PROTOZOA

Kingdom Protista: Protozoa

General Characteristics of Kingdom Protista

• Traditionally includes single-celled and colonial eukaryotic microbes lacking tissue organization.

• 'Protista' - Greek word "protistos," meaning "the very first"

• Typically unicellular with a nucleus bound to organelles.

• Flagella or cilia for locomotion.

• First used the term by Ernst Haeckel in 1866.

• Protists are a polyphyletic grouping of independent clades evolved from the last eukaryotic common ancestor, not a natural group (clade).

  • Clade: a monophyletic group with a common ancestor.

  • Polyphyletic group: organisms with mixed evolutionary origin, excluding their most recent common ancestor.

• Inhabit almost any environment with liquid water.

Sub-Kingdoms of Protista

• Protozoa ('animal like')

• Algae ('plant like')

• Slime & Water Molds ('fungus like')

Protozoa

General Information

• Considered the most engrossing and vivid group of microorganisms.

• Greek origin meaning 'first animals'.

• About 65,000 species exist.

• Single-celled creatures with movement, feeding, and behavior properties.

• Cells contain eukaryotic organelles, except chloroplasts.

• Classified by cell architecture, motility structure, and hosts.

• Unicellular, higher protists, Eukaryote, and binary fission replication.

• Chemoheterotrophic like animals, do not photosynthesize.

• Are 10 times more diverse than bacteria and viruses.

Protozoan Form & Function

• Organelles specialized for feeding, reproduction, and locomotion.

• Cytoplasm divided into:

  • Ectoplasm: clear outer layer involved in locomotion, feeding, and protection.

  • Endoplasm: granular inner region housing the nucleus, mitochondria, and vacuoles.

• Outer boundary - is a cell membrane (not cell wall) that regulates the movement of food, wastes, and secretions.

• Most ciliates have constant shapes; some protozoa change constantly (e.g., ameba).

Feeding

• All protozoa are Heterotrophic: they derive nutrients from other organisms through phagocytosis or osmotrophy.

  • Phagocytosis: proccess of cell engulfing large particles using its plasma membrane, creating a phagosome.

  • Osmotrophy: feeing mechanism involving the movement of dissolved organic compounds by osmosis.

    • Osmotrophs - Organisms that use osmotrophy

Protozoan Locomotion

• Except for Apicomplexa, protozoa are motile via:

  • Pseudopods: 'false foot'

    • Used for locomotion, food capture, and endocytosis.

    • Involves actin filament disassembly and assembly.

    • Actin: fine protein fibers contributing to structure and support.

  

  • Flagella: long whiplike structure

    • Longer and fewer than cilia, but structurally identical.

    • Undulate in a whip-like fashion for movement.

    • Require ATP to move.

  • Cilia: shorter than flagella

    • Numerous, short projections that beat in an oar-like fashion for movement.

    • Consist of microtubule core (axoneme) enclosed in a cell membrane.

    • Ring of 9 doublets, plus two singlets, centrally located (9x2)+2 pattern.

    • Anchored by a basal body (9x3) pattern.

Life Cycle & Reproduction

• General life cycle includes a trophozoite (motile feeding stage); not all produce cysts.

• Life cycle dictates transmission mode to another host.

  • T. vaginalis does not form cysts; transmitted by intimate contact.

  • Cysts can be dispersed by air currents.

  • E. hystolitica and G. lamblia are transmitted via contaminated water and food.

  • Many form a resistant, dormant cyst structure.

• Trophozoite: active feeding stage of parasitic protozoa.

• Both cyst and trophozoite stages may be found in feces.

Encystment and Excystment

• Encystment: Cell rounds up, loses motility, early cyst wall formation, mature cyst (dormant, resting stage) forms during adverse conditions.

• Excystment: Cyst wall breaks open, Trophozoite is reactivated when moisture and nutrients are restored, release of active cellular form.

Taxonomic Classification of Protozoa

Sarcodina (Rhizopoda)

• Motion: by Pseudopodia (Pseudopodes)

• Replication: Binary Fission

• Example: Amoeba / Ameba

• Shape: Pleomorphic

• Pathogenic species for man: Entamoeba hystolytica.

• Disease: Amoebiasis or amoebic disentery

• Three forms:

  • forma manga

  • forma minuta

  • cyst

• Non-pathogenic species:

  • Entamoeba gingivalis

  • Entamoeba coli

• Have a complex cytoskeleton

• Marine, freshwater and terrestrial species

• Diversity of pseudopodia

  • Lobopodia - wide and rounded

  • Filopodia - slender and may be branched

Life Cycle of Entamoeba histolytica

• Host: Homo sapiens

• Transmission: Fecal-oral route (alimentary)

• Infective stage: mature cyst

• Localization: Large Intestine

• Pathogenicity:

  1. Intestinal amoebiasis: formation of ulcerus of the wall of the intestine, acute or chronic diarrhea, stool containing blood and mucus; may be asymptomatic infection.

