As with P. hominis, preventing the contamination of food and water with human faeces should reduce the incidence of infection. In addition, since transmission via Enterobius eggs is a distinct possibility, control of pinworm infections, particularly in children, would be a highly rational strategy.
Although the normal site-specificity of the three human trichomonads (and presumably D.fragilis also) is well established, there are occasional reports of these organisms being recovered from sites other than their normal habitats. Although these organisms are often identified as specific species, it should be remembered that this precision is almost impossible unless fixed and stained material is examined; the existence of detached ciliary tufts (see above) should also not be forgotten. It is likely that in the future newer diagnostic methods (such as PCR) will remove much of the ambiguity from these reports.
Ectopic trichomonads are often recovered from sites also infected with other pathogens, such as anaerobic bacteria, or from seriously or terminally ill patients, and so it is difficult to be sure to what extent they cause or contribute to the observed pathology. A detailed (and fairly sceptical) review of this subject is included in a book chapter by Honigberg (1989) and only a brief account will be given here.
The most frequent reports of this type are trichomonads, normally assumed to be T. tenax, causing respiratory tract pathology (reviewed by Hersh, 1985); the same organism has been apparently found in the submaxillary gland and in children with chronic tonsillitis. Hiemstra et al. (1984) wondered whether T. vaginalis might cause pneumonia in newborn babies and unidentified species of trichomonad have been implicated in bronchitis and found in pleural fluid. In an interesting case of oesophageal intramural pseudodiverticulosis, trichomonads were discovered in some of the pesudodiverticula. Electron microscopy showed them to possess only four anterior flagella, thus identifying them as either T. tenax or T. vaginalis (Guccion and Ortega, 1996).
When injected intraperitoneally or sub-cutaneously in mice, at least some strains of T. vaginalis are highly pathogenic, producing large abscesses. Such lesions in humans are fortunately very rare but a perinephric abscess attributed to T. vaginalis and a trichomonal abscess of the median raphe of the penis have been described, as has the presence of trichomo-nads (and bacteria) in a subhepatic abscess.
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