omalu 2006 human microsporidial infections

7/31/2019 Omalu 2006 Human Microsporidial Infections

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Published QuarterlyMangalore, South IndiaISSN0972-5997Volume 5, Issue 3; Jul - Sep 2006

Review

Human Microsporidial Infections

AuthorsOmalu ICJ,Unit of Entomology and Parasitology, University of Jos, NigeriaDuhlinska DD,Unit of Entomology and Parasitology, University of Jos, NigeriaAnyanwu GI,Unit of Entomology and Parasitology, University of Jos, NigeriaPam VA,Veterinary Research Institute, Vom Plateau State, Nigeria

Inyama PU,Unit of Entomology and Parasitology, University of Jos, Nigeria

Address For CorrespondenceOmalu ICJUnit of Entomology and Parasitology,University of Jos, NigeriaE-mail: [email protected]

CitationOmalu ICJ, Duhlinska DD, Anyanwu GI, Pam VA, Inyama PU. Human MicrosporidialInfections. Online J Health Allied Scs. 2006;3:2

URLhttp://www.ojhas.org/issue19/2006-3-2.htm

Open Access Archiveshttp://cogprints.ecs.soton.ac.uk/view/subjects/OJHAS.htmlhttp://openmed.nic.in

Submitted: Nov 09, 2005; Revised: Jan 19, 2006; Accepted: Jan 22, 2006; Published: Mar 31, 2006

OJHAS Vol 5 Issue 3(2): Human Microsporidial Infectionswww.ojhas.org/issue19/2006-3-2.htm1


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Abstract:Microsporidia are eukaryotic, spore formingobligate intracellular parasites, firstrecognised over 100 years ago.Microsporidia are becoming increasinglyrecognised as infectious pathogens causing

intestinal and extra-intestinal diseases inboth immuno-competent and immuno-suppressed patients. They arecharacterised by the production of resistantspores that vary in size depending on thespecies; and poses a unique organelle, thepolar tubule (polar filament), which iscoiled inside the spore as demonstrated byits ultra structure. Other unusualcharacteristics are the lack of mitochondriaand the prokaryotic-like ribosomes, whichindicate the primitive nature of the group.Presently there are seven genera,Enterocytozoon, Encephalitozoon, Nosema,

Pleistophora, Trachi pleistophora,Brachiola, vittaforma species which havebeen reported from human hosts as agentsof systemic, ocular, intestinal and muscularinfections are described and the diagnosis,treatment, and source of infectionsdiscussed.

Key Words: Microsporidia,Enterocytozoon, Encephalitozoon, Nosema,Pleistophora, Diagnosis

Introduction:Microsporidia are intracellular spore-

forming protozoa that are increasinglybeing recognized as pathogens in humans.They are ubiquitous in the environmentand can infect a wide range of vertebrateand invertebrate hosts, including insects,birds, fish and mammals. The spores varyin size, but those that infect humans aretypically oval and one to two m indiameter. They are highly resistant todegradation, and can survive in theenvironment for up to four months. Theirstructure is distinguished by the presenceof a polar filament within the spore which isinvolved in injecting spore contents intothe host cell.

Although microsporidia were discoveredmore than 100 years ago, the first welldocumented case of humanmicrosporidiosis was reported in 1959.1 Itcould not have been anticipated whenthese organisms were first described thatthey would be recognized as the agents ofdistressing and life-threatening human

diseases. The AIDS epidemic has revealedtheir propensity for infecting man, althoughit is still not known whether microsporidiacause strictly opportunistic zoonosis orexist in healthy people as latent infections,which becomes exacerbated when thepatients becomes immuno-compromised.The ability of these parasites to causedisease in immuno-competent persons isstill being elucidated. Microsporidia cancause a variety of human diseases,involving multiple organ systems, whichinclude intestinal, ocular, sinus, pulmonary,muscular and renal diseases in bothimmuno-competent and immuno-compromised patients.2 The first case ofintestinal microsporidiosis in Nigeria was

reported in 2002.3

This review aimed to summerise theunusual features of the biology ofmicrosporidia, update ourselves with thenew clinical manifestation, latesttechniques of identification and the newtreatment modalities to overcome theseinfections.