  2. Extra-intestinal amoebiasis: abscess of liver, lung, brain, skin.

• Laboratory diagnosis: Fresh stools are examined under the microscope. E. histolytica (forma magna and cysts with 4 nuclei) can be demonstrated in the stools.

• Prophylaxis: Treatment of patients and asymptomatic cyst carriers; protection of foodstuffs and water from flies and contamination with feces, the staff of catering establishments must be examined for cysts carriage, health education of the population.

Shelled Amebas

• Foraminefera or forams (Phylum Foraminifera) and Radiolarians (Phylum Radiolaria) are shelled amebas. They are the responsible for the chalk deposits in the oceans

• Foraminefera (forams)

  • mostly marine organisms.

  • May be benthic or planktonic.

    • Planktonic - have spines to increase surface area, and thus they are buoyant.

  • Forams create natural wonders in the form of chalk and limestone

    • Pink sands of Bermuda

    • White cliffs of Dover in England

    • Block of Pyramids

• Radiolaria

  • Mostly planktonic

  • Siliceous, spherical test.

  • Up to 20 cm in some colonial species

Sporozoa (Apicomplexa)

• Lack locomotor organelles

• All members of Phylum Apicomplexa are endoparasites.

• Sporozoites (Gr. sporos - seed, and zoon - animal) - special sporelike cells produced by sporozoa following sexual reproduction which are important in infection transmission.

• Possess an apical complex

  • Attaches or penetrates host cell

  • Cone contains disgestve enzymes

• It includes the ff:

Malaria

• Anopheles mosquito is the vector carrier of plasmodium.

• Four species of Plasmodium that cause malaria

  • Plasmodium falciparum

    • Diseases: Tropical malaria or malignant tertian (Most fatal form of malaria)

    • Incubation Period: 12 Days

  • Plasmodium vivax

    • Benign Tertian / Tertian Malaria

    • Can cause death to young and old patients

    • Incubation period: 14 days

  • Plasmodium malariae

    • Quartan Malaria

    • Not lethal

    • Incubation Period: 30 days

  • Plasmodium ovale

    • Tertian ovale

    • Very seldom in Phils.

    • 14 days IP

MALARIA PARASITES OF MAN

• Intermediate host: Homo sapiens (Man)

• Definitive host: Anopheles mosquito

• Transmission: by bite of female Anopheles mosquito

• Infective stage for man: sporozoite

• Infective stage for mosquito: gametocyte

• Localisation: blood, liver

• Clinical manifestations: fever, anemia, splenomegaly, hepatomegaly

• Laboratory diagnosis: Microscopy of thin and thick films blood smears. Different stages of the parasite (trophozoites, schizonts, and gametocytes) can be demonstrated in the blood.

• Prophylaxis: Malaria may be prevented by chemoprophylaxis and personal protective measures against the mosquito vector (Anopheles).

Complex life Cycle of Plasmodium

• Sporozoite - motile, infective stage possessing apical complex

  • Injected into blood by mosquito.

  • Attack liver cells.

• Merozoite - motile, reinfective stage, also has apical complex.

  • Reinfect liver cells or move to RBC

  • Cyclic merozoite release correlates w/ chills, fever, fatigue due to hemoglobin loss and capillaries blockage.

• Gametocytes - reproductive stage. Usually, male and female gametocytes pair up and release gametes (sexual reproduction)

• Spore - gametes pair to form zygotes, and a protective capsule is secreted

Toxoplasmosis

• Toxoplasma gondi: transmitted by the ingestion of oocysts from cat feces. Infection can lead to ocular problems and is also a cause of neonatal toxoplasmosis

• Geographical distribution: Cosmopolitan

• 4 forms of Morphology: pseudocysts; trophozoites; cysts and oocysts.

• Definitive hosts: cats and other Felidae

• Intermediate hosts: birds and mammals, including humans

• Localisation: brain, eyes, skeletal and cardiac muscles, liver, and lungs

• Transmitted to humans by:
  1) ingestion of undercooked infected meat (cysts and pseudocysts);
  2) contamination of food or drink with infected cat feces (oocyts);
  3) transplacental (congenital)

Life Cycle of Toxoplasma gondi

1. Oocysts pass from cat intestine to cat feces.

2. Oocysts sporulate in soil and are viable for longer than one year

3. Humans ingest oocysts either from soil or cat raw tissue infected with cysts. The alimentary route of infection takes place on ingestion of meat, milk, and dairy products of animals sick with toxoplasmosis, uncooked eggs of affected birds, and water contaminated by sick animals.

