22Section2ProtozoologyTable2.2:Molecularclassification (2000)ClassKingdomSubkingdomPhylumOrderGenusProtozoaArchezoaMetamonadaDiplomonadidaGiardiaTrepomonadeaEnteromonadidaEnteromonasRetortamonadeaRetortamonadidaRetortamonasChilomastixParabasaliaTrichomonadeaTrichomonadidaTrichomonasPentatrichomonasDientamoebaNeozoaAmoebozoaEntamoebaEntamoebideaEuamoebidaEndolimaxlodamoebaAmoebaeaAcanthopodidaAcanthamoebaPercolozoaHeteroloboseaSchizopyrenidaNaegleria(flagellatedamoeba)EuglenozoaKinetoplasteaTrypanosomatidaLeishmanidTrypanosomaEimeridaEimeriaSporozoaCoccideaToxoplasmaCryptosporidiumCyclosporaIsosporaSarcocystisPlasmodiumHaemosporidaPiroplasmidaBabesiaCiliophoraVestibuliferidaBalantidiumLitostomateaFungiMicrosporaMicrosporeaMicrosporidaEnterocytozoonEncephalitozoonPleistophoraTrachipleistophoraBrachiolaNosemaVittaformaMicrosporumChromistaChromobiotaBigyraBlastocysteaBlastocystisAdapted from: Topley and Wilson's Microbiology and Microbial Infections (Parasitology volume), 10th edition
22 section 2 Protozoology table 2.2: Molecular classifi cation (2000) Kingdom Subkingdom Phylum Class Order Genus Protozoa Archezoa Metamonada Trepomonadea Diplomonadida Giardia Enteromonadida Enteromonas Retortamonadea Retortamonadida Retortamonas Chilomastix Parabasalia Trichomonadea Trichomonadida Trichomonas Pentatrichomonas Dientamoeba Neozoa Amoebozoa Entamoebidea Euamoebida Entamoeba Endolimax Iodamoeba Amoebaea Acanthopodida Acanthamoeba Percolozoa Heterolobosea (fl agellated amoeba) Schizopyrenida Naegleria Euglenozoa Kinetoplastea Trypanosomatida Leishmania Trypanosoma Sporozoa Coccidea Eimeriida Eimeria Toxoplasma Cryptosporidium Cyclospora Isospora Sarcocystis Haemosporida Plasmodium Piroplasmida Babesia Ciliophora Litostomatea Vestibuliferida Balantidium Fungi Microspora Microsporea Microsporida Enterocytozoon Encephalitozoon Pleistophora Trachipleistophora Brachiola Nosema Vittaforma Microsporum Chromista Chromobiota Bigyra Blastocystea Blastocystis Adapted from: Topley and Wilson’s Microbiology and Microbial Infections (Parasitology volume), 10th edition. Chapter 02.indd 22 5/17/2014 5:47:39 PM
23Chapter2IntroductiontoProtozoaEXPECTEDQUESTIONSI. Write short notes on:(a)Isosporaspecies(a)Thetraditional 1980sclassificationof(b)Babesiaspecies(c)Giardiaspeciesparasites(b)Molecular classification (2000)of(d)Blastocystisspecies3.Which of the following protozoaparasites(c)SubkingdomNeozoabelongs to order Schizopyrenida?(a)PlasmodiumspeciesIl.Multiplechoicequestions(McQs):(b)Naegleriaspecies1.Whichofthefollowingprotozoa(c)Acanthamoeba speciesbelongs to phylum Euglenozoa?(d)Entamoebaspecies(a)Leishmania species4.Which of thefollowing protozoa(b)Entamoebaspeciesbelongsto phylum Sporozoa?(c)Cryptosporidiumspecies(a)Giardiaspecies(d)Plasmodiumspecies(b)Toxoplasmaspecies2.Whichof thefollowing protozoa(c)PlasmodiumspeciesbelongstokingdomChromista?(d)EntamoebaspeciesAnswers1. (a)2. (d)3. (b)4. (c)
Chapter 2 Introduction to Protozoa 23 Expected Questions I. Write short notes on: (a) The traditional 1980s classification of parasites (b) Molecular classification (2000) of parasites (c) Subkingdom Neozoa II. Multiple choice questions (MCQs): 1. Which of the following protozoa belongs to phylum Euglenozoa? (a) Leishmania species (b) Entamoeba species (c) Cryptosporidium species (d) Plasmodium species 2. Which of the following protozoa belongs to kingdom Chromista? (a) Isospora species (b) Babesia species (c) Giardia species (d) Blastocystis species 3. Which of the following protozoa belongs to order Schizopyrenida? (a) Plasmodium species (b) Naegleria species (c) Acanthamoeba species (d) Entamoeba species 4. Which of the following protozoa belongs to phylum Sporozoa? (a) Giardia species (b) Toxoplasma species (c) Plasmodium species (d) Entamoeba species Answers 1. (a) 2. (d) 3. (b) 4. (c) Chapter 02.indd 23 5/17/2014 5:47:40 PM
