Amebae

The Amebae – Chapter 7

Old taxonomy: Phylum Sarcomastigophora Subphylum Sarcodina

New taxonomy: Phylum Sarcodina or Super-Group Amebozoa

Amebae move and feed through the ______________________ _____________________________

Some amebae may have a __________________________as well in their life cycle (indicates evolution from the Mastigophora).

Most amebae are free-living organisms in soil and water.

A few species have become parasitic in vertebrates and may cause dangerous diseases in their hosts.

2 Groups of Parasitic Amebae

____________________parasites – can only exist as parasites

- amebae in the family Entamoebidae

- occur in the digestive tracts of vertebrates

____________________parasites – free-living soil and water amebae that can become parasitic if they enter vertebrate tissues

Obligatory Amebae – Family Entamoebidae

Entamoeba histolytica

One of the most important and pathogenic parasites of humans

• Although pigs and primates may be infected, these infections are rare and unimportant. This parasite is transmitted from human to human; thus, this parasite is an _____________________________________

First seen in 1878 but not described until 1903

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

Entamoeba histolytica

DISTRIBUTION - Parasite has worldwide distribution but is most common in the ___________________________________of the world

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

- may cause up to 100,000 deaths each year

- a number of outbreaks have resulted from a breakdown in sanitation

Outbreak in 1933 World's Fair in Chicago caused by defective plumbing (cross connections between water lines and sewer lines) caused over 1000 cases of amebiasis resulting in 58 deaths

PREVALENCE: _________% in Canada and Alaska

_________% in U.S. (________% in Wisconsin in 1987)

_________% in the tropics

Entamoeba histolytica – 2 stages:

1. TROPHOZOITE - 20 to 30 µm in diameter; stained specimens ____________

- cytoplasm consists of clear ectoplasm, finely granular endoplasm; food vacuoles often containing rbc's are common

- characteristic structure is the single nucleus with one endosome:

_____________________________________________________

_____________________________________________________

- living specimens show active, rapid movement

- primary habitat of the trophozoites is the ___________________________ (but can metastasize to other organs)

Entamoeba histolytica trophozoites

Entamoeba histolytica – 2 stages:

2. CYST - encystment is stimulated by ________________________________

- trophozoite condenses into a sphere - the _________________________

- precyst secretes cyst wall to form the round cyst - 10 to 20 m in diameter

- nuclear division begins after encystment:

_______________ cyst ________________cyst _________________

or mature cyst

Entamoeba histolytica cysts

Cyst nuclei possess even peripheral chromatin and a central endosome (endosome position may be off-center in some stained specimens)

- cytoplasm contains rod-shaped _____________________________________ - cigar-shaped areas of packaged _______________ - and vacuoles

- chromatoidal bars and vacuoles are most common in young cysts (uninucleate & binucleate). In mature cysts, _____________________________

Entamoeba histolytica cysts

uninucleate cyst binucleate cyst

Entamoeba histolytica mature cysts

quadrinucleate or mature cysts – diagnostic in feces

Entamoeba histolytica life cycle

DIAGNOSTIC STAGE:

INFECTIVE STAGE:

Cysts are susceptible to heat (above 40 C.), freezing (below –5 C.), and drying

Cysts remain viable in moist environment for 1 month


Infection occurs when infective cysts are ingested in food or water that has been contaminated with human feces.

Thus, this parasite is transmitted from human to human via fecal contamination and is an ______________________


Common source of infection is from the use of ________________________ - _____________________ used to fertilize vegetables


.Excystment:

Metacystic ameba undergoes multiple fission to form _____ trophozoites.

Trophozoites move into the large intestine and invade the mucosa.

