the intermediate host, with sexual and asexual reproduction The intermediate host and the definitive host can infect each other Vector transfer(虫媒传播型) Some protozoa need an insect vector in their life cycle.The ansfer manner of these type protozoa is person to insect and insect to person. In Plasmodium species,sexual method of reproduction occurs in one host(Anopheles mosquito) and asexual replication in another host(man). This process is known as alternation of generation(世代交替) accompanied by alternation of host PHYSIOLOGY The physiologic processes of protozoa include locomotion, ingestion, metabolism, reproduction nd others Locomotion(iz aJ): Protozoa move by four basic types of organelles: flagella, cilia. pseudopodia, and others Movement by means of pseudopodia is a complex form of protoplasmic streaming; Flagella are hair-like projections of cytoplasm; arise from a kinetoplast within the cytoplasm and serve as locomotor organelles in flagellates, In the ciliates, numerous short threads called cilia'( E which are distributed over the surface of the body, perform the function of locomotion In most sporozoan parasites there no specific locomotion organelles, locomotion is accomplished by. undulating ridges. The merozoites(裂殖子), ookinetes(动合子),and sporozoites(fiEf)appear to glide through fluids with no subcellular motion whatever, bu electron microscope studies reveal tiny undulatory waves that form in the cell membrane and pass Nutrition(E): There are several type nutrition are found in protozoa. 1 Permeation (iii), the passing of molecules directly through the out cells membrane: Some protozoa may obtain nourishment from the environment by diffusion or by active transport acros the plasma membrane. Diffusion is possible when the cell membrane is permeable to a particular molecule and when the concentration of that molecule is lower inside the cell than outside The accumulation of molecules against a concentration gradient requires the expenditure of energy and is called active transport. Active transport appears to operate through a carrier in the cell membrane, but the action of the carrier must be coupled with an energy-yield metabolic reaction. Obviously the ultimate value of the molecule or the energy derived from it must be great than the energy expended in acquiring it Some important food molecules such as glucose are brought into the cell by active transport 2) Pinocytosis(胞饮)& phagocytose吞噬);: Protozoa eat fluid food through cell membrane called pinocytosis, and protozoa eat solid food is called phagocytosis. Parasitic protozoa feed by ingesting entire organisms or particles thereof. Their mouth openings may be temporary, as in amebas, or permanent cytostome(HE D), as in most ciliates. Particulate food passes into a food vacuole, which is a digestive organelle that forms around any food thus ingested Pinocytosis and phagocytosis are important activity in many protozoa. Both pinocytosis and phagocytosis are example of endocytosis, differing only in that phagocytosis deal with droplets of fluid, whereas phagocytosis is the process of internalizing particulate matter. Reproduction(4E): Reproduction in protozoa may be either asexual or sexual, although many species alternate types in their life cycle 1) Asexual reproduction(无性生殖)
16 the intermediate host, with sexual and asexual reproduction. The intermediate host and the definitive host can infect each other. Vector transfer（虫媒传播型）Some protozoa need an insect vector in their life cycle. The transfer manner of these type protozoa is person to insect and insect to person. In Plasmodium species, sexual method of reproduction occurs in one host (Anopheles mosquito) and asexual replication in another host (man). This process is known as alternation of generation (世代交替) accompanied by alternation of host. PHYSIOLOGY The physiologic processes of protozoa include locomotion, ingestion, metabolism, reproduction and others. Locomotion(运动): Protozoa