02. Helminths Flashcards
Parasitic helminths are always ____-parasites
Endoparasites
Why does harbouring a parasite affect the host?
Disrupts the nutrient uptake
Name mechanisms of survival that have evolved in parasitic helminths
immune evasion
immunological masking mechanisms
What are the ways that helminths injure their hosts?
- Mechanical means
- Chemical means
What is an example of a helminth that causes obstruction of the intestine?
- Ascaris lumbricoides
- Dog heartworm does a similar thing - blocks the heart
Name the categories of parasitic helminths
- Cestodes (Tapeworms)
- Trematodes (Flukes)
- Nematodes (Roundworms)
What is the shape of cestodes?
segmented and plane (flat)
Do cestodes have a body cavity?
NO
What is the body covering of a cestode?
Tegument (for absorption as well as classic functions)
Do cestodes have a digestive tube?
NO
Which parasitic helminths are hermaphrodites?
- Cestodes
- Trematodes (with the exception of Schisto, which are dioecious)
What category of parasitic helminth are Schistosomas?
Trematodes
What is the sexual morphology of Schistosomes?
Dioecious
What are the organs for attachment to the host in cestodes?
- Sucker (or bothridia)
- and some have a rostellum with hooks
What is the shape of trematodes?
Unsegmented and plane (flat)
Do trematodes have a body cavity?
NO
What is the body covering of a trematode?
Tegument
Do trematodes have a digestive tube?
Yes, but it is incomplete. it ends in the cecum (i.e. they have only an oral opening/not a complete gut)
What is the sexual morphology of trematodes?
Hermaphrotitic, except Schisto
What are the organs for attachment to the host in trematodes?
- Oral sucker
- Ventral sucker (acetalbulum)
What is the shape of nematodes?
Unsegmented, cylindrical (round)
Do nematodes have a body cavity?
YES
What is the body covering of a nematode?
Cuticle
Do nematodes have a digestive tube?
Yes, and it is complete - ends in anus.
What is the sexual morphology of nematodes?
Dioecious
What are the organs for attachment to the host in nematodes?
- Lips
- Teeth
- Filariform extrematies
Name some cestoda species
- Taena saginata
- Taena solium
- Hymenolepsis nana
- Hymenolepsis diminuta
- Echinococcus granulosis
- Diphyllobothrium
What is the site of infection for most cestodes?
Small intestine
Which cestode(s) is/are found in Argentina, Europe, Japan, Siberia, Great lakes area USA and Canada?
Diphyllobothrium
What is the phylum of class cestoda?
Platyhelminthes
What are the two subclasses of class cestoda?
- Subclass Cestodaria
- Sunclass Eucestoda
What is found in Subclass Eucestoda?
Tapeworms
What is the function of the suckers on cestodes?
Attachment, NOT for feeding
Each proglottid has a complete set of ______.
Male and female reproductive organs
What makes the life style of cestodes SIMPLE?
There are no asexual phases
What makes the life style of cestodes COMPLEX
At least one intermediate host is required as well as the definitive host
Name the various stages of the life cycle of cestodes
- Eggs
- Oncosphere
- Cysticercoid/cysticercus
- Coracidium (dont need to know)
- Procercoid (dont need to know)
- Plerocercoid (dont need to know)
- Adult
What types of animals can be the intermediate host of a parasitic helminth?
- Mammal
- Arthropod
- Fish
- Bird
- Reptile
What is the dwarf tapeworm?
Hymenolepis nana
What is the beef tapeworm? (intermediate is the cow)
Taenia saginata
What is the worm that has a pig intermediate?
Taenia solium
What is the fish tapeworm?
Diphyllobothrium latum
What is/are the intermediate(s) of the fish tapeworm? (Diphyllobothrium latum)
- First intermediate is a copepod
- Then it is a freshwater fish
What are the 3 distinct regions of tapeworms?
- Scolex
- Neck
- Strobila
What does the strobila consist of?
Proglottids
What are the 3 stages that proglottids are characterized in?
- Immature
- Mature
- Gravid
Do cestodes have a mouth?
NO
What are the two important orders of class cestoda?
