A CERTAIN PARASITICAL INDEX VOL 1

Question 1

How many morphological forms does E. histolytica have?

Answer 1

three
①Trophozoite
➁Precyst
③Cyst

Question 2

E. histolytica trophozoite

Answer 2

• is the growing stage of the parasite & the only FORM present in tissues.
  -It is large, irregular in shape & actively motile in freshly passed dysenteric stool (contains RBCs)
  -Tend to be smaller in convalescents & carriers
• EXCYSTATION IN TERMINAL ILEUM OR CECUM ->metacyst

Question 3

Precystic Stage of E. histolytica

Answer 3

• Trophozoites undergo encystment in the intestinal lumen.
• Before encystment, the trophozoite extrudes its food vacuoles and becomes round or oval. This leads to the precystic stage of the parasite.
• It contains a large glycogen vacuole and two chromatid bars.
• It then secretes a highly retractile cyst wall around it and becomes
  cyst

Question 4

Cystic Stage of E. histolytica

Answer 4

• It begins as an early cyst with a single nucleus, a glycogen mass & 1–4 chromatoid bodies.
• As the cyst matures, the other structures disappear and the nucleus undergoes 2 successive mitotic divisions to form 4 nuclei.
• The mature cyst is quadrinucleate

Question 5

E. histolytica parasite virulence factors include:

Answer 5

*Amoebic lectin, cystine proteinase which inactivates complement factor C3 and ionophore
*Host factors are: stress, malnutrition,
alcoholism, corticosteroid therapy, bacterial flora & immunodeficiency.
* Glycoproteins in colonic mucus blocks attachment of trophozoites to epithelial cells hence changes in the nature & quality of colonic mucus may influence virulence.

Question 6

Diagnosis of Amoebiasis:

Answer 6

①MICROSCOPY
* Definitive diagnosis depends on microscopic demonstration of actively motile trophozoites in freshly-passed stool.
* Presence of ingested RBCs identifies E. histolytica. Charcot-Leyden crystals are often present.
* Iodine-stained preparation is needed to demonstrate cysts or dead
trophozoites.
➁MACROSCOPIC features include brownish black foul-smelling stool intermingled with blood & mucus
③STOOL CULTURE
④SERO-DIAGNOSIS
*IHA,Latex agglutination test & ELISA.
* lHA & LA are highly sensitive but often give false-positive results as
they remain positive for several years even after successful treatment

Question 7

Morphology of N. fowleri:

Answer 7

1. Cyst
2. Amoeboid trophozoite form
3. Flagellate trophozoite form
   Trophozoite Stage
   * The trophozoites occur in 2 forms, the amoeboid and flagellate

Question 8

N. fowleri Amoeboid trophozoite form

Answer 8

• The amoeboid form has rounded pseudopodia, a spherical nucleus & pulsating vacuoles(used for engulfing RBCs/WBCs).
• It is the feeding, growing & replicating form of the parasite, seen on the surface of vegetation, mud and water.
• It is also the invasive stage & the infective form of the parasite.

Question 9

What causes Primary amoebic meningoencephalitis (PAM) ?

Answer 9

amoeboflagellate Naegleria (the brain eating amoeba).

Question 10

What causes Granulomatous amoebic encephalitis (GAE) and chronic amoebic keratitis (CAK) ?

Answer 10

Acanthamoeba
* Balamuthia have also been reported to cause GAE.

Question 11

N. fowleri Flagellate form

Answer 11

• The biflagellate form occurs within a minute when trophozoites are transferred to distilled water.
• The flagellate can revert to the amoeboid form, hence N. fowleri is classified as amoeboflagellate.

Question 12

N. fowleri Cyst Stage

Answer 12

• It’s the resting or the dormant form & can resist unfavorable conditions such as drying and chlorine up to 50 ppm(2ppm kills the cyst).
• Trophozoites encyst due to unfavorable conditions such as food deprivation, desiccation, cold temperature etc.
• Cysts and flagellate forms of N. fowleri have never been found in tissues of cerebrospinal fluid (CSF)

Question 13

diagnosis of PAM

Answer 13

①MICROSCOPY
*presence of motile Naegleria trophozoites in wet mounts of freshly-obtained CSF.
*The CSF picture resembles that of bacterial meningitis with a cloudy
to purulent appearance, prominent neutrophilic leukocytosis, elevated
protein & low glucose.
*Cysts are not found in CSF or brain.
* At autopsy, trophozoites can be demonstrated in brain histologically
by immunofluroscent staining
➁CULTURE
* N. fowleri can be grown in several kinds of liquid axenic media or non-nutrient agar plates coated with Escherichia coli. Both trophozoites and cysts occur in culture.
③MOLECULAR DIAGNOSIS
* Newer tests based on polymerase chain reaction (PCR) technology are being developed

Question 14

Which Acanthamoeba species cause human infection?

