medical parasitology

1. Balantidium coli

2. INTRODUCTION
• It is largest protozoan
• Only ciliated parasites of humans
• Causes Balantidiasis
Taxonomy:
belongs to Phylum Ciliophora
Class: Litostomatea
Order: Vestibuliferida
Family: Balantidiidae
Habitat: large intestines of man, pig (main reservoir) and other animals.

3. MORPHOLOGY
• Two forms:
a. Trophozoite – in dysenteric stool
b. Cyst: - in carriers and chronic cases
Both forms: binucleated - large macronucleus and small micronucleus

4. TROPHOZOITE
• Found in active stage of disease – invasive form
• shape: oval
• Size: 30-300 µm long x 30-100 µm breadth
• Whole body covered with a row of tiny delicate cilia – organ of locomotion
• Cilia present near the mouth part – longer  called “adoral cilia”
• Anterior end- narrow
- Bears a groove (peristome) that leads to a mouth (cytostome)
- followed by a short funnel shaped gullet (cytopharynx) extending up to one-third
of the body.
• Posterior end- broad, round
- Bears an excretory opening (cytopyge)

5. TROPHOZOITE
• No anus
• Cytoplasm- outer clear ectoplasm and inner granular endoplasm
Endoplasm
- Contains two nuclei: large kidney shaped macronucleus in center
and a small micronucleus in the concavity of the macronucleus
- Two contractile vacuoles: lie side by side or one above the other maintain the
proper osmotic pressure inside cell
- Numerous food vacuole: contains food particles like debris from host gut,
bacteria, starch grains, fat droplets and occasional RBCs, etc.
 Where digestion of food particles takes place.

7. CYST
• Shape: round
• Size: 40-60 µm
• Immobile and dominant
• Surrounded by a thick transparent cyst wall allows the cysts to
resist degradation in the acidic environment of the stomach and the
basic environment of the small intestine
- Contains two nuclei- macronucleus and micronucleus and vacuoles
- Cilia- seen in younger cyst but is absorbed on maturity movement
ceases

8. Development in large intestine- Life cycle
• Mode of transmission: faecal-oral route
• Virulence factor: Hyaluronidase- help to penetrate intestinal mucosa
• Excystation: occurs in small intestine- when trophozoites are produced from cysts
- Multiplication in large intestine
- Single trophozoite forms from each cyst
- trophozoite- is the feeding stage of the parasite  multiply either in gut lumen or
enter the sub mucosa of large intestine
Cell division Asexual reproduction
Sexual reproduction

10. Asexual reproduction
• Division by binary fission
• Micronucleus divide first followed by macronucleus
• A transverse septum forms – separates the cytoplasm into halves.
Sexual reproduction
• Replicate sexually (Syngamy) by conjugation
• Two trophozoites come in contact with each other at their anterior ends
• Exchange the nuclear material for few moments then they detach
• No increase in number of trophozoites
• Both trophozoite and cyst are excreted in faeces
• Trophozoites disintegrates, cysts are resistant and are infective to man and pig

11. Life cycle

12. Risk factors
• Pig’s faeces carrying vast volumes of Balantidium coli contaminates
water sources
• Humans who work with pigs  exposed to Balantidium coli.

13. Clinical features
Asymptomatic carriers
• Results from majority of infection
• Harbours the cyst and spread the infection
Acute disease
• Similar to acute amoebic dysentery
• Trophozoites invade gut sub mucosa- form multiple tiny superficial ulcers
- Ulcers with necrotic base and undermined edge
• Microscopically- cluster of trophozoites are found in sub mucosa with inflammatory cells
(lymphocytic)
• Patients present have frequent diarrhoea with profuse mucus and blood.
• Other features- fever, nausea, vomiting and abdominal pain
• Haemorrhage- may lead to shock and death

14. Clinical features
Chronic disease
• Have periods of increased bowel movements (mucous or rarely bloody)
• Alternate periods of constipations
• Organism load is less and requires repeated stool examination
Complications
• Seen in immunocompromised and malnourished people
• Perforation of large intestine, involvement of appendix, peritonitis, severe
dehydration leading to renal failure
• Extra intestinal manifestations- rare: liver abscess, pleuritis and pneumonia

15. EPIDEMIOLOGY
Balantidiasis:
• Distributed worldwide- in tropical and subtropical countries with
increased pig to human contact
• Highest prevalence- 20% reported from mountain districts of West
Irian (Indonesia)
• Human outbreak reported from Pacific Island of Truk in 1973
• India: rare

16. LABORATORY DIAGNOSIS
• Stool examination-detects trophozoites and cysts
• Histopathology
• Culture
• serology

17. STOOL MICROSCOPY
• Trophozoites- detected in acute disease (dysenteric stool)
-easy to identify by its rotatory motility, large kidney shaped macronucleus and
presence of cilia
• Cysts- seen in chronic cases or carriers
- round, 40-60 µm in size, surrounded by a cyst wall and presence of two nuclei

18. HISTOPATHOLOGY
• Histopathological staining of biopsy tissue or scrapping of the ulcers
taken by sigmoidoscopy
-reveals clusters of trophozoites, cysts and lymphocytic infiltration
found in sub mucosa

19. CULTURE
• Media used: Boeck and Drbohlav egg serum media and Balamuth’s media
• Culture rarely necessary as parasites are easily detected by stool microscopy or
histopathology
Serology
• scrapings of colonic and ceacal
mucosa can be stained with H&E.

20. PREVENTION
• Treatment of carriers shedding the cysts
• Hygienic rearing of pigs and prevention of pig to human contact
• Prevention of contamination of food or water with pig and human
faeces

21. TREATMENT
• DOC: Tetracycline- 500 mg four times a day for 10 days
• Alternatively Metronidazole- 750 mg three times a day for 5-7 days
• Treatment of carriers- preventing spread of the disease.
• No relapse or drug resistance reported

22. Things to remember
Trophozoite
• Shape Oval, pointed at anterior end
• Size 30-300 µm long x 30-100 µm wide
• Surface Covered in cilia
• Not infective
• Reproduction By binary fission or conjugation
• Nuclei: Macronucleus and micronucleus

23. Cyst
• Shape Spherical
• Size 40-60 m across
• Surface Covered with thick, hard cyst wall
• with cilia
• Infectious: Infective
• Reproduction Non-reproductive
• Nuclei: macronucleus and micronucleus