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
how do we diagnose Alaria
eggs on fecal float
where is Nanophyetus salmincola located geographically
Pacific Northwest and Siberia
what are the intermediate and definitive hosts of Nanophyetus salminthoeca
IH: snail and then fish
DH: dogs, cats, mink
what is the morphology of Nanophyetus salmincola
a) adults
b) eggs
a) small, creamy-white
b) small, indistinct operculum
describe Nanophyetus salmincola life cycle
eggs passed in feces mature and release meracidia -> meracidia penetrate snails: sporocyst -> redia -> cercaria -> cercaria penetrate fish and encyst, producing metacercaria -> fish ingested by dogs and cats -> fluke released and moves to small intestine -> adults release eggs
what is the pathogenesis of Nanophyetus salmincola
none from the fluke itself, but Neorickettsia helminthoeca causes febrile illness with fever, vomiting, diarrhea, weight loss and lymphadenopathy
treat with tetracyclines
what is the other name for Paragonimus
lung flukes
What is the morphology of Paragonimus (lung fluke)
a) adults
b) eggs
a) ovoid, relatively large, in reddish-brown cysts in pairs, spiny cuticle
b) small, very distinct operculum (shoulders)
Describe Paragonimus life cycle
eggs laid in feces mature and hatch meracidia -> meracidia penetrate snails: sporocyst -> redia -> cercaria -> cercariae penetrate crayfish and encyst forming metacercariae -> dogs consume/lick/sniff the crayfish -> metacercariae excyst in the small intestine -> migrate to lung and associate in pairs forming fibrotic cysts -> eggs laid in cysts are shed into bronchioles, swept up respiratory tract and swallowed
what is the pathogenesis of paragonimus
fibrotic cyst causes bronchiolitis; atelectasiss; may have coughing, dyspnea, lethargy
how do we diagnose paragonimus
eggs on fecal float; clinical signs; access to water
can we treat paragonimus with medication
yes
is Fasciola hepatica common or uncommon in Canada and in what species?
uncommon; ruminants - usually imported
when is Fasciola hepatica usually diagnosed
post-mortem
what is the appearance of the eggs of Fasciola hepatica
indistinct operulum but otherwise all features
is Fasciola hepatica zoonotic?
yes
what is the life cycle of Fasciola hepatica
eggs mature in water and miracidia hatch -> miracidia penetrate snails: sporocyst -> redia -> cercaria -> cercaria encyst on aquatic vegetation forming metacercaria -> metacercaria ingested by ruminants or people -> adults in bile duct
what is the pathogenesis of Fasciola hepatica
within bile ducts they cause fibrosis; may progress to carcinoma in smokers
where in Canada do we frequently see Fascioloides magna (what animal population)
in wild cervids
when do we diagnose most Fascioloides magna
at post-mortem (mortality is evidence of infection)
what is the appearance of adult Fascioloides magna
leaf-like adults, large; within the liver with ducts leading to the bile ducts
what are the clinical signs of Fascioloides magna
usually NO clinical sign; if in a wild animal then a patent infection forms and eggs may be seen on a fecal float
NOTE: in domestic cattle no connection with the bile duct forms therefore no patent infection and no eggs on a fecal float