move by four basic types of organelles: flagella, cilia, pseudopodia, and others. Movement by means of pseudopodia is a complex form of protoplasmic streaming; Flagella are hair-like projections of cytoplasm; arise from a kinetoplast within the cytoplasm and serve as locomotor organelles in flagellates; In the ciliates, numerous short threads called ‘cilia’(纤毛) which are distributed over the surface of the body, perform the function of locomotion. In most sporozoan parasites there no specific locomotion organelles, locomotion is accomplished by. undulating ridges. The merozoites ( 裂殖子), ookinetes ( 动合子), and sporozoites (子孢子) appear to glide through fluids with no subcellular motion whatever, but electron microscope studies reveal tiny undulatory waves that form in the cell membrane and pass posteriad. Nutrition(营养): There are several type nutrition are found in protozoa. 1）Permeation(渗透), the passing of molecules directly through the out cells membrane: Some protozoa may obtain nourishment from the environment by diffusion or by active transport across the plasma membrane. Diffusion is possible when the cell membrane is permeable to a particular molecule and when the concentration of that molecule is lower inside the cell than outside. The accumulation of molecules against a concentration gradient requires the expenditure of energy and is called active transport. Active transport appears to operate through a carrier in the cell membrane, but the action of the carrier must be coupled with an energy-yield metabolic reaction. Obviously the ultimate value of the molecule or the energy derived from it must be great than the energy expended in acquiring it. Some important food molecules such as glucose are brought into the cell by active transport. 2）Pinocytosis(胞饮) & phagocytosis(吞噬)：Protozoa eat fluid food through cell membrane called pinocytosis, and protozoa eat solid food is called phagocytosis. Parasitic protozoa feed by ingesting entire organisms or particles thereof. Their mouth openings may be temporary, as in amebas, or permanent cytostomes (胞口), as in most ciliates. Particulate food passes into a food vacuole, which is a digestive organelle that forms around any food thus ingested. Pinocytosis and phagocytosis are important activity in many protozoa. Both pinocytosis and phagocytosis are example of endocytosis, differing only in that phagocytosis deal with droplets of fluid, whereas phagocytosis is the process of internalizing particulate matter. Reproduction(生殖): Reproduction in protozoa may be either asexual or sexual, although many species alternate types in their life cycle. 1）Asexual reproduction (无性生殖)
① Binary fission(二分裂) most often., asexual reproduction is by binary fission, in which the individual divides into two. All the internal structures are duplicated before division of the parasite(e. g, Entamoeba histolytica) ② Multiple fission(多分裂): multiple fission occurs in the Sarcodina and Sporozoea.In this type of division the nucleus and other essential organelles divide repeatedly before cytokinesis, thus a large number of daughter cells are produced almost simultaneously. During schizogony the cell is called a schizont(&Ff), meron, or segmenter. The daughter nuclei in the schizont arrange themselves peripherally, and the membranes of the daughter cells form beneath the cell surface of the mother cell, bulging outward. The daughter cells are merozoites, and they finally break away from a small residual mass of protoplasm remaining from the mother cell to initiate another phase of merogony or begin gametogony. Schizogony to produce merozoites may be eferred to as merogony. Another type of multiple fission often recognized is sporogony (EfH M1), which is multiple fission after the union of gametes (see sexual reproduction) Several forms of budding(FiD) can be distinguished. Plasmotomy, sometimes regarded as budding, is a phenomenon in which a multinucleate individual