Parasitic Protozoa: ZOO106 Lecture

Introduction to Parasitic Protozoa

• Study notes related to a lecture about Parasitic Protozoa for ZOO106.

Outline of Lecture

• Definition and basic properties of protozoans.
• Transmission and life cycle of protozoans.
• Major groups of parasitic protozoans: Flagellates, Amoebae, Apicomplexan, and Ciliates.
• Diagnosis and treatment of protozoan parasitic infections.
• Future research directions regarding protozoan parasites.

Learning Outcomes

• Classify the protozoans.
• Describe the morphology of each major group of protozoa.
• Explain the pathophysiology, life cycle, infective stages, modes of transmission, epidemiology, prevention, and control of protozoan parasites.
• Describe the diagnostic features of each parasite.
• Enumerate the different specimens used for appropriate diagnostic procedures for each parasitic infection.

Protozoans

• Protozoans are classified under Kingdom Protista.
• Protozoans were first described over 300 years ago by Leeuwenhoek, who described Giardia from his own intestine.
• Protozoans are unicellular eukaryotes.
• Protozoans are very small, measured in microns and 1um = 1/1000mm.
• Protozoans exhibit complex subcellular organization.

Protozoan Cytoplasm

• Ectoplasm is the denser, less granular outer layer used for ingestion, movement, excretion, protection, and respiration.
• Endoplasm is the less dense, more granular inner layer used for nutrition and reproduction.

Nucleus

• Nucleus is responsible for maintenance and reproduction
• Macronucleus is large, filled with densely-staining granules, and vegetative in function.
• Micronucleus is vesicular, similar to a nucleus, and reproductive in function.

Basic Characteristics

• Protozoans go through movement, feeding, and reproduction

Locomotion

• Ameboid movement involves pseudopodia, which are cytoplasmic extensions.
• Ciliary and Flagellar movement uses cilia (short, hair-like structures) and flagella (long, whip-like structures).
• Movement via undulating membrane, this is a dorsal extension of the cytoplasm associated with flagella.

Nutrition

• Contractile vacuole is for osmoregulation
• Radiating canals for excreting liquid waste
• Micro/Macronucleus both control reproduction
• Cilia used for movement and food detection
• pellicle used for protection
• Oral Groove or Vestibulum is used to detect food
• Buccal overture is where food enters
• Cytostome the cell mouth where food is pulled in
• Food vacuoles for food digestions
• Cytoplasm provides internal material for the protozoan
• Cell membrane is the outer surface
• Cytopharynx is the opening for food

Nutrition - Holozoic

• Holozoic nutrition involves food intake in solid/liquid from the outside and is digested inside their body

Nutrition - Holophytic

• Holophytic protozoans are autotrophic and use phototrophy.
• Phytoflagellates have chloroplasts and chromatophores to synthesize food through photosynthesis with sunlight, carbon dioxide, and water.

Nutrition - Saprozoic

• Saprozoic nutrition involves unicellular protozoans absorbing liquid organic molecules from their surroundings as food.
• Osmotrophy is the absorption of food by osmosis through the general body surface.
• Mixotrophic protozoans are free-living, they capable of photosynthesis from symbionts acquired with each new generation.

Nutrition - Parasitic

• Endoparasites inhabit internal surfaces of hosts and can dwell in the lumen of the alimentary canal.
  • Examples: Entamoeba histolytica, Giardia lamblia, Isospora hominis, and Balantidium coli.
• Some reside in the host mouth cavity like, Trichomonas tenax and Entamoeba gingivalis.
• Some inhabit the genital tract, for example Trichomonas vaginalis.
• Some live within host tissues, through the skin or digestive tract, such as Trypanosoma, Plasmodium, Leishmania, and Babesia.
• Ectoparasites inhabit the external surface of hosts
  • Example: Icthyopthirius multifilis that buries in the epidermis of freshwater fishes.
• Hyperparasites are protozoans that parasitize other parasitic protozoans.
  • Examples: Zelleriella, Nosema notabilis, and Sphaerospora polymorpha.

Life Cycle Stages

• Trophozoite:
  • The release from the cyst
  • Vegetative, feeding stage and easily destroyed by unfavorable conditions
  • Multiplying stage
  • stage usually associated with pathogenesis in parasitic species
• Cyst:
  • Multiplies in the cysts of some species, excystation releases more than one organism.
  • Inactive stage and contains a resistant, membranous cyst wall to protect it from digestive juices and enzymes in the upper GIT.
  • Represents the infective stage associated with passage from host to host.

Modes of Reproduction

• Asexual Reproduction:
  • Binary fission
  • Multiple fission
  • Budding
• Sexual Reproduction:
  • Syngamy, where the fusion of gametes initiates the development of a new individual organism.
  • Isogametes are the same size, no male or female.
  • Anisogametes include macrogametes and microgametes.
  • Conjugation involves where organisms exchange nuclear union

Gametogony/gamogony

• Occurs when a few merozoites develop into the parasite known as gametocytes.

Monogenetic Parasite

• Parasites that require on host only in their life cycle to survive

Digenetic Parasite

• Parasites that require two ore more hosts through their life cycle to survive

Parasite Transmission

• Direct transmission of trophozoites occurs through intimate body contact, such as sexual transmission.
• Faecal-oral transmission involves environmentally-resistant cyst stages, which are passed in faeces, then ingested with food/water by another host.
• Vector-borne transmission of trophozoites taken up by blood-sucking arthropods (insects or arachnids) and passed to new hosts when they feed.
• Predator-prey transmission involves zoites encysted within prey animal tissues being eaten by a predator (carnivore), that sheds spores into the environment to be ingested by new prey animals.

