Pathogenic Protozoa (Kirn) - 5/13/16 Flashcards
What are protozoa?
- Unicellular eukaryotes
- Humans are host to over 70 species of protozoan parasites (Intestinal/luminal, blood, tissue)
Terminology:
Host
Parasite
Reservoir
Vector
Definitive host
Intermediate host
Trophozoite
Cyst
Host: An organism used by another as a source of nutrition and protection
Parasite: An organism that uses another as a source of nutrition and protein, with harm to the host
Reservoir: An organism in which a parasite replicates, from which it is transmitted to host animals
Vector: An organism which transmits a parasite to another animal species; it may or may not be a host
Definitive host: A host in which parasite undergoes sexual cycle (meiosis + fertilization)
Intermediate host: A host in which parasite multiplies asexually
Trophozoite: A growing/multiplying form of a parasitic protozoan
Cyst: A non-growing form, specialized for resistance to unfavorable environments and/or for dispersal
Symbiosis: Two organisms living in close association
a. Mutualism
b. Commensalism:
c. Parasitism
Mutualism: Both members benefit from the association (e.g., Protozoa live in the gut of termites, or in the rumen of ruminates)
Commensalism: When a symbiont benefits from the host but the host neither benefits nor is harmed (e.g., Entamoeba gingivitis in human mouth)
Parasitism: When a symbiont actually harms its host or lives at the expense of the host (E.g., Infections with viruses, bacteria, fungi, protozoa, or helminths)
Diagnostic Techniques used?
- Culture - rarely used
- Acanthamoeba (ocular culture)
- Trichomonas (genital) - Microscopy - common
- Direct smears (Blood, stool, exudates)
- Tissue histology - Serology
- Nucleic acid amplification
Anti-Protozoal Drugs:
- Characteristics (4):
- Examples (9):
Characteristics:
- Protozoa are very similar to human cells, drugs can be toxic
- Many stages need to be targeted
- Different anatomic locations
- Commonly used drugs: OFTEN TOXIC, can be in liquid tablet, and injectable forms are available
Examples:
- Metronizadole (Flyagl): inhibits DNA synthesis
- Tinidazole: contains a nitro group which is reduced to a free nitro radical
- Eflornithine (Ornidyl) [hair removal]: inhibits ornithine decarboxylase of polyamide biosynthesis
- Furazolidone (Furoxone): cross-linking DNA - reacts with two different portions of DNA to block DNA replication
- Hydroxychloroquine (Plaquenil): blocks DNA synthesis
- Iodoquinol (Diquinol, Yodoquinol, Yodoxin): not absorbed, action unknown
- Pentamidine (Pentam 300): may affect mitochondrial functions
- Paramomycin: inhibits protein synthesis, similar as neomycin
- Pyrimethamine: interferes with tetrahydrofolic acid synthesis by inhibiting DHFR enzyme –> blocks DNA and RNA synthesis (b/c these processes needed THF)
Pathogenic Protozoa Classification (5) and examples
- Flagellates (Giardiasis)
- Amoebae (Amoebiasis)
- Ciliates (Balantidiasis)
- Apicomplexa (Sporozoa, Coccidia, Malaria)
- Microspore (Once grouped with Apicomplexa but now known to be related to fungi)
Flagellates
Diseases (4):
Giardiasis (pathogenic flagellate)
Trichomoniasis (pathogenic flagellate)
Trypanosomiasis (hemoflagellate)
Leishmaniasis (hemoflagellate)
Hemoflagellates
Morphology
- Cells are elongate with a single flagellum (originates in a unique organelle, the kinetoplast, a combination mitochondrion and basal body)
- Take on distinctive forms at different stages of the life cycle (defined by the relative positions of the kinetoplast and nucleus, and the presence or absence of flagellum and undulating membrane)
Note: not all species go through all four stages
Hemoflagellates Life Cycle
“You don’t want a hemoflagellate as A PET.”
Amastigote: Nucleus and kinetoplast central; no flagellum
Promastigote: Kinetoplast at anterior end of cell; flagellum present; no undulating membrane
Epimastigote: Kinetoplast migrates centrally; flagellum with short undulating membrane
Trypomastigote: Kinetoplast at posterior end of cell; undulating membrane extends full length of cell
