Tapeworms Flashcards
Tapeworms come from which group of parasites?
Cestodes
Describe the steps in the general lifecycle of tapeworms
- Adults in small intestine (they have no gut so rely on host completely)
- Proglottids break off and eggs/proglottids shed in faeces
- Eggs immediately infective
- Eggs eaten by intermediate host
- Metacestode develops in intermediate host
- Metacestode eaten by definitive host where the adult tapeworm develops in the SI
Name the 4 metacestode types in the intermediate host
- Cysticercus
- Coenurus
- Cysticercoid
- Hydatid
What is a cysticercus?
Single evaginated protoscolex
What is a coenurus?
Complex, several protoscolices, which can all potentially develop into an adult worm
What is a cysticercoid?
Microscopic, single protoscolex, found in invertebrate intermediate host
What is a hydatid?
Highly complex, numerous protoscolices, potential for metastasis to set up another hydatid cyst
Name the 5 species of Taenia that dogs are the definitive host of
- Taenia ovis
- Taenia hydatigena
- Taenia multiceps
- Taenia pisiformis
- Taenia serialis
Dogs are also the definitive host of which 3 other tapeworm spp?
- Echinococcus granulosus
- Echinococcus multilocularis
- Dipylidium caninum
Cats are the definitive host of which cestode?
Taenia taeniformis
Where are adult Taenia found?
Small intestine
Describe the characteristic Taenia eggs
Thick embryophore, hexacanth embryo, ~40μm in diameter (these eggs are also the same as Echinococcus and can’t be differentiated)
Describe the morphology of Taenia
- Large 30cm-5m
- +/- armed rostellum
- Hooks and suckers
How long is the PPP of Taenia?
4-10 weeks (spp. dependent)
Sheep are the intermediate host of which Taenia spp?
Taenia ovis
Taenia multiceps
Taenia hydatigena
Rabbits are the intermediate host of which Taenia spp?
Taenia pisiformis
Taenia serialis
Describe the features of a Taenia ovis infection
- Cysticercus in muscles
- ‘Sheep measles’
- Adult tapeworm is 1.2-1.5m long
Describe the features of a Taenia hydatigena infection
- Cysticercus in peritoneum
- Thin necked bladder worm
- ‘Grape’ appearance
- Adult = 1m long
Describe the features of a Taenia multiceps infection
- Coenurus in brain
- Gid cyst causes neurological disease
- Space occupying CNS lesion
- Circling, head pressing and tilting
- Adult = 1.2m long
Describe the features of a Taenia pisiformis infection
Cysticercus in peritoneum
Adults = 2m long
Describe the features of a Taenia serialis infection
- Coenurus in connective and sub-cutaneous tissue
- Adult = 5m long
What is the intermediate host of Taenia taeniformis in cats?
Mouse
Describe the features of a Taenia taeniformis infection
- Cysticercus in liver
- Adult = 60cm, bell shaped proglottids
- PPP = 4 weeks
How are Taenia spp diagnosed?
- Rarely associated with clinical signs: anal pruritus
- Faecal sample – eggs or proglottids (10g, sampling on 3 consecutive days)
How are Taenia spp treated and controlled?
- Praziquantel treatment to remove adult tapeworm (treatment interval dictated by PPP)
- Break the life cycle through controlling access to intermediate host/metacestode stage
What are the two intermediate hosts of Dipylidium caninum?
Ctenocephalides felis - flea
Trichodectes canis - canine chewing louse
Describe the morphology of Dipylidium caninum
- 50cm long
- Scolex: 4 unarmed suckers, protrusible rostellum bearing 4-7 rows of small hooks
- Many segments, the gravid ones are barrel shaped (rice grains)
- Two genital pores on each proglottid
- Eggs packaged into capsules, each containing 10-15 eggs
Describe the life cycle of Dipylidium caninum
- Adult tapeworm in SI of cat/dog, PPP = 3-4 weeks
- Actively motile proglottids are passed in faeces. Disintegrate and eggs released.
