6.7 Intro to Helminths - Trematodes - Flukes Flashcards
what is the definition of helminth
worm; especially an intestinal worm, used by parasitologists
what is the breakdown of helminths
nematoda (roundworms)
platyhelminthes
- cestodes -> tapeworms
- trematodes -> flukes
annelida
acanthocephala
flukes include (2)
monogenea (anchor worms) and trematoda
Describe the monogenea (location and host; appearance)
often ectoparasites of fish, amphibians or reptiles
have a large posterior sucker
of the trematodes, what order do we care about and why
Digenea -> definitive hosts often mammals therefore important from a veterinary perspective
what are the Digenes of interest (7)
- fasciola hepatica
- fascioloides magnum
- schistosoma
- paragonimus
- alaria
- nanophyetus salmincola
- opisthorchis
what is the general morphology of the flukes
- dorsoventrally flattened
- two suckers (ventral and oral)
- esophagus with a blind ceca
- usually hermaphroditic
- paired testes
- ovary, uterus, vitellaria
- sex organs share a common genital pore
what are the immature stages of flukes aka digeans
miracidium -> sporocyst -> redia -> cercaria
where are most immature stages of flukes aka digeans located and what is the exception
usually within the intermediate host(s) - some may be free in the environment (cercaria) or attached to vegetation (metacercaria)
which immature fluke (digeans) stage is restricted and to what
the miracidium -> to its snail host
what are the 3 characteristics of a digeans aka fluke egg
- yellow-golden brown in colour
- has an operculum (cap)
- embryo fills the entire egg
Do digeans (flukes) have a direct or indirect lifecycle
indirect
what is ALWAYS the first intermediate host of flukes
snails/slugs
Digenetic flukes are normally highly (specific/non-specific) for their intermediate host and (specific/non-specific) for their definitive vertebrate host
Specific; non-specific (somewhat)
what is the consequence of the specificity of digenetic flukes for their intermediate hosts
geographic distribution follows that of the intermediate host, and for infection to occur you need all of the ecosystem together (intermediate and definitive hosts)
what is the general life cycle of digenetic flukes
miracidium leaves the egg via the operculum -> penetrates snail tissues -> asexual replication of sporocysts and redia gives rise to cercaria
what are the 3 choices a cercaria can make
1) penetrate the definitive host to form adults
2) encyst on vegetation or ON an intermediate host (ex. fish) forming a METACERCARIA
3) penetrate the intermediate host forming a MESOCERCARIA
Alaria:
- intermediate host(s)
- definitive host(s)
- paratenic host(s)
intermediate hosts: snails and tadpoles
definitive hosts: dogs and cats
paratenic hosts: numerous, including humans
what is the morphology of Alaria
a) adults
b) eggs
Adults:
- small, ~1cm
- body has an anterior flattened region and a cylindrical posterior region
Eggs:
- 1/10th mm
- segmented embryo
- has 3 typical features of all digenetic fluke eggs
what is the Alaria life cycle
immature eggs passed in feces -> miracidium hatches from mature eggs -> miracidium penetrates snails: sporocyst -> redia -> cercaria -> cercaria penetrate tadpoles and become mesocercariae -> tadpoles work their way up food chain and eventually get ingested by definitive host (dogs/cats) -> migration to lungs -> metacercariae -> metacercariae mature, work up resp tract and get swallowed -> adult flukes mature in small intestine -> eggs passed in feces
what stage of Alaria is a zoonotic threat to humans
mesocercariae in tadpoles
what is the pathogenesis of Alaria
not normally infective unless large infection; found in clusters in the small intestine
T/F Alaria replicates only in the definitive host or paratenic host
F; only replicates in the intermediate host
Why is Nanophyetus salmincola a problem
Not pathogenic on its own but acts as a vector for Neorickettsia helminthoeca
