Protists-Protozoa.pdf

M. A. Freeman Basic Lecture objectives: Protozoa Protozoa Classification (motility) / systematics Some terminology Key characteristics Reproduction Life cycles Parasites of veterinary importance Kingdom Protozoa / Protista – Excavates (flagellates) Phylum Euglenozoa – Kinetoplastea (Trypanosoma) Phy...

M. A. Freeman Basic Lecture objectives: Protozoa Protozoa Classification (motility) / systematics Some terminology Key characteristics Reproduction Life cycles Parasites of veterinary importance Kingdom Protozoa / Protista – Excavates (flagellates) Phylum Euglenozoa – Kinetoplastea (Trypanosoma) Phylum Metamonada – Diplomonads (Giardia, Hexamita) – Parabasalids (Histomonas, Trichomonas) – Phylum Apicomplexa – Eimeria, Neospora etc. – Phylum Ciliophora (ciliates) – Balantidium – Amoebozoa – Entamoeba Protozoan vs Protist Protozoa is a general term for single-celled eukaryotes, either free-living or parasitic, which feed on organic matter A protist is any eukaryotic organism that has cells with nuclei and is not an animal, plant or fungi. So includes algae, slime molds and dinoflagellates Neither form a natural group Protozoa “first and animal-like" implies a kinship with animal (metazoans), so the use of the term protozoa is discouraged by many For this reason, the terms "protist", is now typically preferred for the high-level classification of eukaryotic microorganisms. In 2005, members of the Society of Protozoologists voted to change the name of their organization to the International Society of Protistologists. Protozoa – classified by locomotion Classification of the Protozoa (modified from Taylor et al., 2007) Phylum: Euglenozoa (Excavates) major supergroup of unicellular organisms belonging to the domain Eukaryota. Include the diplomonads (a group of flagellates, most of which are parasitic) and Kinetoplasts. Amoebozoa: The amoebozoans include protists that are distinguished by possessing pseudopods. Subkingdom: Protozoa Unicellular, eukaryotic animals Phylum: Subphylum: Sarcomastigophora (locomotion by pseudopodia and/or flagella) x Sarcodina (amoeboid movement by pseudopodia) Apicomplexa (locomotion by gliding, life cycle largely intracellular, both sexual and asexual phases occur) Ciliophora (locomotion by cilia) Alveolates x x sister to fungi Not protozoans Microspora (intracellular parasites multiplying asexually) Balantidium Encephalitozoon Mastigophora (one or more flagella) Entamoeba Order: Kinetoplastorida (haemoflagellates; parasites of the blood generally transmitted by biting insects) Diplomonadorida Trichomonadorida (flagellates predominantly of the intestines) Eucoccidiorida (parasites of epithelial cells in which both asexual and sexual reproduction takes place) Piroplasmorida (parasites of blood cells; have ticks as vectors in which sexual reproduction takes place) Haemosporida (parasites of blood cells; have biting insects as vectors in which sexual reproduction takes place) Trypanosoma Leishmania Giardia Spironucleus Histomonas Monocercomonas Tritrichomonas Trichomonas Tetratrichomonas Eimeria Cystoisopora Isospora Tyzzeria Wenyonella Cryptosporidium Besnoitia Hammondia Sarcocystis Neospora Frankelia Toxoplasma Klossiella Lankesterella Atoxoplasma Hepatozoon Babesia Theileria Haemoproteus Hepatocystis Leucocytozoon Plasmodium Many important veterinary flagellated parasites Many important veterinary parasites The Tree Of Life: Protozoan Parasites Stramenopiles: (Heterokonts) Algae, kelp to diatoms & Oomycetes Unikonts: amoebozoa and opisthokonts (fungi and animals) Excavates: amitochondriate flagellates, amoeboflagellates, Euglenozoa Alveolates: Ciliates, apicomplexans and dinoflagellates Cercozoa: amoeboids and flagellates that feed by means of filose pseudopods, includes Halposporidians Water molds, Aphanomyces etc