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Parasitology > Cestodes > Flashcards

Cestodes Flashcards

1
Q

Cestodes-tapeworms

Structure

A

Segemented body: body is like a ribbon and it’s composed of segmenets

Hermaphrodite: only need one worm to get eggs in feces

No alimentary canal: nutrient uptake via tegument (tegument is highly absorptive)

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2
Q

Adult cestode

A

Scolex or head: suckers=organs of sttachment- usually cestodes live in SI, suckers combat peristalsis

rostellum= concentric rings of hooks

armed cestode= has hooks

Chain of segments or proglottids (strobila)

Segments bud from neck

more posterior segments get passed out in feces

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3
Q

Tapeworm segments

A

a mature segment contains organs of reproduction (mid-body)

A gravid segment contains eggs ONLY (tail end)- ready to be passed out in feces

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4
Q

Taenia gravid segement

A

Segements are continually budded from the neck region

Organs of sexual reproduction is present in the mature segment

Disappear as proglottid matures and moves down the chain until the uterus is full of eggs (gravid)

Uterus+eggs is what we find in feces of infected individuals.

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5
Q

Taenia egg

A

radially striated eggshell: thick, protective, can live for many years

hexacanth= 6-hooked embryo or onchosphere

Never see all 6 hooks at once because they’re never all in the same plane.

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6
Q

Cestode life cycles

A

ALWAYS INDIRECT

Final host contains adult tapeworm (often in small intestine) and passes out eggs

IMH ingests eggs, hatch and larval stage encysts (usually migrates through IMH)

Final host eats the cyst containing the head of the future tapeworm

Head latches on ot the SI wall and starts to bud segmenets.

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7
Q

Cestode larval stages in IMH

A

no L1, L2, L3 etc

Just egg, larval stage and adult

in IMH, larval form=metacestode

Usually found in tissues

cysticerucs, coenorus, cysticercoid, hydatid (all names for metacestode/larval forms)

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8
Q

Family taeniidae

A

final host: man/cat/dog small intestine (adults always in small intestine)

IMH: mammal- larval stages are encysted

Scolex is armed (except T. saginata)

Adults are relatively non-pathogenic

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9
Q

Taenia saginata

A

Final host- man

get t. saginata from undercooked beef

5-15 metres long

unarmed- head has no hooks

IMH= cow

Metacestode/larval form= cysticercus bovis: small fluid-filled cyst containig a single scolex.

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10
Q

Life cycle of T. saginata

A

Adults in SI (man)–> because worms are SO big, pass many segments per day containing millions of eggs–> resistant eggs–> ingested by susceptible bovine

In bovine, onchopheres released in abomasum, penetrate SI wall–> travels to skeletal muscle and encysts

Cysticercus bovis= cysts in IMH 1mm when it 1st encysts, over 12 weeks grows to 1cm.

Meat gets ingested by man–> latching onto SI stimulates worm to grow–> adults in SI.

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11
Q

T. saginata epidemiology

A

Resource poor settings: sanitation, long-living eggs, high-level of infection in cattle (can be 30-60%), inadequate cooking of meat (due to expense of fuel)

Europe/Australia, etc: low incidence in cattle <1%; role of birds in spreading infection? hypothesis is that seagulls hanging around sewage tx plants can defecate out eggs; eggs are long-lived

Can get cysticercosis “storms” i.e. use of human sludge as fertilizer

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12
Q

T. saginata diagnosis

A

not very pathogenic- usually the only clinical sign is appearance of gravid segments in feces.

diagnosis via meat insepction: masseter, heart, tongue, IC mucles and diaphragm.

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13
Q

T. saginata control

A

Meat inspection: >25 cysts, condemn, <25 cysts, chill infected carcasses (-10c for 10 days). If, however, those 25 or fewer cysts are distributed around the body, carcasse gets condemned.

Cooking meat: 57 degrees C will kills cysts

Restrict use of human sludge to cultivated fields or no cattle grazing for at least 2 years

Hygiene/sanitation.

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14
Q

Taenia solium

A

Final host: man

IMH: pig (normal pork tapeworm) or Man (eggs can be ingested by human and form cyst in human)

Eggs are infective for man: accidental ingestion of eggs; auto infection via reverse peristalsis (tapeworm in SI, gravid segmenets that fall off end go back to stomach and reactivate)

Cysticercus cellulosae (analagous to cysticercus bovis in T. saginata)

Life cycle similar to T. saginata

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15
Q

T. solium pathology

A

adult tapeworm= no pathology

Cysticerci=serious disease–> encysts in CNS or eye

Major problems in latin america.