divides into two or more smaller but still multinucleate, daughter cells. Plasmotomy itself is not accompanied by mitosis. External budding(hs1)is found among some complex ciliates, such as the Suctoria. Here nuclear division is followed by unequal cytokinesis, resulting in a smaller daughter cell, which then grows to its adult size Internal budding, or endopolygeny(P3 yiD), differs from schizogony only in the location of the formation of daughter cells. In this process the daughter cells begin forming within their cell membranes, distributed throughout the cytoplasm of the mother cell rather than at the periphery. The process occurs in some stages of the schizonts of the Eimeriina. Endodyogeny is endopolygeny in which only two daughter cells are formed. 2)Sexual reproduction It occurs by conjugation gametogeny, conjugation. Sexual reproduction involves reduction division in meiosis, causing a change from diploidy to haploidy are the gametes, and the process of production of gametes is gametogony(配子生殖) Cells responsible for the production of gametes are ga Reproduction may be amphimictic, involving the union of gametes from two parents, or automictic, in which one parent gives rise to both gametes. Uniting gametes may be entire cells or only nuclei. When they are whole cell, the union is called syngamy(两性生殖) When only nuclei unIte, the process is termed conjugation(接合生殖). Conjugation is found only among the ciliates(Es), whereas syngamy occurs in all other groups in which sexual reproduction is found. Meiosis is known in both types of sexual reproduction Metabolism (ftiN): the main energy in protozoa, as in other cells, is in the form of high-energy phosphate bonds, primarily in adenosine triphosphate(ATP). Energy is released in the step by step, enzymatic oxidation of food molecules; part of this energy is conserved by coupling these oxidations with the phosphorylation of adenosine diphosphate(ADP) to ATP. Both protozoan and metazoan are unexpectedly variable in their energy metabolism, particularly in the factors to consider are that many parasites must survive in locations in which the oxygen supply is quite limited and that, even in many cases in which oxygen is not limited, neither is glucose; therefore there is no advantage in completely oxidizing glucose. If glucose is in plentiful supply, the organism can live on little more than the energy derived from glycolysis, simply by consuming
17 ① Binary fission (二分裂): most often, asexual reproduction is by binary fission, in which the individual divides into two. All the internal structures are duplicated before division of the parasite (e.g., Entamoeba histolytica) ② Multiple fission (多分裂): multiple fission occurs in the Sarcodina and Sporozoea. In this type of division the nucleus and other essential organelles divide repeatedly before cytokinesis; thus a large number of daughter cells are produced almost simultaneously. During schizogony the cell is called a schizont (裂殖体), meront, or segmenter. The daughter nuclei in the schizont arrange themselves peripherally, and the membranes of the daughter cells form beneath the cell surface of the mother cell, bulging outward .The daughter cells are merozoites, and they finally break away from a small residual mass of protoplasm remaining from the mother cell to initiate another phase of merogony or begin gametogony. Schizogony to produce merozoites may be referred to as merogony. Another type of multiple fission often recognized is sporogony (孢子生 殖), which is multiple fission after the union of gametes (see sexual reproduction). Several forms of budding (芽殖) can be distinguished. Plasmotomy, sometimes regarded as budding, is a phenomenon in which a multinucleate individual divides into two or more smaller, but still multinucleate, daughter cells. Plasmotomy itself is not accompanied by mitosis. External budding (外芽殖) is found among some complex ciliates, such as the Suctoria. Here nuclear division is followed by unequal cytokinesis, resulting in a smaller daughter cell, which then grows to its adult size. Internal budding, or endopolyogeny (内芽殖), differs from schizogony only in the location of the formation of daughter cells. In this process the daughter cells begin forming within their cell membranes, distributed throughout the cytoplasm of the mother cell rather than at the periphery. The process occurs in some stages of the schizonts of the Eimeriina. Endodyogeny is endopolygeny in which only two daughter cells are formed. 