Parasitology - Nematodes Flashcards
Name the 5 main routes of infection in which a helminth can enter and its life cycle can begin or continue?
- ingestion of infective stage
- ingestion of paratenic/intermediate host
- maternal
- skin penetration
- arthropod-borne
Are helminths macro or microparasites?
macroparasites
Helminths - complex or simple? multicellular or unicellular?
complex multicellular
What are the two reproductive products of helminths?
eggs (oviparous) or larvae (ovoviviparous)
Helminths are often _____ specific in its ______ host
host
definitive
What is the common transmission of helminths?
fecal-oral or maybe more appropriately environmental-oral
What are the two main subdivisions of Helminths?
Nematoda and Platyhelminthes
What are the two divisions of playhelminthes?
cestoda and trematoda
What is the morphology of nematoda?
thread, non-segmented, cylindrical, generally tapered at both ends
Which worm is considered to be “most successful”?
nematodes!
What is the general size of nematodes?
micrometers to meters
What do nematodes possess on their body surface? What does this allow for?
cuticle - restriction of growth
Explain the structure of the nematode’s cuticle
flexible similar to arthopod’s exoskeleton
Is the nematode’s cuticle metabolically active?
negative
What can a nematode’s cuticle form?
spines, ridges, secondary sexual structures
What is the nematode’s body cavity filled with? What is suspended in this cavity?
fluid
intestines and repro systems are suspended
What provides the nematode with movement?
body wall has a muscle layer
What neurotransmitters do nematodes possess?
acteylocholine and gaba
Explain the overall digestive system of a nematode
food depends on species and location in host
oral opening: buccal capsule
esophagus (pharynx)
intestine
Explain the overall repro system of nematodes
dimorphism
females usually larger and produce eggs or larvae
males have spicules for mating
Explain the overall development of nematodes
4 molts with each stage between molts referred to as L1, L2, L3, L4
Which nematode molt stage is typically considered to be infective?
L3 (L3 rule)
What shape are Strongylida?
round or circular
Why are Strongylida are considered bursate nematodes
bursa used in reproduction which holds female
Which order of nematodes is considered to be the most important species in the GI tract?
strongylida
Explain 4 pathogenic mechanisms of strongylida
damage from tissue
blood or tissue feeding
inflammation/immune response
anorexia
What is the life cycle of strongylida?
direct
What type of eggs do strongylida produce?
strongylid eggs
Oval, thin shelled, morula containing eggs are called?
strongylid eggs
What diagnostic technique is used when diagnosing strongylida?
fecal flotation
Explain the general strongylid life cycle
-Eggs voided in feces
-L1 hatch and develop to L3 (with 2 molts)
-L3 retains cuticle of L2 as protective sheath
-L3 ingested by host in infective stage
-Larvae travel to predilection site and develop to adults
What do L3 have to do to survive?
move into environment
The cuticle retained in L3 from L2 is retained as protection but ______ eat. When metabolic reserves are exhausted they ____
cannot
die
In general eggs and larvae dont like what 3 things?
temp extremes
freezing-thawing cycles
desiccation
What are the 4 tropisms associated with Strongylida
Hydro +
Thermo +
Geo -
Photo +
Where do strongylida spend a period of larval development before becoming adults?
gut wall before going into lumen as adult
Explain what hypobiosis is in strongylida
Larva become dormant in host tissue site and wait for optimal condition to develop
Which larval stages does hypobiosis occur in?
L3 or L4
In hypobiosis, can parasites be detected?
nope
What are 2 possible stimuli for arrested development?
environmental
host immunity
What is the purpose of hypobiosis?
mechanism for optimizing chances of survival for next generation by synchronizing parasite life cycle with external events
Explain immunity pertaining to strongylida
immunity develops gradually with active infection being required to be fully immunity stimulated
What is premunition?
active infection being required to keep immunity fully stimulated
What are 3 ways in which immunological compromise can shift balance in favor of a parasite and allow numbers to increase?
- parturition - periparturient egg rise
- malnutrition
- concurrent disease
When does clinical disease develop?
when large numbers are present
Which strongylida?most important ruminant helminths
slender
<10cm
GI parasites and one lungworm
trichostrongyloidea
What is the life cycle of trichostrongyloidea?
typically strongyle
What are the 3 trichostrongylye abomasal localized parasites?
haemonchus contortus/placei
ostertagia/teladorsagia
trichostrongylus axei
What are the 3 trichostrongyle small/large intestine localized parasites?
trichostrongylus spp.
cooperia spp.
nematodirus spp
The superfamily trichostrongyloidea have several genera that are in ruminant GI tract. All together what condition can they cause? What parasite is an exception to this?
parasite gastroenteritis
haemonchus
What symptoms does PGE cause?
diarrhea
weight loss
What do all grazing ruminants have in their GI tract?
a worm community
What are the most important helminths in cattle?
ostertagia - brown stomach worms
What is the most important helminths in small ruminants?
haemonchus contortus - barber’s pole worm
Explain the life cycle of ostertagia
after ingestion (in abomasal) in L3 stage, larvae then enter gastric gland where they will molt to L4 - they are able to enter hypobiosis here and can remain for months until conditions are ideal. The larvae will then emerge into the abomasal lumen where it will molt to L5 and become an adult
What is the most pathogenic change in the ostertagia life cycle?
L4 emerging into abomasal mucosa
Explain the impact of larvae on gastric glands in ostertagia
nodules due to cell differentiation and hyperplasia with a reduction in acidity in abomasal fluid from a failure to activate pepsinogen to pepsin
What is the clinical importance of ostertagia in adults vs young or immunocompromised animals?
adult and immune cattle have little/no effect - subclinical
young and immunocompromised animals get diarrhea, weight loss, hypoproteinemia - bottle jaw, death quickly
What is haemonchus contortus?
abomasal parasite of small ruminants
Why is haemonchus contortus more pathogenic than most of the other trichostrongyles?
blood feeding
Which parasite have the adult stage as the most pathogenic - haemonchus or ostertagia?
haemonchus
What is the clinical importance of haemonchus?
if amount of parasites is low, host can compensate blood loss and subclinical infection will occur but if there is a decreased host response or heavier infection with too much blood loss for the body to compensate for, it will result anemia, anorexia, bottle jaw - hypoproteinemia, weight loss, and death
Explain the difference between type 1 disease vs type 2 disease and its relation to haemonchus and ostertagia
type 1
- caused by larvae that have developed without interruption
- represent accumulation of adult worms during grazing season
- usually occurs late-summer or autumn in pastured young animals
Type 2
- happens after larvae that have been arrested resume their life cycle
- synchronous emergence of arrested larvae
- occurs in late-winter or spring
- more common in ostertagia
Any sheep or goat with anemia in the grazing season likely will be diagnosed with
haemonchus
