Other intestinal protozoa, Biology tutorial

Balantidium coli:

This is parasite mainly of cows, pigs and horses. Organism is large (100 x 60 micrometer) ciliate with the macro- and a micro-nucleus. Infection takes place mostly in farm workers and other rural inhabitants by intake of cysts in fecal material of farm animals. Man-to man transmission is unusual but possible. Symptoms and pathogenesis of balantidiasis are like those seen in entamebiasis, comprising intestinal epithelial erosion. Though, liver, lung and brain abscesses are not seen. Metronidazole and iodoquinol are efficient.

Cryptosporidium parvum:

Cryptosporidium parvum (C. parvum) is the small round parasite estimating 3 to 5 micrometers that is found in gastrointestinal tract of several animals and causes epidemics of diarrhea in humans by contaminated food and water. Humans are infected by intake of C. parvum oocysts having seveal sporozoites. Sporozoites are released in upper GI tract and join to gut mucosal cells where they split to produce merozoites. Merozoites invade other mucosal cells and further multiply asexually.

When the large number of humans in the community have diarrhea, most probable cause is C. parvum. The small bolus of infection may cause mild diarrhea, while a larger ingestion of organisms may cause more pronounced symptoms comprising copious watery diarrhea, cramping abdominal pain, flatulence and weight loss. Harshness and duration of symptoms are linked to immuno-competence. In AIDS patients, organism may cause prolonged, harsh diarrhea and organisms may invade gallbladder, biliary tract and lung epithelium. There is no approved efficient treatment for cryptosporidiasis, though paromycin is utilized as investigational drug.

Isospora belli:

Isospora belli is the exceptional infection of normal humans, though it is being seen in increasing numbers in AIDS patients. Infection occurs via oro-fecal route. Infective stage of organism is the oval oocyst that on intake follows same course as C. parvum. Disease generates symptoms like those of giardiasis. In normal individuals, mild infections resolve themselves with rest and mild diet and heavier infections can be treated with sulpha drugs. Treatment may have to be carried on for the prolonged period in AIDS patients.

Luminal protozoa:


Trichomonad is general term utilized for members of Order Trichomonadida that comprises a large number of species parasitising tubular organs of the wide range of hosts. Species readily attained for laboratory study are Trichomonas muris in laboratory mice and rats and Trichomonas gallinae from crop of pigeons.

Epidemiology: Trichomonas vaginalis has the world-wide distribution; occurrence is as low as 5% in normal females and as high as 70% among prostitutes and prison inmates.

Morphology: Trophozoite form is 15 to 18 micrometers in diameter and is half pear shaped with the single nucleus, 4 anterior flagella and lateral flagellum joined by undulating membrane. Two axostyles are arranged asymmetrically. Organism doesn't encyst.

Lifecycle: T. vaginalis colonizes vagina of women and urethra (sometimes prostate) of men. Infection takes place mainly via sexual contact, though non-venereal infections are possible. Organism doesn't encyst and separates by binary fission that is favored by low acidity (pH >5.9; normal pH is 3.5 to 4.5). There is no non-human reservoir.

Trichomoniasis is the disease caused by this organism

Etiology: Trichomonas vaginalis (a flagellate)

Symptoms: T. vaginalis infection is hardly ever symptomatic in men, though it may cause mild urethritis or infrequently prostatitis. In women, it is frequently asymptomatic, but heavy infections in the high pH environment may cause mild to harsh vaginitis with copious foul-smelling yellowish, at times frothy discharge.

Pathology: Organism causes contact-dependent damage to epithelium of infected organ.

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