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The Protists 1 25 Copyright © McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display.

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Presentation on theme: "The Protists 1 25 Copyright © McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display."— Presentation transcript:

1 The Protists 1 25 Copyright © McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display.

2 The Protists Eukaryotes with the taxonomic classification in flux Kingdom Protista (out dated?) is artificial grouping of over 65,000 different single-celled life forms A polyphyletic collection of organisms Most are unicellular Lack the level of tissue organization present in higher eukaryotes 2

3 Distribution of Protists Grow in a wide variety of moist habitats Most are free living Chemoorganoheterotrophic forms play role in recycling nitrogen and phosphorus Terrestrial and planktonic forms Photolithoautotrophic forms usually referred to as algae Parasitic forms cause disease in humans and domesticated animals 3

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5 Nutrition in Protists Protozoa are chemoorganoheterotrophic protists –saprophytes – nutrients obtained from dead organic matter through enzymatic degradation –osmotrophy – absorb soluble products –holozoic nutrition – solid nutrients acquired by phagocytosis Photolithoautotrophic protists –strict aerobes, use photosystems I and II for oxygenic photosynthesis Mixotrophic protists –use organic and inorganic carbon compounds 5

6 Protist Morphology Plasma membrane structure similar to multicellular plants/animals Pellicle structure provides support in protozoa Cell wall in algae Motility –Pseudopodia in amoeboids –Flagella –Cilia –Some with no motility 6

7 Encystment and Excystment Encystment –protists simplify in structure and become dormant (cyst) with a cell wall and very low metabolic activity protects against environmental changes can assist in nuclear reorganization/reproduction (schizogony and plasmotomy) serve as a means of host to host transfer for parasitic species 7

8 Encystment and Excystment Excystment –A return to favorable conditions may stimulate a cyst form to return to its original state –In parasitic protists, this may occur following ingestion of a cyst by a new host organism Giardia 8

9 Protist Reproductive Cells and Structures Protists have asexual and sexual reproduction –Asexual stage usually binary fission but can be schizogony or plasmotomy –Sexual stages use fusion of gametes in syngamy process within a single org (autogamy) or between (conjugation) 9

10 Protists Taxonomy Difficult to define due to vast differences in protists Very much in flux and an area of active research New classification scheme is based on that of the International Society of Protistologists –doesn’t utilize hierarchical ranks (class and order) –6 Super Groups 10

11 Super-Group Excavata –Giardia – causes diarrhea –Trichonympha – symbiotic with termites –Trichomonas vaginalis – common STD –Trypanosoma gambiense – African Sleeping Sickness –Trypanosoma cruzii – Chaga's Disease –Euglena – autotroph and heterotroph 11

12 Trichonympha Obligate mutuals of wood-eating insects such as termites Release cellulose for digesting May account for 1/3 biomass in termite 12

13 Leishmaniasis Caused by Leishmania flagellated protists –Leishmania donovani, L. tropica, L mexicana Transmitted by sandflies when they take a blood meal –animal reservoirs include canines and rodents, also blood transfusions, needles Three forms of infection –mucocutaneous, cutaneous, and visceral 13

14 Leishmaniasis Diagnosis –observation of parasites within infected macrophages, cultural and serological tests Treatment, prevention, and control –antiparasite therapy –vector and reservoir control, and epidemiological surveillance 14

15 Cutaneous Leishmaniasis Lesions of mouth, nose, throat, and skin that cause extensive scarring and disfigurement Papules that develop into crustated ulcers Healing occurs with scarring, permanent immunity 15

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17 Trichomonas vaginalis –trichomoniasis sexually transmitted infection in humans 7 million cases in U.S. 180 million worldwide 17

18 Trichomoniasis Caused by protist flagellate Trichomonas vaginalis Common sexually transmitted disease Clinical manifestations –accumulation of leukocytes at site of infection –in females, yellow purulent vaginal discharge/itching –in males, usually asymptomatic or burning urination Diagnosis –observation of parasite in vaginal discharge, semen, or urine Treatment, prevention, and control –antiparasite therapy 18

