Protozoans are an informal group of “animal-like” unicellular organisms
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| Important note: Protozoans are an informal group of “animal-like” unicellular organisms. For many years the four main groups of protozoa were amoebae, ciliates, flagellates, and spore formers. Because the true evolutionary relationships of many protozoan groups have yet to be elucidated, the taxonomic scheme that we will use continues to follow the principles of traditional taxonomy rather than cladistic taxonomy. Consequently, some of the following taxa may be either para- or polyphyletic (if those terms are not familiar to you, let me know so we can remedy that). The reason for this approach is that it is a compromise between reasonably current evolutionary thinking and the practical need for a system of nomenclatures that allow us to communicate with each other and retrieve information from the older literature.
CHAPTER 4 protozoans – over 64,000 species in 7-30 phyla (depending on system of classification); unicellular and eukaryotic outermost layer is plasma membrane (lipid bilayer with various proteins), next is ectoplasm (gel), both enclose endoplasm (sol) pellicle – rigid body wall of some protozoans; supported by microtubules nucleus – all protozoans have membrane-bound nucleus; some have single, others two or more, others (ciliophorans) two different types: macronucleus & micronucleus (sexual reproduction) endosome = nucleolus (unlike nucleoli, do not disappear during mitosis) lysosomes – contain hydrolytic enzymes; intracellular digestion basal body (also called kinetosome, blepharoplast); anchors flagellum in cytoplasm; 9 + 2 arrangement of microtubules (morphologically identical to centriole) parabasal body – homologous to Golgi complex mastigont (whip) = flagellum + parabasal body (Golgi) + basal body mitochondria – sites of aerobic metabolism; tubular-shaped cristae; kinetoplast: giant mitochondrian in some flagellated protozoans; some parasitic protozoans (eg, Entomoeba histolytica) lack mitochondria (associated with anaerobic metabolism) locomotor organelles flagellate: flagella and undulating membrane 
ciliate: cilia (miniature flagella) amoeba: pseudopods – constant flow of endoplasm in direction of extension (sol/gel transformations) 
lobopodia type of pseudopodia most common form among parasitic amoebae (pseudopods lack internal support structures) 
protozoans excrete ammonia; contractile vacuole is absent in marine and most parasitic protozoans except Balantidium encystment and excystment: trophozoites, trophs, or vegetative state - active, motile form (as opposed to resistant cyst)
Flagellated Protozoans – move by flagella Class Zoomastigophorea – one to many flagella; no chloroplasts Order Kinetoplastida – one or two flagella; kinetoplast (a large specialized mitochondrion) different morphological types of Trypanosoma and Leishmania amastigote, promastigote, epimastigote, trypomastigote 
Trypanosoma – in all vertebrate classes; usually in blood, spleen, lymph nodes, or tissue fluids; most transmitted by blood-feeding invertebrates; usually do not enter or live in cells (exception: T. cruzi); does not produce cysts; no sexual reproduction; amastigote and trypomastigote form found in vertebrate host; amastigote, promastigote, and epimastigote form found in the invertebrate host (infective trypomastigote form also found in the invertebrate host) African trypanosomiasis T. brucei – tropical Africa, transmitted by tsetse flies (Glossina); 3 anatomically indistinguishable subspecies (T. b. brucei, T. b. gambiense, T. b. rhodesiense); anterior station development in tsetse fly (in front/middle portion of digestive tract) T. b. brucei – normal hosts are native grazers, called “nagana”; does not infect humans; deadly to domestic livestock life cycle: trypomastigote enters fly in blood meal and duplicates in midgut - moves to foregut - enters salivary glands and develops to epimastigote - duplicates as epimastigote - transforms into the infective trypomastigote form - enters vertebrate via bite of tsetse fly - duplicates in blood and lymph - invades CNS; host physiological processes are disrupted; lysis of host cells; anemia, edema, fever, watery eyes and nose; death can be in few days or recovery may occur depending on host species and susceptibility control - removal of brush, brushless belts, reservoir elimination, night grazing (flies feed during day), insecticides
in blood, lymph nodes, spleen, cerebrospinal fluid; after the bite, all organs are invaded; intermittent fevers, sleepiness, coma, death in 4 months to 7 years depending on form; Winterbottom’s sign – swollen neck lymph nodes; observation diagnosis, blood tests; drug treatments of varying success VATs (variant antigenic types) - trypanosomes use a genetic set of programmed successive antigenic types (~1000 known to exist) which cause repeated remissions until death; antigenic series sequence is predictable
life cycle: T. cruzi – Chagas’ Disease; South and Central America transmitted by kissing bug, Triatoma; posterior station development in kissing bugs (in hindgut); bugs bite at night; infective forms in bug feces, usually scratched into bite site or eyes; trypomastigotes in blood, transform into amastigotes in host macrophages, muscle and other tissue cells, duplicate in amastigote form - pseudocysts rupture - nearby nerve cells are destroyed; favorite site is cardiac muscle, but also in cells of other muscles (smooth and skeletal), spleen, liver, and lymphatics; many wild and domestic animals (dogs and cats) are reservoirs; organism can cross the placenta diagnosis - find blood forms, lab tests, culture in clean bugs (xenodiagnosis) there is no effective treatment disease - edema of eyelids and face, megacolon, megaesophagus; death in 3 to 4 weeks from heart failure
station development; rat is infected by ingesting flea feces or the flea itself; ablastin - a rat- produced antibody that inhibits parasite reproduction
Leishmaniasis is presently a big problem for our troops serving in Iraq L. tropica & L. major – Oriental Sore; Jericho boil; cutaneous; Africa, Middle East, Asia, India invades the reticuloendothelial system and skin; secondary infections are common Phlebotomus intermediate; only symptom is sore; self-healing, provides immunity L. donovani – kala-azar; visceral; Mediterranean, India, Africa, Central and South America in cells of reticuloendothelial system (spleen, liver, lymph nodes) slowly destroys body’s defense system; liver and spleen enlarge; death in 6 mo. to 3 yrs.
