THE TRICHOMONADS 



91 



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 5jn long. The nucleus 

 is oval or elongated, 2 to 5 by 1 to 3 /li , 

 with a large, conspicuous endosome sur- 

 rounded 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 nor- 

 mal 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 contain- 

 ing trichomonads from pigs with atrophic 

 rhinitis, but Switzer (1951), Levine, 

 Marquardt and Beamer (1954) and Fitz- 

 gerald, 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 Pasteiirella tnultocida and Myco- 

 plasDia 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 in- 

 fections 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 trichomon- 

 ads, 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 spe- 

 cies. 



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 origi- 

 nally 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 pas- 

 sages, 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 



