In ruminants, 1010 - 1011 bacteria per ml live in the rumen, which is immediately accessible to food. These bacteria are the basis for the cellulose decomposing flagellates and ciliates, which reach levels of 105 – 106 per ml. The latter establish food chains of all kinds. In omnovores and carnivores, food at first is made germ-poor by the change of PH in the mouth cavity, stomage and duodenum. Thereafter, a similar density of bacteria will only be reached again in the colon. However, the densities of commensal or parasitic protozoa remain low.
Giardia duodenalis attaches to epithelial cells of the ileum by a ventral adhesive disc and feeds by pino- and phagocytosis on the dorsal side. It posesses 8 flagella, 2 probably haploid nuclei and 2 parabasal bodies (fig. 3.11 a, page 205). It is an aerotolerant anaerobic organism and propagates by binary cross division. For excystment, a preliminary passage of the stomach at PH 2 is essential; thereafter, it hatches at PH 6.8. Encystment by a wall of chitin occurs after 1-2 weeks p.i. The widespread covering of the intestinal cells by dense masses of flagellates causes resorption disorders. The infection is self-limiting but stimulates no protective immunity; the flagellate is thus a balance strategist. The transmission is faecal-oral. For chemotherapy, Metridazol is effective.
Grouping of the genus Giardia is according to the shape of the parabasal body. G. agilis group (1 body, elongate, club-like) in amphibiae. G. muris group (a pair of small globular bodies) in rodents, birds and reptiles. G. duodenalis group (12 sickle-like bodies, crosswise to the long axis of the cell) in birds, reptiles and mammals including man.
Trichomonadidae order Protomonadina. The long recurrent flagellum is provided with an undulating membrane; the cell body stabilizes a long costa. Additionally there are 4-6 anterior shorter flagella, each with a kinetosome, a parabasal body, an axostyle and a single nucleus; the binary division occurs lengthwise (fig. 3.11 c, page205). Flagellates are mostly found in the caecum and colon and sometimes in the mouth cavity, palate, oesophagus, crop, vagina, uterus and prostate of warm-blooded animals. No cysts are formed and transmission takes place via humid contact. In man, Trichomonas vaginalis infections cause inflammation of the mucus membranes in the male and female urogenital tract in 30 50 % of cases. T. tenax is found in the mouth cavity and palate; its prevalence reaches 10 - 25% but its pathogenicity (caries, suppurative inflammation) is doubtful.
Balantidium coli is a ciliate with a cytostome, cytopharynx, micro- and macronucleus and two contractile vacuoles and propagates by binary division and conjugation (fig. 3.11 d, page 205). It lives commensally in the caecum and colon of the domestic pig. Transmission occurs by cysts resistent against exsiccation. It is a facultative pathogen in the colon of man (ulcera, abscesses, diarrhoe). A balantidial dysenteria sometimes quickly ends lethal.