diagnosis - spleen puncture, blood tests; prevention is reservoir and vector control treatment not always successful; inadequate treatment - post-kala-azar dermal leishmanoid
secondary lesion up to 30 years later ulcerates and destroys lips, palate, pharynx, tongue Lutzomyia intermediate; primarily sylvatic - little chance for control L. mexicana – almost always cutaneous; Central America, Mexico, Texas Lutzomyia intermediate; a zoonose - main reservoirs are rodents (recent research – parasite that causes chiclero ulcer is probably L. mexicana) Classification of this group in flux CHAPTER 6 Order Diplomonadida – two nuclei Giardia lamblia (= intestinalis = duodenalis) – giardiasis; cosmopolitan; inhabits small intestine most common flagellate of human digestive tract dorsoventrally flattened; ventral surface is a bilobed adhesive disc 4 pair of flagella; trophozoite has 2 nuclei, fully developed cyst has 4 nuclei interferes with fat absorption in small intestine; many symptomless cases if pathogenic - diarrhea, weight loss, abdominal pain, flatulence many reservoirs including dogs, rats, rabbits, others observation diagnosis - stool exam; drug treatment is Flagyl (=metronidazole) prevention is sanitation and water treatment Order Trichomonadida – 4 to 6 flagella, axostyle, no cysts in reproductive and intestinal tracts of hosts
contact, also in hot tubs; pathogenicity varies; observation diagnosis; drug treatment is Flagyl (Flagyl + alcohol = violent nausea); this parasite survives in frozen semen
5 anterior flagella; inhabits large intestine and caecum Tritrichomonas foetus – abortion disease in cattle; reproductive tract of cattle; cosmopolitan 3 anterior flagella; observation diagnosis; very difficult to treat successfully cow recovery provides immunity; survives in frozen semen
inhabits ceca and liver of turkeys, chickens and related birds; uses cecal nematode as an intermediate host; this flagellate parasitizes the bird and the nematode (Heterakis) in the bird; H. meleagridis develops in the nematode and multiplies, eventually entering ovaries of the adult worm - invades the nematode embryo within the eggs - eggs containing juvenile worms parasitized by these protozoans are shed in the bird feces - eggs hatch when eaten by another bird, which releases H. meleagridis earthworms also accidentally ingest these eggs and become paratenic hosts; in the earthworm the nematode eggs hatch and the juveniles released become dormant in the tissues of the earthworm; birds eat these earthworms survival provides immunity; millions are lost annually to blackhead disease CHAPTER 7 Amoeboid Protozoans – move by pseudopodia Entamoeba – in many hosts; asexual multiple fission in cysts; binary fission in trophozoites young cysts contain chromatoidal bars (packaged RNA) which disappear in older cysts E. histolytica – amoebic dysentery; third most common parasite cause of death in the world cosmopolitan, but most prevalent in the tropics and subtropics; inhabits large intestine trophozoites are 20 to 30 micrometers; cysts are 10 to 20 micrometers trophs have central endosome and commonly contain ingested RBCs and intestinal cells normal fully formed stool contains cysts, but not trophozoites loose stool contains trophs, but cysts are rare early cyst has cigar shaped chromatoid bodies; mature cyst 4 nuclei, no chromatoid bodies; pathogenic and non-pathogenic strains related to host diet and intestinal bacterial composition; ulcers erode intestinal wall, blood carries trophs to other body parts causing abscesses; cysts are not produced in abscesses outside of the large intestine proteolytic enzymes cause ulceration, secondary bacterial invasion, colon perforation cyst viability is 12 days if moist and cool, up to 30 days if in water cysts are resistant to usual levels of chlorine used in water treatment facilities symptoms - bloody stool, abdominal pain, nausea, flatulence, headache, fatigue carriers are non-dysenteric diagnosis is by observation of trophs and/or cysts in stool treatment - first stop dysentery, then treat intestine, then treat parenterally control - sewage and water treatment; fix defective plumbing; stop use of night soil; prevent carriers from working in food handling jobs; control reservoirs (dogs, pigs, monkeys, others) also spread by flies, cockroaches, colonic irrigation
trophozoites are 12 to 15 micrometers; cysts are 5 to 9 micrometers E. coli – cosmopolitan commensal in large intestine of humans; 100% rate in some areas eccentric endosome; 8 nuclei in cysts; chromatoidal bodies with splintered ends; trophs contain intestinal contents; E. coli is easily confused with E. histolytica