Answer 14

• A. culbertsoni (formerly, Hartmanella culbertsoni) mostly
• A. polyphagia, A. castalleni, and A.
  astromyx.

Question 15

MORPHOLOGY OF ACANTHAMOEBA SPP.

Answer 15

**Acanthamoeba exists as active trophozoite form & a highly resistant
double-walled cystic form.
* The trophozoite is large in size & characterized by spine-like pseudopodia (acanthopodia).
* It differs from Naegleria in not having a flagellate stage & in forming cysts in tissues.
* Cysts are present in all types of environment all over the world

Question 16

What’s the infective form of acanthamoeba spp?

Answer 16

Both trophozoites & cysts are infective.

Question 17

Laboratory Diagnosis of Acanthamoeba infection:

Answer 17

①AMOEBIC KERATITIS: demonstration of the cyst in corneal scrapings on wet mount, histology and culture. Growth can be obtained from corneal scrapings inoculated on nutrient agar, overlaid
with live or dead Escherichia coli and incubated at 30°C.
➁GAE is made by demonstration of trophozoites and cysts in brain biopsy, culture & immofluroscence microscopy using monoclonal antibodies.
* CSF shows lymphocytic pleocytosis, slightly elevated protein levels, and normal or slightly decreased glucose levels.
* CT scan of brain provides is inconclusive

Question 18

Balamuthia Mandrillaris morphology:

Answer 18

• It exists as a cyst & an amoeboid trophozoite stage(flagellate stage is absent).
• It is relatively large, irregular in shape & actively motile by broad pseudopodia.
• Cyst of B. mandrillaris are usually spherical surrounded by a three-layered cyst wall comprising an outer irregular ectocyst, a middle mesocyst & an inner endocyst round wall.
• Under light microscopy, it appears to have two walls—an outer irregular wall and an inner smooth wall

Question 19

Lab Diagnosis of B. Mandrillaris:

Answer 19

• Laboratory diagnosis is done by identifying trophozoites of B. mandrillaris in the CSF .
• Also identifying trophozoites & cysts in brain tissue.
• PCR also gives reliable diagnosis.

Question 20

NONPATHOGENIC
INTESTINAL AMOEBA

Answer 20

①Entamoeba coli
➁Entamoeba gingivalis
③Entamoeba hartmanni
④Endolimax nana

Question 21

Quick facts about Entamoeba coli

Answer 21

• Worldwide distribution.
• Larger than E. histolytica with sluggish motility.
• Contains ingested bacteria but no red cells.
• The nucleus is clearly visible in unstained films with thick nuclear
  membrane lined with coarse granules of chromatin.
• Cysts are large with a prominent glycogen mass in the early stage.
• The mature cyst has 8 nuclei.
• Has a similar life cycle as E . histolytica except that its nonpathogenic.

Question 22

Quick facts about Entamoeba gingivalis

Answer 22

• Global distribution.
• Transmitted by direct oral contact.
• The amoeba lives in gingival tissues & is abundant in cases of poor oral hygiene.
• Has also been found in bronchial washings,vaginal & cervical smears, where it can be mistaken for E.histolytica.
• Only the trophozoite is found with no cystic stage.
• The trophozoite is actively motile with multiple pseudopodia.

Question 23

Quick facts about Entamoeba hartmanni

Answer 23

• Found wherever E. histolytica exists
• The trophozoite & cyst are much smaller than E. histolytica.
• Trophozoites do not ingest rbcs and their motility is less vigorous.
• The cyst resembles that of Endolimax nana.

Question 24

Quick facts about Endolimax nana

Answer 24

• Widely distributed.
• The trophozoite is small with a sluggish motility.
• The cyst is small, oval & quadrinucleate with glyocogen mass