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Microspora are obligate intracellular parasites, ranging from 1.5 to 5
micrometer wide and from 2 to 7 micrometer long, and include
approximately 80 genera and over 700 species.
They are categorised by the production of unique spores that contain a
complex tubular extrusion mechanism by which the infective material ,
'sporoplasm', is injected into the host cells.
Since the
first case of intestinal microsporidiosis was reported in 1985,
numerous cases of microsporidiosis have been reported in
immunocompromised patients, especially those in the later stages of
human immunodeficiency virus (HIV) infection.
The vast majority of Microspora primarily infect non-human
hosts, with only Encephalitozoon , Nosema , Pleistophora and
Enterocytozoon infecting human beings.
Two major
microsporidia, Enterocytozoon bieneusi and Encephalitozoon or Septate
intestinali (E. intestinalis) have been identified in the human gut.
The clinical
manifestations of microsporidiosis are diverse and include intestinal,
pulmonary, ocular, muscular, and renal disease.
E. bieneusi is
particularly prevalent in patients with AIDS and causes chronic
diarrhoea.
Recently, this
organism was also reported to have caused self-limited travellers'
diarrhoea in immunocompetent individuals.
E.
Intestinalis was first described in 1992 and infects the small
intestine, the biliary tract, the respiratory tract, renal tubules and
glomeruli, nasal mucosa , conjunctiva and other organs.
E. bieneusi
and E. intestinalis both have a strong predilection for distal
duodenum and proximal jejunum. The colon is rarely involved.
Detection of the
organism:
Initial
detection of microsporidia by light microscopic examination of tissue
sections and of more readily obtainable specimens such as stool,
duodenal aspirates, urine, sputum, nasal discharge, bronchoalveolar
lavage fluid, and conjunctival smears is now becoming routine
practice. Definitive species identification is made by using the
specific fluorescein-tagged antibody (immunofluorescence) technique or
electron microscopy.
Microscopic features :
Image1
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Image2
(EM)
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These two
major microorganisms are quite difficult to detect on routine
haematoxylin and eosin stained biopsy specimens, primarily due to
their minute size, poor staining quality and lack of associated
specific mucosal changes.
The small
intestinal mucosa shows a spectrum of degenerative changes that
generally parallel the burden of parasites.
The small
intestinal mucosa may be normal appearing, but typically shows mild
villous blunting, focally increased intraepithelial lymphocytes, crypt
hyperplasia and some surface epithelial damage including tufting and
vacuolation. Neutrophils are usually absent.
Related Image Link (para-site online)
E. bieneusi:
A tufted and
budding arrangement of groups of enterocytes is common in the upper
half of the villi with clusters of pseudostratified nuclei and a
tendency for these areas to appear tangentially sectioned.
This organism can
be identified in normal, but more frequently abnormal, enterocytes
over the upper portion of villi (rarely seen below the mid-villus), as
small pale haematoxyphilic structures in the supranuclear apical
cytoplasm usually surrounded by an artifactual halo, causing nuclear
indentation of the enterocytes.
Meronts and
sporonts may also be seen by light microscopy as slightly
haematoxyphilic against the cytoplasm. All stages are typically seen
in the cytoplasm on the luminal side of the enterocyte.
The resulting
cupping of the associated enterocyte nucleus is a useful clue to
diagnosis. The presence of small slit-like areas within the organism
is also a useful diagnostic feature.
E. intestinalis:
In contrast, it
can infect the entire length of villi , even the base of crypts, and
appears as clusters of variable refractile bluish bodies in the
supranuclear, apical cytoplasm.
The most notable
feature is the presence of large numbers of spores within enterocyte
vacuoles. These are identified more easily than E. bieneusi spores as
they are slightly larger and more numerous and the pre-spore stages
are more harder.
The other feature
that differentiates them from E. bieneusi is the presence of spores in
macrophages and occasionally free within the lamina propria , perhaps
correlating with its tendency to disseminate. The upper parts of the
villi tend to show greater density of infection and these areas may
show focal necrosis and cell sloughing.
Semi-thin resin
embedded sections may help in the identification and recognition of
the organism.
Both spores are
better visualised with Gram, acid fast, periodic acid-Schiff, Giemsa
or modified trichrome stains.
Image
Link
Frazen et al
successfully amplified Microsporidian DNA from E. bieneusi in duodenal
biopsy specimens.
Detection of microsporidia
(Enterocytozoon bieneusi) in intestinal biopsy specimens from human
immunodeficiency virus-infected patients by PCR.J
Clin Microbiol. 1995 Sep;33(9):2294-6.
Encephalitozoon species
(E. cuniculi and E. hellum)
E.cuniculi and E.
hellum are similar and can only be distinguished by biochemical or
immunological methods.
In 1991 the new
species E. hellum was characterised after isolation from the eyes of
patients with keratoconjunctivitis .
There is systemic
spread of these organisms with wide range of organ involvement (Eg.
Urinary and renal spread, nasal and sinus infection and
tracheobronchial tree and lung involvement).
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