Differently from the parasitic urogental Trichomonads (T. vag.), the extraurogenital trichomonads (T. hominis-intestinalis and T. tenax-buccalis) are considered as symbionts, commensals, mostly inhabiting lower parts of digestive and upper parts of respiratory tract.

Even intraluminally located trichomonads cause the host sensitization, which is stronger if these parasites penetrate deeper into the submucous tissue, and the strongest after their penetration into the lymph ways and blood stream (Piekarski). Clinically is observed the competition of trihomonal infections, i.e. absence of coexisting chronic infections of distant organs with same or different species (Teras J.). This relates to all three mentioned human species of Trichomonas genus (Jirovec) as logical consequence of the common immunity, the interspecies crossimmunity (Teras ).

When they penetrate into bloodstream, trichomonads get into the closest contact with the host immune and hematopoetic apparatus resulting in the strongest antitrichomonas sensitization and still unrecognized blood consequences. From the haemocirculation these single celled parasites have affinity to attach to some organ originated from embryonal gill arches, rich with mucous goblet cells: nose, (naso)pharynx, larynx, from which they are being expelled as cellurar component in postnasal drip,clinically defined entity but etiologically and microscopically unresolved. However the achieved immunity, similarly  to other parasitoses, rarely results with a complete expulsion of the infection.From there, these parasites, by spontaneously, unconscious swallowing, get again into the digestive tract so ending recirculation: digestive tract to short living elusive, immunoenhancing parasitemia- to respiratory tract- and finally closing the circuit, to digestive tract.

In the conditions of unphysiological consuming of food and liquid, parasites not rarely pass the disturbed hypoacidic barrier of the stomach, and after that also evade the first immune barrier of the intestines (Payer’s Patches). Due to human upright posture, the rotation from primordial horizontal line to 90 degrees (upright) significantly reduces the immune efficiency of Payer´s patches because of parasites in intestinal half-liquid content pass by these structures and not gliding across them what is case by quadrupeds.

As in the terminal part of the ileum is locus minoris resistentiae, the secondary parasite-host interaction happens there, upon the descendent autoreinfection described.

The second reason as to why this part of ileum is a predilection place for Crohn´s disease is the fact of a relative motoric insufficiency of the first part of the colon. Namely, because of the human upright posture, differently from quadrupeds, this part of the colon with its peristalsis must overcome the gravity as well.

Because of that, the remains of frequent insufficiently digested food are kept for longer time in the cecum, as the basis for development of microbes including trichomonads, which are frequently found there in vertebrates.

Physical strain and outside pressure, in early post-prandal time, to the lower stomach may push the contents of the colon back, enabling retrograde trichomonad infection dispersal into ileum.

As ileum has no mucous glands, mucus immobilization of parasites does not happen there.

Microulceration of the mucous membrane with roughage and solid indigestble particles and fizzy drinks combined with pressure outside on abdominal wall enables deeper penetration of trichomonads or their antigens,extracelullary secreted parasitic proteinases, into submucosa, causing reactive hyperplasia of the connective and lymph tissues in already sensitized host.

Oral reinfection with similar or different antigenic strains of trichomonads, as well as the coinfections with other microbes, particularly with other parasites, complicate clinical and pathological picture and additionally erodes host’s immune integrity.

Frequent sensitization of the host, even asymtomatic, by genital trichomonads with married persons, make harder infection of the digestive tract, which explains rare Crohn´s disease occurrence in such persons of both sexes. Recessive inheritance of susceptibility to parasites in general, including trichomonads, explains family incidence of CD as well as more frequent getting of the disease in brothers, than stepbrothers.

Unrecognized interaction of circulating antitrihomonad immunity and trichomonads, or just their antigens at the place of their contact, results in the misinterpretation of an autoimmune event the CD.

Favorable placebo effect with the CD may be explained by relief of the immune apparatus from depressing emotional impulses, unless the placebo preparation has itself an unrecognized antitrichomonal effect

Depending of anatomy and physiology of colon the same agents could cause Ulcerative colitis. In contrast to the ileum, the colon is the richest in the body by mucous cells, and from there the similarity with histopathologic pictures similar as chronic hypertrophic trichomonal cervicitis uteri.