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Parasitic Protozoans
Lecture 2
1Amoebae
Remember
In our study
1.
2.
3.
4.
5.
Intermediate host
Geographic distribution
Mode of transmission
Location in definitive host
Pathology
•
Disease, symptoms, diagnosis,
• Life Cycle
Protozoans
We will cover four main groups of singlecelled organisms that are parasites of
humans and other animals.
Amoeba
Ciliates
Flagellates
• Flagellates
• Hemoflagellates
Coccidians
General Life Cycle
Trophozoits
Ingested
Binary
Fission
Out into
environment
Active feeding stage
Cyst
dormant,
usually
dispersal
stage
1- Entamoeba histolytica
Entamoeba histolytica
Definitive Host: Humans.
Reservoir hosts may include dogs, pigs,
and monkeys.
Intermediate Host: None.
Geographic distribution: Cosmopolitan
(worldwide).
500 million people worldwide infected
100 million people suffer acute symptoms
100,000 people die every year
Varies by location (depends on sanitation
and climate)
Entamoeba histolytica
Mode of transmission: Fecal/oral transmission
(Ingestion of food and water contaminated by feces.)
Cysts survive longer in water than in food
Cysts can pass through intestines of cockroaches
Rarely transmitted through anal sex or anal then
oral sex.
Location in host: Usually in the cecum but can be found
in any part of the small and large intestines.
May be carried to liver, lungs, and other body parts
if it perforates the intestines.
Entamoeba histolytica
Pathology
Causes Amebic
Dysentery
A.K.A. Montezuma’s
Revenge
Trophs rupture and
digest cells of the
intestinal mucosa
Dissolves the mucosa
to the muscularis
Pathology
Healthy intestine
Intestine infected
with E. histolytica
Pathology
When amoeba reach muscularis, they travel laterally
Causes large ulceration of the intestines
Ulcers are frequently invaded by bacteria
Bacteria may help dissolve intestinal lining
Can lead to more serious complications of secondary
bacterial infections
Pathology
Once in the submucosa, the
parasite can enter the blood
stream and be swept to other
organs
Called Amebiasis
Liver most commonly invaded
Digests liver cells
Causes abscesses
Lungs are usually invaded next.
May also invade heart, brain,
kidneys, skin and any other
organ.
Symptoms
Depends on host’s previous exposure to
parasite
Chronic, low-level exposure can result in host being
asymptomatic.
Less frequent exposure result in severe symptoms.
May also depend on nutritional status of host
Amebic dysentery
Ranges from minor cramping and diarrhea to
severe cramping and 15 to 20 bloody stools a day
Race has no effect on severity
Symptoms
Amebiasis – Symptoms depend on what
organ the parasite invades.
Abdominal cavity
Peritonitis, abdominal pain, cramping, and
anemia
Liver
Symptoms are similar to hepatitis
Lungs, brains, or heart
May cause the death of the host.
Life Cycle
Life
Cycle
Life Cycle stages
2- Entamoeba coli
General information
Definitive Host: Humans
Intermediate Host: None
Geographic distribution: Cosmopolitan
Much more common than E. histolytica
More hardy, resistant to putrefaction.
Mode of transmission: Ingestion of
contaminated food and water.
General information
Location in Definitive host: Cecum and
large intestine.
Pathology and Treatment: None
Harmless commensal
Feeds on bacteria, yeast, and wastes in
intestines
Diagnosis: Important to distinguish
between it and E. histolytica
Avoid unnecessary treatment
8 nuclei in cyst vs. 4 in E. histolytica
Different shape nuclei.
Infective stage
1- Cyst
E. coli
E. histolytica
Infective stage
2- Trophozoite
Life Cycle
Change in chemistry as trophozoite moves
down colon tells the trophozoite to form a
cyst.
Engested & excystation
Binary
Fission
cystation
Cyst
Out into
environment
Trophozoite
in large
intestines
3- Entamoeba gingivalis
General information
Definitive Host: Humans. Also other
primates, dogs, and cats.
Intermediate Host: None
Geographic distribution: Cosmopolitan
About 50% of the population have it.
Up to 95% of “unhealthy” mouths have it.
Mode of transmission: Direct oral
contact (kissing).
General information
Location in Definitive host: Mouth,
particularly along gums line. Also in tonsils.
Pathology and Treatment: None
More common in mouths with gingivitis and
tonsillitis
Probably doesn’t cause disease
• Most likely due to abundance of food in
“dirty” mouth.
Diagnosis: Sample of scrapings from teeth
Life Cycle
No cyst stage. Never goes out to external
environment.
Binary
Fission
Trophozoites
in mouth
Direct oral contact
passes it to next
host.