05. Trematodes Flashcards
What are trematodes commonly referred to as?
flukes
What is the taxonomy of D. caninum? (recall from last lecture)
Order Cyclophillydea
Family Dipylidiidae
Genus Dipylidium
Species caninum
What is the common name of D. caninum? (recall from last lecture)
Dog/cat tapeworm
All tapeworms are ____-parasites
endoparasites
are trematodes only found in the intestine?
NO - they can inhabit many organs
What organ system do Schistosoma spp. infect?
vasculature of the gastro-intestinal or genitourinary systems
What organ system do Fasciolopsis, Heterphyes heterophyes, and related organisms infect?
They are intestinal flukes, they infect the GI tract
What organ system do Clonorchis sinensis, Fasciola hepatica and Opisthorcis infect?
The liver
What organ system do Paragonimus westermany and related species infect?
They are lung flukes, they infect the lungs and other organs such as the CNS
Why is the life cycle of a digenetic trematode complex?
It involves at least 2 hosts
What kind of animal is the first intermediate host of the digenetic trematode?
A mollusc (usually a snail)
What kind of animal is the DH of the digenetic trematode?
A vertebrate
Do you always have a redia?
NO
Do you always have a sporocyst?
YES
What are characteristic of the adult digenetic trematode?
the two suckers
What are the names and functions of the two suckers in a digenetic trematode?
Oral sucker - for attachment and feeding (mostly feeding)
acetabulum (ventral sucker) - for attachment only, there is no internal opening
What type of muscle is found on the suckers?
smooth muscle - found in bands on the suckers for strong attachment
What kind of body wall do digenetic trematodes have?
tegument
what are the two layers of tegument
syntegument and cytotegument
Describe the syntegument (outer layer)
- it contains mitochondria, secretory bodies and occasional spines
- it is a chemical layer that lies on top of outer cell membrane
Describe the cytotegument (inner layer)
- consists of cell bodies beneath the tegument
- each cell contains a nucleus and organelles (such as the rER and golgi)
- separated from syntegument by layers of tegumental muscle
- connected to syntegument by cytoplasmic bridges
what are the functions of the cytotegument?
- involved in the production of mucus
What are the functions of the tegument? (3)
1- osmoregulation and excretion
2- synthesis and secretion of mucus (to protect against host enzymes)
3- Absorption of nutrients for trematode nutrition
What is the morphology of the adult trematode digestive tract?
- muscular scmooth muscle creates sucking action
- short esophagus leads to 2 long, blind-ending cecum
- no anus
- proteins are digested in the lumen of the intestine and absorbed through the intestinal epithelium
What is the parenchyma?
loosely arranged cells filling space between the organs
What is the role of the excretory system?
to remove excess water that has diffused into the worm
What is the role of flame cells?
- they are something that cestodes do not have, making the digenetic trematodes different in that respect
- they are cells (having a nucleus) that contain beating flagella that create a hydrostatic pressure, which draws pressure from the parenchyma into the collecting duct
- at the posterior end of the worm there is an excretory bladder
Describe the nervous system of the digenetic trematode
there is a ladder type system consisting of a ganglionic mass, lateral nerve trucs, and connecting commissures
Describe the sense organs of adult digenetic trematodes
they are at the cellular level within the tegument
Describe the sense organs of the larval stages of digenetic trematodes
- the sense organs are well-developped
- they seem to be able to differentiate between light and dark
- they have a much more elaborate nervous system because they need to be able to sense if someone is swimming in the water and to be able to swim to that area
Describe the sexual morphology of adult digenetic trematodes
- the reproductive system is elaborate and specialized
- almost all adult digenetic trematodes are hermaphroditic (except Schisto)
What are the three possible ways that trematodes reproduce?
1) Some worms contain both male and female sexual orgas and are capable of auto-fetilisation
2) Others contain both male and female organs but meet up with another worm for cross fertilization
3) Schistosomes are unique among the trematodes in that that have distinct male and female worms. They live together as a long-term life unit, with the larger male surrounding the thinner female worm
What is the sexual morphology of Schistosoma spp.
Sexually dimorphic/diecious
Describe the male reproductive system of digenetic trematodes
- There are 2 testes
- the sperm ducts consist of 2 vas efferentia which join to form a vas deferens
- the vas deferens leads to a cirrus sac (cirrus pouch)
slide 19
What is an important taxonomic character of the male reproductive system of a digenetic trematode?