3AmoebaChapterOutlineNonpathogenic intestinalamoebaClassificationof amoebaIntestinal amoebaFree-livingamoebaPathogenic intestinal amoeba-ExpectedquestionsCLASSIFICATIONOFAMOEBATaxonomical ClassificationAmoeba is a single-celled protozoa that con-Accordingto the traditional 1980s classi-stantlychanges its shape.Theword"amoeba"fication-amoeba belongs to the Phylumis derived from the Greek word“amoibe"Sarcomastigophora,Subphylum Sarcodina,meaning"change".They constantly changeSuperclass Rhizopoda, Class Lobosea, Sub-their shapedue to presence of an organ ofclass Gymnamoebia, Order Amoebida andlocomotioncalledas"pseudopodium"FamilyEndamoebidae.However, inlast30 years,with the adventofClassification Based OnHabitatmoleculartechnique,thetaxonomyischangedandcurrentlythenewmolecularclassificationAmoebaeareclassified as intestinal amoebaeis followed (Table 3.1)andfreelivingamoebae.Intestinal amoebae:Theyinhabitat in thePATHOGENICINTESTINALlarge intestine of humans and animals.AMOEBAEntamoebahistolyticaistheonlypathogenicspecies.Othersarenonpathogenicsuchas-Entamoeba histolyticaE. dispar, E. moshkouski, E.coli, E.polecki,IntroductionE. hartmanni, E.gingivalis, Endolimaxnana,and lodamoebabutschliiE.histolytica is worldwide in distribution but.Free-living amoebae: They are smallmore common in tropical and subtropicalfree livingand opportunistic pathogens.countries.E. histolytica has three subspecies-E.Examples are Acanthamoeba species,.Naegleriafowleri,Balamuthiamandrillarishistolytica subspecies histolytica,disparand Sappiniadiploideaand moshkouskii
CLASSIFICAtION OF AMOEBA Amoeba is a singlecelled protozoa that constantly changes its shape. Th e word “amoeba” is derived from the Greek word “amoibe” meaning “change”. Th ey constantly change their shape due to presence of an organ of locomotion called as “ pseudopodium” Classifi cation Based On Habitat Amoebae are classifi ed as intestinal amoebae and free living amoebae. z Intestinal amoebae: Th ey inhabitat in the large intestine of humans and animals. Entamoeba histolytica is the only pathogenic species. Others arenonpathogenic such as— E. dispar, E. moshkovskii, E. coli, E. polecki, E. hartmanni, E. gingivalis, Endolimax nana, and Iodamoeba butschlii z Free-living amoebae: They are small free living and opportunistic pathogens. Examples are Acanthamoeba species, Naegleria fowleri, Balamuthia mandrillaris and Sappinia diploidea taxonomical Classifi cation According to the traditional 1980s classifi cation—amoeba belongs to the Phylum Sarco mastigophora, Subphylum Sarcodina, Superclass Rhizo poda, Class Lobosea, Subclass Gymnamoebia, Order Amoebida and Family Endamoebidae. However, in last 30 years, with the advent of molecular technique, the taxonomy is changed and currently the new molecular classifi cation is followed (Table 3.1). pAtHOGENIC INtEStINAL AMOEBA Entamoeba histolytica Introduction E. histolytica is worldwide in distribution but more common in tropical and subtropical countries. z E. histolytica has three sub species—E. histolytica subspecies histolytica, dispar and moshkovskii 3 Amoeba Chapter Outline • Classifi cation of amoeba • Intestinal amoeba − Pathogenic intestinal amoeba − Nonpathogenic intestinal amoeba • Free-living amoeba • Expected questions Chapter-03.indd 24 5/19/2014 12:47:32 PM
25Chapter3AmoebaTable 3.1: Taxonomy of AmoebaOrderKingdomSubkingdomPhylumClassGenusNeozoaAmoebozoaEntamoebideaEuamoebidaEntamoebaProtozoaEndolimaxlodamoebaAmoebaeaAcanthopodidaAcanthamoebaPercolozoaHeteroloboseaNaegleriaSchizopyrenida(flagellated amoeba)Cysts and trophozoites of all the threereported annually by WHO (World healthOranization)subspeciesaremorphologicallyindistinIn India, the prevalence rate is around 15%guishableHowever, on the basis ofextensivegenetic,(ranges from3.6%to47.4%)withahigherprevalene reported from Maharashtra,immunological,andbiochemical analysis,Tamilnadu and Chandigarh.currently all the three subspecies areformallyaccepted as different yet closelyrelatedspeciesMorphology.E. histolytica