Synonym: Trichomonas suis Gruby and Delafond, 1843.
Common Name: Large pig trichomonad, pig nasal trichomonad.
Location: Nasal passages, stomach, cecum, colon, occasionally small intestine.
Geographic Distribution: Worldwide.
Prevalence: Switzer (1951) found this species in the nasal passages of 80% of swine affected with atrophic rhinitis and in only 3% of nonrhinitic pigs in Iowa. Shuman et al. (1953) found it in 27% of 36 pigs with atrophic rhinitis and in 17% of 32 unaffected pigs in a herd near Washington, D. C. Levine, Marquardt and Beamer (1954) found it in 91% of 11 pigs with atrophic rhinitis and in 39% of 23 pigs with normal nasal passages in Illinois. Hammond, Fitzgerald and Johnson (1957) found it in the nasal passages of 56% of 64 pigs from Utah, Nebraska and Idaho. Hibler et al. (1960) found it in the nasal passages of 55% of 100 pigs, the stomach of 8% of 512, the cecum of 43% of 496 and the small intestine of 3% of 100 pigs in Utah.
Morphology: This species was described in detail by Hibler et al. (1960), Marquardt (1954) and Buttrey (1956); the latter described it under the name Tritrichomonas sp. from the nasal passages. T. suis is characteristically elongate or spindle-shaped, occasionally piriform or rotund, 9 to 16 by 2 to 6 u, with a mean of 11.3 by 3.4 u. Buttrey described a cytostome, but Hibler et al. did not see one. The 3 anterior flagella are about equal in length, 7 to 17 u long with a mean of about 12.6 u, and end in a round to spatulate knob. The blepharoplast is composed of several granules. The undulating membrane runs the full length of the body and has 4 to 6 subequal folds. Its marginal filament continues as a posterior free flagellum 5 to 17 u long. An accessory filament is present. The costa runs the full length of the body, and fine subcostal granules are present. The axostyle is a hyaline rod 0.6 u in diameter with a bulbous capitulum 1.7 u in diameter. It extends 0.6 to 1.7 u beyond the body as a cone-shaped projection narrowing abruptly to a short tip. There is a chromatic ring around its point of exit. The parabasal body is usually a single, slender, tube-like structure 2 to 5 u long. The nucleus is oval or elongated, 2 to 5 by 1 to 3 u, with a large, conspicuous endosome surrounded by a relatively clear halo.
Pathogenesis: The discovery of this trichomonad by Switzer (1951) in a high percentage of cases of atrophic rhinitis and in a relatively low percentage of normal pigs raised the question whether it was the cause of the condition. Spindler, Shorb and Hill (1953) produced the disease in young pigs with nasal washings containing trichomonads from pigs with atrophic rhinitis, but Switzer (1951), Levine, Marquardt and Beamer (1954) and Fitzgerald, Hammond and Shupe (1954a), among others, were unable to do so with axenic cultures of the protozoon. It is now generally agreed that this trichomonad is not pathogenic. Several other agents, including Pasteurella multocida and Mycoplasma hyorhinis, have been incriminated as causes of atrophic rhinitis, but their roles require further elucidation (see Switzer, 1955 for review). While T. suis is not pathogenic for pigs in its natural locations, it may cause abortion in heifers with experimental infections of the reproductive tract (see below).
Cultivation: This trichomonad can be readily cultivated in any of the media used for T. foetus. In mixed cultures with other species of porcine trichomonads, it survives while the others die out, so that it sometimes seems as tho one species has taken on the appearance of another (Hibler et al., 1960). Because of this fact, cultures of pig cecal trichomonad heretofore used in cross-transmission studies have most probably been this species. Switzer (1959) cultivated T. suis from the nasal passages in pig kidney, nasal mucosa and lung tissue cultures.
Remarks: Uncertainty has existed for many years regarding which of the trichomonads known to occur in swine was T. suis. This specific name was originally given by Gruby and Delafond (1843) to a form found in the stomach. Since that time, trichomonads have been found in the cecum and nasal passages, but it was not certain what their relationship was to the form which Gruby and Delafond had named. However, Hibler et al. (1960) found that the species described above is the only one which occurs in the stomach and that it also occurs in the nasal passages, cecum and small intestine. They found the other 2 trichomonad species of swine only in the cecum.
The relationship between T. suis and T. foetus requires further study. Buttrey (1956) and Hibler et al. (1960) pointed out their great morphological similarity. Doran (1957, 1959) concluded on the basis of metabolic studies that T. suis is a highly adapted strain of T. foetus. The other way around would be more likely in terms of evolution, i.e., T. foetus may well have arisen from T. suis or may be an adapted strain of it.
Fitzgerald et al. (1958) produced vaginal infections in 3 heifers with T. suis from the pig nose; the infections lasted 46 to 133 days. They also produced vaginal infections in 2 heifers with T. suis from the pig cecum which lasted 33 and 84 days, respectively, and in another heifer with T. suis from the pig stomach which lasted 88 days. They produced abortion in a 4-month-pregnant heifer by intrauterine inoculation of T. suis from the pig cecum. In addition, a bull became infected by breeding an infected heifer. He remained positive for 4 months and transmitted the infection to a virgin heifer by coitus. Hammond and Leidl (1957a) infected the preputial cavity of bulls with T. suis from the pig cecum and found that the infections were transmissible by coitus. Kerr (1958) produced vaginal infections in heifers with Hammond’s strains and also with a strain of T. suis which he isolated from pigs in England.
Hammond and Leidl (1957) produced vaginal infections with T. suis from the pig cecum in 4 of 5 sows; the infections lasted 3 to 42 days. Fitzgerald et al. (1958) produced nasal and cecal infections in young pigs with cultures of T. suis from the pig nose, and they produced nasal, gastric and cecal infections with T. suis from the pig stomach and from the pig cecum.
Shaw and Buttrey (1958) were able to infect young chickens with T. suis from the pig nose by rectal inoculation but not by mouth.
Kerr (1958) found that the vaginal mucus agglutination test of heifers infected with T. suis was positive with T. suis and Belfast strain T. foetus antigens but not with Manley strain T. foetus antigen. Sanborn (1955) found by microagglutination tests that a strain of T. suis from the pig nose was antigenically different from a strain of T. foetus and that both differed from a pig cecal trichomonad.
As mentioned above under the discussion of T. foetus, Robertson (1960) found that the Belfast and Manley strains of T. foetus and Strains S2 and 414 of T. suis were serologically related and concluded that the differences between them did not justify separating them into 2 species.
Cattle and swine are often raised together, and the broad host ranges and morphologic, metabolic and serologic similarity between T. suis and T. foetus suggest that they may have had a common origin if they are not indeed the same. Robertson (1960) believed that they are the same and called them all T. foetus, but the correct name, as Hibler et al. (1960) pointed out, would be T. suis. Even so, however, it might still be worth-while to retain both names, simply as a matter of convenience.