- Order pseudophyllidea
- Order cyclophyllidea
Which order contains slit-like suckers or grooves on their scolex? what are they called?
- Pseudophyllidea
- Bothridia
Which order contains 4 suckers and sometimes hooks on their scolex?
Cyclophillydea
What can be used to identify tapeworms?
The scolex
What is the undifferentiated/unsegmented region between the scolex and the strobila of a cestode?
The neck
What is the function of the neck on a cestode?
Contains stem cells that are responsible for giving rise to new proglottids, the older ones move posteriorly to make way for the new ones
What is the strobila?
- The most posterior of the 3 distinct regions on a cestode
- It is a linear series of segments of proglottids
What are the immature proglottids?
- They are newly formed
- They do not yet contain sex organs
What are mature proglottids?
They contain both male and female sex organs
What are gravid proglottids?
- They develop after mating occurs
- They contain hundreds to thousands of embryonated eggs
What develops first, the male or female reproductive system?
Male
What are the structures of the male reproductive system?
- Many testes (3-100s, depending on species)
- Vasa efferentia
- Vas deferens (often highly coiled)
- Cirrus sac with cirrus
- Common genital pore
What are the structures of the female reproductive system?
- Ovaries
- Vitellaria
- Mehlis’s gland
- Uterus - contains eggs in branches
- Vagina
- Common genital pore
What happens to the female and male organs in gravid proglottids?
- The male organs dissapear
- Most of the female organs dissapear except for the egg-filled uterus
Which proglottids will mate?
Mature proglottids in proximity - can be from the same strobila of another if there are multiple worms in the infecton
How are the eggs transmitted? (two different ways that result in the same fecal-oral route of transmission)
Two possible ways
- The proglottid disintegrates and eggs are released in host feces
- The whole proglottid, containing the embryonated eggs, is released
What do the eggs contain? What is that called?
Hexacanth larva - called an oncosphere (life cycle stage)
What are the layers of the cestode egg from inside to out?
- Oncosphere (hexacanth larva)
- Inner envelope
- Ciliated embryophore
- Outer envelope
- Shell
What is the operculum and which genus has this?
- It is like a lid to release the larvae rather than the shells disintegrating
- Diphyllobothrium
Which genus does NOT have a shell on their eggs?
Taenia
Which genus has all the layers of the egg but no operculum?
Hymenolepsis
What is the tegument?
The external surface of a cestode
What is the function of a tegument on cestodes?
- protection
- locomotion
- sensory surface
- more notably; a layer to take up nutrients and through which secretions and excretions can pass
How does the tegument help the parasite survive in the host?
It is resistant to attack from digestive enzymes and immune responses
What is the glycocalyx?
a layer of carbohydrate-containing molecules covering the entire surface of the tegument
What are the purposes of the glyxocalyx?
- Protecting the parasite from host digestive enzymes
- Enhancing nutrient absorption
- Maintaining the parasite’s surface membrane
What is the purpose of the microvilli
They increase the surface area of the tapeworm ~ 20X
What are the two layers of the tegument?
- Syntegument
- Cytotegument
What composes the syntegument?
It is the outer, anucleate, synctial cytoplasmic layer containing mitochondria and secondary bodies
- has dense granules
- circular and longitudinal muscle
What composes the cytotegument?
Nucleated cell bodies lying beneath the tegumental muscles and connected to the syntegument
- Nucleus and mitochindria
What kind of compounds do the cestodes absorb?
- Low molecular weight compounds
- They do not produce digestive enzymes and they rely on the host to breakdown high molecular weight compounds into low MW
What are the two pairs of excretory canals?
- Ventrolateral
- Dorsolateral
What are osmoconformers
they absorb and reduce absorption of water depending on the tonicity of the medium - little ability to regulate their body volume on their own
What is the main nerve center of a cestode?
the scolex
Pork tapeworm
Taenia solium
Beef tapeworm
Taenia saginata
Fish tapeworm
Diphyllobothrium latum
Dwarf tapeworm
Hymenolepis nana
Rat tapeworm
Hymenolepis diminuta
Dog tapeworm
Diphylidium caninum