2）Sexual reproduction: It occurs by conjugation gametogeny, conjugation. Sexual reproduction involves reduction division in meiosis, causing a change from diploidy to haploidy are the gametes, and the process of production of gametes is gametogony (配子生殖). Cells responsible for the production of gametes are gamonts. Reproduction may be amphimictic, involving the union of gametes from two parents, or automictic, in which one parent gives rise to both gametes. Uniting gametes may be entire cells or only nuclei. When they are whole cell, the union is called syngamy (两性生殖). When only nuclei unite, the process is termed conjugation (接合生殖). Conjugation is found only among the ciliates (纤毛虫), whereas syngamy occurs in all other groups in which sexual reproduction is found. Meiosis is known in both types of sexual reproduction. Metabolism (代谢): the main energy in protozoa, as in other cells, is in the form of high-energy phosphate bonds, primarily in adenosine triphosphate (ATP). Energy is released in the step by step, enzymatic oxidation of food molecules; part of this energy is conserved by coupling these oxidations with the phosphorylation of adenosine diphosphate (ADP) to ATP. Both protozoan and metazoan are unexpectedly variable in their energy metabolism, particularly in the factors to consider are that many parasites must survive in locations in which the oxygen supply is quite limited and that, even in many cases in which oxygen is not limited, neither is glucose; therefore there is no advantage in completely oxidizing glucose. If glucose is in plentiful supply, the organism can live on little more than the energy derived from glycolysis, simply by consuming
more glucose, and the partially oxidized products can be excreted as waste Excretion(IF itb): most protozoa appear to ammonotelic; that is, they excrete most of their rogen as ammonia, most of which readily diffuse directly through the cell membrane into the surrounding medium. Other, sometimes unidentified waste products are also produced, at least by intracellular parasites. These substances are secrete and accumulated within the host cell and the death of the infected cell, have toxic effects on the host. Carbon dioxide, lactate, pyruvate, short chain fatty acids are also on waste products PATHOLOGIC CHARACTERISICS OF PROTOZOA Protozoan infections often are chronic lasting months or years. These typically are associated with tissue damage leading to various clinical manifestations of the disease. various mechanisms are suggested to be responsible for producing tissue damage in the host in many protozoan diseases 1)Multiplication(#%1): protozoa reproduce in their host, when the number is enough, they may destroy the infected cells, or they may invade other tissue of host, and produce pathological 2) Opportunistic pathogen(机会致病): Some symbiotic protozoa are nonpathogenic or cause only limited clinical symptoms in immunocompetent host, but produce serious symptoms in immunodeficient persons Protozoan infections produce a variety of clinical manifestations depending upon the tissue affected, the hosts immunity state and factors in microenvironment CLASSIFICATION OF PROTOZOA The Protozoa are classified into six Phyla by a Committee on Systematica and Evolution of the Society of Protozoologists(1985). This classification is based on the morpholog protozoa as demonstrated by light and electron scanning