Question
Intestinal flagellates
Answer
Intestinal flagellates are protozoan parasites characterized by locomotion via one or more whip-like flagella, inhabiting the human gastrointestinal tract, ranging from significant pathogens to harmless commensals.
Key examples:
- Giardia lamblia (G. intestinalis) — the most clinically important intestinal flagellate; a pear-shaped trophozoite with two nuclei and four pairs of flagella, causing malabsorptive diarrhoea; transmitted faecal-orally via the environmentally resistant cyst form; a common cause of traveller’s and waterborne diarrhoea.
- Trichomonas hominis (also called Pentatrichomonas hominis) — a non-pathogenic commensal flagellate of the large intestine, distinguished from the pathogenic, sexually-transmitted Trichomonas vaginalis (a genitourinary, not intestinal, species) by its habitat and clinical insignificance; possesses only a trophozoite form (no cyst stage), similar to T. vaginalis.
- Chilomastix mesnili — another generally non-pathogenic (or minimally pathogenic) commensal intestinal flagellate, possessing both trophozoite and a characteristic lemon-shaped cyst form; primarily of diagnostic interest as it must be distinguished from pathogenic parasites on stool microscopy, rather than for its own clinical significance.
Clinical significance: among intestinal flagellates, only Giardia lamblia is a well-established, clinically significant human pathogen; the others are generally regarded as harmless commensals, though their identification on stool examination is still important to avoid misdiagnosis/inappropriate treatment, and to distinguish them accurately from Giardia and from pathogenic amoebae on routine stool microscopy.
Laboratory diagnosis (general): stool microscopy (wet mount, concentration techniques, and permanent stained smears — trichrome or iron-haematoxylin) for trophozoites (in loose/watery stool) and cysts (in formed stool), with morphological features (nuclear number/arrangement, flagellar number, presence/shape of cyst) allowing species differentiation.