Entamoeba histolytica pathology

1. COLONIZATION OF THE LARGE INTESTINE

flask-shaped lesions:

proteolytic enzymes :

Symptoms:

Ulcers may form sinuses and extend into the submucosa


1. COLONIZATION OF THE LARGE INTESTINE

primary ulcer:

Mucosa

submucosa


2. COMPLICATIONS IN LARGE INTESTINE A. Ulcers extend deep into the _______________________________and may extend completely through the large intestine causing a _______________________________ _______________________________________(bacterial infection in the abdominal cavity) - this complication results in a high percentage of fatalities B. Trophozoites invade the blood vessels of the submucosa and metastasize to ectopic sites

Entamoeba histolytica pathology3. EXTRA-INTESTINAL LESIONS occur

in 3 ECTOPIC SITES

A. HEPATIC AMEBIASIS Trophozoites in submucosa are carried by hepatic portal vein to the liver.

Trophozoites digest away liver tissue forming _________________________ - some to size of grapefruit

B. PULMONARY AMEBIASIS Liver abscess ruptures

Trophozoites digest through the ______________________into the lungs to form a______________________________

C. CEREBRAL AMEBIASIS Trophozoites in bloodstream reach ________________________& form fatal _________________________

Liver abscess

Diagram of pathology from text on page 112

Shows movement of trophozoites from large intestine to lungs via hepatic portal vein

Diagnosis and Treatment of Entamoeba histolytica

DIAGNOSIS – microscopic identification of cysts and trophozoites in fecal samples

• Differentiation of E. histolytica from other non-pathogenic amebae is important.

• Why?

TREATMENT –_______________________________+ antibiotics are effective against large intestinal forms

Treatment difficult once ectopic sites are invaded

Non-pathogenic Amebae

We will examine 3 species in laboratory:

Entamoeba coli

Very common parasite in the ______________________________________________________________________________________________________

Often co-exists with E. histolytica but is_______________________________________

Cosmopolitan in its distribution

Prevalence in U.S. is estimated at _________ %; prevalence in tropics may be up to 100%

Entamoeba coli life cycle stages

1. TROPHOZOITE - 20 to 30 m in diameter

- granular endoplasm is coarser than E. histolytica

- structure of nucleus: ____________________________________________

________________________________________________________________

- lives in large intestine and feeds on bacteria and any other cells available to it; does not invade tissue

Entamoeba coli life cycle stages

2. CYST - encystment is similar to that of E. histolytica

- immature cysts are rare in fecal smears

- mature cyst is large, 10 to 33 m, has _____ nuclei

- chromatoidal bodies, if present, have splinter-like ends (disappear in most cysts)

- cyst is released in the feces into the external environment

- importance of human infection?

Entamoeba coli life cycle

Endolimax nana

Non-pathogenic parasite in the _______________________________________________________________

Cosmopolitan - __________ prevalence in the world

2 stages in the life cycle:

1. TROPHOZOITE - small in size; 6 - 15 µm (usually under 10 m)

- structure of nucleus:

- moves slowly; feeds on bacteria and food debris

Endolimax nana

2. CYST - forms as feces dehydrates

- small in size (5 - 14 m)

- contains ____ nuclei with large endosomes

- importance of human infection:

Endolimax nana life cycle

Iodamoeba bütschlii = I. buetschlii

Parasite in the ___________________________________________________

Non-pathogenic

Cosmopolitan in distribution

Prevalence in world is ___________ (much less than E. coli & Endolimax)


1. TROPHOZOITE - 9 to 20 m in diameter

- structure of nucleus:

- feed on bacteria and yeast; do not invade tissue


2. CYST - 6 to 15 m in diameter

- ________________ nucleus with large endosome and lightly-stained granules

- large ___________________________(appears clear) in cytoplasm

- stains deeply with iodine; hence, the genus name

Method of human transmission:

Iodamoeba bütschlii life cycle

3 Other Non-Pathogenic Amebae (we will not examine these in lab)

Entamoeba hartmanni

Originally thought to be a "small race" of E. histolytica, it is now considered to be a separate species.

