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
Incomplete trypanosoma factors of pathogenicity
- molecular mimicry
- Masking
- intracellular location
- Suppression of parasite-specfic B & T-cell responses
What is masking
mimic host molecules to pretend to be part of the host
Replication in the host occurs in
all protozoa but NOT all helminths
Plasmodium falciparum unique factor of pathogenicity
toxin production
Strongyloides unique factor of pathogenicity
hydrolytic enzymes
Pathogens that cause mechanical tissue damage
Helminth larvae (migration through tissue)
Blockage of internal organs (cestodes)
