ZOO106 Lecture 3: Parasitic Protozoa

• ZOO106 Lecture 3 introduces parasitic protozoa

Major Groups of Parasitic Protozoans

• Protozoa are categorized into: Sarcodina, Flagellata, Sporozoa, and Infusoria
• Sarcodina includes Amoeba
• Flagellata includes Leishmania, Trypanosoma, Giardia, and Trichomonas
• Sporozoa includes Plasmodium, Sarcocystis, Cryptosporidium, Toxoplasma, Babesia, and Isospora
• Infusoria includes Balantidium

Parasitic Sporozoans (Apicomplexa)

• Apical complex contains organelles involved in host cell invasion and anchoring
• Obligate parasites are intracellular
• Reproduction can be sexual (anisogametes) or asexual (schizogony)
• Host specificity exists among Sporozoa
• Sporozoa cause diseases such as malaria, toxoplasmosis, and cryptosporidiosis
• The Phylum Sporozoa includes Class Telosporea, Subclass Coccidia, Order Haemosporida, Family Plasmodiidae, Genus Plasmodium, Order Eucoccida, Family Eimeriidae, Genus Toxoplasma, Subclass Gregarina, Order Eugregarina, Suborder Cephalina, Family Gregarinidae, Genus Gregarina, Suborder Acephalina, Family Monocystidae, Genus Monocystis

Phylum Sporozoa - Plasmodium spp.

• Morphology: elongated, motile sporozoites, ring-shaped trophozoites, multinucleated schizonts, and merozoites
• Diversity: Subgenus Laverania infects humans and non-human primates
• Non-Laverania species infect reptiles, birds, and rodents

Stages of Plasmodium parasites

- Plasmodium falciparum: Parasitized red blood cells (pRBCs) not enlarged
- RBCs containing mature trophozoites are sequestered in deep vessels
- Total parasite biomass equals circulating and sequestered parasites
- Applique forms and 1-2 chromatin dots are occasionally observed in delicate cytoplasm

• The trophozoite is seldom seen in peripheral blood having compact cytoplasm and dark pigment

• The mature schizont has 8-24 small merozoites and a clumped dark pigment mass, also seldom seen in peripheral blood

• The gametocyte is crescent or sausage shaped, having chromatin in a single mass or diffused with a dark pigment mass

• Plasmodium vivax: Parasites prefer young red cells, pRBCs are enlarged, and all stages are present in peripheral blood

  • Large cytoplasm with occasional pseudopods and a large chromatin dot is present within the ring stage
  • Trophozoite - large ameboid shaped

• Parasites of Plasmodium malariae prefer old red cells and all stages are present in peripheral blood, pRBCs are not enlarged

• Ring - sturdy cytoplasm and has large chromatin

• 6-12 merozoites and large nuclei, clustered around mass of coarse dark brown pigment; occasional rosettes can be found

• Plasmodium ovale: pRBCs are slightly enlarged and have an oval shape with tufted ends, and all stages are present in peripheral blood

  • The ring has sturdy cytoplasm and large chromatin
  • The trophozoite is compact with large chromatin and dark brown pigment
  • The schizont - 6-14 merozoites with large nuclei, clustered around a mass of dark brown pigment
  • The gametocyte - round to oval, compact and may almost fill RBC, compact chromatin

• Plasmodium knowlesi: pRBcs are not enlarged and multiple invasion/high parasitaemia can be observed

• All stages are present in peripheral blood

  • The ring has double chromatin dots
  • Trophozoites - pigment spreads inside cytoplasm, like P. malariae band form may be seen
  • Schizont - up to 16 merozoites

Life Cycle of Plasmodium spp.

