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What are the 3 classes of helminths
Phylum Platyhelminthes
Phylum Nematoda
Phylum Acanthocephala
Phylum Platyhelminthes is also….
flat worms
Phylum Nematoda is also…
Round worms
Phylum acanthocephala is also…
Thorny-headed worms
Which phylum is the most common?
Nematoda (roundworms)
What classes fall under Platyhelminthes (flatworms)?
Class Trematoda (flukes)
Class Cestoda (tapeworms)
Why do worms rule?
-Complex life cycles
-May use multiple hosts
-extensive tissue migrations
-co-evolved with hosts
-highly complex and large genomes
Host-parasite relationship
-usually do not directly cause mortality
-infections usually chronic and may be disabling
-goal of worm is to reproduce
Helminths can do what to their advantage
Can modulate the host immune system
-few anti-helminth vaccines have been developed
What are the 3 ways that helminths can invade the host?
Ingestion of an infective stage by the host
Direct penetration through skin
Penetration through a skin wound by an insect vector
What is the most common method for helminth invasion into host?
Ingestion (licking ground most common)
What is an example of a helminth that directly penetrates through the skin?
Hookworms
Nematodes larval stages and infectious stage
L1—> L2—>L3 (infectious stage) —>L4—>L5—>adult
Trematodes larval stages and infectious stage
miracidium —> rédia —> cercaria —> metacercaria (infectious stage)
Primitive cestodes larval stages and infectious stage
Coracidium —> procercoid —> plerocercoid (infectious stage)
True cestodes larval stages and infectious stage
Onchophere —> hexacanth —> metacestode
Cysticercus, strobiolocercus, coenurus (infectious stages)
Definitive host
**most important
Where the parasite matures and reproduces
Intermediate host
Where immature stages develop in the case with parasites with indirect lifecycles
**essential for life cycle
Transport host
Takes up immature form but does not retain it
No development
**Not essential for completion of life cycle
Accidental host/dead end host
Immature stages are retained in host tissue but no development
**Not essential for completion of life cycle
What is the infectious stage of most nematodes?
L3
Pre-patent period of nematodes
The time taken in definitive host from infection to presence of reproducing adults (L3—>adults)
Nematode locations in the host
GI tract, Respiratory tract, Cardiovascular system, skin
Physiological Hypobiotic/arrested state
Larvae that temporarily stopped developing, but can resume development later
When are larvae reactivated after hypobiosis?
~3 weeks prior to parturition and migrate to infect fetus
Seasonal arrested development
Larvae ingested in autumn, over winter in gastric glands of abomasum, larvae development resumes in the spring
Trematodes are dorsoventrally flattened worms. The majority reproduce asexually. What life cycle do they have?
Indirect
Intermediate host for trematodes is always a….
mollusk (usually a snail)
Cestodes consist of
scolex, neck, strobila
What is a proglottid?
segment
What is the function of the scolex?
Anchor
Suckers function in cestodes
Attach to mucosa with hooks
What is strobila in cestodes?
chains of proglottid
Where do sexual organs of cestodes reside?
proglottid
What are the 2 groups of cestodes?
Cyclophyllidean “true” (most common)
Pseudophyllidean “primitive”
Appearance of nematodes
worm-like
cross section of nematodes
cylindrical
body cavity of nematodes
fluid-filled
gut of nematodes
true gut
life cycle of nematodes
direct and indirect
reproduction of nematodes
dioecious
Appearance of trematodes
leaf-like
cross section of trematodes
flattened
body cavity of trematodes
absent
gut of trematodes
Blind sac (one hole to eat and poop)
life cycle of trematodes
indirect
reproduction of trematodes
monoecious
appearance of cestodes
tape-like
Cross section of cestodes
flattened
body cavity of cestodes
absent
Gut of cestodes
absent
life cycle of cestodes
indirect
reproduction of cestodes
monoecious