Classification and Taxonomy:

The viability of the silk industry wasthreatened in the 19th century, because ofa mysterious disease of silk worms,Bombyx mori. The causative agent wasfirst named microsporidian Nosemabombycis, which was classified asSchizomycetes which, at the time includeyeasts and bacteria.4 The orderMicrosporidia was defined and separatedinto the Phylum Microspora within thezoological kingdom, protozoa.5,6 Landmarksin the recording of microsporidian speciessince these early beginnings are themonograph of Kudo7 in which 14 generaand about 170 species were listed,Sprague, in which 44 genera and over 700

species were listed6

, Canning and Hollister,in which 96 genera and almost 1000species were listed8 and to date 143genera and more than 1200 species havebeen described as parasites infecting awide range of vertebrate and invertebratehosts.9 Microsporidia were classified andgrouped taxonomically on the basis of theirnatural host and ultra structural featuressuch as size of the developing and matureorganisms, nucleus arrangement


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(monokaryon or diplokaryon), number ofpolar filament coils, interface with the hostcell during development (direct contactwith host cell cytoplasm, replication withina host cell derived parasitophorousvacuole, replication of organismssurrounded by endoplasmic reticulum,

sporogony within a parasite generatedsporophorous vesicle and mode of cell andnuclear division (binary division,karyokinesis with delayed cytokinesis).10Molecular biology methods havesubsequently been used to further classifythe microsporidia. The eukaryoticmicrosporidia that possessed prokaryotic-like ribosomes because the ribosomalgenes encoded 16S and 23S subunitswithout an independent 5.3S subunit that istypically observed in eukaryotes has beenreported.11,12 These results suggested thatthe microsporidia were early branchingprotozoa.

Morphology of Genera and SpeciesInfecting Man:Encephalitozoon Species

Encephalitozoon is parasitic in vertebrates.Development occurs in parasitophorousvacuoles in host cells. Meronts lie close tothe vacuolar membrane, which is of hostorigin, and divide mainly by binary fission.Sporonts become free in the centre of thevacuole, divide into two sporoblasts(disporoblastic), which mature into spores.Mature parasitophorous vacuoles arepacked with spores. Nuclei of all stages areunpaired.

Examples are Encephalitozoon cuniculiwhich measure approximately 2.53.2 x1.21.6m with 4.55 coils of the polartube, although 57 coils have beenrecorded in isolates from dogs andEncephalitozoon hellem which are morerounded, measuring 2.0 2.5 x 1.0 1.5m.8

Enterocytozoon Species

Enterocytozoon is a parasite of vertebrates.Development takes place in direct contactwith host cell cytoplasm. Meronts andsporonts are multinucleate, traversed by

electron-lucent slits, which are probablyexpanded and irregularly elongate. There ismarkedly precocious development of sporeorganelles in sporonts, includingmorphogenesis of polar-tube from electron-dense discs. The endospore layer of thespore wall is poorly developed. Example is

Enterocytozoon bieneusi known only fromsmall intestinal enterocytes of AIDSpatients. Spores measure approximately1.1 - 1.6 x 0.7 - 1.0m, are ellipsoidal with5 7.5 coils of the polar tube.8

Nosema Species

Numerous species have been describedchiefly in invertebrates. Developmentoccurs in direct contact with host-cellcytoplasm, i.e., there are noparasitophorous vacuoles or sporophorousvesicles. Nuclei are paired (diplokaryotic).

Sporonts are disporoblastic. Examples areNosema connori spores are oval with 11coils of the polar tube and Nosemacorneum with about 6 coils of the polartube they measure 4.0 - 4.5 x 2.0 - 2.5m.8

Pleistophora Species

Pleistophora is a parasite of vertebrates,chiefly fish. A thick amorphous surface coatsurrounds Meronts, which are multi-sporous culminating in a large and variablenumber of spores within the persistingvesicle. Nuclei are unpaired. Pleistophora

species has been found, parasitic in themuscles of an immuno-compromised, butHIV negative man. The oval sporesappear less rounded with 11 coils of thepolar tube and measure approximately 3.2 3.4 x 2.8m.8

Microsporidium Species

Microsporidium is a collective generic namegiven to species for which the genuscannot be determined on availableinformation. Examples are Microsporidiumceylonensis and Microsporidium africanus.

