Parasitology - Echinococcus & Hydatid disease (esp. liver) Flashcards
What type of worm is Echinococcus?
A/ Nematode (round worm)
B/ Trematode (flat worm, fluke)
C/ Cestode (tapeworm)
D/ None of the above
C. Tapeworm
What are the two main Echinococcus species we need to study, and why? What organ do they damage the most in the body and in what species?
Echinococcus granulosus & E. multicularis
E. granulosus especially is very important to study because its metacestode stage (develops inside intermediate hosts), hydatid cyst, can develop in humans.
The hydatid cysts develop in different organs, depending on the intermediat host.
In sheep: liver & lungs
Cattle: lungs
Horse: liver
Human: mostly liver, much less lungs and other sites.
In which species does Echinococcus granulosus develop into hydatid cysts (metacestode stage in intermediate hosts) in the LIVER?
Sheep
Horses
Humans
NOT CATTLE (lungs)
How does the morphology of the adult tapeworm, Echinococcus granulosus, differ in size, infection site & intermediate host to Moniezia spp, another tapeworm that infects sheep?
E. granulosus adults reside in the small intestine, with the scolex deeply buried in the intestinal crypts of its final canid hosts.
E. granulosus uses ruminants and horses as its intermeditae hosts, where it develops it hydatid cysts. The adults is very small, only 0.5 cm long with only 3-4 segments (a bit more like the chicken tapeworm, Davainea spp)
Monieza cluster around the ileo-caecal junction in the caecum. Its intermediate host is the pasture mite, which sheep eat while grazing. The adult can grow up to two meters in length!
How big is the Echinococcus granulosus oocyst compared with a strongyle egg?
It’s about half the size, at just 40 µm.
Echinococcus has low biotic potential, with the adults dropping off one gravid segment a week. They are identical to Taenia eggs.
What are the intermediate hosts that end up eating these eggs?
Sheep, Horses, People (and cattle, but we’re concerned mostly with animals for whom hydatid cysts cause liver problems).
What are the two strains of Echinococcus granulosus recognised in Britain?
Dog-sheep & Dog-horse strains
How do dogs get infected with E. granulosos from sheep?
The sheep eat the gravid segments or oocytes left in dog faeces in field & develop hydatid cysts in their livers (mestacestode stage).
Dogs ingest the cysts when they are fed infected offal or when they scavenge road kill, etc.
How can dogs be protected against Echinococcus granulosus infestation?
- Register all dogs
- Define local epidemiology and get base-line stats
- Regular dosing with PRAZIQUANTEL, starting at six-week intervals
- Educate owners in area about not letting their dogs eat dead sheep, etc.
- Regular testing of all dogs using antigen testing
- Don’t let dogs go near raw offal
- Legislation
What is the big deal with Echinococcus multicularis?
It’s not in the UK but it’s spreading all over Europe and it’s in N. America. China is also at high risk.
What is the intermediate host of E. multicularis and what are the final hosts?
Intermediate hosts are microtine rodents such as voles, which have a very short life span, so they develop alveolar hydatid cysts really quickly.
Final hosts are canids and cats to a lesser extent, and humans.
Echinococcus multilocalaris develops into an alveolar hydatid cyst as a metacestode. Where are these found and what is different about them?
This tapeworm produces many cysts (multilocularis) throughough the internal organs of the intermediate host (vole), mostly in liver.
They bud EXTERNALLY instead of internally so they’re very invasive.
What is the ONLY drug that can prevent tapeworm in canids and is used with the Pet Travel Scheme?
Praziquantel
