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H. De Bosschere, S. Roels

Veterinary Agrochemical Research Centre (VAR)

Department of Biocontrol

Groeselenberg 99, B-1180 Brussels (Ukkel), Belgium



This is a description and photographic illustration of two commonly detected ciliated protozoans in chelonian stools of Mediterranean tortoises. They are mostly considered as comensal flora of the digestive-tract flora, however in certain conditions they may become pathogenic.


Balantidium sp. and Nyctotherus sp. are ciliated protozoans which are frequently encountered in chelonians stools. They are considered as normal inhabitants of the normal chelonian digestive-tract flora and play a usefull role in the digestion of cellulose. Therefore, in most cases, they appear to cause their hosts little or no distress. However, from time to time, due to a variety or reasons (such as dietary mismanagement; drugs treatments; …), these protozoans may outnumber their normal proportions resulting in pathogenic consequences (severe irritation of the intestinal walls). The symptoms may range from acute diarrhea, resulting in dehydration and weight loss into chronic cases with a complete loss of normal digestive-tract flora and inanition as a result of an inability to digest and metabolise the food consumed.


Fresh fecal samples were collected and mixed with a saturated saline solution in a container into a watery solution. Some drops of this solution were placed on a microscope slide, covered with a cover slip and microscopically examined. It should be stressed that these were fecal examinations on a regular basis. None of the examined tortoises did show any digestive symptoms.


Protozoans are single celled eukaryotes. There are many types of protozoa, and these could be difficult to identify from each other. Ciliates are characterized by the presence of numerous (short) cilia spread over the organism's body.

Balantidium sp.

Balantidium sp. is one of the easiest protozoa to identify. This organism is large, egg-like shaped, quite active but slow moving. It is frequently encountered in fecal examinations.

The Tortoise Trust has observed Balantidium sp. in Testudo hermanni, Testudo graeca, Geochelone pardalis, Malacochersus tornieri and Kinixys homeana. It has also been observed in Galapagos and Indian Ocean giant tortoises.

Life cycle Balantidium sp.:

Cysts are the infectious stage responsible for transmission of balantidiasis.  The host most often acquires the cyst (Figure 1) through ingestion of fecally contaminated food or water.  Following ingestion, excystation occurs in the small intestine, and the trophozoites colonize the large intestine (Figure 2).  

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 into the environnement.

Every book on reptile parasites seems to have a different opinion as to how pathogenic Balantidium is. In pigs and human, Balantidium coli is associated with host pathology. Eguro's opinion is these parasites are generally not a problem (in iguanas).

The recommended treatment for balantidiasis is 125 mg/kg Metronidazole (brand name Flagyl or other) orally every day for three days, followed by tetracycline orally for 5-8 days at 25-50 mg/kg; or a single dose of 260 mg/kg Metronidazole has also been described as effective.

Nyctotherus sp.

Nyctotherus sp. is a large, lemon-like shaped, active slow moving organism.

Ernst and Nichols (1974) reported finding this ciliate in Geochelone carbonaria and Geochelone elegans imported into the USA. In the present paper, Nyctotherus sp. is observed in Testudo hermanni.

The life cycle of Nyctotherus sp. is identical to this of Balantidium sp.. Cysts are the infectious stage (Figure 3) and the trophozoites (Figure 4) can be found in the intestines. It is of doubtful pathogenicity.



Protozoan organisms can represent a major hazard to captive collections of chelonia but not all occurrences are pathogenic. The best prevention is good hygiene. Special attention should be paid to food handling and feeding routines. Cleaning and disinfection of husbandry infrastructure is highly recommended on a regular basis.

Preventive screening of fecal (and urine) samples for pathogenic agents may help in preventing built-up of severe protozoan outbreaks and tortoise losses in captive conditions. If pathogenicity is suspected, veterinary treatment should be sought ASAP.

However, effective treatment exists, but detection and diagnosis of the "real" pathogens (e.g. Hexamita sp.) is primordial, before treatment is installed (if not, more harm than good can be done!).


Ruben Liebaert is thanked for providing reference literature.


Aucott, J.N., an Ravdin, J.I., (1993) Amebiasis and "nonpathogenic" intestinal protozoa. Infect. Dis. Clin. North Am., 7:3 467-485.

Division of Parasitic Diseases, Balantidiasis. Website:

Eguro M.,(1999) Fecal examination. Website:

Ernst, C.H., and Nichols,J.N., (1974) Internal Ciliates of Tortoises, Brit. J. Herpetology, 5:3 450-451.

Garcia, L.S., (1999) Flagellates and ciliates. Clin. Lab. Med., 19:3 621-638, VII.

Highfield, A.C., Protozoan infections in Chelonians. Tortoise Trust Website:

Highfield, A.C., (1996) Practical Encyclopedia of Keeping and Breeding Tortoises and Freshwater Turtles. Carapace Press, London, 115.

Henkel, M., and Degardin, A., Website:

Klingenberg, R.J., (1993) Understanding Reptile Parasites. Advanced Vivariums Systems, Lakeside, 59-66.

McArthur, S., (1996) Veterinary Management of Tortoises and Turtles. Blackwell Science Inc., Cambridge, 82.

Yang, Y., Zeng, L., Li, M., and Zhou, J., (1995) Diarrhoea in piglets and monkeys experimentally infected with Balantidium coli isolated from human faeces. J. Trop. Med. Hyg., 98:1 69-72