Spores have 1113 coils of the polar tubeand measure about 3.5 x 1.5m.8 Table 1shows the pathologic spectrum ofmicrosporidia infecting man.


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Table 1: Pathologic Spectrum of Microsporidia Infecting Man13

Species Size of Spore(m) Habitat References

Small intestinal

epithelial epithelium Orenstein et al., 1990

Small intestinal subepithelial infection

Schwartz et al. 1994 b

Biliary tractepithelium

Pol et al. 1993; Bryan et al., 1993 andMcwhinney et al., 1991

Gall bladderepithelium

Pol et al. 1993 and Bryan et al., 1993

Pancreatic ductepithelium

Bryan et. a1993

Enterocytozoonbieneusi

1.1-1.6x0.7-1.0

Bronchial epithelium Weber et al., 1993

Corneal and

conjunctival

Schwartz et al., 1993b and Cali et al.,

1993b.c

Sino-Nasal epitheliumCanning et al., 1992 and Schwartz et al.,

1993a

Tracheo-bronchialmucosa

Schwartz e. al., 1992 and 1993c.d

Renal tube infection Schwartz et al., 1992

Urethral and urinarybladder mucosa

Schwartz e. al., 1992

Encephalitozoonhellem

2.0-2.5x1.0-1.5

Protastic abscess Schwartz et al., 1994 a

Bronchial andBronchiolar DeGroot et. al., 1995

Tongue DeGroot et al., 1995E. cuniculi 2.5-3.2x1.2-1.6

Peritonitis Zender et al., 1989

Hepatitis Terada et al., 1987E. intestinalis 1.2 x 2.2

Small intestine Accoceberry et al., 1999

Nosema conori 4.0-4.5x2.0-2.5 All organs Canning and Hollister, 1992

N. corneum 3.7 x 1.0 Corneal Stroma Canning and Hollister ,1992

Pleistophora Sp. 3.2 3.4 x 2.8 Skeletal Muscles Chupp et al., 1993

Microsporidiumceylonensis

3.5 x 1.5 Corneal Stroma Canning and Hollister, 1992

M. africanum 4.5 x 2.5 Corneal Stroma Canning and Hollister, 1992.


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Biology of Microsporidia:Spores have a resistant wall composedof an outer proteinaceous exosporeand a thicker electro-lucent endospore,which contains chitin. The wallsurrounds the infective sporoplasm,

which may be uninucleate orbinucleate, and an extrusionapparatus, which controls infection ofnew cells. The extrusion apparatusconsists of a polar tube, coiled in theposterior half of the spores andconnecting via a straight section withan anterior anchoring disc, the polarsac. The straight section of the polar-tube is surrounded by an array ofmembranes being continuous with theouter membrane of the polar tube.When stimulated by the cells, usuallyin the gut of a new host, the polar tubeis everted and the sporoplasm passesthrough it and, if the tip of the tubechances to penetrate a host-cellmembrane, the sporoplasm isinoculated into the cell. This infectionmechanism is unique in the animalkingdom.

The spore is the only stage surviving inthe open air and serving to aidtransmission to the new host incontaminated water and food. In

water, spores usually live more thanone year at 4oC; in infected tissues,they survive even longer. Spores alsopass across the placenta in animals toinfect the foetus and infection acquiredtransplacentally is severe. Spores arerefringent, oval, usually all of the same

size and shape. Sporoblasts are usuallylarger and the measurements togetherwith mature spores bring disputedvariability in descriptions of spore size.In ultra-thin sections, mature sporesare usually dark and not differentiated

in their interior, and only young sporesare differentiated in the cross sectionsof the polar filaments. The number ofcoils in cross-section and the location(parallel coils, tilt) is characteristic forthe species.8,14

In development, they have aproliferative phase of binary ormultiple fission, termed merogony; thestages have simple unit membranes atthe surface and little differentiation ofthe cytoplasm. This is followed by a

sporulation phase, initiated when adense surface coat is secreted on cellscalled sporonts, which divided intosporoblasts that mature into spores asdescribed above. In some genera, thespores lie free in the host-cellcytoplasm; in others, the sporesderived from a single sporont aregrouped together within asporophorous vesicle of parasite origin[Figure 1]. The vesicle arises as anadditional envelope on the surface ofthe sporonts and separates from the

surface as development progresses.Microsporidia spread rapidly in mosttissues as a result of the extensiveproliferation in merogony andsometimes when there is autonomous,hatching of spores.8


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Fig 1: Spore structures and life cycles of Microsporidia (Source: Canningand Hollister,1992)

.