• The life cycle involves infective sporozoites and begins with transmission by a female Anopheles mosquito to a human host
• The parasite begins its asexual intraerythrocytic cycle after the initial liver stage
• Sexual forms that develop from intraerythrocytic parasites can then be transmitted to mosquitoes
• Mosquito parasites undergo meiotic/mitotic replication to form sporozoites to infect another human host
• Human Liver Stages: Exo-erythrocytic Cycle and schizont is ruptured
• Human Blood Stages: Erythrocytic Cycle which releases merozoites, matures and undergoes schizogeny, gametes rupture

Treatment and Preventions for Plasmodium Spp

• Oral treatments include: artemether-lumefantrine (Coartem) and atovaquone-proguanil (Malarone)
• IV: clindamycin or tetracycline
• Treatment and prevention also includes: Malaria Vaccines, indoor residual spraying and long lasting insecicidal nets

Phylum Sporozoa - Toxoplasma Gondii

• Morphology includes oocyst, tachyzoite, and bradyzoite stages
• Tissue cysts form in neural and muscle tissues with bradyzoites (dormant stage)
• Host range: warm-blooded animals (mammals, birds)
  • Life cycle involves sexual reproduction in Felids (definitive hosts) and asexual reproduction in intermediate hosts

The Toxoplasma gondii life cycle

• Transmission via oral, fecal-oral route, blood transfusion, organ transplantation, or vertical transmission
  • Pathogenicity includes toxoplasmosis with possible asymptomatic or mild flu-like symptoms.
  • Congenital infection may cause birth defects and neurological complications

Diagnosis, Treatment, and Prevention of Toxoplasma gondii

• Diagnose with serology, biopsy, or DNA detection
• Prevent by avoiding cats, washing fruit and vegetables thoroughly, not eating raw meat, and regular hand washing
• Treatment regimens include: Pyrimethamine and sulfadiazine, Trimethoprim-sulfamethoxazole, Clindamycin, pyrimethamine, sulfadiazine and many more as recommended

Phylum Sporozoa - Cryptosporidium spp.

• Morphology: The shape is a small (2-6µm) sphere
• There are two forms: oocyst and sporozoite
• Habitat- Gastrointestinal epithelial cells
• Host Specificity- Vertebrate host and zoonotic
• Reproduction- Sexual and asexual
• Transmission: fecal-oral route

Life cycle and pathogenicity of Cryptosporidium spp.

• Thick-walled oocyst ingested by host (water or food with oocysts)
• Thick-walled cocyst (sporulated) exits host
• Symptoms include diarrheic stool, abdominal cramps, nausea, vomiting, and low-grade fever
• Diagnose via stool examination, acid-fast staining for oocyst detection, or PCR-based techniques
• Prevention for the waterborne pathogen can be as simple as washing your hands

Phylum Sporozoa - Gregarina Spp.

• Morphology: elongated and worm-like in shape
• Lacks cilia or flagella and does not have a distinct motility organelle
• Habitat: Digestive tract of orthopterans (grasshoppers, cockroaches) Host
• Specificity: Invertebrates Host
• Reproduction: Schizogony (Multiple fission) and Endopolygeny (multiple rounds of nuclear division)

Life cycle, Pathogenicity, and Ecology of Gregarina Spp

• odonate ingests oocyst, releases sporozoites, attach to epithelium- Trophozoites absorb nutrients from the lumen
• Trophozoites attach as gamonts, form mating pairs in gametocyst
• Gametes fuse to produce oocyst
• Ecological Role: decomposers aiding breakdown of organic matter and contributing to nutrient cycling
• Pathogenicity: non- or mildly pathogenic

Phylum Sporozoa - Monocystis spp.

• Morphology: elongated and worm-like with one elongated nucleus, lacks locomotor organelles
• Body Structure: simple, single cell not divided into differentiated organelles
• Habitat: reproductive organs and ducts of earthworms (seminal vesicles/funnels) and tissues/lumen of reproductive system
• Specific to earthworm hosts (Lumbricidae family)
• Reproduction: asexual (schizogony or multiple fission) and schizogony that undergoes multiple rounds of nuclear division to form daughter cells

Lifecycle, Pathogenicity and Ecology of Monocystis spp.

• Lifecycle: sporozoites infect, Trophozoites - feeding, then become gametocytes
• Sporogony- Oocysts excreted into environment
• Sporozoites released, travel to seminal vesicles, and feed as trophozoites
• Zygotes undergo meiotic then mitotic division forming 8 sporozoites, Gamonts form and join in syzygy
• Pathogenicity: non-pathogenic and reside within the reproductive organs of earthworms without causing harm or disease
• Ecological Role: infects ecology of earthworms, no major impact on health/survival