Download (direct link):
A number of genes, including those for small subunit ribosomal RNA and two elongation factors, have been partially sequenced (mainly for taxonomic analyses) but no detailed studies of the molecular biology of this organism have been carried out.
In the absence of any resistant cyst, the only plausible route of acquisition is by direct oral contact although, hypothetically, very close range droplet transmission and spread by shared toothbrushes, saliva-contaminated food, etc. is possible. One report has described T. tenax surviving for up to 48 hours in saliva. Exactly the same factors are involved in the dissemination of Entamoeba gingivalis; not surprisingly, the two parasites are common in the same population groups and are not uncommonly recovered from the same patient.
Although T. tenax may be isolated from diseased gums in a significant number of cases, this is widely supposed to be a consequence, not a cause, of periodontal disease and no specific clinical entity due to the organism is recognized.
According to many published surveys, T. tenax is surprisingly common; Honigberg (1978) gave some examples that showed a prevalence in Europe and the USA which varied from 4% to 54%. In a later review, Honigberg (1989) examined the factors affecting prevalence and concluded that a major one is age, the organism being very rare in young children. Whether the subsequent increase in positivity is solely due to the passage of time is, however, unlikely and it is more probable that the deterioration in the condition of teeth and gums provides an increasingly favourable environment for the parasite. In agreement with this, the organism is uncommon in edentulous elderly persons. Other factors, such as sex or socioeconomic status, appear to be either irrelevant or surrogate markers for the healthiness of the gums. Having said that, the incidence was not increased in children with drug-induced gingivitis and it is not actually clear what aspect of ‘poor oral condition’ is causally linked to enhanced risk of infection.
Virtually all accounts of infection with T. tenax have depended either on the examination of wet film prepared for gingival scrapings or on culture of the same specimens to make the diagnosis. A PCR-based diagnostic test has been developed (Kikuta et al., 1997) but is not yet in widespread use.
No treatment of this infection is normally considered necessary, although metronidazole has been shown to be active in vitro and would probably be effective in vivo.
PREVENTiON AND CONTROL
No significant effort has been devoted to trying to reduce the incidence of infection with T. tenax and the obvious approach—improved oral hygiene—might or might not be effective.
PRiNCiPLES AND PRACTiCE OF CLiNiCAL PARASiTOLOGY
PENTATRICHOMONAS HOMINIS (DAVAINE)
A long-standing controversy has existed concerning the correct nomenclature of the human faecal trichomonad, largely due to the fact that not all organisms in culture possess the full complement of five anterior flagella. Thus, while most authorities consider that Pentatrichomonas hominis is the correct name, a minority still refer to the same organism as Trichomonas hominis and this name is widely found in the older literature.
description of the organism
Trophozoites of P. hominis (Figures 11.1, 11.4) are pear- or teardrop-shaped and, in fixed and stained preparations, 6-14 ^ long x 4-6.5 ^ wide. They possess five anterior flagella and an undulating membrane whose recurrent flagellum extends well beyond the length of the body. A moderately thick axostyle extends through the
body from the region of the nucleus and appears to project some way beyond the posterior end. In fresh preparations or in culture, the flagella and undulating membrane beat rapidly (and are thus impossible to observe), propelling the organism with a characteristic jerky motion.
The ultrastructure of P. hominis has been described (Honigberg et al., 1968) and is basically similar to that of other trichomonads; interestingly, the basal body of the fifth anterior flagellum is perpendicular to the other four. Also surprisingly, the number of anterior flagella is not invariable, at least in culture, a minority of organisms having a lesser number (Flick, 1954). Microbodies (presumably hydrogenosomes) are visible and many enzyme activities have been detected during studies on isoenzyme characterization, including superoxide dismutase, but few detailed biochemical studies appear to have been undertaken, although the purine salvage pathway is known and some cysteine proteases have been detected. Axenic culture is possible (Linstead,
Pentatrichomonas hominis is normally regarded as non-pathogenic, but Honigberg, in a recent review (1989), was prepared to admit that in occasional cases it might cause diarrhoea, and Chung et al. (1988) have described 45 heavily infected patients with chronic gastrointestinal symptoms which were abolished by chemotherapy. Diarrhoea in children has also been attributed to this infection but if the organism does cause disease, the mechanism is not known. Unlike T. vaginalis, P. hominis is apparently not cytopathic for mammalian cells in culture.