(Section D: Other Infectious Agents) Lecture 26 Flashcards
Parasite
“Parasitos”
* Para = On
* Beside = Food
What organisms can be parasites?
- Animals
- Plants
- Fungi
- Bacteria
- Viruses
How are parasites organized?
- Protozoa
- Metazoa
What are examples of metazoa?
- Helminths
- Arthropods
What type of organisms are protozoa?
Single cell eukaryotes
What type of organisms are metazoa?
Macroscopic, multicellular, eukaryotes
Advantages of Parasitism
(8)
- No need for searching once host is found
- Food permanently available
- Limited requirement for complicated food capturing mechanisms
- Reduced need for food processing
- Protection from environmental extremes
- Protection from predators and diseases
- Reduced need for dispersal
- Can devote energy to reproductive output
Disadvantages of parasitism
(6)
- Extreme host specificity increases vulnerability to extinction
- Must locate at optimal site on/in host to ensure food/survival
- Must adapt to host’s internal physiological environment
- Must overcome host’s immune defenses
- Spread limited by host’s geographic range
- Transmission extremely risky
Different forms of parasites
- Facultative
- Obligate
- Endoparasites
- Ectoparasites
Facultative parasites
Free living or Live inside host
Obligate parasites
Must live in host
Endoparasites
Live inside host
Ectoparasites
Live outside host
Parasitic protozoa
* Number described
* Number currently living
* Number adapted as parasites
* Number isolated from humans
- Over 200,000 species
- 35,000 species
- 10,000 species
- ~70 different species
Can protozoa infect invertebrates?
Yes, parasitic protozoans infect a wide spectrum of vertebrate and invertebrate life
All protozoans are…
Eukaryotic, single-celled organisms
What is the conventional classification of parasites?
By motility
1. Flagellates
2. Amoeboids
3. Apicomplexans
4. Ciliates
Flagelletes
Mastigophora
* Use flagella to move
Amoeboids
Sarcodina
* Protoplasm pushes them around
Apicomplexans
Sporozoa
* Glide to move
Ciliates
Ciliophora
* Cilia help facilitate movement
Do parasites group only into a single category of motility?
No, they can have multiple forms of motility (overlapping between categories)
What is used in modern classification of parasites?
Metabolism and Genotype
What is are mechanisms of entry for parasites?
- Oral (Giardia duodenalis)
- Sexual (Trichomonas vaginalis)
- Inhalation (Toxoplasma gondii)
- Direct Contact (Trypanosoma cruzi)
- Arthropod vectors (Plasmodium falciparum)
What are the different types of parasite hosts?
- Definitive (Final)
- Intermediate
- Reservoir
Definitive host
- Sexual maturity
- Sexual reproduction
- Most crucial for parasite’s lifecycle
Intermediate host
- Asexual reproduction
- Development stage, not at sexual maturity
Reservoir host
Serves to harbour the parasite and be a source of infection
What type of reproduction can parasites undergo?
- Asexual
- Sexual
- Both
Oral transmission
Ingest
Sexual transmission
Keeps the parasite in human conditions, prevents exposure to outside environment
Inhalation transmission
Aerosolized particles that are breathed in
Direct contact
Parasite enters via direct contact (rubbing a wound etc.)
Aseuxal reproduction
Kind of like binary fission and mitosis
Sexual reproduction
Kind of like meiosis where sperm and eggs come together
Do some organisms have both asexual and sexual reproduction?
Yes
State the term for:
- One host
- 2 different hosts
- 3 different hosts
- Monoxenous
- Diheteroxenous
- Triheteroxenous
What are methods for parasite survival and pathogenesis?
- Antigenic variation
- Molecular mimicry
- Immune modulation
- Intracellular habitation
- Encapsulation
- Protease secretion
- Thermal tolerance
- Toxin production
- Nutrient deprivation
- Others…
Pathogenesis Methods:
Expressing different surface proteins, changing frequently
Antigenic variation
* Helps hides from immune system
Pathogenesis Methods:
Proteins and molecules that look like the host
Molecular mimicry
* Tricks host into thinking it isn’t foreign
Pathogenesis Methods:
Releasing thing that suppress/modulate immune system
Immun modulation
Pathogenesis Methods:
Get inside host cells to hide
Intracellular habitation
Pathogenesis Methods:
Forming capsule or cyst to protect from external conditions
Encapsulation
Pathogenesis Methods:
Destroy proteins inside the host
Protease secretion
Pathogenesis Methods:
Adapt to temperatures
Thermal tolerance
True or False:
Toxin production is intentional
Not all the time; sometimes it is a by product
Giardia duodenalis
* What is it
* Living place
* Nucleus
* Type of parasite
* Life cycle
* Transmission
- Most prevalent protozoan human intestinal pathogen
- Upper small intestine of vertebrate host
- Binucleated
- Obligate parasite, aerotolerant anaerobe (no mitochondria)
- Monoxenous, two stages (trophozoite and cyst)
- Fecal-oral route
Giardia duodenalis:
Cyst
- Environmentally stable
- Facilitates transmission
- Tetranucleate
- Oblong shape (5 μm by 7-10 μm in size)
- Metabolic rate is low (10-20% of a trophozoite)
Giardia duodenalis:
Trophozoite
- Adapted for survival within small intestine
- 8 μm by 12-15 μm in size
- Binucleate (both transcriptionally active, diploid)
- Four pairs of flagella
- Adhesive disc
- Mitosomes (no mitochondria)
Lifecycle
- Ingestion (cyst)
- Excystation (due to low pH in stomach)
- Forms 2 trophozoites (in small intestine)
- Adhere/Residence (in villi of small intestine)
- Reproduces asexually
- Encystation (some repackage into cysts)
What can the tropozoites adhering to the small intestinal mucosa result in?
Atrophy and flattening of the villi
What are major reservoir hosts for G. duodenalis?
Beavers
* Hence the nickname “beaver fever”
Giardia duodenalis secretions
- Proteases
What secreted and expressed proteins are present in G. duodenalis?
- Excretory secretory products (ESPs)
- Variant-specific proteins (VSPs)
Diagnosis for Giardia duodenalis
- Gold standard: Microscopy
- Antigen capture ELISA
- Direct fluorescent antibody test (DFA)
- Nucleic Acid Amplification Tests (NAATs)
Treatment for Giardia duodenalis
Nitroimidazoles (e.g. metronidazole)
* Inactivated when taken
* Ferredoxin responsible for reducing pyruvate to ATP activates the drug by reducing it
* Can’t happen in human cells as the reduction power isn’t strong enough
