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• Balantidium coli


  Largest protozoan parasite, only ciliate known to cause human disease
• Balantidium coli initially identified as Paramecium coli by Malmsten


  1857
• Balantidium coli described and placed under separate genus

  1863
• Balantidiasis, balantidiosis, or balantidial dysentery


  Zoonotic disease caused by Balantidium coli
• Trophozoite


  • 30 to 50 um long and 25 to 120 um wide
  • Covered with cilia arranged in a longitudinal pattern
  • Has a cytosome
  • Has an oral apparatus at the tapered anterior end and a cytopyge at the rounded posterior end
  • Capable of attacking the intestinal epithelium and creating a characteristic ulcer
  • Has two dissimilar nuclei: macronucleus and micronucleus
  • Has two contractile vacuoles that act as osmoregulatory organelles
• Cyst


  • Spherical to slightly ovoid in shape, 40-60 um in diameter
  • Covered with thick cell walls (double-walled)
  • Formed principally as protection for survival outside the host
  • Infective stage
• Human infection

  1. Ingestion of food and/or water contaminated with B.coli cysts

  2. Ingested cysts excyst in the small intestine and become trophozoites

  3. Causes pathologic changes in the colonic wall and mucosa

  4. Parasite reproduction occurs asexually, through asymmetric binary fission

  5. The parasite encysts during intestinal transport or after evacuation of semi-formed stools
• Intrinsic host factors

  • Nutritional status, intestinal bacteria flora, achlorydia, alcoholism and presence of chronic disease
  • Contribute to host susceptibility to and severity of B.coli infection
• Presence of Salmonella in the intestines


  Aggravates balantidiasis by invading the ulcers caused by the protozoan
• Clinical manifestations

  • Asymptomatic carriers
  • Fulminant balantidiasis or balantidyal dysentery
  • Chronic form
• Fulminant balantidiasis or balantidyal dysentery


  • Involves diarrhea, with bloody and mucoid stools
  • Acute cases may have 6-15 episodes of diarrhea per day accompanied by abdominal pain, nausea, and vomiting
• Chronic form

  • Diarrhea may alternate with constipation, and may be accompanied by nonspecific symptoms such as abdominal pain or cramping, anemia, and cachexia
• Complications of balantidiasis

  • Intestinal perforation and acute appendicitis
  • Intestinal hemorrhage and shock
  • Intestinal perforation
  • Sepsis
• Diagnosis

  1. Microscopic demonstration of trophozoites and cysts in feces using direct examination or concentration techniques

  2. Repeated stool examinations

  3. Sigmoidoscopy

  4. Bronchoalveolar washings may also contain B. coli trophozoites in the case of pulmonary infection
• Epidemiology

  • Cosmopolitan distribution, more prevalent in areas with poor sanitation, close contact with pigs or pig feces, and in overcrowded institutions
  • Warm and humid climates in tropical and subtropical countries
• Pigs


  Major host of balantidiasis
• Prevention and control


  1. Proper sanitation, safe water supply and good personal hygiene

  2. Protection of food from contamination

  3. Limit contact of pigs with water sources and food crops

  4. Avoid utilizing pig feces as fertilizer

  5. Cysts easily inactivated by heat and by 1% sodium hypochlorite

  6. Ordinary chlorination of water is not effective against B. coli cysts
• Sarcosystis

  Derived from Greek word sarx= flesh and kystis= cyst
• Sarcosystis


  • Globally distributed genus of intracellular protozoa
  • Infecting both humans and animals
  • Infection known as sarcosporidiosis or sarcocystosis
• Discovered by Miescher as a white threadlike cyst in striated muscle of a house mouse


  1843
• Recognized Sarcosystis species

  • S. hominis
  • S. suihominis
• Forms of Sarcosystis

  • Zoite - banana-shaped cell with pointed end for entering host cells
  • Sporocyst - composed of 4 zoites, oval, 9-16 um length, can survive on ground and infect intermediate host
• Accidental ingestion of Sarcosystis sporocysts can result in direct infection of humans without intermediate host
• Oocysts of Sarcocystis in human feces measure 15-20 um long by 15-20 um wide
• Both sporulated oocysts and individual sporocysts may be shed in feces due to the fragile nature of mature oocysts
• Life Cycle of Sarcosystis


  1. Sexual reproduction in definitive hosts (carnivores like cats and dogs)

  2. Asexual reproduction in intermediate hosts (herbivores or omnivores)
• Pathology types


  • Rare invasive form with vasculitis, myositis
  • Intestinal form with nausea, abdominal pain, diarrhea
• Invasive form may involve lymph nodes, muscle, larynx
• Intestinal sarcocystosis in humans

  Often asymptomatic and clear spontaneously, occasionally mild fever, diarrhea, chills, vomiting
• Sarcosystis in humans as dead-end intermediate host


  Muscle cysts, symptoms like myalgia, muscle weakness, transitory edema
• Diagnosis methods

  • Stool examination
  • Fecal flotation wet mount (for intestinal sarcocystosis)
  • Biopsy with H&E stain and PAS staining (for muscle sarcocystosis)
• Treatments


  • Trimethoprim-sulfamethoxazole
  • Pyrimethamine
  • Sulfadiazine (for intestinal form)
  • Albendazole, metronidazole, co-trimoxazole (for myositis)
  • Corticosteroids for asymptomatic relief
• Sarcosystis infections are relatively low in frequency despite worldwide distribution
• Locations where sarcocystosis has been reported

  • Africa
  • Europe
  • United States
  • Central and South America
  • China
  • India
  • Tibet
  • Southeast Asia
• Prevention and control measures

  • Adequate cooking of beef and pork
  • Freezing meat at -5C for several days before ingestion
  • Preventing food animals from ingesting sporocysts from contaminated water, feed, bedding
  • Proper care and disposal of potentially infected animal stool
• Cytoisospora belli


  Previously known as Isospora belli, the Causative Agent of a medical condition affecting the small bowel called Cytoisosporiasis
• Isospora hominis


  The other known species, now taxonomically grouped under the genus Sarcocystis
• Cyst


  • Thin walled, transparent, and ovoid in shape
  • Appear as translucent and oval structures measuring 20-30 micrometers in length by 10-19 micrometers wide
  • Fully mature (sporulated) oocyst of genus Isospora is a spindle-shaped body that has two sporocysts that contain four sporozoites each
• Parasite Biology


  1. Sporulated Oocyst contains two sporocysts each containing four sporozoites (infective stage)

  2. Schizont ruptures the host epithelial cell liberating merozoites into the lumen

  3. Merozoites infect new epithelial cells in the process of asexual reproduction in the intestine continues

  4. Gametogony produce macrogametes and microgametes (sexual stages), which fuse to form a zygote

  5. Zygote eventually matures and forms an unsporulated oocyst, usually occurs within 48 hours after passage with the stool
• Life Cycle of Cytoisospora belli

  • The sporulation time of this parasite's egg is usually 1–4 days, and the entire life cycle takes about 9–10 days
  • The infective stage found in stool is the mature oocyst
  • The mature oocyst for Cytoisospora belli can remain infective in the environment for months