microscopy. The Sarcomastigophora(A 足鞭毛门), the Apicomplexa(顶复门) and Ciliophora(纤毛门), are three important phyla which contain species of medical importance causing disease in man(Table 1). According their locomotion organelles, protozoa can be divided into four groups: Amoebae, flagellates, ciliates and sporozoan. The common parasitic protozoa are list in table 1-1-1 Table 1l-I-1 Common parasitic protozoa arasitIc Scientific Species an Order Class Mononu-clear Leishmania donovani Trypanosomatidae kinetoplastida 杜氏利什曼原虫 锥虫科 动基体目 Zoomastigoph Leishmania tropica (单核吞噬系统)热带利什曼原虫 动鞭纲 Leishmania braziliensis 巴西利什曼原虫 Blood血 Trypanosoma Urogential canal Trichomonasva 泌尿生殖道 ginalis 毛滴虫科 毛滴虫目 阴道毛滴虫 Oral cavity trichomonAs 口腔 tenax 口腔毛滴虫
18 more glucose, and the partially oxidized products can be excreted as waste. Excretion (排泄): most protozoa appear to ammonotelic; that is, they excrete most of their nitrogen as ammonia, most of which readily diffuse directly through the cell membrane into the surrounding medium. Other, sometimes unidentified waste products are also produced, at least by intracellular parasites. These substances are secrete and accumulated within the host cell and, on the death of the infected cell, have toxic effects on the host. Carbon dioxide, lactate, pyruvate, and short chain fatty acids are also common waste products. PATHOLOGIC CHARACTERISICS OF PROTOZOA Protozoan infections often are chronic lasting months or years. These typically are associated with tissue damage leading to various clinical manifestations of the disease. Various mechanisms are suggested to be responsible for producing tissue damage in the host in many protozoan diseases. 1) Multiplication (增殖): protozoa reproduce in their host, when the number is enough, they may destroy the infected cells, or they may invade other tissue of host, and produce pathological change on host. 2) Opportunistic pathogen (机会致病) ：Some symbiotic protozoa are nonpathogenic or cause only limited clinical symptoms in immunocompetent host, but produce serious symptoms in immunodeficient persons. Protozoan infections produce a variety of clinical manifestations depending upon the tissue affected, the host’s immunity state and factors in microenvironment CLASSIFICATION OF PROTOZOA The Protozoa are classified into six Phyla by a Committee on Systematica and Evolution of the Society of Protozoologists (1985). This classification is based on the morphology of the protozoa as demonstrated by light and electron scanning microscopy. The Sarcomastigophora(肉 足鞭毛门), the Apicomplexa（顶复门）and Ciliophora（纤毛门）, are three important phyla which contain species of medical importance causing disease in man (Table 1). According their locomotion organelles, protozoa can be divided into four groups: Amoebae, flagellates, ciliates and sporozoan. The common parasitic protozoa are list in table Ⅱ-Ⅰ-1. Table Ⅱ-Ⅰ-1 Common parasitic protozoa Parasitic location Scientific Species Name Family Order Class Mononu-clear phagocyte system (单核吞噬系统) Leishmania donovani 杜氏利什曼原虫 Leishmania tropica 热带利什曼原虫 Leishmania braziliensis 巴西利什曼原虫 Trypanosomatidae 锥虫科 kinetopastida 动基体目 Zoomastigoph ora 动鞭纲 Blood 血 Trypanosoma sp 锥虫 Urogential canal 泌尿生殖道 Trichomonasva ginalis 阴道毛滴虫 Trichomonadidae 毛滴虫科 Trichomonadida 毛滴虫目 Oral cavity 口腔 Trichomonas tenax 口腔毛滴虫
Trichomonas 人毛滴虫 Dientamoeba fragilis 脆弱双核阿米巴 Giardia lambli Diplomonadida Lobosea 蓝氏贾第鞭毛虫 六鞭毛科 双滴虫目 叶足纲 Entamoebidae histolytica 内阿米巴科 阿米巴目 溶组织内阿米巴 Entamoeba dispa 迪斯帕内阿米巴 哈门氏内阿米巴 Entamoeba coli 结肠内阿米巴 lodamoe ba butschlii 布氏噬碘阿米巴 Endolimax nana 微小内延阿米巴 Oral cavity Entamoeba gingivalis 口腔 齿龈内阿米巴 moebidae sp amoebidae 棘阿米巴 棘阿米巴科 Naegleria fowleri Dimastiamoebidia 福氏耐格里阿米巴 双鞭阿米巴科 erythrocyte Plasmodium vivax Plasmodiidae Eucoccidiid Sporozoea 间日疟原虫 疟原虫科 真球虫目 孢子纲 三日疟原虫 Plasmodium falciparum 恶性疟原虫 Plasmodium ovale 卵形疟原虫 Undefined 卡氏肺孢子虫 Toxoplasmatidae Eucoccidiida 刚地弓形虫 真球虫目 Tissue组织 Sarcocystis sp Sarcocystidae 肉孢子虫 肉孢子虫科 Epithelium of|/ coRpora sp等孢子虫 Eimeriidae,爱美虫 small intestine 科 mucosa Cryptosporidium sp 小肠黏膜上皮隐孢子虫 Cryptosporidae 隐孢子虫科 Balantidium coli Balantidiidae Trichostomatida Kinetofrag- 结肠小袋纤毛虫 小袋科 毛口目 Minophorea 动基裂纲