Amoebozoa; fungi/microsporidia Trypanosoma & Diplomonads Many coccidian/apicomplexan parasites. Also ciliates and some parasitic dinoflagellates Ascetosporea (Haplosporidians) shellfish parasites (Marteilia) Mikrocytos ? Generalized Protozoan Cells Trichomonas Schematics vs the real thing (TEM) Infective stage of a coccidian a sporozoite Merocystis kathae Protozoa – terminology Zoite – little creature Prefixes are added to the term “zoite” to denote a portion of the life history. Sporozoite – infective form Trophozoite – form which feeds and grows Tachyzoite – form which divides rapidly Bradyzoite – form which divides slowly Merozoite – many (can also be infective in the case of two hosts being involved) Protozoa (Protists): unicellular, eukaryotic ‘animals’ Nucleus, endoplasmic reticulum, mitochondria, a Golgi body and lysosomes Anerobic or aerobic Absorb nutrients or have a “pseudo-mouth” Feed on bacteria, other protozoa, organic matter or tissues of the host Protozoa may take in food by ‘osmotrophy’ absorbing nutrients through their cell membranes; or they may feed by phagocytosis, either by engulfing particles of food with pseudopodia (as amoebae do), or taking in food through a mouth-like aperture called a cytostome. Protozoa – key characteristics Many are part of the normal microbiota; do not cause disease (Entamoeba – commensal intestines; ciliates in sea urchins, Cryptobia stomach lumpfish; gregarines intestinal ‘parasites’) Locomotion via pseudopodia, flagella, gliding movements or cilia Gregarine apicomplexan Protozoa – key characteristics Asexual reproduction = large exposure = significant damage Host(s) – Host specific or broad spectrum – Zoonotic or non-host specific (Toxoplasma) Chronic infections; immunity (Giardia) Many form cysts (in the environment or in a host). (Sarcocystis in muscles) Protozoa Asexual reproduction Protozoa – –asexual reproduction Binary fission, budding, schizogony / multiple fission (merogony) Protozoa that divide asexually have a short generation time Schizogony (merogony) – Exponential increase in numbers – Destruction of host cells in proportion to the infection – Stops after a fixed number of repetitions Protozoa – binary fission It is the most common form of reproduction in prokaryotic organisms and occurs in some single-celled Eukaryotes like the ciliate Paramecium. Protozoa – schizogony a.k.a merogony Asexual reproduction of protozoans characterized by multiple divisions of the nucleus and cell Common in many apicomplexans. Intermediate host: Asexual reproduction: Merocystis kathae in scallops Very pathogenic https://www.nature.com/articles/s41598-018-26158-1 Protozoa – sexual reproduction Gametogony or sporogony https://www.nature.com/articles/s41598-018-26158-1 Merozoites becomes either a Macrogametocyte (macrogamont) and then a macrogamete OR a Microgametocyte (microgamont) and then several microgametes A microgamete fertilizes a macrogamete forming a zygote; a wall forms around this and it becomes an oocyst Definitive host: sexual reproduction: Merocystis kathae in common whelk Not pathogenic Protozoa -- flagellates SubPhylum ‘Mastigophora’ Class Kinetoplastida (excavates) Locomotion by flagella Diplomonadorida Kinetoplastorida Trichomonadorida Haemoflagellates Flagellates Order Parasites of the blood Predominantly of the intestines Generally transmitted by biting insects Trypanosoma cruzi Giardia Spironucleus Protozoa genera Histomonas - poultry Tritrichomonas Trypanosoma is a genus of kinetoplastids, a monophyletic group of unicellular parasitic flagellate protozoa. Trypanosomes infect a variety of hosts and cause various diseases, including the fatal human diseases sleeping sickness, caused by Trypanosoma brucei, and Chagas disease, caused by Trypanosoma cruzi. Protozoa – flagellates - Giardia Giardia sp. Gardiner et al., 1998 Protozoa – flagellates - Giardia Giardia sp. Aztec emperor of Mexico Montezuma's revenge is a colloquial term for traveler's diarrhea contracted in Mexico. Protozoa – flagellates - Histomonas Histomoniasis/osis is a commercially important disease of poultry, particularly of chickens and turkeys, due to Histomonas meleagridis Clinical signs of Histomoniasis/osis include lethargy, yellow diarrhoea, appetite/weight loss, discoloration of the head (blackhead) and death Histomonas specifically infects the cecum and liver Histomonas is transmitted to the bird by the nematode parasite Heterakis gallinarum, usually in the egg or in an earthworm containg infected eggs No current treatment Histomonas life cycle Protozoa -- ciliates Ciliophora Phylum Protozoa Locomotion by cilia Balantidium sp. Protozoa -- ciliates Balantidium coli Balantidium coli is a parasitic species of ciliate (alveolate) that causes the disease balantidiasis. It is the only member of the ciliate phylum known to be pathogenic to humans, also found in pigs and other mammals Zoonotic Asymptomatic in pigs Transmission contaminated water Protozoa -- ciliates White spot disease, Ichthyophthirius multifiliis Balantidium sp. Encystment and division Protozoa -- ciliates Ciliate in a stranded dolphin lymph node Comparison: ciliates and flagellates Protozoa -- Apicomplexa Phylum Order Locomotion by gliding Life cycle largely intracellular Sexual and asexual phases occur Eucoccidiorida Piroplasmorida Haemosporida Parasites of Parasites of Parasites of epithelial cells blood cells blood cells Sexual and asexual Ticks as vectors Biting insects as reproduction occurs Sexual vectors in epithelial cells reproduction Sexual takes place in reproduction ticks takes place in insects Eimeria / Goussia Isospora Protozoa Toxoplasma genera Cystoisospora (pigs) Sarcocystis Babesia Theileria Plasmodium Protozoa -- Apicomplexa Eucoccidiorida Parasites of epithelial cells Sexual and asexual reproduction occurs in epithelial cells Eimeria Toxoplasma Isospora Cryptosporidium Hepatozoon Sarcocystis Neospora Toxoplasma Diagnostic stage for final host can be small Asexual stage causes damage Many have a cyst stage (oocyst) Oocyst ‘the diagnostic feature’ a cyst containing a zygote formed by a parasitic protozoan Goussia oocysts - four sporocysts each with two sporozoites Release of the sporozoites from the sporocysts is via a longitudinal suture oocyst G. lucida G. aculeati G. acipenseris G. sinensis G. iroquoina G. janae Photos from Lom and Dyková (1992) SEM of Goussia gadi from swim bladder of common ling, Molva molva, note 4 sporocysts per oocyst 2 sporozoites per sporocyst Thin oocyst wall Clear suture present Eimeria oocysts - four sporocysts each with two sporozoites Release of the sporozoites from the sporocysts is via Stieda body at the apex of a sporocyst E. variabilis E. hexagona E. catalana E. isabellae E. harpodoni E. truttae Photos from Lom and Dyková (1992) Epieimeria sp. ? As Eimeria but with epicellular development E. anguillae Crystallospora sp. Sporocysts with a regular crystalline appearance C. crystalloides Photo from Lom and Dyková (1992) Redfish (Sebastes spp.) Crystallospora sp. Goussia sp. x3 Common ling (Molva molva) Goussia gadi Swim bladder completely filled with goo Lumpfish (Cyclopterus lumpus) Breakdown of epithelium in the pyloric caeca No sporulated oocysts yet seen 18S rDNA >99% identity to Goussia balatonica : silver bream Eimeria subepithelialis : common carp Oocyst is the diagnostic feature !! This is a bit weird ! Protozoa – Apicomplexa – one host Many Eimeria and Goussia spp. sporulate outside of the host. In particular those infecting the intestine. Others usually sporulate endogenously Protozoa – Apicomplexa- two hosts Sarcocystis spp. Sarcocystis neurona – horse is aberrant host (broad) (narrow) Cause of equine