Cestodes Flashcards
Platyhelmenthes
Phylum containing flat worms
Cestodes
Tapeworms
Structure
Segmented body
Hermaphrodite (only need a single worm for infection)
No alimentary canal
Tegument is highly absorptive
Body plan
Scolex with suckers, rostellum and hooks (armed) organs of attachment
Proglottids (strobila)- chain of segments
Mature segment
Contains organs of reproduction
Gravid Segment
Contains eggs only
Taenia egg
Radially striated shell with hexacanth (6 hooked) embryo/onchosphere
Life cycle
Indirect
Final host has adult worm (usually in SI) and passes out eggs
Intermediate host ingests eggs, they hatch and the larval stage encysts
Final host eats the cyst (w/ head of future worm)
Head latches on to SI wall and starts to bud segments
Stages in intermediate host
Metacestode/larval form
Cysticercus, coenorus, cysticercoid, and hydatid are stages usually in tissues
Family Taeniidae
Final host- man/cat/dog and usually in SI
IMH- mammals and larval stages encyst
Scolex is armed (except for saginata)
Adults are relatively non-pathogenic
Taenia saginata
Beef tapeworm
Final host is man with an IMH of cow
Unarmed and can be 5-15 meters long
causes cysticercus bovis (small fluid filled cyst containing a single scolex)
Taenia saginata epidemiology
In resource poor settings- low sanitation, eggs are long lived, so theres a high level of infection in cattle (30-60%), and inadequate cooking of meat bc of expense of fuel
In Europe/Oz- Present in low instance of cattle (<1%), potential role of birds spreading infection (bc birds can eat eggs and they pass right through, so spread eggs), eggs are resistant, all of which can lead to cysticercosis storms esp with use of human sludge as fertilizer
Teania saginata diagnosis
At meat inspection
Look for cysts, but want to conserve the value of the carcass so look for them in masseter, heart, tongue, intercostals, and diaphragm
Taenia saginata control
Meat inspection- if find greater than 25 cysts meat is condemned, <25 found you can chill at -10oC for 10 days (value of carcass is lowered) but if those are distributed throughout the body its condemned
Cook meat at a min of 57oC
Restrict use of human sludge to cultivate fields or cattle are not allowed to graze there for at least 2 years
Practice good hygiene
Taenia solium
Final host- man with IMH of pig or man
Has a life cycle similar to saginata, but cystic form is cysticercus cellulosae
Eggs are infective to man and can get by accidental ingestion of eggs, auto-infection via reverse peristalsis (eggs go back up into stomach where they’re activated and hatch
Taenia solium pathology
Adult doesn’t really cause a problem, but the cysticerci are serious bc can happen in CNS or eye (large problem in Latin America where 10% of humans and 40% of pigs are sero positive in endemic areas of SA)
Taenia solium epidemiology
Close association with man/pig
Unrestricted access of pigs to human waste
Poor meat inspection
Taenia solium control
Mass treatment to kill adult worms in human (abendazole or praziquantel)
Detection and treatment of carriers
Health education
Mass treatment of pigs with oxfendazole (kills cysts)
Meat inspection
Pig corralling
Vaccinate pigs
There are also cultural, cost, and sustainability issues with this too
Vaccine efficacy affected by recombinant proteins from egg, but there is a prototype vaccine for it
Taenia multiceps
Final host- dog with IMH of sheep and cyst stage is Coenorus cerebralis (causes brain problems)
Can also cause gid, where gate of the sheep is affected
Adult ~100 cm long
Not uncommon to see in UK bc of dog/sheep interaction
Taenia hydatigena
Final host of dog and IMH of sheep with cystic stage of cysticercus tenulcolls
Adult~ 500 cm long
Common in abattoir and is a persistent cause of condemnation of livers
Taenia ovis
Final host- dog and IMH sheep and cystic stage is cysticerus ovis (sheep measles)
Adult is ~200cm and is relatively common
High economic losses even though other parasites are more common
1st recombinant vaccine against helminth parasite was for this
Taenia ovis vaccine
Has progressed through all trials, and registered for use in NZ but never marketed
Important prototype for vaccines against T. sollum, T. saginata, and E. granulosus
Taenia taeniaeformis
Final host is cat and IMH is mouse and rat causing cysticercus fasciolaris
Adult ~60 cm long
Dipylidium caninum
Final host is dog, cat or man with IMH of flea/louse with a single hard cysticercoid in haemocoel
PPP ~3 weeks and adults are ~50 cm long
Only larvae of flea is affected bc adult mouthparts cant ingest the eggs, but all stages of lice can be infected.
