Parasites Flashcards
Source of infected patients?
- missionaries
- Peace Corps volunteers
- tourists
- increasing number of refugees (developing countries)
- immunosupressed patients
Where are diseases caused by parasites usually found?
- tropics
- subtropics
- more temperate climates
Most common parasitic infection?
- Trichomonas
Parasitic disease that is a frequent cause of recreational water-related disease outbreaks?
- Cryptosporidiosis
Cyst definition
- thick-walled, resistant and resting cell
Trophozoite definition
- active, feeding and multiplying stage of most protozoa
Oocyte definition
- zygotic cyst
Schizogony definiton
- asexual reproductive stage of parasite (sporozoite stage)
- multiple fission: nucleus divides then cell divides into as many parts as there are nuclei
Vector definition
- living organisms carrying pathogen to new host
Intermediate host definition
- hosts immature form of the parasite
Definitive host definition
- hosts mature form of the parasite
Classifications of parasites
- protozoa
- helminths
Protozoa
- microscopic unicellular eukaryotes with complex internal structures
: Flagellates
: Amoeba (Rhizopods)
: Ciliates
: Sporozoa (Apicomplexa)
Helminths
- worm-like parasites
: trematodes
: cestodes
: nematodes
Parasite life cycles
Protozoa: classification and morphology
- many have typical eukaryotic organelles
- membrane-bound nucleus (contains chromosomes)
- endoplasm & ectoplasm
- variety of morphologies
- usually in moist environments
- obtain nutrients from environment
- cytosome mouth can ingest food
Motility of Protozoa: flagella
- one or few flagella
- wave-like beat
- can form undulating membranes
e. g. flagellates
Motility of Protozoa: Cilia
- usually covers protozoa
- coordinated; function like oars to propel
e. g. ciliates
Motility of Protozoa: gliding motility
- glides
e. g. Plasmodium species
Motility of Protozoa: Ameboid movement- crawling
- Pseudopodium attach to surface and pull forward
- force generated by cytoskeletal system composed of actin & myosin
e. g. Entamoeba histolytica
: inhabits human colon and causes human dysentry (bloody diarrhea)
Protozoa asexual reproduction
asexual reproduction
- binary fission, budding
- multiple fission or segmentation
- several rounds of nuclear replication occur without cytokinesis
- formed multinucleated cell produces multiple progeny simultaneously
Protozoa sexual reproduction
- production and fusion of gametes
Helminth: classification and morphology
- worm-like parasites
- multicellular with complex reproductive systems and life cycles involving intermediate hosts and a definitive host
- tough outer cuticle
- Nematodes: roundworms
- Cestodes: tapeworms
- Trematodes: flukes
Helminths: flukes
- trematode
- adult flukes are leaf-shaped flatworms
- bind pocket alimentary tract
- prominent oral and side suckers
- hermaphroditic (except blood flukes- bisexual)
- life-cycle includes mollusks (snails and clams) as intermediate hosts
Helminths: tapeworms
- cestodes
- adult tapeworms are elongated & segmented
- hermaphroditic flatworms inhabit intestinals
- larval forms inhabit extra-intestinal tissues
- head (scolex) of worm usually has 4 muscular cup-shaped suckers and crown of hooklets
- individual tapeworm segments are proglottids
- chain of proglottids is called a strobila
- end part of proglottides are almost completely made up of a uterus full of eggs
Proglottids definition
- individual tapeworm segments
Strobila definition
- chain of proglottids
Helminths: Roundworms
- nematodes
- adult & larval roundworms are bisexual and cylindrical
- inhabit intestinal and extra-intestinal sites
- large sites
- live primarily as adult worms in intestinal tract, and infections most commonly confirmed by detecting eggs in the feces
: can infect the blood and tissues too
Parasite pathogenicity
EAR D DIE
1. Entry & Exposure Route
2. Attachment
3. Replication
4. Damage- cell & tissue
5. Disruption, envaion and inactivation of host defences
Parasite pathogenicity: Entry and Exposure Route
- exogenous source
: ingestion
: direct penetration of anatomical barriers
: bites of anthropod vectors
- infective does and exposure
Parasite pathogenicity: Attachment
- can be non-specific
- mechanical or biting mouthparts
- parasite adhesins
- distinguishes pathogenic from nonpathogenic strains
Parasite pathogenicity: replication
- protozoa replication can occur intracellularly or extracellularly in human host
- helminth replication is generally not observed
Parasite pathogenicity: Damage- cell & tissue
- toxic products (proteases and phospholipases)
- mechanical tissue damage (migration, blockage)
- immunopathological reactions (hypersensitivity)
- longevity
Parasite pathogenicity: Disruption, evasion and inactivation of host defense
- antigenic variation/ shift in antigenic expression
- intracellular expression
Laboratory Parasitology: Diagnosis
- Helminth diseases: peripheral eosinophilia recognized as useful indicator of parasitic disease
- rely on detailed travel, food intake, transfusion history
- Lab techniques
: isolate appropriate specimen
: macro- & microscopy: morphology
: serology
: detection of parasitic antigen
: PCR
Laboratory Parasitology: Importance of Life Cycles
- features of parasitic life cycles must be considered for proper diagnosis
: eggs vs larvae
: nocturnal
: life cycle stages may result in certain clinical manifestations in the host