19 Trypanosomiasis Caused by trypanosomes –group of flagellated protists –changes its protein coat (antigens) and evades the immunologic response Transmitted by tsetse flies (African trypanosomiasis) or kissing bug (Chagas’ disease) –reservoirs include domestic cattle and other animals Diagnosed by observation of motile parasites in blood or antibody levels 19

20 Trypanosomes Antigenic variation –thick glycoprotien layer coating cell wall surface which is changeable –enables the parasite’s escape from the host immune system –no vaccines –new drugs may target flagellar proteins important for division 20

21 African Trypanosomiasis Clinical manifestations –interstitial inflammation and necrosis within lymph nodes and small blood vessels of brain and heart, leading to lethargy (hence name, sleeping sickness) and death within 1 to 3 years Drug therapy is available Vaccines not useful due to antigenic variation 21

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24 Chagas’ Disease Triatome ("Kissing") bug takes blood meal, defecates in wound –Trypanosome in feces is scratched into body Acute disease –rapid onset, trypanosome moves through bloodstream, enters cells, becomes amastigote, replicates –may be cleared or develop chronic form –treatment may be effective at this stage 24

25 Chagas’ Disease Chronic disease –amastigotes reach heart, gastrointestinal and other cells –replicate causing heart disease and other disorders due to destruction of parasitized cells in the liver, spleen, lymph nodes, GI, and central nervous system –Leading cause of heart disease worldwide and previlence is increasing in the U.S. Only investigational treatment currently available at chronic stage vaccines not effective due to antigenic variation of trypanosome 25

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27 Giardiasis Caused by Giardia intestinalis –forms cysts and trophozoites –trophozoites attach to intestinal epithelium and interfere with nutrient absorption Transmission usually by cyst-contaminated water –numerous animal reservoirs –asymptomatic human carriers are common –more serious disease in children 27

28 Giardiasis Clinical manifestations –acute giardiasis - severe diarrhea, epigastric pain, cramps, voluminous flatulence, and anorexia –chronic gastritis - intermittent diarrhea with periodic appearance and remission of symptoms Diagnosis –observation of cysts or trophozoites in stools, and ELISA Treatment, prevention, and control –antiprotozoal agents –avoiding contaminated water and use of slow sand filters in processing of drinking water 28

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30 Euglena Commonly found in fresh water 1/3 photoautotrophic, rest are chemoorganotrophs Euglena is the representative phototroph –pellicle - proteinaceous strips, microtubules –red eye spot (stigma) orients to light –chlorophylls a and b, carotenoids –contractile vacuole and flagella 30

31 Super-Group Amoebozoa Entamoeba histolytica –causes amoebic dysentery –third leading cause of parasitic death worldwide –acquired by consuming E. histolytica cysts –may migrate to lungs, brain, liver, or skin Naegleria fowleri Acanthamoeba Slime Molds (previously classified as fungi) 31

32 Amebiasis (Amebic Dysentery) Caused by Entamoeba histolytica Infection by ingestion of mature cysts from fecally contaminated water, food or hands, or from fecal exposure during sexual contact Clinical manifestations –asymptomatic to fulminating dysentery, exhaustive diarrhea, appendicitis, and abscesses of liver, lungs, and brain 32

33 Amebiasis Diagnosis –observation of trophozoites in fresh warm stools or cysts in ordinary stools, and serological tests Treatment, prevention, and control –antiprotozoal agents –avoiding contaminated water and food and hyperchlorination or iodination of water supplies to destroy waterborne cysts 33

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35 Amebic Meningoencephalitis and Keratitis Caused by the free-living amoebae Naegleria and Acanthamoeba –facultative (opportunistic) parasites Clinical manifestations –primary amebic meningoencephalitis –Granulomatous amoebic encephalitis –keratitis – progressive ulceration of the cornea Diagnosis –demonstration of amoebae in clinical specimens Treatment, prevention, and control –no drug therapy available –do not use water for contact lens care 35

