Intro to Protozoa & Parasites

• Intro to Protozoa protist study guide

Protozoa Objectives

• Classification (motility)
• Systematics
• Terminology
• Key characteristics
• Reproduction
• Life cycles

Parasites of Veterinary Importance

• Kingdom Protozoa / Protista includes several phyla
• Excavates (flagellates) are one group within Protozoa
  • Phylum Euglenozoa includes Kinetoplastea (e.g., Trypanosoma)
  • Phylum Metamonada includes Diplomonads (Giardia, Hexamita) and Parabasalids (Histomonas, Trichomonas)
• Phylum Apicomplexa includes Eimeria, Neospora, etc
• Phylum Ciliophora (ciliates) includes Balantidium
• Amoebozoa includes Entamoeba

Protozoan vs. Protist

• Protozoa is a general term for single-celled eukaryotes that are either free-living or parasitic
• They feed on organic matter
• A protist is any eukaryotic organism with cells that have nuclei but is not an animal, plant, or fungus
• Protists include algae, slime molds, and dinoflagellates
• Neither protozoa nor protists form a natural group
• The term "protozoa" implies kinship with animals (metazoans) and is discouraged by many
• "Protist" is typically preferred for the high-level classification of eukaryotic microorganisms
• In 2005, The Society of Protozoologists voted to change their name to The International Society of Protistologists

Protozoa Classification

• Protozoa are classified by locomotion
• The Metamonada include Diplomonads, which are mostly parasitic flagellates
• Trypanasomes are other flagellates found in the Phylum Euglenozoa
• Amoebozoa includes protists distinguished by their pseudopods
• Apicomplexa is a group of veterinary and medical parasites
• Apicomplexa are Alveolates related to Ciliates and Dinoflagellates

Tree of Life

• Stramenopiles (Heterokonts) Algae includes kelp to diatoms & Oomycetes
• Unikonts includes amoebozoa and opisthokonts (fungi and animals)
• Excavates includes amitochondriate flagellates, amoeboflagellates, Euglenozoa
• Alveolates includes Ciliates, apicomplexans and dinoflagellates
• Cercozoa: amoeboids and flagellates that feed by means of filose pseudopods, includes Halposporidians

Generalized Protozoan Cells

• Protozoan cells contain typical eukaryotic organelles
• Different protozoa show different organelles present, they are complex

Terminology

• Zoite means "little creature"
• Prefixes are added to the end of the term "zoite" to denote a portion of the life history
• Sporozoite refers to the infective form
• Trophozoite form feeds and grows
• Tachyzoite form divides rapidly
• Bradyzoite form divides slowly
• Merozoite means many (can also be infective in the case of two hosts being involved)

Protozoa Characteristics

• Protozoa are unicellular, eukaryotic "animals"
• They possess a nucleus, endoplasmic reticulum, mitochondria, a Golgi body, and lysosomes
• Protozoa can be anaerobic or aerobic
• They absorb nutrients or have a "pseudo-mouth"
• They feed on bacteria, other protozoa, organic matter, or tissues of the host
• Protozoa take in food by 'osmotrophy' absorbing nutrients through cell membranes
• Protozoa can also feed by phagocytosis, either by engulfing food with pseudopodia (as amoebae do), or taking in food through a mouth-like aperture called a cytostome

Key Characteristics

• Many protozoa are part of the normal microbiota, and do not cause disease (e.g., Entamoeba, Cryptobia, Gregarines intestinal 'parasites')
• Protozoa show Locomotion via pseudopodia, flagella, gliding movements or cilia,

Asexual Reproduction

• Key characteristic include asexual reproduction results in large exposure producing significant damage
• Host(s) can be host-specific or have a broad spectrum
• Zoonotic species can affect animals and humans
• Protozoa can cause chronic infections, and elicit an immunity
• Many protozoa form cysts (in the environment or in a host)

Protozoa Reproduction

• Binary fission, budding, schizogony / multiple fission (merogony) can occur
• Protozoa that divide asexually have a short generation time

Schizogony

• Schizogony (merogony) results in an exponential increase in numbers
• This results in destruction of host cells in proportion to the infection
• This stops after a fixed number of repetitions

