline rod with a crescent- or sickle-shaped capitulum. It extends a relatively long distance beyond the body (0.6 to 6.3 u with a mean of 4.3 u). There is no chromatic ring at its point of exit from the body. The nucleus is practically spherical, 2 to 3 u in diameter, with an endosome surrounded by a clear halo. The parabasal body measures 2.3 to 3.4 by 0.4 to 1.3 u. It is composed of 2 rami which form a V; each ramus has a parabasal filament.
Cultivation: T. rotunda grows readily on primary culture in standard trichomonad media, but dies out on subculture and can no longer be found after the 4th or 5th subculture. However, it can be maintained indefinitely in a cecal extract-serum medium provided that Pseudomonas aeruginosa is present (Hibler et al., 1960).