Platyhelminths 2 Cestoidea David Humber 1

Cestodes - Tapeworms

 Endoparasites  No mouth or alimentary tract  Attachment organ - anterior  Elongated body - divided into proglottids  Adults in intestines of vertebrates  Larval stages in 1 or 2 intermediate hosts 2

Cestoidea

Tissue & Intestinal  Tissue cestodes • • • • • • (extra-intestinal) Echinococcus grqnulosa Echinococcus multilocularis • • Multiceps spp Spirometra mansonoides Diphyllobothrium spp Taenia solium • • • • Disease Hydatid disease (6k) Hydatid disease (rare) Coenurosis (rare) Sparganosis (rare) Sparganosis (?) Cysticercosis (?) 3

Cestoidea

Tissue & Intestinal  Intestinal Cestodes • • • • • • Diphyllobothrium latum Taenia solium Taenia saginata Hymenolepis nana Hymenolepis diminuta Dipylidium canis Cases 16 million 5 million 76 million 36 million Rare Rare 4

Intestinal Cestodes

Tapeworms  Attached via a scolex to mucosa (small intestine)  Composed of proglottids forming a strobila  Each proglottid contains male & female reproductive organs  Immature >> Mature >> Gravid 5

Tapeworms



Hymenolepis nana

• Dwarf tapeworm (upto 40mm - largely children ) 

Taenia saginata -

• Beef tapeworm (upto 25m) 

Taenia solium

• Pork tapeworm (upto 7m)

World-wide distribution

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Hymenolepis nana

Dwarf Tapeworm  Intermediate host not required • infection via intermediate insect host rare • commonest tapeworm in UK and US (<1%)  Eggs via oral-faecal route  Hatch in stomach/small intestine  Larvae (onchospheres) penetrate villi  Develop into cysticercoid stage  Migrate back into lumen 7

Hymenolepis nana

Dwarf Tapeworm  Maturation 2-4 weeks  Length dependent on parasitemia  Scolex - 4 suckers + short rostellum with hooks  Eggs released by disintergration of terminal proglottids  Eggs immediately infectious 8

Hymenolepis nana

Dwarf Tapeworm  Often asymptomatic even with high worm burden • • headache, dizziness, anorexia, abdominal pain, diarrhea, low grade eosinophilia Heavy infections via auto infection (in intestine)  Diagnosis by egg morphology seen) (adults v rarely 9

Hymenolepis nana Control

 World-wide incidence 4%  Treatment usually Praziquantel previously Niclosamide (both single oral dose)  Health education  Rodent reservoir?

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Taenia saginata

Beef Tapeworm  Commonest taenia infection (Ethiopia)  Ingestion of raw or poorly cooked beef  Larvz digested & evaginates in small intestine  Scolex 4 suckers no hooks  Proglottids 1-2k (lateral unterine branches 15-20) 11

Taenia saginata

Beef Tapeworm  Motile proglottids crawl through anus during day  Eggs identical to

T. solium

(viable upto 159 days)  Larvae (onchospheres) hatch in cattle intestine  Migrate through villi via lymphatics/blood to striated muscle  Develop into cysticerci (bladder worm) 12

Taenia saginata

Beef Tapeworm  Usually asymptomatic • hunger pains, weight loss • discomft & embarrassment at voiding proglottids  Diagnosis based on recover of gravid proglottid (uterine branches >15)  Praziquantel or niclosamide  Health education 13

Taenia solium

Pork Tapeworm  Recognised since biblical times  Risk of cysticercosis  Evagination > six hooked four suckers larva (onchophore) in small intestine  Attaches to mucosa (penetrates in cysticercosis)  Matures in 5-12 weeks  Usually long lived (25 years) single worm  Less than 1000 proglottids 14

Taenia solium

Pork Tapeworm  Usually asymptomatic similar to

S. saginata

• • Low grade eosinophilia <15%  Treatment • praziquantel niclosamide 15

Taenia solium

Cysticercosis  Onchospheres penetrate intestine (adult worm not usually found)  Distributed via mesenteric venules  Most organs including brain, eyes, sucutaneous and intramuscular  Sometimes multiple organs (geographical variations) 16