is the pathogenic speciesE. histolytica has three stages—(1) trophozoite,causing amoebic dysentery and a wide(2) precyst and (3) cyst (immature and mature).range ofother invasive diseases, includingTrophozoiteamoebic liver abscess, where as othertwo are considered as nonpathogens thatIt is the invasive form as well as the feedingand replicatingform oftheparasitefound incolonize the large intestine.the feces of patients with active disease..Itmeasures12-60 μm(average15-20μm)HistoryindiameterE.histolytica was first described by FedorCytoplasm of trophozoite is divided into aLosch(1875)fromRussiaclearectoplasm andagranularendoplasm.The species namewas first coinedby FritzGranularendoplasm looks asgroundglassSchaudinnin1903appearanceand containsred blood cellsBrumpthad described anddesignatedthe(RBCs),white blood cells (WBCs) andfoodvacuoles containingtissuedebris andnonpathogenic form of E.histolytica asbacteria.RBCs arefound only in the stageE. dispar in 1993.ofinvasionPseudopodia:Ectoplasm has long fingerEpidemiologylikeprojections called as pseudopodiaAmoebiasisisamajorhealthproblem(organ oflocomotion);whichexhibitsworldwide.active,unidirectionalrapidprogressiveand:The largestburden of the disease occurs inpurposefulmovementtropics ofChina,Central and SouthAmerica,Nucleus is single, spherical, 4-6 μmand Indian subcontinents affecting 10% ofsize, contains central dot like compactthe world's population. (500 million)karyosome surrounded by a clear halo..It is the third most common parasiticNuclear membrane is thin and delicatecause of death in the world (after malariaand is lined bya layer of fine chromatinand schistosomiasis).Approximately50granules.The number of chromosomesmillion cases and 110, 000 deaths arevariesbetween30and 50
Chapter 3 Amoeba 25 z Cysts and trophozoites of all the three subspecies are morphologically indistinguishable z However, on the basis of extensive genetic, immunological, and biochemical analysis, currently all the three subspecies are formally accepted as diff erent yet closely related species z E. histolytica is the pathogenic species causing amoebic dysentery and a wide range of other invasive diseases, including amoebic liver abscess, where as other two are considered as nonpathogens that colonize the large intestine. History E. histolytica was fi rst described by Fedor Losch (1875) from Russia. z Th e species name was fi rst coined by Fritz Schaudinn in 1903 z Brumpt had described and designated the nonpathogenic form of E. histolytica as E. dispar in 1993. Epidemiology Amoebiasis is a major health problem worldwide. z Th e largest burden of the disease occurs in tropics of China, Central and South America, and Indian subcontinents aff ecting 10% of the world’s population. (500 million) z It is the third most common parasitic cause of death in the world (after malaria and schistosomiasis). Approximately 50 million cases and 110, 000 deaths are reported annually by WHO (World health Oranization) z In India, the prevalence rate is around 15% (ranges from 3.6% to 47.4%) with a higher prevalene reported from Maharashtra, Tamilnadu and Chandigarh. morphology E. histolytica has three stages—(1) tropho zoite, (2) precyst and (3) cyst (immature and mature). Trophozoite It is the invasive form as well as the feeding and replicating form of the parasite found in the feces of patients with active disease. z It measures 12–60 µm (average 15–20 µm) in diameter z Cytoplasm of trophozoite is divided into a clear ectoplasm and a granular endoplasm z Granular endoplasm looks as ground glass appearance and contains red blood cells (RBCs), white blood cells (WBCs) and food vacuoles containing tissue debris and bacteria. RBCs are found only in the stage of invasion z Pseudopodia: Ectoplasm has long fi nger like projections called as pseudopodia (organ of locomotion); which exhibits active, unidirectional rapid progressive and purposeful movement z Nucleus is single, spherical, 4–6 µm size, contains central dot like compact karyosome surrounded by a clear halo. Nuclear membrane is thin and delicate and is lined by a layer of fine chromatin granules. The number of chromosomes varies between 30 and 50 table 3.1: Taxonomy of Amoeba Kingdom Subkingdom Phylum Class Order Genus Protozoa Neozoa Amoebozoa Entamoebidea Euamoebida Entamoeba Endolimax Iodamoeba Amoebaea Acanthopodida Acanthamoeba Percolozoa Heterolobosea (fl agellated amoeba) Schizopyrenida Naegleria Chapter-03.indd 25 5/19/2014 12:47:32 PM