75% rate in some areas in people over 40; does not produce cysts trophs contain WBCs and host cells Order Schizopyrenida – uninucleate; amoeboid; most have temporary flagellate stages Naegleria fowleri – facultative in humans; meningoencephalitis; almost always fatal enters nose from swimming pools, lakes, thermal springs - follows olfactory nerve to brain death can be in just a few days; seldom diagnosed before death
most common amoeba in soil and freshwater usually enters eye in contaminated contact lens saline solution; corneal ulcers
Phylum Apicomplexa protozoans possessing structures known collectively as the apical complex apical complex found in sporozoite and merozoite stages of life cycle all parasitic schizogony (=merogony) - asexual multiple fission - produces merozoites gametogony - merozoites become gametocytes - gametocytes produce microgametocyte and macrogametocyte which become or produce gametes sporogony - multiple fission of a zygote - produces sporozoites Class Gregarinea - spores (=oocyst) simple; contain sporozoites; Order Eugregarinida – gametogony, sporogony, schizogony absent parasites of annelids and arthropods
Class Coccidea, Order Eimerida - schizogony, gametogony, sporogony called coccidians; disease is coccidiosis; treated with anticoccidials usually a one host life cycle; self limiting; alternate sexual and asexual phases coccidiosis is the greatest protozoan loss to domestic and game animals
most are parasites of birds I. belli - a severe disease in humans diarrhea; self limiting Toxoplasma gondii - toxoplasmosis; cosmopolitan in birds and mammals rate in humans is about 13%; most human cases are without symptoms symptoms - swollen lymph nodes and/or lesions in the eye, lung, liver, heart, brain intracellular - schizogony produces “tissue cysts” or pseudocysts (=zoitocysts) that may persist for years; tissue cyst rupture causes flare up of symptoms cats are the only final host, all others are intermediates; cats show few symptoms gametogony, schizogony, and oocyst formation are in cat small intestinal cells only schizogony occurs in non-cat hosts; oocyst like that of Isospora prenatal infections are a major cause of birth defects; anyone who eats rare meat and/or has a pet cat should read the text material on toxoplasmosis transmission is via oocysts from cats and uncooked flesh containing the “tissue cysts” also transmitted by fecal contamination, nursing, placental crossing, flies, earthworm pilings lab test diagnosis; drug treatments Cryptosporidium and Pneumocystis – opportunistic coccidians Cryptosporidium – infects microvilli of small intestine; unlike other coccidians, lack host specificity; transmission by ingestion of oocyst, usually in contaminated drinking water; AIDS patients develop cholera-like symptoms Pneumocystis – extracellular parasite in alveoli of the lungs; of the opportunistic diseases associated with AIDS, PCP (Pneumocystis carinii pneumonia) is the most common cause of death; asymptomatic in immunocompetent individuals CHAPTER 9 Order Haemosporida – no sporocysts, motile zygote (ookinete) malaria is one of the most important human diseases in the world today 127 species of Plasmodium cause malaria in vertebrates (humans and many others) four species in humans are spread by 390 species of female Anopheles mosquitoes malaria as a disease has been known since antiquity 1902 Nobel Prize in Medicine went to Ronald Ross for his work on malaria the liver cycle part of the overall life cycle was not worked out until 1948 symptoms occur when RBCs rupture releasing contents acute - chills, fever (104o to 106o F), sweating, headache; lasts 8 to 12 hours chronic - anemia, enlarged spleen and lymph nodes; hemozoin buildup malaria RBC stages break down hemoglobin producing a pigment called hemozoin diagnosis is by finding RBC stages in blood smears (see Plates 1 - 7) malaria life cycle: mosquito bite injects sporozoites into blood stream - sporozoites flow to liver and enter liver cells - schizogony - schizont - cell rupture releases merozoites whether they can enter other liver cells is uncertain - merozoites enter RBCs - schizogony (ring stage, schizont, merozoites) in RBCs - RBC rupture releases merozoites which enter other RBCs - schizogony - RBC cycle can go on and on - eventually some merozoites become gametocytes in RBCs - RBCs containing gametocytes taken in blood meal by mosquito - male microgametocyte produces 6 to 8 microgametes by exflagellation - female macrogametocyte becomes a single macrogamete - gamete formation and fertilization occur in mosquito stomach - zygote in stomach becomes motile ookinete which penetrates to outer stomach wall - develops cyst wall, now called an oocyst - nuclear divisions in the oocyst produce sporoblasts - sporozoites form from sporoblasts – sporoblasts produce thousands