Taenia solium

Cysticercosis  Bladder worms upto 60ml in volume (usually around 5 x 800 mm)  Diagnosis • surgical removal • X ray - calcified larvae • • • CT scan or MRI for brain lesions Fine needle aspirate Serology/PCR 17

Taenia solium

Cysticercosis  Treatment • surgical removal • • praziquantel (15 day course) – only treatment for cysticercus albendazol (8 day course) 18

Tissue Cestodes

• • • • • • Taenia solium Echinococcus grqnulosa Echinococcus multilocularis Diphyllobothrium spp Multiceps spp Spirometra mansonoides 19

Echinococcosis - Hydatid disease



Echinococcus granulosa

• worldwide 

Echinococcus multilocularis

• Europe, Russia, China, Canada 

Echinococcus vegeli

• Central & South America 20

Distribution

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Hydatidosis

 Known since Hipporates 400BC  Most serious of the tapeworm infections 22

Hosts

 Definitive Host • Canids & felids – 59% dogs in Istanbul ( E.granulosa

)  Intermediate Host • humans +60 species – ungulate,marsupials, elephants,primates, – rodents for E. multilocularis 23

Lifecycle

Definitive host Egg production Worm lives 2+ years Cyst evaginates Intermediate host Hatch - onchosphere invades mucosa & penetrates capillaries Cysts form in liver & lungs Secondary metastasis 20+ years Secondary daughter cysts bud in E. multilocularis 24

Clinical Features

 Definitive Host • usually asymptomatic  Intermediate Host • dependent on burden & site • usually single - 50% in liver, 3% brain (E.g) • • • incubation +5 years 6-10% diagnosed cases fatal Eosinophilia in 25% cases 25

Diagnosis

 Parasitological • eosinophilia • palpation  Radiological (CT & MRI) & ultrasound • differente from tumor  Immunological • Skin test - Casoni test - 18% false +ves • Serology 26

Treatment & Control

 Surgery • drainage + 5 mins 10% formalin  Praziquantel or albendazol • steroids to prevent inflammation • aspiration + 95% ethanol  Health education • sanitation - dogs cats raw meat 27

Diphylobothrium - Sparganosis



Diphylobothrium latum

• Broadfish tapeworm  Definitive host • humans/dogs/cats/pigs/bears/otters, seals etc  First intermediate host • Copepods  Second intermediate host • trout/salmon/perch/pike 28

Intestinal infections

 Limited to fish eating areas • raw or improperly cooked • dumping untreated raw sewage  Adult worms (upto 10m) • attach to lining of intestine • • • Ovoid operculated eggs released Eggs dormant in water (8-12 days) motile coracidium hatches ingested by freshwater copepod 29

Intestinal infections

 Ciliated embryophore shed & naked hexacanth larva attaches by hooks  Bores through intestinal wall into haemocoel  Hexacanth metamorphose into procercoid (14-18 days) 500um in length 30

Intestinal infection

 In fish procercoid penetrates intestinal wall  migrates to muscles  develops into plerocercoid (20-40mm) in  7-30 days with fully developed scolex  In definitive host attaches to mucosa  grows at 30 proglottids a day  Full sexual maturity in 3-5 weeks 31

Sparganosis

 Some species of Diphylobothrium and Spirometra  larva invade 32

Nematode Infections

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Nematodes

 Half million species  50% free living  animal & plant parasites  Animal • vertebrate & invertebrate hosts • infection by ingestion • penetration 34

Nematodes

 Generally elongated, cylindrical & tapered at each end (99%)  fluid filled pseudocoelom logitudinal muscle only  no vasculature or respiratory system  usually sexual dimorphism (some parthenogenetic)  males usually smaller than females  most between 1mm and 150mm 35

Ascaris

 Large intestinal round worm  mouth with I dorsal & 2 ventral lips  female 40cm male 30cm  Uterus of mature female 20+ million eggs  Sheds 200,000 golden brown ovoid eggs per day  Eggs resistant to desiccation 36