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Life Cycle of Microsporidia:1) Spores are ingested by a host (manor animal). 2) The spore extrudes itspolar tubule and infects the host cell.3) The spore injects the infectivesporoplasm into the eukaryotic host

cell through the polar tubule. 4) Insidethe host cell, the sporoplasmundergoes extensive multiplicationeither by merogony (binary fission) orschizogony (multiple fission). 5) Thisdevelopment can occur either in directcontact with the host cell cytoplasm(e.g. Ent. bieneusi) or inside a vacuoletermed parasitophorous vacuole (e.g

E. intestinalis). Either free in thecytoplasm or inside a parasitophorousvacuole, microsporidia develop bysporogony to mature spores. 6)During sporogony, a thick wall isformed around the spore, which

provides resistance to adverseenvironmental conditions. When thespores increase in number andcompletely fill the host cell cytoplasm,the cell membrane is disrupted andreleases the spores to the surrounding[Figure 2]. 7) These free mature sporescan infect new cells thus continuingthe cycle.9

Figure 2: Generalized life cycles of microsporidia



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Geographic Distribution:Microsporidia are being increasinglyrecognized as opportunistic infectiousagents worldwide. Cases ofmicrosporidiosis have been reported in

developed as well as in developingcountries, including: Argentina,Australia, Botswana, Brazil, Canada,Czech Republic, France, Germany,India, Italy, Japan, The Netherlands,New Zealand, Spain, Sri Lanka,Sweden, Switzerland, Thailand,Uganda, United Kingdom, UnitedStates of America, and Zambia.9 Latelycases of microsporidia have beenreported in Nigeria.3,15

Origin/ Sources of Acquisition of

Microsporidia:Faecal oral transmission is the likelyroute of infections in humans withintestinal microsporidiosis when sporescontaminate the environment.Infection can occur by both inhalationand ingestion. Encephalitozooncuniculi is known to pass across theplacenta in animals to infect thefoetus. E. cuniculi infects a wide rangeof mammals, including carnivores, anddogs are likely source of infection toman.

The microsporidium Enterocytozoonbieneusi is known from AIDS patientsonly. It is thought that it might have aworldwide distribution. This and itshigh prevalence suggest that it may bea natural parasite of man, perhapscausing transient diarrhoea, butnormally remaining below thedetection level, only becoming aproblem in severely immuno-compromised people. It is not knownwhether there is an animal reservoir.

The only other known species infectssalmonid fish but as well as being anunlikely source of human infection, ithas different morphologicalcharacteristics. The sources of the eyeinfections are just as mysterious. A

Tamil boy had been gored in the eyeby a goat 6 years before onset of hisinfection and it suggested that the

microsporidia might have beenacquired from the goat, becausetapeworms infesting goats arefrequently hyper-parasitised withNosema helminthorum.16 However, thespore sizes are widely different. In a

later study ofEncephalitozoon cuniculiin the lenses of a rabbit, the absenceof infection in the ocular envelope andnot in the lenses indicated that theinfection had entered the eye from asystemic source before the lenscapsule had matured and thus that theinfection had been acquiredtransplacentally.17 Nosema corneumwas isolated from a woman inBotswana who had no previous historyof trauma in the eye.18 A man fromwhom Nosema corneum was isolatedalso had no history of trauma; and theprobable source of infection could befrom his travel to the Caribbean andCentral America, where infections ininvertebrates were likely to be morecommon, and also the fact that helived near (and perhaps swam in) alarge recreational lake, in which sporesof invertebrate origin could have beenabundant.19 The restriction of Nosemacorneum to the epithelium of thecornea and conjunctiva suggests thatinfections are acquired topically. Ofother cases observed, one person hadowned a parrot; another had lookedafter a cat for several days but onlyafter his infection had developed.