19 Intestine 肠 Trichomonas hominis 人毛滴虫 Dientamoeba fragilis 脆弱双核阿米巴 Giardia lambli 蓝氏贾第鞭毛虫 Hexamitidae 六鞭毛科 Diplomonadida 双滴虫目 Lobosea 叶足纲 Entamoeba histolytica 溶组织内阿米巴 Entamoeba dispar 迪斯帕内阿米巴 Entamoeba hartmanni 哈门氏内阿米巴 Entamoeba coli 结肠内阿米巴 Iodamoeba butschlii 布氏噬碘阿米巴 Endolimax nana 微小内延阿米巴 Entamoebidae 内阿米巴科 Amoebida 阿米巴目 Oral cavity 口腔 Entamoeba gingivalis 齿龈内阿米巴 Brain Acanthamoebidae sp 棘阿米巴 Acanthamoebidae 棘阿米巴科 Naegleria fowleri 福氏耐格里阿米巴 Dimastiamoebidia e 双鞭阿米巴科 erythrocyte Plasmodium vivax 间日疟原虫 Plasmodium malariae 三日疟原虫 Plasmodium falciparum 恶性疟原虫 Plasmodium ovale 卵形疟原虫 Plasmodidae 疟原虫科 Eucoccidiida 真球虫目 Sporozoea 孢子纲 Alveolus 肺泡 Pneumocystis carinii 卡氏肺孢子虫 Undefined Karyocyte 有核细胞 Toxplasma gondii 刚地弓形虫 Toxoplasmatidae Eucoccidiida 真球虫目 Tissue 组织 Sarcocystis sp. 肉孢子虫 Sarcocystidae 肉孢子虫科 Epithelium of small intestine mucosa 小肠黏膜上皮 Isospora sp 等孢子虫 Eimeriidae爱美虫 科 Cryptosporidium sp 隐孢子虫 Cryptosporidae 隐孢子虫科 Colon Balantidium coli 结肠小袋纤毛虫 Balantidiidae 小袋科 Trichostomatida 毛口目 KinetofragMinophorea 动基裂纲
I ENTAMOEBAHISTOLYTICA(溶组织内阿米巴) Species in the Endamoebidae(内阿米巴科) are parasites or commensals(共生物 of the digestive of arthropods(节肢动物) and vertebrates(脊椎动物) The gerera and species are oeba(内阿米巴属)are both vertebrate and invertebrate(无脊椎动物)host. Several species of the protozoan parasite genus Entamoeba infect humans, Entamoeba coli(结肠内阿米巴), Entamoeba hartmanni(哈门 氏内阿米巴, Entamoeba dispar(迪斯帕内阿米巴) and Entamoeba histolytica.E. histolytica is the only species known to cause disease. The other (non-pathogenic)species are important because they may be confused with E. histolytica in diagnostic investigations Entamoeba histolytica causes amoebiasis(阿米巴病). The infection is worldwide in distribution. The parasite is the third leading parasitic cause of death in the developing countries. It remains as an important cause of diarrhoea in homosexual men suffering from the AlDs in the developed countries. Through the years it became obvious that E. histolytica occurs in two sizes. The as have trophozoites 12 to 15 um in diameter and cysts 5 to 9 um wide. This form is encountered in about a third of those who harbor amebas and is not associated with discase The larger form has trophozoites 20 to 30 um in diameter and cysts 10 to 20 u m wide. The larger fc The small, nonpathogenic type is considered here as a separate specie called E. dispar. Ever since E. histolytica was first described in association with dysenteric disease by Lesh in 1875, there has been an ongoing discussion as to whether the same species of amoeba, which causes the notable pathological and clinical symptoms of amoebiasis, was also the same one associated with asymptomatic carrier cases. Observations, particularly in more temperate climates, that only a mall percentage of people infected with Entamoeba exhibited disease symptoms, prompted Brumpt(1925, 1949)to suggest that there were in fact two morphologically identical species which he proposed should be named E. dispar, as an asymptomatic species and E. dysenteriae, the causative agent of symptomatic amoebiasis. This was not widely accepted and led to much discussion on diagnosis and treatment strategies bases of their isoenzyme patterns or zymodemes, by Sargeaunt et al (1987), and more recently by differences observed in antigenic specificity, and at the level of genomic DNA and ribosomal rNA and also in the epidemiological picture, has confirmed Brumpt's original assertion of two distinct species. This has lead to the recognition and acceptance of the establishment of two distinct pecies. Entamoeba dispar-( Brumpt 1925) Asymptomatic commensal in which carriers have no amoebic antigens in their serum, do not mount a serum anti-amoebic antibody response Entamoeba histolytica(Schaudinn 1903)Although most infections with this pathogenic organism are also asymptomatic, carriers develop an anti-amoebic antibody response have amoebic antigens in serum samples may have evidence of colonic invasion. Only about 10% of people infected with this species present with invasive amoebiasis Its life cycle, general morphology, and overall appearance, with the exception of size, are identical to those of E. histolytica, but their antigenicity and gene are completely different