26Section2 ProtozoologyThespacebetweenthekaryosomeandthe.Itmeasures10-20μm (average12-15μm)nuclearmembraneistraversed byspokeindiameter (Fig.3.1C)likeradialarrangementofachromaticfibrilsNuclear structures are same as intropho-(cartwheelappearance)zoites.First, the cyst is uninucleated; later.Amoebic trophozoites are anaerobic para-thenucleus dividestoformbinucleated andsites.Theylackmitochondria,endoplasmicfinallybecomes quadrinucleated cystreticulum and Golgi apparatus. (Fig.3.1A)..Cytoplasmofuninucleatedcystcontains1-4numbersrefractilebarswithroundedPrecystends called as chromatoid bodies (aggre-It is the intermediate stage between trophogation of ribosome)and a largeglycogenmass (stainsbrownwithiodine)zoiteand cyst.Bothchromatoidbodyandglycogenmass:Itis smallerto trophozoitebutlargertocystgraduallydisappear,andtheyarenotfound(10-20 μm).It is oval with a blunt pseudopodia.Foodinmature quadrinucleated cystCystsarepresentonlyinthegutlumen;theyvacuoles and RBCs disappear.Nuclearnever invadethe intestinal wall.structuresaresameasthatoftrophozoite"Minuta"form of Entamoeba histolytica:(Fig.3.1B).Theyarethe commensal phaseof E.Cysthistolytica, living in the lumen of gut.TheyIt is the infectiveformas wellas thediagnosticare usually smaller in size (trophozoite 12-14formoftheparasitefoundinthefecesofμmandcyst<10μm)and often mistakenasE.hartmanni.carriersaswellaspatientswithactivedisease.PseudopodiumEctoplasmWBCEndoplasmKaryosome (central)PeripheralFood<chromatinvacuolesgranule (fine)RBCABNucleus彩福福福SAChromatidbody彩茶GlycogenmassaUninucleated cystBinucleatedcystQuadrinucleated cystFigs 3.1A to C: Entamoeba histolytica (schematic diagram) (A) trophozoite; (B) precyst; (C) cysts
26 Section 2 Protozoology z The space between the karyosome and the nuclear membrane is traversed by spoke like radial arrangement of achromatic fibrils (cart wheel appearance) z Amoebic trophozoites are anaerobic parasites. They lack mitochondria, endoplasmic reticulum and Golgi apparatus. (Fig. 3.1A). Precyst It is the intermediate stage between trophozoite and cyst. z It is smaller to trophozoite but larger to cyst (10–20 µm) z It is oval with a blunt pseudopodia. Food vacuoles and RBCs disappear. Nuclear structures are same as that of trophozoite (Fig. 3.1B). Cyst It is the infective form as well as the diag nostic form of the parasite found in the feces of carriers as well as patients with active disease. z It measures 10–20 µm (average 12–15 µm) in diameter (Fig. 3.1C) z Nuclear structures are same as in trophozoites. First, the cyst is uninucleated; later the nucleus divides to form binucleated and finally becomes quadrinucleated cyst z Cytoplasm of uninucleated cyst contains 1–4 numbers refractile bars with rounded ends called as chromatoid bodies (aggregation of ribosome) and a large glycogen mass (stains brown with iodine) z Both chromatoid body and glycogen mass gradually disappear, and they are not found in mature quadrinucleated cyst z Cysts are present only in the gut lumen; they never invade the intestinal wall. “Minuta” form of Entamoeba histolytica: They are the commensal phase of E. histolytica, living in the lumen of gut. They are usually smaller in size (trophozoite 12–14 µm and cyst < 10 µm) and often mistaken as E. hartmanni. Figs 3.1A to C: Entamoeba histolytica (schematic diagram) (A) trophozoite; (B) precyst; (C) cysts A C B Chapter-03.indd 26 5/19/2014 12:47:33 PM