There did not appear to be a commonanimal source for the infections.

Pleistophora species are commonparasites of fish, in which themyofibrils are infected in a similarmanner to the deltoid and quadricepsmuscles of a man.20 As the man wasimmuno-compromised, it is possiblethat infection was acquired by eatingfish but the fish would have had to beuncooked.


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Clinical Aspects of Human

Microsporidiosis:

The well documented case ofmicrosporidian infections in humanswas reported in 1959, in a Japanese

boy exposed to farm animals whopresented with headache, convulsionand recurrent fever. Examination ofthe cerebrospinal fluid revealedorganisms identified as microsporidia,genus Encephalitozoon.1 The next tworeports were in 1973: An immuno-compromised infant with athymicaplsia died of severe diarrhoea andmalabsorption.21 The microsporidiiumNosema connori were identified inmost organs. The other report was ofcorneal involvement in a 11-year old

boy of Sri-Lanka.16

Humanmicrosporidiosis can be classified asbelow:

Systemic Infection

A single case was described of anewborn infant with thymic deficiencyand presented with acute respiratorydistress, diarrhoea and malabsorption.

The respiratory problem was linkedwith Pneumocystis carnii infection. Thepatient died at 4 months of age and a

post-mortem examination revealed anoverwhelming disseminated infectionwith microsporidia, Nosema connori inalmost every organ. There was apredilection for muscular tissue but thekidney, adrenal cortex, lungs and liverwere also infected. The spleen was notinfected and the central nervoussystem was not examined. Although,pneumocystis pneumonia may havebeen the primary cause of death, thereis little doubt that the microsporidiosiswas the contributory cause.21 The

combined immunodeficiency, withmarked leucopenia andhypogammaglobulinaemia, due to thedefective lymphoid system, clearlyenabled the microsporidia to take holdand multiply, but the mystery lies inthe source of the infection. The childfell ill shortly after birth, so that it isnot clear whether the infection was

acquired transplacentally orperinatally. Four cases, identified as E.cuniculi have been reported in man.

The identifications were based onmorphological data before evidencewas presented of the existence of a

second species, E. hellem, in man.

1, 22,23

Ocular Infections

Several different types ofmicrosporidia have been found in thehuman eye. Interestingly, theinfections in immuno-competentpeople have extended deeply into thecorneal stroma, whereas those in AIDSpatients have been restricted to thesuperficial epithelium. The cornea ofthe right eye of an 11-year-old Tamil

boy in Sri-Lanka was scarred andvascularised, and granulomatoustissue was present over theconjunctival surface of the upper lid.16

The spores lay free and inmacrophages deep in the cornea butnot below Descemets membrane. Thegenus of the organism could not beidentified and was later placed in thecollective Microsporidium and namedM. ceylonensis.24

The left eye of a 26-year-old woman in

Botswana was removed because of apainfully inflammed conjunctiva and nolight perception.18 A perforated cornealulcer was found, adjacent to which thecorneal stroma was necrotic andinfiltrated with inflammatory cells.Again, the stroma was packed withmicrosporidial spores both free andphagocytosed. The genus was notestablished, although Nosema wassuggested, and the isolate was laternamed Microsporidium africanum.24

Bilateral infections in the superficialepithelium of the cornea andconjunctiva of AIDS patients have beenreported several times in patients inthe United States.25,26 The clinicalmanifestations in five of these patientshave been summarized.27 All hadconjunctival inflammation anddecreased visual acuity and diffuse


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punctate keratopathy. One patient hadcorneal inflammation and another hadcorneal ulceration. Thesemicrosporidial infections are visible asfine or coarse epithelial opacitiescausing redness and irritation of the

eye and most patients also sufferedphotophobia. Corneal or conjunctivalscrapings appeared identical to E.cuniculi when examined by electronmicroscopy, but the new isolates weredifferentiated from E. cuniculi on theirprotein profiles separated by SDS PAGE and by immunoblotting. The newspecies was named E. hellem.28 Aninfection, probably due to the samespecies has also been identified inBritain.29 In this case, the infection alsospread to the basal mucosa, whichbecame inflammed and hypertrophic.Examination showed multiple nasalpolyps and a CT- Scan showedopacities in the nasal sinuses. Thechronic nasal obstruction did notrespond to antimicrobial therapy.30