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16
Q

T. solium epidemiology

A

Close association man/pig–> increased number of infections in rural areas

unrestricted access of pigs to human waste

poor meat inspection

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17
Q

T. solium control

A

Mass treatment to kill adult worms in humans

e.g. albendazole or praziquantel (really effective against tapeworms)

Detection and tx of carriers

health education

mass tx of pigs: oxfendazole

meat inspection

pig corralling

vaccination of pigs

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18
Q

T. solium control- issues

A

cuultural considerations- i.e. home slaughter in some cases

costs and long term sustainability of control

efficacy of vaccines: recombinant proteins from egg (antigens from egg)

prototype vax for t. ovis, saginata, solium and E. granulosus

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19
Q

Taenia multiceps

A

seen in UK- lifecycle between dog and sheep

Final host: dog

Adult worm ~100cm long

IMH: sheep

Cyst in sheep= coenorus cerebralis (multiple heads; often found in brain of sheep)

Causes “gid” in sheep= altered gate

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20
Q

Taenia hydatigena

A

Final host: dog

Adult worm: ~500cm long

IMH: sheep

cystic form in sheep: cysticercus tenuicolis (single head)–burrows through sheep liver and encysts on surface

Common in abattoir: persistent cause of condemnation of livers (usually lambs)

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21
Q

Taenia ovis

A

similar to T. saginata

Final host: dog

Adult worm ~200cm long

IMH: sheep

Cyst in sheep: cysticerus ovis–causes sheep measles

Relatively common in abattoirs

First recombinant vaccine against helminth parasite

22
Q

T. ovis vaccine

A

progressed through all trials

registered for use in NZ

never marketed

important as prototype for vaccines against t. solium, t. saginata and e. granulosus.

23
Q

Taenia taeniaeformis

A

Final host: cat

adult worm ~60cm long

IMH: mouse, rat

cyst in mouse/rat: cysticercus fasciolaris

24
Q

Dipyldium caninum

A

Can infect dogs, cats, humans

V. common parasite in dogs; prevalent in animals that aren’t well looked after

25
Q

Dipylidium caninum life cycle

A

Adults in SI of dog/cat/man 50cm–> 3 weeks post infection, gravid segments shed–>eggs ingested by flea/louse IMH

Cysticercoid in haemocoel (body space of flea/louse)

cysticercoid=tiny solid cyst with single head

Ingestion of flea/louse by dog/cat–> head latches in SI

Adult worms have different shaped segments

Has rostellum with hooks and suckers

26
Q

IMHs for Dipylidium caninum

A

Fleas: larvae, not adults, adult mouthparts can’t ingest eggs

important IMH (flea larvae): Ctenocephalides canis, Ctenocephalides felis, Pulex irritans

Lice: all stages–Tricodectes canis

27
Q

Diagnosis of D. caninum

A

active motile segments, elongate shape (rice grain)

DOUBLE GENITAL PORE: little holes in sides of tegument where eggs can be released from

EGG PACKETS: can tease segment apart in saline and egg packet will pop up

nb: don’t usually see eggs in feces because they’re enclosed

double genital pore and egg packets are diagnostic features

28
Q

Distinguishing features of taenia and dipylidium

A

Double genital pore in dipylidium and presence of egg packets

also, in d. caninum, segments looks like rice grains and have motile segments

Why do we need to distinguish? Control

Taenia= praziquantel

Dipylidium: praziquantel + flea/lice tx

29
Q

Echinococcus granulosus granulosus

A

Final host: dog, wild canids

Site: SI

IMH: ruminants, pig, man

Zoonotic

30
Q

Echinococcus granulosus equinus

A

final host: dog, red fox

Site: SI

IMH: horse/donnkey

not zoonotic

31
Q

Echinococcus sp.

A

small ~6mm

scolex plus 3-4 segments

in SI of dog

gravid segment is usually about 1/2 length of the whole worm.

Eggs similar to taenia: 6 hooks, radially striated, passed in dog feces.

32
Q

Life cycle of echinoccocus

A

Adults in SI of dog (Final host)–> gravid semgents shed 1 per week–> egg resistant (thick, striated egg shell)

Egg ingested by IMH–> onchosphere released and penetrates SI well–> hydatid cyst in IMH liver/lungs 6+ months post infection

Hydatid cysts can form anywhere in the body but usually found in liver/lungs. Hydatid cysts have protoscoleces.

Cysts ingested by final host–> adults in SI

Tiny worm takes ~7 days for next segment to become gravid, however SI likely has thousands of worms in an infected dog.

PPP= 40-50 days from ingestion of cyst to eggs shed in feces.

33
Q

Pathology of echinnococcus

A

Pathology is associated with cystic stage not the adult worm

34
Q

E. granulosus sp. hydatid cysts

A

Horses and cattle (cattle not natural IMH): 90% of hydatids in liver

Sheep: 70% in lung, 25% in liver

most cysts in cattle are sterile- don’t have all heads of future tapeworms in hydatid

35
Q

Hydatid cyst in IMH

A

Cyst wall: thick

Germinal epithelium: cells similar to stem cells

Protoscoleces bud off from germinal epithelium- this process just carries on happening. Liver/lung constrains cyst size, but if cyst is in peritoneal vaity, cyst can get quite big.

