Week 5: Parasitology Flashcards
What is a parasite?
An organism that lives on or in an organism and gets its food from or at the expense of host
What is a vector?
- A living transmitter of disease
- involved in essential steps of the parasitic life cycle
What is a parasite reservoir?
- Sources of parasites in the environment
- could be ecological system where an infectious agent survives indefinately
- Includes all the component host populations including that of any intermediate host or vector
What is a definitive host?
- Host in which parasites have sexual reproduction
- Primary host
What is the intermediate host?
Host in which parasites asexually reproduce or do not reproduce at all but do develop into a new stage
What is an incidental host?
- Host that is infected but not required for the maintenance of the population
Features of Protozoa
- Single-celled Eukaryotes
- Replication inside the host
- Trophozoite
- active form
- replicates by binary fission
- Cyst
- Dormant, non-replicative form
- Protected by double-membranes
Features of Helminths
- Multicellular Animals
- Complex life-cycles
- do not complete life cycle within a single human host
- Reproduce sexually
- May form cysts
- protected by an impermeable cuticle
Features of Amoebas
- Psuedopod used for motility
- Alternate between trophozoite & cyst forms
Features of Flagellates & Ciliates
Use flagella or cilia for locomotion
Features of sporozoa
- Gliding motility
- Intracellular replication
Types of protozoa parasites
- Amoeba
- Flagellates & Ciliates
- Sporozoa
Examples of protoza locomotion
- Giardia lamblia trophozoite “falling leaf”
- Cryptosporidium sporozoite gliding motion
Protozoa reproduction
- Asexual reproduction
- Trophozoite form reproduces by binary fission inside host
Categories of helminths
- Nematode (Roundworm)
- Trematode (Flatworm)
- Cestode (Tapeworm)
Nematode reproduction
- Most are dioecious: sexes are separate
- Some are hermaphroditic
Trematode reproduction
- Hermaphroditic
- includes both male and female gonads & generates both sperm and eggs
- Can reproduce sexually or asexually
- sexually self- or cross-fertilization
- Asexually (break off half)
Cestode reproduction
- Hermaphroditic
- can reproduce sexually or asexually
What is the infective dose and exposure
- specific route of exposure
- infection does not always result in disease
Describe the penetration of anatomical barriers
- Direct penetration through skin or via arthropod vectors
- Oral ingestion
Describe attachment to specific host cells or organs
- Tissue tropism facilitated by parasite surface adhesins and glycoprotein or glycolipid receptors on some cell types
Factors associated with pathogenicity
- Antigenic variation
- Molecular mimicry
- Masking
- Intracellular location
- Immunosuppression
- suppression of parasite-specific B & T-cell responses
- Degradation of immunoglobulins
Possibly incomplete plasmodium factors of pathogenicity
- Antigenic variation
- Molecular mimicry
- Intracellular location
- Suppression of parasite-specific B & T-cell responses
Incomplete Schistosoma factors of pathogenicity
- Molecular mimicry
- Masking
- Degradation of immunoglobulins
