2. FAMILY ENTAMOEBIDAE:
• Parasites or commensals- digestive systems of Arthropods and Vertebrates.
• Genera, species- differentiated by:
Size.
Nuclear structure.
• Three genera contain parasites of humans and domestic animals:
1. Entamoeba.
2. Endolimax.
3. Iodamoeba.
3. GENUS ENTAMOEBA:
• Vesicular nucleus-small endosome near center.
• Chromatin granules- periphery of nucleus.
• Cytoplasm- food vacuoles- bacteria/ starch grains.
• Golgi bodies and mitochondria- absent.
• 5 species occur in humans.
4. Entamoeba histolytica
One of the most important and pathogenic parasites of humans.
Although dogs, cats and primates may be infected, these infections
are rare and unimportant. This parasite is primarily a human parasite
and is transmitted from human to human.
First seen in 1878 but not described until 1903.
Causative agent of the disease amebiasis (old name is Amebic
Dysentery).
11. INFECTIVE STAGE: Cyst
• Several stages present in life cycle including trophozoite, pre-cyct,
cyst, metacyst and metacystic trophozoids
• Cysts are susceptible to heat (above 40 °C), freezing (below –5 °C),
and drying.
• Cysts remain viable in moist environment for 1 month.
Entamoeba histolytica Life Cycle
12. Life Cycle
• CYST-ingested with fecal
contaminated food or water.
• Excystation occurs in the small
intestine in an alkaline
environment.
• Metacystic amoebas emerge, divide
and move down into the large
intestine.
13. • Trophozoites colonize the large
intestine and invade the mucosa.
• They live within the crypts and mucosa
of the large intestinal lining.
• Trophozoites may live and multiply
indefinitely within the crypts of
mucosa feeding on starches and
mucous secretions.
14. Life Cycle:
• Cysts form in response to
unfavorable (deteriorating)
environmental conditions, as
they move down the LI.
• They are released in formed
feces.
15. Entamoeba histolytica
• E. histolytica has surface enzymes that can digest epithelial cells and
therefore hydrolyze host tissues and cause pathology.
• Usually the hosts’ repair of the epithelial cells can keep pace with
the damage.
• However, when the host is stressed, has too much HCl, or a high
bacterial flora, the digestion will be ahead of repair.
16.
17.
18.
19. Pathology:
1. A Primary Ulcer Can Occur: A primary ulcer can cause
rupturing of the bowel and can cause Peritonitis.
Flask Shaped Ulcers
20. Shows movement of trophozoites from large intestine to liver via hepatic portal vein.
22. Pathology:
Frequently, intestinal lesions will heal themselves.
Two exceptions- External ulcers that did not come from the intestine.
• Ocular amebiasis.
• Genital amebiasis.
Amebiasis of skin
23. Symptoms:
• 10% of people in the world infected with ameba, but only 3% ever
have some sort of clinical signs.
• Abdominal discomfort.
• Intense pain localized on the right side.
• Dysentery.
24. So How Bad is This?
• In theory, ingestion of 1 cyst could kill you.
• In practice, probably it will never happen.
25. Prognosis:
• 90% of time recovery.
Damage:
- Body will repair itself but this repaired connective tissue in bowel
will not function.
27. Seriousness of Diagnosis
• Could expose someone to unnecessary treatment.
• Will not be treating the real problem.
• There is an expense.
• Time factor.
28. Treatment
• Current drug of choice Metronidazole (Flagyl)
• Low in toxicity and effective against for both extra-intestinal and
colonic infections
• Side effects: Insomnia, headaches, vomiting, intense vasodilation,
mutations on bacteria, and carcinogenic in mice.
29. Distribution:
Parasite has worldwide distribution but is most common in the
tropical and subtropical areas of the world.
• it is estimated that up to 500 million people may be affected.
• - may cause up to 100,000 deaths each year.
30. Prevalence:
PREVALENCE: < 1% in Canada and Alaska
• 0.9% in U.S.
• 40% in the tropics
A number of outbreaks have resulted from a breakdown in sanitation or behavioral
practices of people.
Outbreak in 1933 World's Fair in Chicago caused by defective plumbing (cross
connections between water lines and sewer lines) caused over 1,000 cases of
amebiasis resulting in 58 deaths.
Outbreak in the late 1970’s in New York City among gay men.
31. REFERENCES:
1. Ryan KJ, Ray CG, eds. (2004). “Sherris Medical Microbiology” (4th ed.). McGraw Hill. pp. 733–8.
2. American Water Works Association (June 2006). “Waterborne Pathogens”. American Water Works
Association.
3. Gunther, Janelle; Shafir, Shira; Bristow, Benjamin; Sorvillo, Frank (1 December 2011). "Amebiasis-
Related Mortality among United States Residents, 1990–2007". The American Journal of Tropical
Medicine and Hygiene. 85 (6): 1038–1040.
4. Caler, E & Lorenzi, H (2010). "Entamoeba histolytica: Genome Status and Web Resources". Anaerobic
Parasitic Protozoa: Genomics and Molecular Biology. Caister Academic Press.
5. Diamond LS, Mattern CF, Bartgis IL (Feb 1972). "Viruses of Entamoeba histolytica. I. Identification of
transmissible virus-like agents.“ Journal of Virology. 9 (2): 326–41.
