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The Protozoa

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The Protozoa The Protozoa Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Classification • Protozoans • Eukaryotic (Domain Eukarya) • Unicellular exclusively • Chemoheterotrophic • Kingdom: Protista • Phylum: Archaezoa or Mastigophora (“flagellates”) • Phylum: Amoebozoa or Sarcodina (“amoebas”) • Phylum: Ciliophora (“ciliates”) • Phylum: Apicomplexa (“obligate parasites”) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings General terminology and life cycles • Trophozoite - “the feeding and growing stage”; the vegetative form • Eats bacteria and free nutrients (like sugars) • Reproduction - Asexual • Schizogony - “multiple fission” - nucleus divides repeatedly, allowing one cell to give rise to many daughter cells • Binary Fission - one nuclear division gives rise to two daughter cells (closest to mitosis) • Budding - outgrowth of a mature cell grows and becomes a new daughter cell • Reproduction - Sexual • Conjugation - cells that have undergone a reduction division fuse, exchange haploid micronuclei, and separate - each gives rise to two daughter cells Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings General terminology and life cycles • Encystment - in certain circumstances, a protective capsule forms called a cyst. This is a “dormant” stage, but may be observed in/required for parasitic infection. It can allow parasitic protozoa to survive outside the host. • Life Cycles • Parasitic protozoa often have complex life cycles with multiple hosts involved: • The DEFINITIVE HOST harbors the SEXUALLY REPRODUCING stage • INTERMEDIATE HOSTS harbor the ASEXUALLY REPRODUCING stage(s) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Kingdom Protista/Sub-kingdom Protozoa • Eukaryotic • Unicellular • Chemoheterotrophs • Vegetative form is a trophozoite • Asexual reproduction by fission, budding, or schizogony • Sexual reproduction by conjugation • Some produce cysts Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Phylum Archaezoa or Mastigophora (flagellates) • Move using multiple flagella • Giardia lamblia • Trichomonas vaginalis (no cyst stage) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Giardiasis • Transmitted by Giardia lamblia contaminated water, usually in rural areas • Inhabits small intestine of various mammals • Causes severe gastroenteritis, also called “Beaver fever” • Diagnosed by microscopic examination of feces for cysts Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Trichomoniasis - a type of vaginitis • Found in semen or urine of male carriers (no symptoms) Trichomonas vaginalis • Usually sexually transmitted, possible to acquire from public facilities • May be carried and cause no symptoms in women. • Vaginal infection causes irritation and profuse discharge • Diagnosis by microscopic identification of protozoan • Since there is no cyst, cannot survive outside of host Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Amoebozoa or Sarcodina (amoebas) • Move using pseudopods “false feet” • Entamoeba (parasitic) • Amoeba (generally non- parasitic) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Amoebic Dysentery • Entamoeba histolytica • Causes diarrhea containing blood and mucus • Amoeba feeds on RBCs and GI tract tissues • Diagnosis by observing cysts in feces • Transmitted through ingestion of cysts Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Amoebic Dysentery Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Ciliophora (ciliates) • Move by cilia, which are shorter and more numerous than flagella • Generally free-living • Balantidium coli is the only human parasite, which causes a severe but rare dysentery Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Apicomplexa • Nonmotile • Intracellular parasites • Complex life cycles • Plasmodium - Malaria is the fourth leading cause of death by infectious disease • Cryptosporidium - can cause respiratory and gall bladder infections in immunosuppressed individuals, and may be a major cause of death. • Cyclospora Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Plasmodium life cycle: example of a complex protozoan parasite • Plasmodium grows by sexual reproduction in the Anopheles mosquito; if the mosquito “bites” a human, the infective particles, called sporozoites, enter the blood and travel to the liver. • They multiply (by schizogeny) in the liver, and the new cells are called merozoites; these enter the blood and infect red blood cells (ring stage). • As they grow asexually, the red blood cells eventually rupture, releasing more merozoites and toxins which cause the fever and chills associated with the disease. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Plasmodium life cycle • Some sexual cells called gametocytes are also formed, and can be picked up by another mosquito to repeat the cycle. • The mosquito is called the DEFINITIVE HOST because it harbors the sexual stage; humans are called the INTERMEDIATE HOST, because asexual reproduction occurs in us. • Fever and chills are caused by toxins associated with the organisms, and occur cyclically. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Cryptosporidiosis • Cryptosporidium parvum • Transmitted by oocysts in contaminated water • Causes severe diarrhea, as it resides in the intestine • Treated with oral rehydration Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Cyclospora Diarrheal Infection • Cyclospora cayetanensis • Transmitted by oocysts in contaminated water • Diagnosed by microscopic examination for oocysts • Mostly shows up in immunosuppressed individuals Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings .
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