4. Transmitted via placenta when mother develops infection during gestation-congenital infection.

5. Invade intestinal wall after entering host (usually orally) and disseminate via lymphatics and bloodstream forming trophozoites. Toxoplasma gondii can spread to many host cells.

Mastigophora (Zoomastigophora)

• Flagellates

• Motion: by flagella. Flagellum arises posteriorly and can be connected to other parts of body, pulls animal through the blood.

• Reproduction: longitudinal binary fission.

• Complex life cycles include alternation of hosts.

• Intermediate hosts commonly serve as vectors, which transport developing parasites from one definitive host to another.

• Parasitical species parasites of tissues and blood(Their transmission requires a biological vector.):

  • Trypanosoma

  • Leishmania

• Species living in the digestive tract and genitals (ransmission does not require a biological vector):

  • Lamblia intestinalis

  • Trichomonas vaginalis

  • Trichomonas hominis

Mastigophora Species includes:

• Trypanosoma brucei gambriense

• Trypanosoma brucei rhodesiense

• Trypanosoma cruzi

• Leishmania donovani

• Leishmania tropica

• Lamblia intestinalis

• Trichonomas vaginalis

• Trichonomas intestinalis

• Trichonomas buccalis

Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense

• Parasites: Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense

• Disease: African trypanosomiasis, (sleeping sickness)

• Geographical distribution: West and Central Africa

• Morphology: spindle-shaped cells with an undulatory membrane and pointed flagella at the ends. The organisms are motile, 25-40 micron in length. Transmission: by bite of infected tsetse flies (Glossina palpalis)

• Reservoir hosts (T.b.gambiense): man, domestic pig, cattle, dog, antelope.

• Reservoir hosts (T.b.rhodesiense): hartebeest, lion, hyena. Localisation: blood, lymph nodes, cerebrospinal fluid, brain, muscles.

Trypanosomiasis

• Pathogenicity

  1. From the site of bite trypanosomes reach the blood and lymphatics where they multiply.

  2. There is perivascular infiltration with chronic inflammation, leading to meningoencephalitis.

  3. The patient suffers from fever, rash, headache, lymphadenopathy, oedema of the brain. There are alternating periods of fever and apparent recovery. This is followed by depression and progressive lethargy.

  4. Rhodesien form develops within weeks to months, Gambian form develops within years. The disease becomes chronic and persists for months and even years.

• Labarotatory Diagnosis:

  1. microscopic examination of blood and of material obtained by puncture of the enlarged lymph nodes;

  2. examination of the cerebrospinal fluid (availability of trypanosomes).

• Prophylaxis:

  1. treatment of patients;

  2. protection of the population from the bites of tsetse flies (Glossina palpalis);

  3. the use of insect repellents, extermination of vector flies.

Chaga's Disease

• Parasite: Trypanosoma cruzi

• Disease: American trypanosomiasis, or Chagas' disease

• American trypanosomiasis (Chagas' Disease) was discovered in 1909 by C. Chagas in Brazil.

• Geographical distribution: South and Central America

• Morphology: typical, small (20 micron) trypomastigotes (with flagella) are found in peripheral blood and amastigotes (intracellular without flagella) - in tissues.

• Transmission:
  1) by bite of infected bug species of the family Triatomidae;
  2) congenital;
  3) by blood transfusion.

• Reservoir hosts: armadillos, opossums, rodents, monkeys, dogs, cats.

• Localisation: blood (in acute phase), cells of lymph nodes, spleen, liver, brain, muscles.

• Clinical manifestation: fever, edema of the face, and enlargement of the thyroid gland, lymph nodes, spleen, and liver, heart alterations.

• Laboratory diagnosis:
  1) examination of patient's blood;
  2) guinea pig inoculation with 5-10 ml of patient's blood;
  3) serologic tests.

• Prophylaxis:
  1) extermination of bugs;
  2) chemoprophylaxis with special preparations in endemic areas.

Leishmaniasis

• Parasite: Leishmania tropica

• Disease: Cutaneus leishmaniasis

• Geographical distribution: Asia, Africa, Europe

• Morphology: Intracellular amastigotes (without flagellum) 3 to 6 micron long by 1.5 to 3 micron in diameter live in men. Promastigotes (with flagellum) develop in the intestine of the sand fly.

