large ciliated protozoan parasite.
Cysts are the
parasite stage responsible for transmission of balantidiasis
The host most often acquires the cyst through ingestion of contaminated
food or water
Following ingestion, excystation occurs in the small intestine, and the
trophozoites colonize the large intestine
The trophozoites reside in the lumen of the large intestine of humans
and animals, where they replicate by binary fission, during which
conjugation may occur
Trophozoites undergo encystation to produce infective cysts
Some trophozoites invade the wall of the colon and multiply. Some
return to lumen and disintegrate. Mature cysts are passed with feces
Because pigs are an animal reservoir, human infections occur more
frequently in areas where pigs are raised. Other potential animal
reservoirs include rodents and nonhuman primates.
Most cases are
asymptomatic. Clinical manifestations, when present, include persistent
diarrhea, occasionally dysentery, abdominal pain, and weight loss.
Symptoms can be severe in debilitated persons.
Diagnosis is based
on detection of trophozoites in stool specimens or in tissue collected
during endoscopy. Cysts are less frequently encountered.
Balantidium coli is passed intermittently and once outside the colon
is rapidly destroyed. Thus stool specimens should be collected
repeatedly, and immediately examined or preserved to enhance detection
of the parasite.
comparison with other intestinal parasites
The drug of choice
is tetracycline*, with metronidazole* and iodoquinol* as alternatives.
Tetracycline is contraindicated in pregnancy and in children less than 8
* This drug is
approved by the FDA, but considered investigational for this purpose.