Intestinal Infections

Intestinal infections have been foundonly in AIDS patients and thecommonest of these is due toEnterocytozoon bieneusi. This species

was described and named byDesportes et al., and further studies atthe ultra structural level by Curry etal.31,32 First diagnosed in a Haitian manin France, the species has, to date,been found in about 150 patients. Itcauses severe watery, non-bloodydiarrhoea, which is exacerbated byfood intake. There is slow weight lossof about 1kg per week. In groups ofpatients with persistent diarrhoea, whowere negative for other specific entericpathogens by normal microbial

examinations, prevalence of Ent.bieneusi ranged between 27% -30%.27,33

Parasites are restricted to the smallintestinal enterocytes and were rathermore common in the jejunum than inthe duodenum. They lie betweenunaltered brush-border and the cellnucleus, which is often indented by the

parasites. Several parasites can befound in one cell. There is no bulbousappearing as ridges or long tongues oftissue.27 Infected cells are sloughedinto the lumen of the intestine. Thediarrhoea caused by this species is

debilitating and life threatening, withas many as ten episodes each day, anddoes not respond satisfactorily totherapy. It must be considered as asignificant cause of deaths in thesepatients. Two additional infections byunidentified microsporidia have beenreported in the intestine of AIDSpatients. The species involved in thefirst case was reported to exceed thelevel of infection normally achieved byEnt. bieneusi in the jejunum andduodenum and invades the histiocytesas well as the enterocytes.27Identification in the second case wasnot possible on available evidence and,as it occurred as a double infectionwith Ent. bieneusi, its pathogenicitycould not be assessed.34

Muscle Infections

A 20-year-old man with a low T-helper/suppressor cell ratio presentedwith an illness of 7 months durationcharacterised by generalized muscle

weakness and contractures,generalized non-tenderlymphadenopathy, fever and an 18kgloss of weight.20 Muscle biopsy fromthe arm, taken on admission and 5months later showed masses of sporesamid trophic and degenerating musclefibres with an intense inflammatoryreaction. The spores were identified asPleistophora species, as they weregrouped in large numbers withinsporophorous vesicles. Ten monthsafter diagnosis, and after some

antibiotic therapy, he was afebrile andthe myopathy had improved slightly.


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Laboratory Diagnoses of

Microsporidiosis:

Diagnosis of microsporidia in general isbased on the microscopic identificationof the organism, the electronic

microscopic findings, nucleic acidmethods and serological assays.Several groups of workers havetherefore developed microsporidialspore staining methods forexamination of faecal samples. Sporeshas also been detected in sputum,nasal washings, conjunctival scrapingsand vaginal swab samples.Microsporidial spores are of the sameorder of size, as bacteria so thatstaining has to differentiate betweenthe spores and faecal bacteria. The

methods must also allow themicroscopist to differentiate betweenmicrosporidial spores and those ofyeasts and fungi as well as the oocystsof coccidian protozoal parasites.

Spores stain light blue with Giemsa,red with Ziehl Neelsen, magenta withGrams stains, spore wall stains pink tored and the interior of the spore isunstained with a diagonal linerepresenting the polar tube with

Trichrome stain, and spores appear

bluish white at a wavelength of 395 to415 nm with Calcoflor white stain; ontheir own these stains are not specificbut the different colourationscollectively build up a reliablediagnostic picture. Any lingeringdoubts can be removed by revealingspore structure by electronmicroscopy.

Infections in the eye can be diagnosedby slit-lamp examination and bydetection of parasites in corneal or

conjunctival scrapings.

A variety of serological tests havebeen developed to detect residualantibodies to E. cuniculi. Of these, theindirect immunoflourescent test (IFAT)and enzyme linked immunosorbentassay (ELISA) are probably the mostuseful. Both have been used to detect

antibodies in human sera.35,36 It hasbeen mentioned that serologicaltesting is most useful. Serologicaltesting is not useful in immuno-compromised persons and reagentsnot available commercially.