20 Ⅱ ENTAMOEBA HISTOLYTICA (溶组织内阿米巴) Species in the Endamoebidae (内阿米巴科) are parasites or commensals (共生物)of the digestive of arthropods (节肢动物) and vertebrates (脊椎动物). The gerera and species are differentiated on the basis of nuclear structure. Species of Entamoeba (内阿米巴属) are found in both vertebrate and invertebrate (无脊椎动物) host. Several species of the protozoan parasite genus Entamoeba infect humans, Entamoeba coli (结肠内阿米巴), Entamoeba hartmanni (哈门 氏内阿米巴), Entamoeba dispar (迪斯帕内阿米巴) and Entamoeba histolytica. E. histolytica is the only species known to cause disease. The other (non-pathogenic) species are important because they may be confused with E. histolytica in diagnostic investigations. Entamoeba histolytica causes amoebiasis (阿米巴病). The infection is worldwide in distribution. The parasite is the third leading parasitic cause of death in the developing countries. It remains as an important cause of diarrhoea in homosexual men suffering from the AIDs in the developed countries. Through the years it became obvious that E. histolytica occurs in two sizes. The smaller-sized amebas have trophozoites 12 to 15 μm in diameter and cysts 5 to 9 μm wide. This form is encountered in about a third of those who harbor amebas and is not associated with discase. The larger form has trophozoites 20 to 30 μm in diameter and cysts 10 to 20 μm wide. The larger form sometimes pathogenic. The small, nonpathogenic type is considered here as a separate specie called E. dispar. Ever since E. histolytica was first described in association with dysenteric disease by Lesh in 1875, there has been an ongoing discussion as to whether the same species of amoeba, which causes the notable pathological and clinical symptoms of amoebiasis, was also the same one associated with asymptomatic carrier cases. Observations, particularly in more temperate climates, that only a small percentage of people infected with Entamoeba exhibited disease symptoms, prompted Brumpt (1925, 1949) to suggest that there were in fact two morphologically identical species which he proposed should be named E. dispar, as an asymptomatic species and E. dysenteriae, the causative agent of symptomatic amoebiasis. This was not widely accepted and led to much discussion on diagnosis and treatment strategies. The establishment of distinct non-pathogenic and pathogenic strains of Entamoeba on the bases of their isoenzyme patterns or zymodemes, by Sargeaunt et al (1987), and more recently by differences observed in antigenic specificity, and at the level of genomic DNA and ribosomal RNA and also in the epidemiological picture, has confirmed Brumpt's original assertion of two distinct species. This has lead to the recognition and acceptance of the establishment of two distinct species. Entamoeba dispar - (Brumpt 1925) Asymptomatic commensal in which carriers have no amoebic antigens in their serum, do not mount a serum anti-amoebic antibody response. Entamoeba histolytica (Schaudinn 1903) Although most infections with this pathogenic organism are also asymptomatic, carriers develop an anti-amoebic antibody response have amoebic antigens in serum samples may have evidence of colonic invasion. Only about 10% of people infected with this species present with invasive amoebiasis. Its life cycle, general morphology, and overall appearance, with the exception of size, are identical to those of E. histolytica., but their antigenicity and gene are completely different