The shape and position of the testes
What is an important taxonomic character of the female reproductive system of a digenetic trematode?
the shape and position of the ovary in relation to the testes
Describe the female reproductive system of the digenetic trematode
a single ovary produces eggs which pass along the oviduct to the ootype
Describe the constituents of the digenetic trematode egg
- well-developped egg shell enclosing the ovum
- one or more sperm cells
- and a number of vitelline cells
What is an opperculum?
a “lid” at one end of the egg
T/F the digenean egg is usually opperculate
True, except Schisto
What develops following fertilization?
an embryo of miracidium
What characters are used for identification of digenetic trematode eggs
Size, morphology and color
Which digenean species that infect humans have spines?
Schistosoma mansoni and Schistosoma heamatobium
What are the 3 species of Schistosoma that infect humans?
Schostosoma japonicum, Schistosoma mansoni and Schistosoma heamatobium
What is an example of a species where the egg is ingested before hatching?
Dorocoelium dendriticum (lancet fluke) - the eggs hatch inside and it penetrates the intestinal epithelium to invade the molluscan tissues
What is an example of a species where the egg hatches in water before ingestion?
Fasciola hepatica (liver fluke)
What are important factors for an external egg hatching?
- Light
- Temperature
- Change in osmotic pressure
What is released upon hatching of the egg?
The miracidium
What are the organs of locomotion of the miracidia of the digenetic trematode?
cilia
Is the miracidium usually free swimming?
YES
Who is the target of the miracidium?
the primary (possibly the only) IH of the parasite
Who is the IH of digenetic trematodes?
molluscs (snails usually)
What is the role of the germinal mass?
development of the parasite in the snail
What is ALWAYS the first development after the hatching of the miracidium?
the miracidium develops into the early sporocyst stage
What characterizes the development into the early sporocyst stage?
the loss of ciliated cells, the penetration glands and the apical gland
When does the development of the miracidium into early sporocyst stage usually occur?
at the site of penetration of the mollusc (1st IH)
what does the early sporocyst develop into and in which location?
it develops into the mother sporocyst
What occurs after the development of the mother sporocyst?
The germ cells in the mother sporocyst multiply and develop into the daughter sporocysts, which are essentially the same as their parent sporocysts
In what case would the redia not develop?
if the daughter sporocysts are formed
What is an example where the redia stage is absent?
Schistosomes, there are two generations of sporocysts in the snail host
What is the advantage of the asexual reproduction in the snail?
increases the potential of reproduction of the organsims. a single moracidium can give rise to hundreds of thousands of cercariae
What is the second larval form to develop in the molluscan host?
the redia
How are redia similar to sporocysts?
Redia are similar to sporocysts, containing germinal masses withing a fluid-filled cas, which may develop into either second generation daughter redia, or more commonly into the final larval stage within the mollusc, the cercaria
How are redia different from sporocysts?
Redia differ from sporocysts in that they are much more active and aggressive and possesses a mouth and a simple gut (a little more advanced)
What the order of the digestive tract in digenetic trematode larvae?
mouth –> large muscular pharynx –> opens into a simple intestine
What do many redia have behind the mouth?
a ridge-like collar
What is below the ridge-like collar?
the birth canal opening from which either cercariae or daughter redia emerge
What stage emerges from the mollusc in dingenetic trematode larvae?
in most cases, the cercarial stage - the infective form for the vertibrate host
What are the types of cercariae? (4)
- Gymnocephalus
- Trichocercous
- Furocercous
- Microcercus
Are cercaria released from the mollusc usually free swimming?
yes
What happens to the tail of the cercaria after they penetrate skin?
they shed the tail
Are the cercaria free swimming?
YES
In what case would the cercariae penetrate the DH directly?
Scistosoma
in what case will a mesocercaria develop?
If there are two or three IH and the cercaria penetrates the second IH to form the resting stage (mesocercaria)
in what case will a metacercaria develop?
If there are three IH and the cercaria penetrates the third IH, where the paracite encysts to form metacercaria
What are the infective stages?
metacercaria and cercaria themselves
What are the possible final IHs? (3)
- a fish
- an arthropod
- another mollusc
What parasite uses a fish as a final IH?
Opisthorchis sinensis
What parasite(s) use(s) an arthropod as a final IH?
Dicrocoelium dendriticum - uses an ant
Paragonimus westermani - a crustacean
