SN2 SHORT NOTE 5M ★ High-yield

Describe Trichomonas vaginalis with its clinical features, diagnosis and treatment.

Microbiology · 2nd Professional — Para-Clinical

The Parasite

Trichomonas vaginalis is a flagellate protozoan that exists only as a trophozoite — there is NO cyst stage
This single fact determines its epidemiology: without a resistant cyst it cannot survive drying or the environment, so transmission must be direct — almost exclusively sexual
Morphology — pear-shaped, about the size of a leucocyte, with a single nucleus, four anterior flagella and a fifth running along an undulating membrane that extends only half the body length, together with a stiffening axostyle. Motility is characteristically jerky and twitching
It is the commonest non-viral sexually transmitted infection worldwide
It raises the vaginal pH above 4.5 and adheres to and damages the squamous epithelium

Clinical Features

Group	Features
Women	A profuse, frothy, yellow-green, offensive discharge with vulval itching, soreness and dysuria. The cervix may show punctate haemorrhages — the "strawberry cervix" — which is characteristic but present in only a minority. Vaginal pH is raised above 4.5
Men	Usually asymptomatic, which is why men act as a silent reservoir and why treating the woman alone guarantees reinfection. May cause urethritis, prostatitis and epididymitis
In pregnancy	Associated with preterm labour, premature rupture of membranes and low birth weight
Association with HIV	The mucosal inflammation and microulceration increase both acquisition and transmission of HIV, so treating it has a public health value beyond the symptoms themselves

CLINICAL PEARL

The absence of a cyst stage explains everything about trichomoniasis. No cyst means no environmental survival, so it cannot be waterborne or food-borne and must pass by direct contact — hence it is a sexually transmitted infection while its intestinal flagellate relatives are faecal-oral. It also means the specimen must be examined fresh and warm, because the trophozoite dies and stops moving within minutes, and motility is what identifies it.

Diagnosis and Treatment

Wet mount of vaginal discharge in warm saline — examined immediately at the bedside, showing the characteristic jerky twitching motility. It is cheap and rapid, but only about 60 to 70% sensitive and falls rapidly with delay
Culture in Diamond or Feinberg-Whittington medium is more sensitive; nucleic acid amplification tests are the most sensitive and are now the reference method, usable on urine and self-collected swabs
Rapid antigen tests are available for point-of-care use
It is frequently an incidental finding on a cervical smear, which is not a sensitive test but is a common route to diagnosis
Distinguish the three causes of vaginal discharge — and the bedside pH is what separates them

Feature	Trichomoniasis	Bacterial vaginosis	Candidiasis
Discharge	Profuse, frothy, yellow-green, offensive	Thin, homogeneous, grey-white, fishy odour	Thick, white, "cottage cheese"
Vaginal pH	Raised, above 4.5	Raised, above 4.5	Normal, below 4.5
Itching	Present	Usually absent	Intense
Whiff (amine) test with KOH	May be positive	Positive	Negative
Microscopy	Motile trophozoites and many pus cells	Clue cells; few pus cells	Budding yeasts and pseudohyphae
Partner treatment	Essential	Not required	Not usually required

Treatment and Applied Aspects

Metronidazole or tinidazole — a single 2 g dose or a 7-day course; it is effective and cheap
Treat the partner, always and simultaneously, whether or not he has symptoms; failure to do so is the commonest cause of apparent treatment failure, which is in fact reinfection
Avoid alcohol during and for 48 hours after metronidazole because of the disulfiram-like reaction
Topical treatment is inadequate, since the organism also infects the urethra and periurethral glands, which topical agents do not reach
Screen for other sexually transmitted infections — gonorrhoea, chlamydia, syphilis and HIV; the presence of one implies risk of the others
Treat in pregnancy, since the association with preterm birth and low birth weight makes it worth treating even when symptoms are mild
Syndromic management is used in India where laboratory facilities are limited, treating vaginal discharge for trichomoniasis and bacterial vaginosis together at the first visit — a pragmatic approach that also requires partner notification

All questions in Parasitology I — Protozoa

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