Sexual Reproduction

• Merozoites become either a Macrogametocyte (macrogamont) then a macrogamete OR a Microgametocyte (microgamont) then form several microgametes
• A microgamete fertilizes a macrogamete forming a zygote; a wall forms around this and it becomes an oocyst

Ciliates

• Key characteristic is locomotion by cilia
• Balantidium sp. are ciliate protozoa

Protozoa – Flagellates

• 'Mastigophora' Class Kinetoplastida (excavates)
• These flagellates show Locomotion by flagella
• Kinetoplastorida order:
  • Haemoflagellates/parasites of the blood
  • They are generally transmitted by biting insects
  • Flagellates are found in Diplomonadorida Trichomonadorida
  • They are Predominantly of the intestines
  • Examples of flagellate Protozoa genera include: Trypanosoma cruzi, Giardia, Spironucleus, Histomonas

Trypanosoma

• Trypanosoma is a genus of kinetoplastids, a monophyletic group of unicellular parasitic flagellate protozoa
• Trypanosoma infects hosts and cause diseases, including sleeping sickness, caused by Trypanosoma brucei, and Chagas disease, caused by Trypanosoma cruzi

Giardia

• Giardia sp. usually lives in the duodenum
• Montezuma's revenge is a colloquial term for traveler's diarrhea contracted in Mexico
• It is transmitted through infected water from cysts

Histomonas meleagridis

• Histomoniasis/osis is a commercially important disease of poultry, especially those farmed
• Histomoniasis/osis is caused by Histomonas meleagridis
• Clinical signs of Histomoniasis/osis include lethargy, yellow diarrhea, appetite/weight loss, discoloration of the head (blackhead) and death
• Histomonas specifically infects the cecum and liver
• Histomonas is transmitted to the bird by Heterakis gallinarum, usually in the egg or in an earthworm containing infected eggs
• There is currently No treatment (FDA ban)

Histomonas lifecycle

• Transmission is within the egg of the cecal nematode chickens and turkeys (Heterakis gallinarum)
• Trophozoites from the cecum of an infected bird are ingested by the nematode and invade the eggs
• Infected eggs of the nematode are released onto the soil where they are eaten by young birds during pecking activities
• As nematode eggs hatch in the small intestine, Histomonas trophozoites are released to invade the cecum and liver

Protozoa

• The phylum Apicomplexa is known for Locomotion by gliding
• The Life cycle is usually largely intracellular with sexual and asexual phases
• Eucoccidiorida are parasites of epithelial cells

Apicomplexa characteristics

• Sexual and asexual reproduction occurs in epithelial cells
• The diagnostic stage for the final host can be small
• The asexual stage causes damage
• They often have a cyst stage (oocyst)
• An oocyst is 'the diagnostic feature' when a cyst contains a zygote from a parasitic protozoan

Apicomplexa

• Goussia oocysts contain four sporocysts each with two sporozoites
• The sporozoites Release from the sporocysts via a longitudinal suture

Sarcocystis neurona

• The cause of equine protozoal myeloencephalitis
• Only present in the Americas and cause infection in the spinal cord and brain
• It can lead to muscle atrophy and ataxia
• Possible link with S. falcatula in birds

Apicomplexa survival strategy

• Utilizes cysts for survival
• Survives in either environment or in the intermediate host

Protista

• Protozoa can complex taxonomy, that is changing with 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
• They feed by osmotrophy or phagocytosis utilizing pseudopodia, or the cytostome mouth-like structure
• Usually grouped by methods of movement (Pseudopodia, cilia, flagella, gliding etc)
• It can reproduce both asexually and sexually and form cysts
• They can be host specific or not host specific (zoonotic)
• Balantidium (ciliate); Histomonas, Trypanosoma and Giardia (flagellates) are examples to study
• Apicomplexans are mostly intracellular and Schizogony significantly increases numbers, merizoites, and cause damage
• Fusions of micro and macro gamonts results in a zygote forming, that develops into an oocyst
• Apicomplexa: Eimeria/ Goussia is identified by sporocyst morphology, Sarcocystis; and Toxoplasma (cat)
• Oocysts diagnostic outside the host
• Piroplasmids: Includes study species Babesia and Theileiria