Clinical Parasitology Module 2 PDF

MODULE 2 PROTOZOA Unit 1: General characteristics of Protozoa Unit Learning Outcomes: State the general characteristic...

MODULE 2 PROTOZOA Unit 1: General characteristics of Protozoa Unit Learning Outcomes: State the general characteristics of protozoa as to: 1. morphology 2. life cycle 3. reproduction 4. transmission, pathology, and diagnosis Engage Protozoa is one of the three major groups of parasites that are of medical importance to man. Recall the discussion in Module 1, Unit 1 and characterize the protozoa as to: Kingdom (based on 5-kingdom classification) ________________________________ Cell type ( eukaryotic or prokaryotic) ________________________________ Cell organization (unicellular or multicellular) ________________________________ Nutritional type (autotroph or heterotroph) ________________________________ Explore The single cell unit that protozoa consists of performs all the functions of life, i.e., reproduction, respiration, excretion, etc., that in higher organisms are carried on by specialized cells. They have remarkable range in size and form, some visible to the naked eye, while others require magnification up to a thousand fold before they can be seen. Some are spherical or ovoidal, while others have bizarre contours. Protozoa are found in all moist habitats. They are common in sea, in soil and in fresh water. Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited. 2 Protozoa, from the Greek ‘protos’ and ‘zoon’ meaning “first animal”, were historically regarded as "one-celled animals" because they often possess animal-like behaviors, such as motility at some stage of their life cycle. Most of the protozoa are nonpathogenic but few may cause major diseases. The succeeding units of this module will describe the three phyla of protozoa of medical interest in humans. Phylum Sarcomastigophora which includes subphylum Sarcodina, and, subphylum Mastigophora. Phylum Ciliophora Phylum Apicomplexa Although, protozoa exhibit marked diversity in size, shape, and other characteristics, there are fundamental characteristics common to the entire group. Explain A. General Morphology of Protozoa The structure of a protozoan cell is composed of (1) cytoplasmic body, and (2) a nucleus. The various life functions are carried out by specialized intracellular structures known as organelles. 1. Cytoplasm The cytoplasm consists of a thin outer Schematic diagram of a protozoan cell with a vesicular ectoplasm and a voluminous inner nucleus. endoplasm that the electron ect, ectoplasm; end, endoplasm; inc, inclusion; kar, microscope has demonstrated to be karyosome; ln, linin network; nuc, nucleus; nm, nuclear membrane; pc, peripheral chromatin; pm, plasma membrane. very complex. a. Ectoplasm The ectoplasm, under the light microscope, appears more transparent, less granular, and more homogeneous. It is covered with plasma membrane that is like those found in all cells. It functions in movement, respiration, procurement of food, discharge of metabolic wastes, and protection. The locomotory organelles of protozoa arise from the ectoplasm. Pseudopodia are temporary extensions of the ectoplasm and are found in amoebas under the subphylum Sarcodina. Flagella are long, slender, whiplike structures seen in subphylum Mastigophora, thus collectively called the Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited. 3  flagellates. They may have one or more than one flagellum, and these may be inserted into the cell at different angles. Cilia, which are structurally similar to flagella but shorter and covering the entire surface of the body, are seen in phylum Ciliophora (ciliates). Undulating membrane is a lateral expansion of the plasma membrane with a flagellar rim extending out like a fin along the outer edge of the body of certain flagellates. Pseudopodia Flagella Cilia Undulating membrane Note: The parasites are NOT drawn to scale. Protozoa in phylum Apicomplexa do not exhibit an obvious mode of mobility but can glide nonetheless. Food may be taken in at any place in the cytoplasm or ingested at a Cytostome particular point. Pseudopodia in amoebas function for feeding by phagocytosis. Balantidium coli, I n s o m e s p e c i e s , l i k e trophozoite. Cytopyge Balantidium coli - a ciliate, food passes directly into a specialized "cell mouth" structure called cytostome which is located near the anterior end of the body. Similarly, excretion of undigested particles are discharged at the general surface or through a specialized " cell anus", the cytopyge. Certain protozoa at times enter