protozoal myeloencephalitis Only present in the Americas Infection in the spinal cord and brain Can lead to muscle atrophy and ataxia Possible link with S. falcatula in birds (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6 732708/) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4461864/ Protozoa -- Apicomplexa Cyst for survival Either environment or in the intermediate host Protozoa -- Apicomplexa Toxoplasma gondii is an obligate intracellular, parasitic alveolate that causes the disease toxoplasmosis. dead-end host Can alter the behavior of the true intermediate host, to facilitate completion of the life-cycle i.e. predation Apicomplexa – Toxoplasma gondii The cat is out of the bag: How parasites know their hosts (PLOS Biology 2019 https://doi.org/10.1371/journal.pbio.3000446) Protozoa -- Apicomplexa Phylum Order Locomotion by gliding Life cycle largely intracellular Sexual and asexual phases occur Eucoccidiorida Piroplasmorida Haemosporida Parasites of Parasites of Parasites of epithelial cells blood cells blood cells Sexual and asexual Ticks as vectors Biting insects as reproduction occurs Sexual vectors in epithelial cells reproduction Sexual takes place in reproduction ticks takes place in insects Eimeria / Goussia Isospora Protozoa Toxoplasma genera Cystoisospora (pigs) Sarcocystis Babesia Theileria Plasmodium Protozoa -- Apicomplexa Piroplasmorida Parasites of blood cells Ticks as vectors Sexual reproduction takes place in ticks (DH) Asexual reproduction in host mammal (IH) Babesia Theileria Important parasites of cattle: Babesia microti causes Texas cattle fever Theileria annulata causes tropical theileriosis and T. parva causes East Coast fever TEXAS CATTLE FEVER: Babesia microti Babesia microti, a zoonotic intraerythrocytic parasite, is the primary etiological agent of human babesiosis in the United States. Human infections range from subclinical illness to severe disease resulting in death, with symptoms being related to host immune status. https://jcm.asm.org/content/55/10/2903 Apicomplexa – Babesia microti The Babesia microti life cycle involves two hosts, which include a rodent, primarily the whitefooted mouse and a tick in the genus Ixodes. Other species become infected when bitten by infected ticks. The definitive host is the tick. Protozoa -- Apicomplexa Canine babesiosis is a significant tick-borne disease caused by various species from the protozoan genus Babesia. Babesia canis Intraerythrocytic parasite A review of canine babesiosis: https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-016-1596-0 Apicomplexa – Babesia canis Review: Protozoa / Protista Complex taxonomy, that is changing with newly advanced molecular methods Protozoa/protists are NOT a single group and occupy most branches (super-groups) of the Eukaryotic tree of life Usual cellular characteristics of Eukaryotic cells, some have a pseudo-mouth Feed by osmotrophy or phagocytosis / pseudopodia, or via the mouth-like structure the cytostome Traditionally grouped by methods of movement (Pseudopodia, cilia, flagella, gliding etc) Can reproduce both asexually and sexually Many form cysts in the environment or in the host Can be host specific or not host specific (zoonotic) Examples: Balantidium (ciliate); Histomonas, Trypanosoma and Giardia (flagellates) Apicomplexans are mostly intracellular: Monoxenous and Heteroxenous Schizogony results in significant increases in numbers (merozoites) and often results in serious cellular damage Fusion of micro and macro gamonts results in a zygote forming, that develops into an oocyst Apicomplexa: Eimeria / Goussia (differences in morphology of sporocysts only) ; Sarcocystis; Toxoplasma (cat) Oocysts can develop outside the host (hard for diagnosis, as the oocyst is the diagnostic feature in most cases) Piroplasmids: Babesia and Theileiria