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Ameba: Formally Phylum Sarcodina

R & J Ch 7 Protozoa with pseudopodia (or if not, distinct

locomotive protoplasmic flow present).

Mitochondria when present never in the form

of a kinetoplasts.

Without apical complex.

Without axostyles.

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Ameboid Movement

Ameboid locomotion is used by certain

protists including parasitic amoeba.

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(gel-like)

(more fluid)

Complex changes in cell

fine structure, chemistry,

and behavior.

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Mechanisms of Ameboid Movement

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Mechanisms of Ameboid Movement

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Ameba Diversity

Most amoebas are harmless single cell

protozoans living in mud, water, and soil

feeding on other protozoans and bacteria.

Some species are parasitic and

endocommensals and are quite commoninhabitants of animals.

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Endocommensal and Parasitic

Ameba Diversity Domestic animals

Birds are free

Reptiles one species that is pathogenicin snakesEntamoeba invadens

Frogs and salamanders

Leeches, termites, and cockroaches

Hydra

Humans

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Some Ameba are Pathogenic

Amebiasis- The pathological condition of

having an amoebic infection.

-iasis- indicates a pathological

condition

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Entamoeba histolytica

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One of the most important and

pathogenic parasites of humans.

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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.

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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 isprimarily a human parasite and is transmitted from human to

human.

First seen in 1878 but not described until1903.

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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 isprimarily a human parasite and is transmitted from human tohuman.

First seen in 1878 but not described until 1903.

Causative agent of the disease amebiasis(old name is Amebic Dysentery).

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Active, feeding stage

Growing stage

Amoeboid with bluntpseudopodia

Non-foamy cytoplasm

Uninucleated; nucleuswith fine peripheral

chromatin granules,

small central endosomeTrophozoite: 20-30 m

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Entamoeba histolytica Trophozoites

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Dormant/resistant

stage

Spherical

1-4 nuclei, (4 in

mature cysts)

Bluntly rounded

chromatoidal bars

Cyst:10-20 m

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Entamoeba histolytica Cysts

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Uninucleate cyst Binucleate cyst

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Quadrinucleate or mature cysts

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Entamoeba histolytica Life Cycle

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INFECTIVE STAGE: Cyst


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Cysts are susceptible to heat (above 40

C), freezing (below5 C), and drying.


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Cysts are susceptible to heat (above 40 C), freezing

(below5 C), and drying. Cysts remain viable in moist environment

for 1 month.


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CYST: ingested with fecal

contaminated food or

water.

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contaminated food or water.

Excystation occurs in the

small intestine in an

alkaline environment.

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contaminated food or water.

Excystation occurs in the smallintestine in an alkaline environment.

Metacystic amebas

emerge, divide and movedown into the large

intestine.

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Trophozoites colonize the

large intestine and invade

the mucosa.

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Trophozoites colonize the large

intestine and invade the mucosa.

They live within the crypts

and mucosa of the large

intestinal lining.

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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 the LI mucosafeeding on starches and

mucous secretions.

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Cysts form in response

to unfavorable

(deteriorating)environmental

conditions, as they move

down the LI.

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Cysts form in response to

unfavorable (deteriorating)

environmental conditions, as

they move down the LI.

They are released in

formed feces.

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E. histolytica has surface enzymes that

can digest epithelial cells and therefore

hydrolyze host tissues and cause

pathology.

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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.

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E. histolytica has surface enzymes that can digest epithelial cellsand 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.

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Entamoeba histolytica Pathology

1. A Primary Ulcer Can Occur.

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Flask Shaped

Ulcers

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A primary ulcer can cause rupturing of the

bowel and can cause Peritonitis.

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Shows movement of

trophozoites from largeintestine to liver via hepatic

portal vein.

Liver Abscesses

b hi l i P h l

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2. Extra-Intestinal

Lesions and AbscessOccurs

E b hi l i P h l

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2. Extra-Intestinal


A. Hepatic Amebiasis

E b hi l i P h l

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2. Extra-Intestinal



B. Pulmonary Amebiasis

E b hi l i P th l

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2. Extra-Intestinal



B. Pulmonary Amebiasis

C. Cerebral Amebiasis

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Frequently, intestinal lesions will heal

themselves.

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Frequently, intestinal lesions will heal

themselves.

Two exceptions- External ulcers that didnot come from the intestine.

Ocular amebiasis

Genital amebiasis

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Amoebic Amebiasis of the Skin

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Symptoms

10% of people in the world infected with

ameba, but only 3% ever have some sort

of clinical signs.

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Symptoms

10% of people in the world infected with

ameba, but only 3% ever have some sort of

clinical signs.

Abdominal discomfort.

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Symptoms

10% of people in the world infected with ameba, but

only 3% ever have some sort of clinical signs.


Intense pain localized on the right side.

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Symptoms

10% of people in the world infected with ameba, but

only 3% ever have some sort of clinical signs.


Intense pain localized on the right side.

Dysentery.

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So How Bad is This?

In theory, ingestion of 1 cyst could kill

you.

In practice, probably it will never

happen.

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Prognosis

90% of time recovery.

- How much damage.

- Body will repair itself but this repaired

connective tissue in bowel will not

function.

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Diagnosis

Fecal smear/Nested PCR and monoclonal

antibody methods.

Biopsy.

Serological/Immunological tests (ELISA).

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Seriousness of Diagnosis

Could expose someone to unnecessary

treatment.

Will not be treating the real problem.

There is an expense.

Time factor.

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Treatment

Current drug of choice Metronidazole

(Flagyl).

Side effects: Insomnia, headaches,

vomiting, intense vasodilation, mutations

on bacteria, and carcinogenic in mice.

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Epidemiology

How an infectious organism spreads

through a population.

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DISTRIBUTION - Parasite has worldwidedistribution but is most common in the tropical and

subtropical areas of the world.

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- it is estimated that up to 500 million people may be affected.

- may cause up to 100,000 deaths each year.

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- it is estimated that up to 500 million people may be affected.

- may cause up to 100,000 deaths each year.

PREVALENCE: < 1% in Canada and Alaska0.9% in U.S.

40% in the tropics

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A number of outbreaks have resultedfrom a breakdown in sanitation or

behavioral practices of people.

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A number of outbreaks have resulted from a breakdown insanitation 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.

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A number of outbreaks have resulted from a breakdown insanitation 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 ofamebiasis resulting in 58 deaths.

Outbreak in the late 1970s in New York

City among gay men.

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