Blastocystis hominis is a common intestinal parasite that infects humans. It was originally classified as a yeast but is now known to lack a cell wall. It reproduces by binary fission or sporulation under anaerobic conditions. Symptoms of blastocystosis include diarrhea, abdominal pain, and nausea. Diagnosis involves microscopic examination of stool samples. Treatment is with metronidazole or other antibiotics. Prevention involves safe drinking water and basic sanitation practices.

2. Wet mount

3.  Initially described by Prowasek and
Alexeieff, then named by Brumpt in
1912
 Blastocystis hominis is an inhabitant of
the lower intestinal tract of humans and
other animals
 Formerly classified as a yeast under the
genus Schizosaccharomyces, while
other taxonomists considered it to be
related to Blastomyces

4.  Lacks a cell wall but has a mitochondrion
with protozoan morphology.
 Capable of pseudopodial extension and
retraction
 Asexual reproduction by binary fission or
sporulation under strict anaerobic conditions
 Optimal growth= 37 oC in the presence of
bacteria; does not grow on fungal media

5. Parasite Biology
 Multiplication of Blastocystis hominis is by
binary fission
 Transmitted by fecal-oral route
 Morphological forms:
1. Vacuolated
2. Ameba-like
3. Granular
4. Multiple fission
5. Cyst
6. Avacuolar

6. Vacuolated form
 Most predominant form in fecal specimen
 Spherical in shape, measuring 5-10 µm in
diameter
 Large central vacuole pushes the cytoplasm
and nuclei to the periphery of the cell
 Sometimes, very thick capsule surround them
 Prominent central vacuole has been found to be
a reproductive organelle
 Main type of Blastocystis causing diarrhea

7. Ameba-like forms
 Occasionally observed in stool samples
 Exhibit active extension and retraction of
pseudopodia
 The nuclear chromatin, when visible,
characteristically shows peripheral clumping
 Appears to be an intermediate stage
between the vacuolar and pre-cystic form
 Allows the parasite to ingest bacteria to
enhance encystment

8. Granular forms
 Mainly observed from old cultures
 Diameter of the cell varies from 10 -60
µm
 Granular contents develop into daughter
cells of the ameba-form when the cell
ruptures

9. Multiple Fission
 Arise from vacuolated forms
 It is believed that these multiple fission
forms produce many vacuolated forms.

10. Cystic form
 Size in about 3-55 µm
 Has a very prominent and thick osmophilic
electron dense wall
 Appears as a sharply demarcated polymorphic,
but mostly oval or circular, dense body
surrounded by a loose outer membranous layer
(seen in contrast microscopy)
 Membranous layer corresponds to the fibrillar
layer described around the cyst at ultrastructural
level; easiest diagnostic feature

11.  It is assumed that the thick-walled cyst
might be responsible for external
transmission while those cysts with thin
walls might be the cause of re-infection
within a host’s intestinal tract

14. Pathogenesis and Clinical
Manifestation
 Blastocystosis- infection with Blastocystis
hominis
 Blastocystis hominis as a cause of
gastrointestinal pathology is controversial
 Several studies showed that the presence of
parasite in a majority of patients was not
associated with symptoms, or is found with
other organisms that are more likely to be
cause of the symptoms

15.  Other studies concluded that presence of
Blastocystis in large numbers produce a
wide variety of intestinal disorders:
abdominal cramps, irritable bowel syndrome,
bloating, flatulence, mild to moderate
diarrhea without fecal leucocytes or blood,
nausea, vomiting, low grade fever, and
malaise
 Symptoms usually last about 3-10 days, but
may sometimes persist for weeks or months

16.  It has been found out that in subjects
suffering from Blastocystis showed a
significant association with
gastrointestinal symptoms
 Other studies also provided evidence of
cellular immune function changes in
infected individuals

17. Diagnosis
 Laboratory detection from stool is needed for
confirmation
 Stool samples should be collected more than
once from patients showing signs and
symptoms
 Microscopic examination using direct fecal
smear is useful but sensitivity is increased
when concentration techniques are used

18.  Hematoxylin or trichome staining offers
a very convenient and easy method to
differentiate the various stages of
Blastocystis
 Leukocytes are usually seen in fecal
smears and stool eosinophilia may also be
observed
 The organism can be cultured using the
Boeck and Drbohlav’s or the Nelson
and Jones media

19. Treatment
 Blastocystis is difficult to erradicate
 Hides in the intestinal mucus, sticks and
holds on the intestinal membranes
 Drug of choice is metronidazole given at
750 mg 3x daily for 10 days (Pedriatric
dose: 35-50 mg per kg per day in 3 doses
for 5 days) or iodoquinol given at 650
mg 3x daily for 20 days.

20.  However, there are reported cases of
resistance of Blastocystis to
metronidazole
 Trimethroprim-sulfamethaxazole
(TMP-SMX) has been found to be highly
effective against Blastocystis

21. Epidemiology
 Reported practically worldwide, with
infections common in tropical , subtropical
and developing countries
 In general, studies from developed
countries report approx. 1.5% - 10% overall
prevalence of Blastocystis hominis
 All ages are affected but symptomatic
cases are commonly found in children and
in those with weakened immune systems

22.  A prevalence of up to 11.6% was reported
from Stanford University Hospital
 Occurrence of parasite in temperate
countries is generally associated with
recent travel to the tropics and
consumption of untreated drinking water,
an indication that infection is possibly
through the oral route and it is more likely
to occur in crowded and unsanitary
conditions

23.  Outbreaks of Blastocystis hominis in day
care centers were reported in Spain, Brazil
and Canada
 In the Philippines, results of 355 stools
examined in 1997 by the Department of
Parasitology, College of Public Health,
University of the Philippines Manila,
showed a prevalence of 22.8% with or
without other intestinal parasites or
organisms

24.  In 1988, the prevalence was 20.7% in
772 stool samples examined.
 Studies have shown prevalence rates of
40.6% among food service workers in a
tertiary hospital and 23.6% among food
handlers in selected school canteens in
Manila

25.  Several animals like the pig-tailed
macaques, chicken, dogs, and ostriches
harbor Blastocystis similar to those found
in humans.
 Evidence also shows that it is present in
house lizards and cockroaches, thus
implying that food and water contaminated
by fecal droppings of these “home visitors”
may transmit Blastocystis

26. Prevention and Control
 Disease can be prevented by consuming
safe drinking water
 Provisions for sanitary preparation may
be of value in efforts to prevent and
control this infection
 The cysts of Blastocystis hominis can
survive up to 19 days in water at normal
temperature and have shown resistance
to chlorine at the standard concentrations