- Eggs eaten by flea larvae e.g Ctenocephalides felis
- Flea larva on floors, carpets, nooks etc
- Oncospheres hatch and develop into cysticercoids in body cavity of adult flea
- Infected adult flea is eaten as the dog grooms
How is Dipylidium caninum treated?
Praziquantel
Flea Control!
What spp are the definitive and intermediate hosts of Echinococcus granulosus?
Definitive host: dog
Intermediate hosts: sheep & cattle
What is the definitive host of Echinococcus multilocularis?
Fox
Echinococcus cause which disease type?
Hydatid disease
Describe the hydatid disease of Echinococcus granulosus
- Cystic/hydatid echinococcosis
- Outer bladder wall with daughter cysts within
- Lots of protoscolices within endogenous cysts
Describe the hydatid disease of Echinococcus multilocularis
- Alveolar echinococcosis
- Break off into smaller cysts
Describe the morphology of adult Echinococcus
- Very small – 5mm
- Only have three proglottids + head
- Final proglottid is largest and gravid, shed in faeces
- Normally non-pathogenic in the dog
Describe the morphology of Echinococcus eggs
- 40 μm
- Thick embryophore (outer wall)
- Indistinguishable from Taenia eggs
Describe the life cycle of Echinococcus
- Metacestode with a hydatid cyst is ingested from the intermediate host
- The protoscolices from the cyst emerge and develop into adult worms within the gut
- They then produce all of the eggs within the final proglottid which are released into the environment where they infect the intermediate most
What is the PPP of Echinococcus granulosus?
6 weeks
What is the PPP of Echinococcus multilocularis
4-5 weeks
Which Echinococcus spp is not found in the UK?
Echinococcus multilocularis
Which spp are the definitive and intermediate hosts of Echinococcus multilocularis?
Definitive host = fox and dog
Intermediate host = small mammals/rodents
How are Echinococcus spp diagnosed?
- Rare to see clinical signs except anal pruritis
- Faecal sample – eggs or proglottids: 10g, sampling on 3 consecutive days – as egg release is slower and delayed
How are Echinococcus spp treated and controlled?
- Praziquantel treatment to remove adult tapeworm (treatment interval dictated by PPP)
- Break the life cycle through controlling access to intermediate host/metacestode stage
- Same as hookworms
How do human cases of Echinococcosis (E. granulosus) occur?
Infection by ingesting eggs from dogs in contaminated soil, water, food
Describe the pathogenesis of human Echinococcosis (E. granulosus)
- Space occupying cyst (hydatid metacestode stage)
- Liver, lungs, bone marrow, brain
- Slow growing
- Asymptomatic incubation period – several years
What are the clinical signs of human Echinococcosis (E. granulosus)?
- Clinical signs associated with location of the cyst - hepatic and pulmonary symptoms common.
- Jaundice, cholangitis, abdominal pain
- Pleurisy (pleural inflammation around the lungs)
- Rupture of the cyst – fever, eosinophilia and anaphylactic reaction
Describe the pathogenesis of human Echinococcosis (E.multilocularis)
Very serious pathogen in humans
- Large, slow growing cysts - asymptomatic incubation period of 5–15 years
- Tumour-like lesions in the liver
- Metastasize and spread to lungs and brain
- Invade and destroy tissues
What are the clinical signs of human Echinococcosis (E.multilocularis)
Pain, Weight loss, Malaise, Liver failure
How is human Echinococcosis diagnosed?
- Ultrasonography imaging and CT/MRI scans
* Serology
How is human cystic Echinococcosis treated?
Percutaneous treatment of the hydatid cysts with the PAIR (Puncture, Aspiration, Injection, Re-aspiration) technique, drug treatment, surgery
How is human alveolar Echinococcosis treated?
Early diagnosis and radical (tumour-like) surgery followed by treatment with albendazole
How is human Echinococcosis controlled?
- Controlling disease in definitive and intermediate hosts
- Improved hygiene in slaughtering animals
- Education programmes
What are the 3 specific PET travel scheme requirements relating to tapeworms in dogs?
- All dogs must be treated with praziquantel 1 – 5 days before ENTRY into the UK
- A vet must record treatment in the animal’s passport.
- Repeat treatment again 28 days after returning
