Post on 11-May-2015
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
Entamoeba histolytica life cycle
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 ______________________
Entamoeba histolytica life cycle
Common source of infection is from the use of ________________________ - _____________________ used to fertilize vegetables
Entamoeba histolytica life cycle
.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
Entamoeba histolytica pathology
1. COLONIZATION OF THE LARGE INTESTINE
primary ulcer:
Mucosa
submucosa
Entamoeba histolytica pathology
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)
Iodamoeba bütschlii = I. buetschlii
1. TROPHOZOITE - 9 to 20 m in diameter
- structure of nucleus:
- feed on bacteria and yeast; do not invade tissue
Iodamoeba bütschlii = I. buetschlii
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