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• 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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• 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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• 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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• 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
– 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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• 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
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• 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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• 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 – symbiotic with termites
– Trichomonas vaginalis – common STD
– Trypanosoma gambiense –
African Sleeping Sickness
– Trypanosoma cruzii – Chaga's
Disease
– Euglena – autotroph and heterotroph
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• 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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• 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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• 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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• 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
– trichomoniasis sexually transmitted infection in humans
• 7 million cases in U.S.
• 180 million worldwide
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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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
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Super-Group Amoebozoa continued :
Acellular and Cellular Slime Molds
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• Most have internal skeleton made of siliceous material
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• 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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• 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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• 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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• 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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• 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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• 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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• Diagnosis
– demonstration of parasites within Wright- or Giemsastained 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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• 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
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• 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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• 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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• 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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• 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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• 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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