36 36 Super-Group Amoebozoa continued : Acellular and Cellular Slime Molds

37 Super-Group Rhizaria Radiolaria Most have internal skeleton made of siliceous material 37

38 Foraminifera Called forams ~20  m – several centimeter size range Filopodia are arranged in branching network (reticulopodia) May harbor endosymbiotic algae –contribute to foram nutrition Have characteristics tests arranged in multiple chambers that are sequentially added as organism grows 38

39 More about Forams Complex life cycle –sexual and asexual reproduction Found in marine and estuarine habitats Foram tests make up most modern-day chalk, limestone, and marble 39

40 Supergroup Chromoaveolata A diverse group including autotrophic, mixotrophic, and heterotrophic protists Some of the most significant parasitic protists Examples: –Dinoflagellata (dinoflagellates) –Balantidium coli causes diarrhea and dysentery –Plasmodium species cause Malaria –Toxoplasma gondii causes Toxoplasmosis –Cryptosporidium parvum causes diarrheal disease –Diatoms - found in marine plankton –produce 40% to 50% of organic carbon in ocean –golden and brown algae (seaweeds and kelp) 40

41 Dinoflagellates Large group found in marine plankton –cause phosphorescence/toxic blooms in seawater Nutritionally complex Symbiotic forms –live in association with reef building corals 41

42 Arthropod Borne Diseases Malaria –caused by four species of Plasmodium –transmitted by bite of an infected female mosquito –life cycle of plasmodial protists sporozoite injected with mosquito bite replicates as merozoite in hepatic cells released, enters erythrocytes and replicates lyses erythrocytes – correlates with fever 42

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45 Malaria Clinical manifestations –periodic attacks of chills and fever –anemia can result and the spleen and liver often hypertrophy –can cause cerebral malaria in children and nonimmune individuals 45

46 Malaria Diagnosis –demonstration of parasites within Wright- or Giemsa- stained red blood cells and serological tests Treatment, prevention, and control –antimalarial drugs resistance has been observed chemoprophylaxis for travelers to endemic areas –prevention via netting/insecticide to control mosquitoes –new vaccine shows promise 46

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48 Toxoplasmosis Worldwide very common disease caused by Toxoplasma gondii –apicomplexan (nonmotile) protist –most are asymptomatic –reservoir wild rodents, birds, small mammals 48 Fecal-oral transmission from infected animals –also by ingestion of undercooked meat, congenital transfer, blood transfusion, or tissue transplant

49 Toxoplasmosis Clinical manifestations –usually asymptomatic or resembles mononucleosis –encephalitis can be fatal in immunocompromised hosts –tachyzoites cross the placenta and infect fetus, causing serious congenital defects or death diagnosis –serological tests treatment, prevention, and control –antiparasite therapy –minimizing exposure by: avoidance of raw meat, washing hands after soil work, cat-handling practices 49

50 Cryptosporidiosis Emerging disease caused by Cryptosporidium parvum –forms cysts, sporozoites, and merozoites sporozoites parasitize intestinal epithelial cells Transmitted from animal reservoirs in contaminated food or water –many birds and mammals shed oocysts in feces 50

51 Cryptosporidiosis Clinical manifestations –diarrhea, abdominal pain, nausea, fever, and fatigue –usually self-limiting –can be fatal in late stage AIDS patients and other immunocompromised individuals Diagnosis –microscopic examination of stools Treatment, prevention, and control –symptomatic/supportive therapy –cysts very resistant to chlorine 51

52 Diatoms Chlorophylls and accessory pigments Frustule – two-piece cell wall of silica –unique, beautiful patterns Important in global carbon cycling –marine planktonic diatoms produce 40–50% of organic ocean carbon Diatomaceous Earth – significant economic algae 52

53 Supergroup Archaeplastida All higher plants and many algal species are included Chlorophytya (green algae) Phototrophs have chlorophylls a/b and carotenoids Many have cellulose cell walls Exhibit a diverse morphology 53

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