Immunofloresence may also be used.

Molecular techniques are beginning tobe applied to microsporidial problems,particularly for use in thedifferentiation of species and theirdetection in clinical samples. Randomamplified polymorphic DNA (RAPD)obtained by means of the polymerasechain reaction (PCR), as well asrestriction enzyme digests (RED), haveshown clear differences amongisolates. Ribosomal DNA gene

sequences are available forEnterocytozoon and Encephalitozoonspecies. PCR analyses are performedusing specific primers. To raise thesensitivity of PCR, powerful and fastDNA extraction method including stoolsedimentation, glass bead disruption,and proteinase K and chitinasedigestion. Primer pairs V1-PMP2, V!-EB450, and V1-SI500, are used for thisanalysis, and the nature of the PCRproducts are confirmed by southernblot hybridization.37

Treatment of Microsporidiosis:Microsporidial infections are difficult totreat because of their intracellular

habit and the resistant nature of the

spores. Enteric microsporidialinfections have been treated with

varying degree of success with severaldrugs. The most promising anti-

microsporidial drug to date is

albendazole.34 It does not eliminate

infection with E. bieneusi but in manycases alleviates the diarrhoea. The

species, which develop inparasitophorous vacuoles, appear tobe more susceptible to albendazole, as

indicated by the disappearance of E.intestinalis from the intestine38 and

regression of hypertrophic nasalepithelium in a patient with sinusitis

due to Encephalitozoon species.30Several drugs are reported to reduce


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levels of microsporidial infections in

invertebrates, notably; Fumagillin

which includes topical fumagillin fortreatment of keratoconjunctivitis39,

Benomyl40, Buquinolate41, Toltrazuril42and Itraconazole.43

No sustained improvement has beenreported for the diarrhoea due to Ent.

bieneusi. Chemotherapy for

microsporidial disease is clearly apriority area of research.

Disinfection of Microsporidia:Disinfection of surfaces contaminatedwith microsporidia has received littleattention. A rabbit isolate ofE. cuniculicultured in a rabbit choroid plexus

(RCP) cell line has been used forin

vitro experiments in testing the factorsinfluencing the infectivity andreplication of this organism in RCPcells32 Aliquots of cells used for testingcontained variable proportions ofspores, sporoblasts, sporonts andschizonts, although a typical poolcontained about 80% spores, are madevisible by electron microscopy.Penicillin, Streptomycin or Gentamicindid not affect E.cuniculi, nor was itaffected by sonication, freezing andthawing or distilled water. Organismssurvive for 60 minutes but not up to120 minutes at 56 oC. They were killedafter 10 minutes of autoclaving at 12oC or exposure to 2% (v/v) lysol, 10%(v/v) formalin and 70% (v/v) ethylalcohol for 10 minutes. It is not knownwhether all microsporidia are affectedto the same degrees as E. cuniculi bythe physical conditions and chemicalsused in the study.32

Animal Model:

Several animal models have beenestablished to study microsporidialinfection24,44,45 as well as for producingmonoclonal antibodies13,46,47 Balb/c andC57B1/6 athymic mice have been usedand have been injectedintraperitoneally with Encephalitozooncuniculi, Encephalitozoon hellem or

Vittaforma cornea. SCID mice werealso been infected by oral inoculationof Encephalitozoon cuniculi spores.48Successful transmission ofEncephalitozoon cuniculi to rabbits byadministration of spores orally and

rectally has been reported.

44

Conclusions:Microsporidia are an important causeof disease in AIDS patients and arenow increasingly also recognized aspathogens in non-HIV-infected patientswith or without immuno-suppression.

Therefore, a high index of suspicion isneeded for both clinicians,parasitologists, pathologists andmicrobiologists.

As is true for many other new andemerging pathogens, we have justscratched the surface of a complexand evolving relation betweenmicrosporidia and humans. There isneed for an in-depth study onapplication of molecular techniques todiagnosis, species differentiation andphylogenetic analysis of microsporidiawhich will increase the knowledge ofthese organisms and help greatly inevaluating its threat to health inNigeria.

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