Hydatid sand: protoscoleces or heads of future tapeworm. This is what you would see if you took an aspirate from it.

36
Q

E. granulosus diagnosis

A

IMH: abattoir

Final host: fecal egg count; copro-antigen test (picks up antigen released by parasite); copro-PCR (picks up DNA released by parasite)

In sheep, see clincal signs if cyst is in a weird place i.e. brain/pancreas

37
Q

E. granulosus pathogenesis

A

Mostly well tolerated in IMH unless cyst is in an unusual site

Most cases detected in abattoir

not pathogenic in dog final host

always of significance in humans

38
Q

Epidemiology of echinococcus

A

E. granulosus sylvatic cycle: host- wild dog, IMH- ruminant- maintained by predation/carrion feeding

E. granulosus domestic cycle: host-dog, primary IMH- sheep (hydatid more infective from sheep)– Man becomes infected from dog (i.e. man is IMH instead of sheep)

E. equinus (not v. common in UK, but rather from european imports): host-dog/red fox– equine abattoirs/hunting kennels–maintained by feeding hunting dogs on equine viscera.

39
Q

E.g. granulosus

A

IMH depends on local animal husbandry

in UK, sheep is most important, but elsewhere can be camels or reindeer.

40
Q

E.g. granulosus zoonotic infection

A

Man is accidental IMH

Most common in sheep farming areas

Requires close man-dog contact

Man becomes infected via ingestion of onchospheres from water, foodstuffs or coat of dog

41
Q

Control of hydatid disease

A

break cycle by: regular deworming of dogs with praziquantel, proper disposal of infected carcasses, deny access of dogs to abattoirs, hygiene to control human infection.

42
Q

E.g. granulosus in Australia

A

introduced with sheep

spread from domestic animals into dingoes as final host and wild marsupials as IMH- sylvatic cycle established

cycle re-introduced to domestic dogs in some areas by hunters allowing dogs to feed on offal from wildlife.

Control: praziquantel, dried dog food too, better diagnosis (ELISA to detect copro-Ag), education

43
Q

Echinococcus multilocularis

A

final host: dog, cat, wild canids

IMH: lemings, voles, man

Life cycle similar to E.g. granulosus

Important zoonosis

Prevalent in europe

44
Q

E. multilocularis life cycle

A

similar to granulosus

Adults in SI (fox)–> gravid segments shed in feces–> eggs resistant to -50C–> ingested by rodent IMH–> embryo released, penetrates SI wall–> usually goes to liver via hepatic portal vein where embryo rapidly vesiculates (sits in liver and forms big vesicles). IMH usually gets sick, can’t run as fast

rodent+cyst ingested by fox

45
Q

Pet passport and human cases

A

Dogs and cat must be treated against E. multilocularis 24-48 hours prior to returning to UK (praziquantel)

Human cases: 15% prevalence in parts of china and tibet

urban foxes in zurich and stuttgart infected, prevalence rates 20-47%

no +ve foxes in recent UK survey

46
Q

E. multilocularis in humans

A

Causes alveolar echinococcosis

potentially fatal

if untreated, long asymptomatic periods (5-15 years) followed by clinical signs

tx: liver transplant, section or albendazole

Alb+ surgery improves 10 year survival rates from 6-25% to 80-83%

47
Q

Horse cestodes

A

Anoplocephala perfoliata**

Anoplocephala magna

Paranolocephala mamillana

Site: small and large intestine

IMH: orbatid forage mites

48
Q

Anoplocephala perfoliata

A

prevaelence 14-81%

High prevalence at temperate climates

Ulcerations at site of attachment of parasites–> risk factor for ileo-caecal colic.

A. perfoliata have suckers and lappets just underneath sucker. not sure what lappets do, but maybe they’re sensory organelles? either way, very characteristic for A. perfoliata

Segements are MUCH wider than long.

49
Q

Anoplocephala perfoliata life cycle

A

Adults at ileo/caecal junction–> eggs pased in feces–> ingested by forage mite IMH–> forms cysticercoid in mite

Infected mite ingested by horse–> attaches to gut wall in horse–> adults at ileo/caecal junction

PPP=6-10 weeks

50
Q

A. perfoliata and colic

A

Horses with tapeworms are more likely to suffer colic

80% of 20 cases of ileal impaction colic were tapeworm associated

22% of 95 spasmodic colic cases were tapeworm associated

Treat with PZQ +/- ivermectin

51
Q

A. perfoliata diagnosis

A

FEC: low sensitivty, high specificty

Eggs are misshapen- odd-looking- have pyriform appartus. In fresh specimen, looks like a stalked mushroom and embryo sits on top.

ELISA and Corp-Ag PCR.

Parasitology (12 decks)

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