Cestodes (tapeworms) Flashcards
Characteristics
Long, segmented, ribbon-like form
Usually live in small intestine
Absorb nutrients through cuticle; have no digestive tract
Cyclophyllidean – true tapeworms – in terrestrial food chains
Pseudophyllidean – pseudotapeworms – in aquatic food chains
Cyclophyllidean tapeworms
Scolex – “head” or anterior end; may have a mobile, often retractable structure called a rostellum
“Armed” if has a # of hooks
Suckers – total of 4 on the sides
of the scolex; may be more anteriorly located on an unarmed scolex
Strobila – body of the tapeworm
Consists of segments called proglottids that grow by being budded off from the neck of the scolex; therefore, the most mature proglottids are at the distal end
Reproductive organs (male & female for each segment) appear as segments mature
Genital pores usually open at the lateral margins
Tapeworm Eggs
Spread by detaching a whole gravid segment full of eggs from the distal end of the tapeworm. Segment passes out in the feces – doesn’t lay eggs in the intestinal tract.
**Hard to diagnose infection unless see segments being passed.
Once outside the body, some segments discharge eggs through the genital pore; in others, the entire segment disintegrates
Cysticercoid
single invaginated scolex with no fluid (usually in invertebrate IH)
Cysticercus
single bladder with 1 scolex – fluid filled
Strobilocercus
cysticercus that has begun to elongate and segment while still in the IH
Cyclophyllidean metacestodes – larval forms
cystercercoid, cysticercus, strobilocercus, coenurus
Coenurus
single fluid filled bladder with many scolices
Hydatid
Cyst – contains brood capsules which release scolices. Grows slowly – usually only a few cm. in diameter in slaughter animals
Alveolar – cyst with exogenous budding – invasive – doesn’t remain contained within CT capsule – proliferates and infiltrates like a “cancer”
Dipylidium caninum
flea tapeworm
Up to 50 cm long; well developed rostellum with several rows of hooks
Proglottids “cucumber seed” shaped; resemble dried rice grains when found stuck to fur or in animal’s bedding; have bilateral genital pores
Dipylidium caninum (clinical signs, pathology)
Not highly pathogenic; may rarely be associated with diarrhea
Most common clinical complaint is anal pruritus (“scooting”)
Dipylidium caninum (diagnosis)
Tapeworm segments perianally or in feces
Rarely see eggs in fecal exams
May do squash prep of segment to see egg packets
Dipylidium caninum (treatment)
Praziquantel (Droncit®)
Epsiprantel (Cestex®)
Must also treat for fleas; prepatent period only 2-3 weeks.
Taenia sp.
Adults live in small intestine of carnivores and man; IHs all mammalian (man may serve as IH as well as being infected by adults)
Several species found in dogs/cats
Taenia sp. (morphology and egg)
Segments usually rectangular
Genital pores open in irregular sequences at either side
Scolex usually has an armed rostellum with a double row of hooks (except T. saginata, which is unarmed);
Egg: small, spherical with hexacanth embryo; thick shell with radial striations
Metacestode form = cysticercus
Taenia sp (important species)
Taenia pisiformis – common in dogs; rabbits IHs – common in hunting and farm dogs who eat rabbits
Taenia hydatigena – dogs and wild canids; IHs ox, pig, sheep – more common in farm dogs; up to 5 meters long
Taenia taeniaeformis – cat; rodents His; prepatent period only 16-18 days
Taenia saginata
Beef tapeworm of man
IHs ox, reindeer, wildebeest, etc.; encyst in muscle of IH
5-15 meters long in small intestine of man;
UNARMED scolex
greater than 100,000 eggs/gravid segment – segments crawl about spreading eggs as they go
Taenia solium
Pork tapeworm of man; pig IH; up to 7 meters long; armed; man may serve as IH
Echinococcus sp.
Smallest cestode – scolex and two-four segments
Double row of hooks on rostellum
Two important species
Echinococcus granulosus
Hosts – dogs and other canids – no pathology
IH – usually herbivores; also pig, man, and other mammals
Importance is as zoonosis – man as IH
Lung common site for onchosphere to encyst as hydatid cyst – real danger to man
Worldwide distribution, especially sheep-raising areas
Echinococcus multilocularis
Hosts – canids/felids
IH – Usually rodents and insectivores; occasionally man
Public health significance – form alveolar hydatids in man as IH
Mesocestoides sp.
In some ways, a link with pseudophyllidean tapeworms
Genital pore on midline
Needs 2 IHs
Hosts – carnivores, birds, occasionally man
Example: Mesocestoides lineatus
IH I – coprophageous beetles; orabatid mites
IH II – vertebrates such as the rabbit – develop in pleural and peritoneal cavities
Small intestine in final host – no pathology
Anoplocephalidae
Host range: Mammals, birds, reptiles
**Vet importance – herbivores
Unarmed scolex, segments much wider than long
Embryophore has irregular shape
Life cycle – segments from FH eggs released IH mites, etc. FH ingests IH