Has active motile rice shaped segments with a double genital pore and egg packet both of which are diagnostic
Flea species that can transmit D. caninum
Ctenocephalides canis
C. felis
Pulex irritans
Larvae only
Lice that can transmit D. caninum
Tricodectes canis
All stages of life cycle
Important facts about tapeworm
Cestodes dont have L1, L2, ect
Always have a final and IMH (usually encysted)
Most of the pathology is in the IMH
T. solium is pathogenic in humans
T. ovis is a major cause of economic loss
Echinococcus granulosus granulosus
Final host- dog and wild canids (SI)
IMH- ruminants, pig, man
Zoonotic
Echinococcus granulosus equinus
Final host- dog, red fox
IMH- horse/donkey
Not zoonotic
Echinococcus body plan
Small (~6mm)
Scolex plus 3-4 segments (shed about 1/week)
Egg similar to taenia with radial striations and 6 hooks
E. g. sp pathology
Pathology associated with cystic stage (hydated cyst )
Horses and cattle (sterile in cow, no head), cysts tend to be in the liver
Sheep, 70% in lung and 25% in liver
Hydatid cyst has a cyst wall, and germinal epithelium where protoscoleces bud from creating hydatid sand with heads of future tapeworms
E. g. sp diagnosis
In IMH usually in abattoir
Final host- fecal egg count, Copro- antigen test, or copro-PCR
E. g. g. pathogenesis
Mostly well tolerated in IMH unless cyst is in a weird spot. In man, it is always a problem
Not pathogenic in dog final host
E.g.g.
IMH depends on local animal populations, in UK sheep is most important, but could be camel or reindeer
Man as accidental IMH is most common in sheep farming areas and requires a close man-dog relationship. May become infected via oncospheres from water, food, or coat of dog
Control of hydatid disease
Break the cycle with regular deworming of dogs with prazyquantel, proper disposal of infected carcasses, deny access of dogs to abattoirs, and good hygiene
E.g.g. in Oz
Introduced with sheep, spread from domestic animals into dingoes as final host and wild marsupials as IMH, so slyvatic cycle was established
Cycle re-introduced to domestic dogs in some areas by hunters allowing dogs to feed on offal from wildlife
Control via praziquantel, dried dog food, education, and better diagnosis via ELISA and copro-ag
E.g.g in Wales
There was a voluntary hydatid control program and ovine hydatidosis rates decreased, once treatment stopped and resurveyed the numbers of positive sheep increased bc it wasn’t entirely eliminated to start with
Risk factors for e.g.g.
Allowing dogs to roam freely with no anthelmintic treatment, fed raw offal, improper disposal of slaughter offal, lack of knowledge, and age factor (<6yrs, increased positive cases)
Echinococcus multilocularis
Final host- dog, cat, wild canids
IMH- rodent and man
Very resistant eggs (can survive in -50oc)
Prevalent in Europe and important zoonosis
Under pet passport, dogs and cats must get praziquantel 24-48 hrs before coming back into UK
No positive foxes in UK yet
Echinococcus multilocularis in humans
Causes alveoplar echinococcosis and is potentially fatal
If untreated, there’s a long asymtomatic period (5-15 years) followed by clinical signs
Treat with liver transplant, section, or albendazole (shrinks cyst)
Albendazole plus surgery increases 10 year survival rate significantly
Anoplocephala perfoliata
Final host- Horse
IMH-orbatid forage mites
Prevalence of 14-81% with a high prevalence in temperate climates
Cause ulceration at site of attachment and is a risk factor for ileo-caecal colic (live in LI and SI)
Anoplocephala perfoliata diagnosis
Fecal egg count (low sensitivity but high selectivity bc of weird egg with pyriform apparatus), ELISA, and copro- ag PCR
