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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

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

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

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

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

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

plasmotomy

– Sexual stages use fusion of gametes in syngamy process • within a single org (autogamy) or between (conjugation)

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

–

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

Trichonympha

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

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

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

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

Trichomonas vaginalis

•

Trichomonas vaginalis

– trichomoniasis sexually transmitted infection in humans • 7 million cases in U.S. • 180 million worldwide

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

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

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

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

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

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

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

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

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

and

, carotenoids – contractile vacuole and flagella

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)

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

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

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

Super-Group Amoebozoa continued : Acellular and Cellular Slime Molds

Super-Group Rhizaria

Radiolaria

• Most have internal skeleton made of siliceous material

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

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

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)

Dinoflagellates

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

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

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

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

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

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

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

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

Supergroup Archaeplastida

• • All higher plants and many algal species are included

Chlorophytya (

green algae) • Phototrophs have chlorophylls

and carotenoids • Many have cellulose cell walls • Exhibit a diverse morphology