of sporozoites which fill the oocyst - rupture of the oocyst wall releases the sporozoites which enter the salivary glands of the mosquito; the mosquito is infective for life some sporozoites of relapsing species (P. vivax, P. ovale) become dormant in liver cells and are called hypnozoites (a true relapse is due to hypnozoites becoming reactivated) immunity develops in vertebrate hosts Plasmodium - while life cycles of species that infect humans are basically similar, there are a number of differences:P. malariae - 72 hour cycle; 7% of the world’s malaria; widespread; continuous blood cycle up to 53 years; blood forms do not re-invade fixed cells; no true relapses, just recrudescence P. vivax - 48 hour cycle; 43% of the world’s malaria; Asia, North Africa; continuous liver cycle up to 8 years; blood forms can re-invade fixed cells; true relapses occur P. falciparum - 48 hour cycle; 50% of the world’s malaria; tropics; blood forms do not re-invade fixed cells; no true relapses, just recrudescence; most virulent of the human malarias brain, spleen, and bone marrow cells are also attacked; blackwater fever
control - destroy mosquito breeding places; biological controls; DDT treatment - quinine, used since 1640 chloroquine - effective on blood forms primaquine - effective on liver forms including hypnozoites
larval tick (called a seed tick), Boophilus annulatus, injects sporozoites while sucking blood - indefinite schizogony cycles destroy up to 75% of RBCs (in fatal cases) - red urine is excess hemoglobin from RBC destruction - when uninfected larval seed ticks feed on infected cattle, gametocytes are taken in the blood meal and resulting sporozoites enter all cells of the tick - ticks develop to adults and mate, females fall off - all eggs laid by female are infected (called transovarial transmission) - all hatching seed tick larvae are infected
sporogony and gametogony occur in the tick, schizogony occurs in cattle control - cattle quarantine; cattle dips in tickicides
hundreds of human cases in northeast US - transmitted by nymph stage of Ixodes scapularis adults of I. scapularis feed on deer
Phylum Myxozoa (probably cnidarians) - over 1200 species; mostly parasites of fishes spores of multicellular origin containing sporoplasms and one or more polar capsules enclosing polar filaments which explode punching an anchoring hole into intestinal epithelium through which the sporoplasm enters the cell
high mortality in young fish, permanent deformities if fish survives no effective treatment exists spore (called triactinomyxon) exsporulates in fish epidermis - sporoplasm migrates to head and spine cartilage - growth, division, spore production - spores released when fish is eaten or dies, and enter tubifex oligochaetes - duplication and development in tubifex worms - production and release of triactinomyxon spores Phylum Microspora - less than 1000 species spores of unicellular origin without polar capsules Class Microsporea - spores with polar filaments spore ingested - polar filament discharges penetrating host cell membrane - sporoplasm enters cell through hollow polar filament - schizogony and sporogony - spores Nosema apis - nosema disease of bees midgut epithelium; spores in feces; parasitic castration of queen bee N. bombycis - disease of silkworm larvae in all host tissues; transovarial transmission four genera reported in AIDS patients - no effective treatment
spores of multicellular origin, no polar capsules, no polar filaments Haplosporidium nelsoni (named after Julius Nelson and son, Thurlow) Captain John Smith enters Chesapeake Bay in 1607 - amazed at oyster abundance at peak of oyster industry - 15 million bushels worth $112 million per year disaster starts in Delaware Bay in 1957 - east coast oyster industry ruined MSX (multinucleate sphere X) - eventually named H. nelsoni method by which oysters become infected is still unknown 30 years of oyster breeding has produced strains with some resistance
Phylum Ciliophora - cilia; two types of nuclei (macronucleus and micronucleus) Class Litostomatea - body cilia similar to mouth cilia
cosmopolitan in large intestine of humans (parasitic) and pigs (commensal) trophozoite and cyst stages; cytostome and cytopyge (cellular anus) invades, digests, and spreads like Entamoeba histolytica in humans intestinal perforation (in humans) is usually fatal Class Oligohymenophorea - body cilia different than mouth cilia Ichthyophthirius multifiliis - “ick” pustules form in skin of freshwater fishes’ skin causes excessive mucus production from skin of host pustules rupture releasing trophozoites - settle to bottom - encyst - many internal divisions - infective trophozoites released - bore into skin or attack gill filaments Protozoans |