The morphology of E. hartmanni is nearly identical to E. histolytica except it is SMALLER IN SIZE

- trophozoites are typically 12 - 15 m in diameter

- nuclear structure is similar (endosome in center) but peripheral chromatin is more irregular

- cysts are 5 - 9 m in diameter and contain 4 nuclei

Pathology:

Importance:

Entamoeba dispar

1993 E. dispar was proposed as the name for non-pathogenic E. histolytica.

Substantial biochemical and molecular data has been accumulated showing that the non-pathogenic isolates of E. histolytica are genetically distinct from the pathogenic isolates

Identical to E. histolytica but does not invade tissue so is non-pathogenic.

_________________________________

Entamoeba gingivalis

Habatit:

Hosts: Prevalence is from 50 to 95%. Stage: Trophozoite lives on the surface of teeth and gums. Parasites feed on epithelial cells of the mouth, bacteria, food debris, and other cells available to them.

Organisms are more common in persons with pyorrhea (gum disease) but they are not the cause of the condition. Transmission:

Facultative Amebae

Facultative amebae are normal inhabitants of soil and water where they feed on bacteria.

A few members have the ability to become parasitic when an opportunity to enter a vertebrate exists.

Three are able to infect humans:

Naegleria fowleri

This ameba is responsible for over 200 cases of _____________________________________________________

During 1989-2000, CDC documented 24 fatal cases of PAM in the United States. Only 7 cases were successfully treated; all others were fatal!

Naegleria fowleriTrophozoites can occur as an ameboid form or a flagellated form in freshwater. Parasite can form a cyst in dry periods.

Flagellated trophozoites enter the nasal passages when a victim swims or dives into freshwater.

All victims have had a history of _______________________________________________________________________________________a few days before the onset of symptoms

Naegleria fowleriOnce it enters a human, the parasites always revert to the ameboid form.

- contains ____________________________________

- usually forms ____________________________________

Naegleria fowleri pathology

After entering the nose and nasal cavities, the trophozoites migrate along the ___________________________ to the _________________________

Ameboid trophozoites multiply rapidly by binary fission in the brain and cause ___________________________________

Symptoms include a headache, fever, neck rigidity, and mental confusion followed by coma and death

Death usually occurs in ___________________________

Naegleria fowleri

DIAGNOSIS – most cases have been diagnosed at _____________________by identification of large numbers of amebae in the brain tissues

- Look for trophozoites each with a nucleus with _____________________________

- Disease is so rare and the brain tissue destruction is so rapid that diagnosis is seldom made in time

Naegleria fowleri

TREATMENT – the drug __________________________ has been successful in the treatment of only 7 cases

DISTRIBUTION - Most cases of this disease have been in the _____________________ U.S. (see case reports in lab).

Cases have also been described in Europe, Africa, and Australia.

In Wisconsin?

Acanthamoeba spp.

At least 5 species of Acanthamoeba have been identified in human tissues.

Free-living trophozoites and cysts occur in both the soil and freshwater.

Trophozoites occur only as ameboid forms:

- structure:

Acanthamoeba spp. pathology

These species cause 2 pathological effects:

(1) Over 100 cases of granulomatous amebic meningoencephalitis caused by Acanthamoeba have been documented

Disease was much more chronic in infected patients, all of which were __________________________________

Most, however, resulted in death in a few months.

Mode of transmission is not known, as no history of swimming occurred in some cases.

Possibility?

Acanthamoeba spp. pathology

(2) I ncriminated in a number of cases of __________________________ (inflammation and opacity of the cornea).

Most of these ocular infections were in contact lens wearers who used home-made saline

It appears that a ____________________ or swimming with contact lenses were necessary for invasion

Diagnosis by identifying amebae in corneal scrapings

Drug treatment has been successful in most cases

Several cases have been reported in Wisconsin - see case reports in lab

New faculative ameba recently identified

A new freshwater ameba called Balamuthia has been incriminated is some 80 cases of amebic meningoencephalitis in humans since 2001.

• only 2 survivals

• most reports from ______________

• easily misidentified so some of the cases of granulomatous amebic meningoencephalitis caused by Acanthamoeba may well have been caused by Balamuthia

Amebae

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