PARA 410 Lecture Notes - Lecture 5: Digenea, Dipylidium Caninum, Fasciolopsis
12 Jun 2018
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Parasitology – lecture 05 (January 16th, 2018)
Review
- What are the two main characteristics of the two cestodes (not pertaining to the life cycle) that are specific for
Hymenolepsis spp.
o They are larger than they are long
o Mature proglottids contain a small number of testes
o Gravid proglottids disintegrate in the host and release eggs
- What is special about the life cycle of Hymenolepis nana
o They have insects as their intermediate hosts – they have only 1 host?
- The cestode Diphylidium caninum can be distinguished from the other cestodes through which three traits
o Double pore dog tapeworm
o The uterus breaks down to dots which are the egg capsules
- The order Cyclophyllidea and Pseudophillidea differ in numerous aspects; name at least 3
o They have two bothria, not suckers (slit-like grooves)
o They need at least three hosts
o The male and female genital pores are separate
- Which drug us used specifically to treat cestode infections
o Niclosamide
Phylum Platyhelminthes: Trematodes
Slide 1
❖ Class Cestoda - tapeworms
❖ Class Trematoda – digenetic flukes
❖ Class Monogenea – monogenetic flukes
❖ Class Turbellaria – planarians
Trematodes are commonly referred to as flukes
Order Cyclophillydea
- Family Dipylidiidae
o Dipylidium caninum – dog/cat tapeworm
Slide 2 – Digenetic trematodes
- All trematodes are obligate endoparasites in all classes of vertebrates
o Inhabit many vertebrate organs (not limited to the intestine)
o Many species infect humans and domestic animals and are of medical and veterinary importance
Slide 3 – Digenetic trematodes
- Trematodes infect the blood vessels, gastro-inestinal tract, lungs, or liver. They are often categorized
according to the organ system they invade
o Schistosoma spp. (blood flukes) infect the vasculature of the gastro-intestinal or genitourinary systems
o Fasciolopsis, Heterophyes heterophyes, and related organisms (intestinal flukes) infect the lumen of
the GI tract
o Clonorchis sinensis, Fasciola hepatica, and Opisthorcis spp. (liver flukes) infect the liver
o Paragonimus westermani and related spp. (lung flukes) infect the lungs and sometimes other organs as
well as the CNS
find more resources at oneclass.com
find more resources at oneclass.com
Slide 4 – Digenetic trematodes – Life cycle
- Life cycles are complex involving at least 2 hosts (usually 3 or more)
- The term “digenea” means 2 beginnings, representing the 2 hosts
o First intermediate host is a mollusc (usually a snail)
o Definitive host is a vertebrate
o Almost all species life cycles have a third host between the snail and vertebrate – the second
intermediate host
- Many larval stages occur in the intermediate host(s)
- Adult trematodes are found in the definitive host
Slide 5
- almost always free swimming with cilia
- adult parasites in the water, in the water there will be the release of eggs
- from the eggs you have the hatching of the miracidium (almost always free swimming from with cilia)
- almost always the miracidium will then penetrate the first intermediate host → the snail
o sometimes the snail can take-up the eggs but almost always it will be the miracidia
- the miracidia develops into a sporocyst
o this sporocyst can become a mother → daughter sporocyst → cerciaria
o or it can become a ridia → cercaria
o or it can become a mother ridia → daughter ridia → cercaria
▪ this is all happening within the snail
- the sporocyst or ridia will develop onto the cercaria, the cercaria will then leave the snail
- they again will be free swimming in the water (almost always)
- they will swim until they contact a secondary intermediate host or a DH
o some cercaria like Shisto will directly penetrate the DH (no IH)
- all the other ones will pass through a second IH, which is a vertebrate or animal, and that will be the
metacercaria → eaten/taken-up by the DH
o if you have a cercaria and they go onto vegetation, that’s also going to be metacercaria, they form a
cyst on the vegetation of the second IH, and then that vertebrate is eaten by the DH (at the same time
ingesting the parasite)
find more resources at oneclass.com
find more resources at oneclass.com
▪ cercaria → metacercaria → adult
o if you have a third intermediate host, the one in between is the mesocercaria (sometime you have an
animal/vertebrate that is eaten by a next animal/vertebrate, and then that is eaten by the DH
o so you will have:
▪ cercaria → mesocercaria → metacercaria → adult worm
- NB: anything before the DH is always called the metacercaria, mesocercaria is not always present (only in
more complex life cycles)
Slide 6
- You don’t always have redia, but you always have a sporocyst
- You don’t always have mesocercaria or metacercaria, because it depends at what stage you infect the
definitive host
Slide 7
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
What are the two main characteristics of the two cestodes (not pertaining to the life cycle) that are specific for. Hymenolepsis spp: they are larger than they are long, mature proglottids contain a small number of testes, gravid proglottids disintegrate in the host and release eggs. The cestode diphylidium caninum can be distinguished from the other cestodes through which three traits: double pore dog tapeworm, the uterus breaks down to dots which are the egg capsules. The order cyclophyllidea and pseudophillidea differ in numerous aspects; name at least 3: they have two bothria, not suckers (slit-like grooves, they need at least three hosts, the male and female genital pores are separate. Which drug us used specifically to treat cestode infections: niclosamide. Family dipylidiidae: dipylidium caninum dog/cat tapeworm. All trematodes are obligate endoparasites in all classes of vertebrates. Inhabit many vertebrate organs (not limited to the intestine: many species infect humans and domestic animals and are of medical and veterinary importance.