• Transmission: by sand fly vector

  • Phlebotomus sergenti (in Iran, Iraq, and India); Phlebotomus papatasi (in southern France, Italy, and certain Mediterranean islands).

• Reservoir hosts: man, dogs, wild rodents.

• Localisation: cells of skin.

• Clinical manifestation: development of a cutaneous papule that evolves into a nodule, breaks down to form an indolent ulcer, and heals, leaving a depressed scar.

• Laboratory diagnosis: detection of the Leishmania parasites in cells of skin.

• Prophylaxis: early diagnosis, extermination of sandflies and dogs and rodents infected with leishmaniasis, and vaccination

Disease Table

Lambliosis

• Parasite: Lamblia intestinalis

• Disease: lambliosis

• Geographical distribution: cosmopolitan.

• Morphology: Trophozoites are bilateral, symmetrical, pear-shaped organisms with an elongated posterior and two symmetrically placed nuclei. The body of the parasite is from 10 to 18 micron long with four pairs of flagella. Cysts are oval-shaped which are 10-14 micron and have four nuclei.

• Host: man

• Transmission: fecal-oral (alimentary)

• Infective stage: cyst

• Localisation: the small intestine (duodenum) and gall-bladder.

Trichomoniasis

• Parasite: Trichomonas vaginalis

• Disease: Urogenital trichomoniasis

• Geographical distribution: cosmopolitan.

• Morphology: Trophozoite is a pear-shaped (7 to 23 micron long) with four anterior flagella and a fifth forming the edge of an undularing membrane. The axostyle extends the length of the body.

• Host: man

• Transmission: by sexual contact; otherwise (through contact with toilet seats and towels, for example).

• Localization: vagina, urethra, prostate.

• Clinical Manifestations: vaginitis in women, more commonly asymptomatic in men, but may lead to prostatitis or urethritis. The main symptoms are dysuria, pruritis, yellow and frothy discharge.

• Laboratory diagnosis: microscopic examination of the vaginal fluid, scrapings, or washing.

Giardiasis

• Giardia lamblia - Parasite lives in small intestine

Ciliophora

• Or Ciliates are sophisticated protozoans

• Trophozoites are motile by cilia

• Most have definite mouth and feeding organelle.

• Reproduce by transverse binary fission and sometimes by conjugation.

• Ciliates have both macronuclei and micronuclei.

  • Macronucleus - genes are actively transcribed

  • Micronucleus - master copy of genome; inactive except during cell division

• Shapes and numbers of these nuclei varies across genera

  • Bean shaped in Paramecium

  • String of beads in Stentor

• Most ciliates are free-living and harmless.

• Function of alveoli is to store Ca^{2+}

• Release of Ca^{2+} causes changes in ciliary beat, and discharge of extrusomes

  • Trichocysts - long shafts that are thought to defend against predators

  • Toxicysts - longs shafts with toxin that are used for prey capture

  • Mucocysts - release mucus and creates sticky surface for prey capture or protective cysts

Balantidiasis

• Parasite: Balantidium coli

  • a large motile ciliated parasite that lives in the colon of pigs, humans and rodents and can lead to colonic ulceration

• Disease: Balantidiasis

• Morphology: The trophozoite is from 75 to 200 micrometer, in length, asymmetrical, oval, with cilia, a cytostome, anal pore, the macronucleus, the micronucleus, two contractile vacuoli. Cyst with a double-layer membrane, from 30 to 60 micron in diameter.

• Hosts: man, domestic swine

• Transmission: fecal-oral (alimentary)

• Localization: large intestine

• Clinical Manifestations: colitis, ulcers and abscesses of colon, diarrhoea, blood and mucus in the stool.

• Laboratory diagnosis: microscopic examination of the feces.

• Prophylaxis: protection of foodstuffs and water from contamination with swine feces and observation of individual hygiene when talking care of the animals (domestic swine).

Microspora

• Unique feature: lack mitochondria

• Intracellular parasites (live inside host cells)

• The term microsporidia is also used as a general nomenclature for the obligate intracellular parasites belonging to the phylum Microsporidia.

• Microsporidia, are characterized by the production of resistant spores that vary in size, depending on the species. They possess a unique organelle, the polar tubule or polar filament, which is coiled inside the spore as demonstrated by its ultrastructure. The microsporidia spores of species associated with human infection measure from 1 to 4 μm and that is a useful diagnostic feature.

• There are at least 15 microsporidian species that have been identified as human pathogens.

• Enterocytozoon bienusi: a microsporidian that parasitises the small intestine. Also more common in the immunocompromised.

• Keratoconjunctivitis, skin and deep muscle infection

Clinical manifestations of Microsporidian Species