ENTAMOEBA SPP.E. hartmanni

E. coli

E. polecki

E. Gingivalis

Balasta, Darwin C.

Scientific Classification

Domain: Eukaryota Phylum: Amoebazoa Class: Archamoeba Genus: Entamoeba Species: E. hartmanni, E. coli, E. Polecki,

E. gingivalis

Life Cycle of E. hartmanni, E. coli, E. polecki

Like E. histolytica it under go successive stages: trophozoite, precyst, cyst, metacyst and metacystic trophozoite.

1. Both cysts and trophozoites of these species are passed in stool and considered diagnostic 

1. Cysts are typically found in formed stool, whereas trophozoites are typically found in diarrheal stool.  The trophozoites multiply by binary fission and produce cysts, and both stages are passed in the feces. Colonization of the nonpathogenic amebae occurs after ingestion of mature cysts in fecally-contaminated food, water, or fomites . 

3. Excystation occurs in the small intestine  

1. and trophozoites are released, which migrate to the large intestine. 

**Because of the protection conferred by their cell walls, the cysts can survive days to weeks in the external environment and are responsible for transmission. Trophozoites passed in the stool are rapidly destroyed once outside the body, and if ingested would not survive exposure to the gastric environment.**

Entamoeba hartmanni E. hartmanni is a non-pathogenic

amoeba with world wide distribution. Its life cycle is similar to that of E. histolytica but it does not have an invasive stage and does not ingest red blood cells.

It has now attained general acceptance as the name for the amoeba formerly designated as “small race” E. histolytica. the confusion surrounding the relationship between the two forms is based on their morphologic similarity

MorphologyTrophozoite: usually measure 5-15 µm.  Possess a single nucleus that contains a small, compact

centrally.  Nuclei are usually not visible in unstained specimens.  The cytoplasm is finely granular.  Movement in living trophozoites is described as

nonprogressive.

Cyst: Similar to  E. histolytica but smaller, measuring 5-10 µm.  Mature cysts contain four nuclei that possess a small, discrete

centrally-located karyosome and evenly-distributed peripheral chromatin. 

Cysts may not be visible in unstained specimens.  The cytoplasm in mature cysts may contain diffuse glycogen and

rounded or elongated chromatoid bodies with rounded ends.

Host: human

Mode of transmission: Ingestion of fecal contaminated food and water sources

Infective stage: cyst

Diagnostic stage: identification is made by observing cysts and/or trophozoites in stool

specimens, both concentrated wet mounts and permanent stained smears. Habitat:

Intestine (colon) Epidemiology:

Worldwide, primarily human-to-human transmission.

Entamoeba coli Entamoeba coli is a non-pathogenic

amoeba with world wide distribution. Its life cycle is similar to that of E. histolytica but it does not have an invasive stage and does not ingest red blood cells.

E. coli is a non pathogenic ameba that very closely resembles E. histolytica; the two species may be confused, leading either to superfluous treatment for non pathogenic parasite or to omission of appropriate theraphy for pathogen

MorphologyTrophozoite

usually measure 15 to 50 µm. 

possess a single nucleus with a characteristically large, eccentric karyosome and coarse, irregular peripheral chromatin. 

The cytoplasm is usually coarsely granular and vacuolated (often described as "dirty" cytoplasm). 

Pseudopodia may be seen, and are often short and blunt.

movement in living trophozoites is nondirection/sluggish.

Cyst

usually spherical, but may be elongated, and measure 10 to 35 µm. 

Mature cysts typically have 8 nuclei but may have as many as 16 or more.  

The nuclei may be seen in unstained as well as stained specimens. 

Karyosomes may be compact or diffuse, and are usually eccentrically located. 

Peripheral chromatin is present and is often coarse and granular, and irregularly arranged along the nuclear membrane, but may be more uniform. 

The cytoplasm of mature cysts may contain diffuse glycogen. 

*Entamoeba coli is the only species in the genus encountered in humans with more than four nuclei in the cyst stage. 

Host: human

Mode of transmission: ingestion of fecal contaminated food and water source

Infective stage: cyst

Diagnostic stage: identification is made by observing cysts and/or trophozoites in stool

specimens, both concentrated wet mounts and permanent stained smears.   Habitat:

intestine (colon) Epidemiology:

Worldwide, primarily human-to-human transmission

Entamoeba polecki

First reported as an intestinal parasite of pigs and monkeys, E. polecki has been found occasionally in humans. In parts of Papua New Guinea, it is apparently the most common intestinal ameba of humans.

MorphologyTrophozoite often rounded, measuring 10 to 25 µm.  The single nucleus is often distorted and irregularly-shaped,

with a small to minute centrally-located karyosome.  Peripheral chromatin is usually delicate and uniform.  The

cytoplasm is often vacuolated with a hyaline border.  Blunt pseudopodia may be seen.

