Blastocystis hominis (2)

8/4/2019 Blastocystis hominis (2)

1/25

Blastocystis

hominis


2/25


3/25

HistoryA species of parasitic protozoa found inthe intestines of humans and otherprimates.It was classified as a yeast in 1912. Over

the years, questions arose about thisdesignation. In 1967, many physiologicaland morphological B. hominis characteristics were reported that fit aprotozoan classification.


4/25

It is now recognized as aprotozoan parasite of humanscausing intestinal disease withpotentially disabling symptoms.


5/25

IntroductionDisease caused by this parasite:BlastocystosisBlastocystis Hominis is a protozoan intestinalparasite belonging to the Blastocystis genusof Stramenopiles.It has a widespread geographic distributionand is found in countries of all income levelsacross the world.Its status as a true pathogen is controversial- while it has been found in patients withgastrointestinal symptoms, it is not proven tobe the cause, and many carriers areasymptomatic.


6/25

VacuolatedUnicellular, it is 5-30 micra indiameter, with the usual range

being 8-10 micra.spherical, oval, or ellipsoidal,with usually one, butsometimes 2-4 nuclei locatedin the rim of the cytoplasm.

Morphology


7/25


8/25

Morphology

Granular form is morphologicallysimilar to vacuolar form except that

distinct granules are observed in thecentral vacuole or cytoplasm.These granules appear in 3 differentforms: Metabolic, Lipid and Reproductivegranules.These granules may be an indication thatthe cell is dying.


9/25

Morphology

Multivacuolar and avacuolar forms: These contain many smaller vacuoles or novacuoles within a smaller cell of between 5 and8 micrometers in diameter.1 nucleus tends to be present, with a maximumof two.


10/25

Morphology

Ameboid form:This is a very rare form withirregularly shaped cells

from 2.6 to 7.8 micrometersin diameter.Pseudopodia are oftenattached. A large centralvacuole may or may not bepresent.


11/25

Morphology

Amoeboid formnon-motile and strongly adhesive.

A study has reported that amoeboid formsare produced only in cultures taken fromsymptomatic individuals. The studysuggested using amoeboid forms for

diagnosing symptomatic infection.Symptoms is due to strongly adhesiveamoeboid forms in the hosts intestinalwall.


12/25

Morphology

Cyst form:A hard, resistive formbetween 3 and 10micrometers indiameter.A thick wallencapsulates the

structure whichincludes manyvacuoles and 1 or 2nuclei.


13/25

Morphology

Cyst form Most resistant form of the parasite, it

is able to survive harsh conditionsbecause of its thick multilayered cystwall.


14/25

Form Size(micra) SourceCentralvacuole

Surfacecoat

Number ofnuclei

Otherremarks

Vacuolar 2 - >200 Culture,feces

Present Present(thin) or

absent

1-4 Centralvacuole

occupiesmost of cellvolume

Granular 5-80 Culture,feces

Present Present(thin) orabsent

1-4 Granules incentralvacuole;

morphologysimilar tovacuolarform

Multivacuolar 5-8 Feces,culture

Absent Present(thick)

1 or 2 Multiplesmall

vacuoles(may be toosmall toresolve bylightmicroscopy)


15/25

Avacuolar ~5 Intestine,feces

Absent Absent 1 or 2 Rarelyreported

Amoeboid 2.6-7.8 Feces,culture Absent Absent 1 or 2 Rarelyreported;conflictinginformation onmorphology

Cyst 3-10 Feces,culture

Absent Presentor absent

1-2 Cyst wallpresent(beneathsurfacecoat)


16/25

Life Cycle


17/25

This is a proposed life cycle for B.

hominis 1) The cyst form is found in human stools, which

varies in size from 6 to 40 m .2) The thick-walled cyst present in the stools is

responsible for external transmission, possibly bythe fecal-oral route through ingestion ofcontaminated water or food .

3) The cysts infect epithelial cells of the digestive tractand multiply asexually.

4) Vacuolar forms of the parasite give origin to multivacuolar and amoeboid forms.

5) The multi-vacuolar develops into a pre-cyst thatgives origin to a thin-walled cyst , responsible forautoinfection.

6) The amoeboid form gives origin to a pre-cyst ,

which develops into thick-walled cyst byschizogony . The thick-walled cyst is excreted in


18/25

LIFE CYCLE

Infective Stage: Thick-walledCystDiagnostic Stage: all forms,cyst and vacuolated forms are

most common


19/25

Clinical Presentation in Humans:

Blastocystosis, as well as its diagnosis, iscontroversial because it has not been proven thatassociated symptoms come from Blastocystishominis itself. It is argued that many people

found to harbor blastocystis might have othersources of their symptoms.

Watery diarrhea

Abdominal pain / crampsPerianal pruritis (itch)Excessive flatulence


20/25

Transmission

Transmission is thought to be throughthe fecal-oral route, much like that of

other better-known GI protozoa,although there is no experimentalconfirmation. It is probable that the

infectious form is the cyst form.


21/25

Diagnostic Tests:B. hominis is usually diagnosed by microscopicexamination of fecal material stained withiodine or trichrome.Permanent stained smear is preferred becausefecal debris might be mistaken for theorganism in wet preparations.ELISA and fluorescent-antibody tests

Most prominent form in the feces is thevacuolar form, all forms have been found.


22/25

Management and Therapy:Anti-protozoan drugs have been usedUsually treated with Metronidazole , which hasbeen effective, but shows signs of resistance

by B. hominis or limited effectiveness in others.Also used the drug combinationTrimethoprim/Sulfamethoxazole (TMP/SMX)with similar effects.More recently, Nitazoxanide has been with

much more positive effects,


23/25

Epidemiology

This disease is not well-tracked, but appears tooccur worldwide. Case reports indicate thatwhile nearly worldwide in distribution, it is more

common in less developed nations and mayprefer tropical and sub-tropical climates.Proximity to pets and farm animals alsoappears to be linked with increased infectionrates.

2-3 times higher in day care centers and 4-6times higher in primary schools than in the

general population.


24/25

Public Health and PreventionStrategies

Following ways to prevent infection with B.hominis:Wash hands with soap and water afterusing the toilet and before handling food.Avoid water or food that may becontaminated.Wash and peel all raw vegetables andfruits before eating.


25/25

REFERENCES:

Centers for Disease Control and Preventionhttp://www.stanford.edu/group/parasites/ParaSites2010/Delamon_Alfredo_Rego/paraSITEfinalweb.htm

Documents

Blastocystis hominis (2)