an inactive cystic state, in which they secrete a membranous cyst wall. It is necessary for the protection and survival outside the body and against the acidic digestive juices of the gastrointestinal tract. b. Endoplasm The endoplasm consists of a moderately dense granular protoplasm that immediately surrounds the nucleus. It is principally Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited. 4  concerned with metabolism and nutrition, and storage of food. The endoplasm contains the organelles mitochondria, Golgi apparatus, microbodies, and endoplasmic reticulum. It may also contain contractile vacuoles, food vacuoles, food reserves, and foreign bodies. In some species, contractile vacuoles act as osmoregulators. Contractile vacuoles Freshwater protozoa are hypertonic to their Balantidium coli, environment, so they imbibe trophozoite. water continuously by osmosis. Contractile vacuole collects excess water in their cytoplasm and pumps them out of the cell. Some species maintain a reserve food supply such as glycogen vacuole and chromatoidal bodies found in some immature amoebic cysts. Glycogen vacuole represents the main storage form of glucose. In wet mount preparation, they are demonstrated by staining a brown color with iodine solution. Source: WHO Bench aids for the diagnosis of intestinal parasites, second edition. Chromatoidal bodies (or bars) are dense structures which are made up of crystalline RNA and RNA-binding proteins. Cyst of Entamoeba histolytica/dispar in an unstained concentrated wet mount of stool. Notice the chromatoid bodies with blunt, rounded ends (arrow). Source: CDC DPDx Endoplasm of some protozoa may show food vacuoles or inclusions such such as red blood cells , bacteria, or other ingested materials. Trophozoite of Entamoeba histolytica with ingested erythrocytes (arrow), under differential interference contrast (DIC) microscopy. Source: CDC DPDx Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited. 5  In apicomplexans, the cystic form is an oocyst. ENCYSTATION Entamoeba histolytica Entamoeba histolytica Giardia lamblia Giardia lamblia EXCYSTATION ENCYSTATION. The protozoa possess the property of being transformed from the active trophozoite stage to an inactive cyst stage, losing its power of motility, growth and reproduction, and enclosing itself in a tough wall. Conditions favoring encystment, in most cases, involve some adverse environmental events such as: nutritional deficiency desiccation pH or temperature changes increased tonicity decreased oxygen concentration overpopulation EXCYSTATION. When the condition becomes favorable again, the organism leaves the cyst stage and continues its life cycle in the trophozoite stage. Mechanisms for excystation may include: absorption of water with consequent swelling of the cyst secretion of lytic enzymes by the protozoan action of host digestive enzymes on the cyst wall Note, however, that both processes, encystation and excystation, occur only within the host. Trophozoites that are passed in feces during diarrhea, in unfavorable condition outside the host, do NOT encyst but disintegrate, thus must be examined or preserved within a short time after passage. Cysts are passed in semi-formed or formed stool. Transference to another susceptible host is required so that they can continue their life cycle and grow as trophozoite stage. C. Reproduction of Protozoa Protozoan reproduction may be either asexual or sexual, or alternate the two types in their life cycles. Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited. 7  2. Nucleus The nucleus contains the chromosomes that are essential for life, reproduction, and genetic composition of the organism. It is bounded externally by a well-defined nuclear membrane similar to that of most eukaryotic cells. There are two types of nucleus among the protozoa. a. Vesicular nucleus is found in most protozoa. It is characterized by an irregular distribution of chromatin materials that clear areas are apparent in the nucleoplasm. The chromatin granules may line the inner side of the nuclear membrane forming the Tr o p h o z o i t e s o f E n t a m o e b a histolytica with ingested erythrocytes peripheral chromatin, or form a linin stained with trichrome. The ingested network of fibrils radiating towards the erythrocytes appear as dark inclusions.The parasites above show periphery of the nucleus. Inside the nuclei that have the typical small, nucleus is a single mass or aggregate of centrally located karyosome, and dense chromatin, called the karyosome thin, uniform peripheral chromatin. The space