Cyst measure 9 to 25 µm and are usually uninucleate, but

binucleate forms are seen rarely.  The nucleus is often large, measuring up to one-third of the

diameter of the cyst.  The karyosome is pleomorphic, and may be minute to large

and compact to diffuse, and centrally or eccentrically-located.  Peripheral chromatin may be light to heavy but is usually evenly

distributed.  contain an inclusion mass of variable size and numerous

chromatoid bodies, which may be small and round to large rods with round or splintered ends.

Host: pig, monkey, and sometimes human.

Mode of transmission: Pig-to-human transmission is the most likely route of human infection Human-to-human transmission exists where the prevalence of infection is

high Infective stage:

cyst Diagnostic stage:

 identification is made by observing cysts and/or trophozoites in stool specimens, both concentrated wet mounts and permanent stained smears.

Habitat: Intestine (colon)

Epidemiology Although Entamoeba Polecki is rarely found in humans, it has a

widespread and relatively unpredictable epidemiology. The disease is much more common in rural regions than urban areas. Most commonly, Entamoeba polecki is associated with Papua New Guinea, where a study estimated that the prevalence was as high as 19 percent of the population. This is not surprising given the economy and culture of this country where pigs play a key role and many pigs are even allowed to live in residences. There are three other countries in which E. polecki is endemic, including Cambodia, Venezuela, and Vietnam. Additionally, E. polecki infections have been reported in Southeast Asian refugees living in other locations, namely France, Minnesota, and Venezuela.

Entamoeba Polecki was first identified in 1912 in Czechoslovakia by Von Prowazek in the stool samples of two students from Kampuchea.

Pathogenicity Few cases of E. polecki infection have been followed

for any length of time. One human case for about 3 years without any indication of disease. A few reports describe patients with diarrhea apparently caused by infection with this parasite. Some doubt is cast on the validity of this species by isoenzyme studies of a number of isolates showing the morphologic characteristic of E. polecki. In every case, the isoenzyme pattern fell within one or another of what are now recognized as E. dispar groupings.

Entamoeba gingivalis

Bearing a close morphologic resemblance to E. histolytica. E. gingivalis is often found in pyorrheal pockets between the teeth and gums and in tonsillar crypts. It has been reported to multiply in brochial mucus and to appear in the sputum, where it might be mistaken for E. histolytica from a pulmunary abscess.

Morphology

There is no known cyst stage for Entamoeba gingivalis

Measure 10-20 µm.  Possess a single nucleus that contains a small, centrally-

located karyosome and fine peripheral chromatin.  The cytoplasm often contains ingested leukocytes,

bacteria and other debris, very rarely red blood cells.  The trophozoites also possess pseudopodia; living

specimens can move quickly.  **Entamoeba gingivalis normally lives in the gingival pockets near the base of the teeth in the human mouth, and may be coughed up in sputum specimens.  As such, it is important to differentiate this species from E. histolytica, which may be found in sputum from pulmonary abscesses.**

Life Cycle of Entamoeba gingivalis A There is no known cyst stage

for Entamoeba gingivalis; trophozoites live in the oral cavity of humans, residing in the gingival pockets near the base of the teeth .  They are not considered pathogenic, and feed on bacteria and other debris. 

1 Trophozoites are transmitted person-to-person orally by kissing or fomites (such as eating utensils) . 

**The trophozoite stage of E. gingivalis is morphologically similar to that of E. histolytica, and the two should be differentiated, as both can be coughed up in sputum specimens (for the latter, when present in pulmonary abscesses).**

Entamoeba gingivalis Host:

mostly human Mode of transmission:

E. gingivalis is transmitted either directly kissing or indirectly contanct via trophozoite-contaminated food, chewing gum, toothpicks and so on.

Infective stage: Trophozoite

Diagnostic stage: Identification of E. gingivalis is made by the finding of trophozoites in scrapings of the

gums and teeth. Habitat:

abounds in people with unhealthy oral condition (i.e. gingivitis, periodontitis), a cause and effect relationship has not been established.

Entamoeba gingivalis normally lives in the gingival pockets near the base of the teeth in the human mouth, and may be coughed up in sputum specimens.

Epidemiology: Worldwide, primarily human-to-human transmission

Treatment As these six species are generally considered nonpathogenic,

there are currently no treatment recommendations for them. In rare occasion E. polecki is reported by some to cause

disease Entamoeba Polecki has been successfully treated with the use of

three antiparasitic drugs. Metronidazole, Ornidazole, and Furamide have been proven effective, though Metronidazole is the most common and debatably most effective. This drug is effective at a dosage of 750mg three times a day for 5, 7, or 10 days. Ornidazole and Furamide have been shown to treat the parasite in combination with Metronidazole, though it is still not known if these drugs are effective on their own. Interestingly, all the the commonly employed antiamebic drugs have been ineffective in the treatment and management of this parasitic infection.

Prevention Travelers to countries where sanitary standards

are low can reduce their chances of acquiring amebiasis by: Drinking only water that has been bottled in sanitary

conditions or boiled (water-purifying tablets are ineffective against amoebic cysts)

Eating only cooked or peeled vegetables or fruits Protecting food from fly contamination Washing hands after defecation and before

preparing or eating food

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