(Parasites(Protozoal ciliates

Protozoal parasites-Ciliates
Balantidium coli

Balantidium coli is the only ciliate which infects humans. It is found world wide, but like many other fecal-oral transmitted diseases, it is more prevalent in the tropics. However, prevalence rates rarely exceed 1% . B. coli also infects a wide variety of mammals and is especially common in monkeys and pigs. Prevalence in pigs ranges from 20–100% and human balantidiosis usually exhibits an increased prevalence in communities that live in close association with pigs. For example, in Papua New Guinea, where pigs are the principal domestic animals, the prevalence among swine herders and slaughterhouse workers has been reported to be as high as 28%. Human-to-human transmission has also been documented and this mode of transmission is likely to occur in environments with crowding and poor personal hygiene such as mental hospitals and prisons.
The life cycle
The life cycle of B. coli is simple, involving ingestion of infectious cysts, excystation, and invasion of trophozoites into the mucosal lining of the large intestine, caecum, and terminal ileum.
B. coli is the only pathogenic ciliate and is the largest of the protozoa that parasitize humans. There are two nuclei within the trophozoite, one very large bean-shaped macronucleus and the smaller round micronucleus. The organisms normally live in the large intestine. The cyst is formed as the trophozoite moves down the intestine.
This ciliate undergo both an asexual reproduction (ie, binary fission) and a sexual reproduction involving conjugation, nuclear division does not occur in the cyst.









Clinical Disease
Severe B. coli infections may resemble amebiasis. Symptoms include diarrhea, nausea, vomiting, and anorexia. The diarrhea may persist for long periods of time resulting in acute fluid loss. Balantidium coli also has the potential to penetrate the mucosa resulting in ulceration just as those of Entamoeba histolytica, but perforation is more common. Metastatic lesions do not occur. Extra-intestinal disease has also been reported, but is rare.
B. coli usually lives as a non-pathogenic commensal in the large intestine and produces no symptoms. Superficial inflammation of the colonic mucosa may occur which can result in diarrhea and colicky pain. Mild or chronic infections are characterized by intermittent diarrhea and constipation, weight loss, and abdominal pain. On rare occasions the trophozoites will invade the intestinal epithelium and produce ulceration. Clinically this results in an acute diarrhea with mucus and blood (ie, dysentery). This balantidial dysentery is similar to the dysentery produced by Entameoba histolytica . Rare extra-intestinal infections involving lungs, vagina, ureter and urinary bladder and intestinal perforations leading to peritonitis have been reported.


Laboratory diagnosis
is made by identifying the organism in feces. Balantidium exhibits a typical fecal-oral life cycle consisting of trophozoite and cyst stages. The large size and unique morphological features of Balantidium precludes its confusion with any other protozoa found in human feces ?. The trophozoite is ovoid and has an average size of 70 x 45 µm, but can range upwards to 150-200 µm. The cyst has a distinctive cyst wall (CW) and is more spherical with an average diameter of 55 µm. In stained specimens the most obvious internal structure is the large macronucleus (maN). The micronucleus (miN) may not always be apparent because of its close association with the macronucleus. Contractile vacuoles (CV), which function in osmotic regulation, are often visible and occasionally the cytostome (Cy) is detectable. Similar to many other ciliates, Balantidium is covered by rows of cilia. The cilia give the parasite surface a fuzzy appearance and are less pronounced in the cyst stage.
The treatment of choice is tetracycline given at 500 mg four times per day for 10 days. Iodoquinol is the recommended alternate drug. Metronidazole has not produced consistent results. Preventive measures are the same as other diseases transmitted by the fecal-oral route. In addition, pig sewerage should be kept away from supplies of drinking water and food.