Taxonomic Overview

• Four classes of protozoa, amoebae, flagellates, ciliates, sporozoa

Taxonomic Overview - Sporozoa

• Sporozoa are spore-formers.
• Sporozoa recognized by non-motile spores as transmission stages
• Pre-spore stages move using tiny undulating ridges.

Taxonomic Overview - Flagellates

• Phytoflagellates:
  • With chloroplasts, derive energy by photosynthesis
  • Are free-living aquatic organisms and some exhibit periodic blooms
  • Some contain potent neurotoxins and cause paralytic shellfish poisoning
• Zooflagellates:
  • Without chloroplasts, derive energy by absorption of nutrients or the ingestion of food particles
  • Many species occur as free-living aquatic organisms
  • Live in insects and some vertebrates as symbiotes, commensals or parasites

Taxonomic Overview - Ameoba

• Rhizopod amoebae produce broad lobopodia, fine filopodia, or net-like reticulopodia without regular microtubule arrays.
  • Aquatic species contribute to water quality by consuming bacteria and algae.
  • Terrestrial species contribute to soil health via nutrient cycling.
• Actinopod amoebae form radial axopodia stiffened by internal arrays of microtubules, which arising from an organizing centre.
  • They are free-living planktonic organisms with marine and freshwater species

Taxonomic Overview - Cilates

• Ciliates possess two types of nuclei: vegetative macronuclei and reproductive micronuclei.
• They possess cilia.
• Three groups are recognized on the basis of their patterns of somatic and buccal ciliation.
• Lower holotrichs - simple body and oral ciliation
  • Most are free-living aquatic species but some are highly specialized symbionts aiding cellulose digestion in herbivores.
• Higher holotrichs - simple body ciliation but more specialized oral in membranelles
  • Most occur as free-living aquatic organisms but some live as commensals or parasites in a range of animals.
• Spirotrichs - reduced body ciliated but well developed oral ciliature forming an adoral zone of membranelles
  • Majority are bactivores living in aquatic and terrestrial habitats.

Taxonomic Overview - Sporozoans

• Sporozoans are obligate parasites, form temporary non-motile spores containing infective cells.

  • Four major groups are recognized based on different spore morphology

• Apicomplexan parasites form distinctive oocysts containing infective sporozoites.

  • While many species occur only in invertebrates, some infect vertebrates causing severe diseases, like malaria, tick fever, diarrhoea, or abortion.

• Microsporan parasites form unicellular spores containing coiled polar tubes used to infect host cells.

  • Most species infect invertebrates like insects, some form cysts in vertebrates like fish.

• Haplosporidian parasites form unicellular spores without polar filaments in the tissues of aquatic invertebrates.

  • They cause significant morbidity and mortality in oysters.

• Paramyxean parasites form unique spore-within-spore arrangements within the tissues of bivalves and polychaetes, and cause QX and Aber disease in oysters.

Phylum Mastigophora

• Giardia lamblia
  • Colonizes and reproduces in the small intestine, causing Giardiasis.
  • Attaches to the epithelium with a ventral adhesive disc and reproduces via binary fission.
  • Trophozoites absorb nutrients from the lumen of the small intestine.
  • Lacks mitochondria.
  • Is anaerobic.
  • Also infects cats, dogs, birds, cows, beavers, deer, and sheep.
• Colonization leads to reduction of gut's absorptive capability
  • Symptoms: diarrhea, malaise, excessive gas, epigastric pain, bloating, nausea, lost of appetite and pale, foul smelling, greasy stools
  • Zoonotic transmission: occurs while swimming in contaminated streams or lakes

Phylum Mastigophora - Trichomonas vaginalis

• Oval shaped.
• Does not have cyst form.
• Barb-like axostyle.
• Survives for 24 hours in urine, semen, or water samples and has worldwide distribution.
• Trichomonas vaginalis is a sexually transmitted disease
  • Incubation period of 5 to 28 days
  • Diagnosed through vaginal discharge
  • PCR treatments include metronidazole and tinidazole

Phylum Mastigophora - Trypanosomatid

• Greek mastig refers to the trypanosome's whip-like flagellum and is a typical eukaryotic cell, having major organelles
• Each has a condensed mitochondrial DNA structure, associated with the basal body of the flagellum
  • The cell also features a dense coat of variable surface glycoproteins (VSGs)
• Trypanosoma brucei which comes in gambiense, rhodesiense, and brucei types are transfered by the tsetse fly
  • They cause African sleeping sickness where diagnosis involves screening tests, physical exams, microscopy in spinal tap with pentamidine, suramine, and Fexinidazole during the first stage of the dieseas.
• Trypanosoma cruzi has a kissing bug vector and are commonly known for causing the Chaga's Disease
  • Triatomine Bug Stages have trypomastigotes transfered through feces
• Leishmania sp, is transfered by sandly
  • Is has to well defined nucleus and kinetoplast
    • The various species are not distinguishable morphologically from one another

Taxonomic Overview - Leishmania

• Three types of Leishmaniasis
  • visceral leishmaniasis
    • L. Donovani
      • Fatal form and incubation. It is typically Diagnoses through Serological thru Direct Agglutination Test (DAT) with RK39 dipstick, in a long is difficult and requires the discovery of new drugs.
  • Treatment is extremely difficult to treat, often requiring a long course of pentavalent antimony drugs and necessitates the discovery of new drugs
• Cutaneous leishmaniasis L. tropica and L. major
• muco-cutaneous leishmaniasis -L. braziliensis

Non-pathogenic flagellates of the digestive tract

• Indicator of fecal contamination of ingested food and water with Chilomastix mesnili, Trichomonas tenax ,Pentatrichomonas hominis types
  • Treatment is not necessary