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The Protists
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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
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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
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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
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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
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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
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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
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)
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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
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–
Giardia –
causes diarrhea –
Trichonympha –
termites symbiotic with –
Trichomonas vaginalis –
common STD –
Trypanosoma gambiense –
African Sleeping Sickness –
Trypanosoma cruzii –
Disease Chaga's –
Euglena –
heterotroph autotroph and
Super-Group Excavata
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Trichonympha
• Obligate mutuals of wood-eating insects such as termites • Release cellulose for digesting • May account for 1/3 biomass in termite
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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
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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
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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
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Trichomonas vaginalis
•
Trichomonas vaginalis
– trichomoniasis sexually transmitted infection in humans • 7 million cases in U.S. • 180 million worldwide
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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Amebic Meningoencephalitis and Keratitis
• Caused by the free-living amoebae
Naegleria Acanthamoeba
and – 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
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Super-Group Amoebozoa continued : Acellular and Cellular Slime Molds
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Super-Group Rhizaria
Radiolaria
• Most have internal skeleton made of siliceous material
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Foraminifera
• Called forams • ~20 m 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
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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
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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)
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Dinoflagellates
• Large group found in marine plankton – cause phosphorescence/toxic blooms in seawater • Nutritionally complex • Symbiotic forms – live in association with reef building corals
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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
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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
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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
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Toxoplasmosis
• Worldwide very common disease caused by •
Toxoplasma gondii
– apicomplexan (nonmotile) protist – most are asymptomatic – reservoir wild rodents, birds, small mammals
Fecal-oral transmission from infected animals
–
also by ingestion of undercooked meat, congenital transfer, blood transfusion, or tissue transplant 48
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
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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
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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
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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
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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
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