Parasitology Flashcards
In host parasite relationships, what is the difference between the terms definitive host and intermediate host?
- Definitive host: animal where parasite develops into adulthood &/ undergo sexual REPRO. phase
- Intermediate host: short-term host (parasite not grow till adult & NO repro. phase)
What is an ectoparasite? What is an endoparasite? Give examples.
- Ectoparasite: parasite that lives on/close to the surface of the host e.g. lice, scabies (burrow in epidermis)
- Endoparasite: parasite that lives (deep) inside the host e.g. tapeworm
List 5 ways that a parasite can harm a host?
- mechanical inquiry e.g. attach to mucosa
- Obstruction
- produce metabolic products = toxic to host
- competing w/ host for nutrients
- Host IR when parasite dies = inflammation
List 4 ways that a parasite may gain entry to the host?
- Oral (bc poor food hygiene)
- percutaneous (penetrate through soft skin
- Inhalation (of eggs)
- Sexual intercourse
~ Intraplacenta (applicable to bact.)
Define the three types of specificity required for a human parasite to become established in vivo.
- Ecological specficity: external environment allow for survival of infective form
- Ethological specificity: human behaviour in that environment allows parasitic stage to enter human tissues
- Physiological specificity: the potential host’s internal environment suitable for development of parasite
Give an example of a geographical factor that can affect the distribution of parasites?
- Climate
- Soil type
- Coprozoic organisms (digest poo e.g. earth worms)
- surface water
- vegetation
Which common protozoan parasite is responsible for causing diarrhoea, mucus secretion and flatulence
Giardia lamblia
What is the rostellum?
is the “beak” that hooks onto the host’s intestinal walls - using the hooks. Located at the apical of the scolex (head)
Some parasitic eggs (ova) look very similar. How could you decide which parasite they belong to in a clinical laboratory?
- Consider the size
- Use fine focus to detect other potential features like peritrichous flagella
Draw a lifecycle of Taenia sp.
- Cattle (T.saginata) & pigs (T.solium) eat eggs or gravid proglottids in contaminated vegetation
- Oncospheres hatch penetrate intestinal wall & circulate to muscle
- Cyst develop in muscle (infective stage)
- Humans eat raw/undercooked infected meat
- Taenia sp. develop in gut
- reproduce releasing eggs/proglottids in poo (diagnostic)
List the scientific group names for the three categories of worms/helminths (flukes, tapeworms and roundworms)?
- Platyhelminths (flatworms):
- Trematodes (flukes)
- Cestodes (tapeworms) - Nematodes (roundworms)
What is the common name for:
a) Enterobius vermicularis
b) Trichuris trichiura
c) Ascaris lumbricoides
d) Hookworms
e) Strongyloides stercoralis
a) E.vernicularis: Pin worm or thread worm
b) T.trichiura: whipworm
c) A.lumbricoides: round worm
d) Hookworms: New & Old world
e) Strongyloides stercoralis (no common name)
Draw a simple lifecycle diagram for Enterobius vermicularis.
- Female worms lays eggs on perineal folds (diagnostic stage)
- Embryonated eggs ingested/inhaled by human (usually scratching butt) (infective stage)
- larvae hatch in sml int. & grow to adulthood in colon
Draw a simple lifecycle diagram for Ascaris lumbricoides
- Human poo contains (un- and) fertilised eggs. Fertilised eggs become infected in soil (infective phase)
- human ingests fertilised eggs from soil-contaminated hands/food
- larvae hatch in sml GIT & Penetrate mucosa into blood -> lungs
- mature in lungs 10-14 days then ascend bronchial tree to be swallowed
- mature in sml int. (diagnostic)
- Adult female lays eggs 2-3 months after infection
In the lifecycle of Clonorchis sinensis, what are the names of each of the parasitic stages of development that occur after the egg hatches until ingestion?
- Embryonated eggs passed in poo (diagnostic)
- Eggs ingested by freshwater snail & develop: miracidia > Sporocysts > Rediae > Cercariae
- Cercariae swim freely in water & can penetrate skin or flesh of fish
- Metacercariae ingested when eat raw freshwater fish (infective)
a) What is the diagnostic form of Strongyloides stercoralis?
b) Why are eggs not usually seen in faeces?
a) Rhabditiform larvae in stool (180-380 ug long).
b) Eggs not seen in poo bc eggs secreted in intestinal mucosa and hatch
Which parasites in this lecture are capable of autoinfection?
- Strongyloides stercoralis
- Hymenolepis nana
- not need to exit into environment
How can you differentiate between T.saginata and T.solium in the clinical laboratory?
By examining the proglottids or scolex.
T.saginata: Tall & skinny uterine tubes in proglottids
T.solium: short & thick uterine tubes in proglottids
Describe what cysticercosis is and how this is different from the normal infection caused by the cestode responsible?
Cysticerosiss: Human ingest the embryonated egg -> oncospheres hatch & penetrate intestinal wall into circulation -> develop in any organ (e.g. brain)
Normal: oncopheres usually hatch in GIT of pig & circulate to muscles -> human ingest cysterci in pig muscle
Give an example of a socio-economic factor that can affect the distribution of parasites?
- Housing
- Coprophagic animals
- Urbanisation
- Economic activities
- Domestication of animals
- Migration, war, tourism
Draw a simple lifecycle diagram for Hookworms.
- Eggs in faeces (diagnostic)
- Rhabditoform larva hatches in soil & develops into filariform larvae after 5-10 days
- Filariform larvae penetrates skin (infective)
For Fasciola hepatica name the:
a) diagnostic form
b) infective form
c) if applicable, name the type of intermediate host
a) diagnostic: unembryonated eggs in poo
b) infective: metacercariae
c) intermediate host: (water) snail
For Clonorchis sinensis name the:
a) diagnostic form
b) infective form
c) if applicable, name the type of intermediate host
a) diagnostic: embryonated eggs in poo
b) infective: metacercariae in flesh/skin of fish
c) intermediate host: freshwater snail
For Schistosomiasis sp. name the:
a) diagnostic form
b) infective form
c) if applicable, name the type of intermediate host
a) diagnostic: eggs in urine
b) infective: cercariae (free-swimming)
c) intermediate host: freshwater snail
For Hymenolepis nana name the:
a) diagnostic form
b) infective form
c) if applicable, name the type of intermediate host
a) diagnostic: embryonated eggs in poo
b) infective: embryonated eggs in poo
c) intermediate host: can have = insects)
For Taenia sp. name the:
a) diagnostic form
b) infective form
c) if applicable, name the type of intermediate host
a) diagnostic: embryonated eggs in poo
b) infective: embryonated eggs in poo
c) intermediate host: pig (T.solium) & cattle (T.saginata)
For Echinococcus granulosus name the:
a) diagnostic form
b) infective form
c) if applicable, name the type of intermediate host
a) diagnostic: hyatid cysts in liver, lung
b) infective: embryonated eggs in poo
c) intermediate host: sheep, goats
* human accidental hosts)
For Trichuris trichuria name the:
a) diagnostic form
b) infective form
c) if applicable, name the type of intermediate host
a) diagnostic: unembryonated eggs in poo
b) infective: embryonated eggs
c) intermediate host: n/a
For Dracunculus medinensis name the:
a) diagnostic form
b) infective form
c) if applicable, name the type of intermediate host
a) diagnostic: L3 larvae in copepod in water
b) infective: embryonated eggs
c) intermediate host: copepod
For Giardia lamblia name the:
a) diagnostic form
b) infective form
c) if applicable, name the type of intermediate host
a) diagnostic: cysts & trophozoites in poo
b) infective: cysts in poo
c) intermediate host: n/a