between the karyosome (AKA endosome), which may be and the nuclear membrane is located centrally or eccentrically, and traversed by a fine thread of linin network having a "spokes wheel" may be surrounded by chromatin arrangement particles that appear to be arranged in Source: CDC DPDx. an achromatic network. b. Compact nucleus is found in a few protozoa only, primarily in ciliates. The Macronucleus Micronucleus chromatin granules are dense so that there are no clear areas of nucleoplasm Balantidium coli, observed in light microscopy, although trophozoite. present. B. General Life Cycle of Protozoa Although the life cycles of protozoa can vary a great deal, there are two developmental stages commonly encountered in protozoa: (1) trophozoite, and (2) cyst. 1. Trophozoites are the motile forms. They are the vegetative stage, i.e, they have reproductive powers, and the feeding stage, some feeding on host cells, thus are responsible for the pathogenic effects in the host. However, they are delicate and do not survive long outside the host. 2. Cysts are the resting, nonmotile stage of protozoa. They are bounded by tough cell wall so they show considerable resistance in unfavorable environment. Thus, the cyst is closely associated with transfer from host to host and constitutes the infective stage of most of the protozoa. Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited. 6  1. Asexual reproduction a. Binary fission Most often asexual reproduction is by binary fission, in which one individual divides into two of more or less equal parts. The plane of fission is random in amoebas, longitudinal in flagellates, or transverse in ciliates. Before division, all structures are duplicated. b. Multiple fission Multiple fission occurs in Apicomplexa, as in the malaria parasite in the genus Plasmodium. In this type of division, the nucleus and other essential organelles divide repeatedly followed by cytokinesis (cytoplasmic division). Thus, a large number of daughter cells are produced almost simultaneously. A type of multiple fission is schizogony. Cells undergoing schizogony are called schizonts or meronts. When the multiplication is completed, the schizont ruptures and liberates daughter cells called merozoites, to initiate another phase of merogony (schizogony producing more asexually reproducing merozoites) or to begin gametogony (gametocyte formation). Alternation of generations in the life cycle of Apicomplexa Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited. 8  Another type of multiple fission often recognized is sporogony, which is meiosis immediately after the union of gametes, The products of sporogony, however, are sporozoites in resistant oocysts. 2. Sexual reproduction a. Syngamy In this process, sexually differentiated cells, called gametes (female macrogamete, and male microgamete) unite permanently and a complete fusion of the nuclear material takes place. The resulting product is then known as the zygote. Cells that produce macrogametes and microgametes are the gametocytes or gamonts formed by gametogony. b. Conjugation Conjugation, in which only the nuclei unite, is found only among ciliates. A temporary union of two organisms occurs during which time interchange of nuclear material takes place. Later on, the two organisms separate, each being rejuvenated during the process, although probably not essential for perpetuation of the species. Elaborate There are two major methods of transmission of protozoal infection: through ingestion of the infective stage of the protozoa or via an arthropod vector. A few are transmitted by sexual contact. The mode of transmission is specific for each species. Protozoa, in contrast to worms, multiply in their hosts, so disease can result from infection initiated by only a few organisms. Pathologic changes are due to invasion and destruction of cells or tissues by the parasite itself or its products. Tissue damage secondary to immune response, or immunopathology, may occur. Generalized systemic symptoms, e.g., fever, and signs like splenomegaly and lymphadenopathy are common. The early stage of infection may be subclinical, or it may be severe, leading to death or into a chronic latent stage, with relapses at times before eventual recovery. The diagnosis of some diseases, e.g., malaria or leishmaniasis, may be strongly suspected on clinical grounds from characteristic signs and symptoms. But clinical impressions should always be confirmed by laboratory diagnosis that identified the parasite in the specimen. Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited. 9