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Clinical Parasitology - Cestodes, Study notes of Parasitology

Manila Central University (MCU)Parasitology

Clinical Parasitology tackles different kinds of parasites that can be seen in human, plants or animals.

Typology: Study notes

2022/2023

Available from 04/18/2024

jeremiah-reyes
jeremiah-reyes 🇵🇭

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CESTODES
General information
• Flat and ribbon-like body
• White or yellowish
• Dorsoventrally flattened
• Few mm to several meters
• Sexes are not separated
• Adult tapeworms live in the small
intestine, attached to the mucosa.
• Tapeworms do not have a digestive
system.
• Body cavity and alimentary cavity are
absent.
• Excretory and nervous systems are
present.
• Complete reproductive systems are
present in every proglottid.
• Cestodes body parts:
o Scolex – anterior attachment organ
o Neck
o Proglottids/strobila
▪ Immature – new segments
• Male and female organs are
not differentiated.
▪ Mature – contain either one or two
sets of both male and female
reproductive organs.
• Male and female organs have
become differentiated (male
organs appear first)
▪ Ripe or gravid – filled with eggs.
• May become detached in the
intestine and pass out with a
stool in a process called
apolysis.
• Other organs have become
atrophied or disappeared.
• Types of cestodes:
o Order Pseudophyllidea – possess a
scolex bearing grooves called bothria.
o Order Cyclophyllidea – have four
muscular, cup-shaped suckers on the
scolex.
Points of
difference
s
Pseudophyllid
ean
cyclophyllid
ean
trematode
s
Ova
No
coracidium
Coracidium
(embryonat
ed ova)
Meracidiu
m
(embryona
ted ova
SHOCE –
lahat may
eova
Larval
stage
>Coracidium
(egg)
>1st IH:
procercoid
>Plerocercoid
or sparganum
>Cysticerco
id
>Cysticercu
s hydatid
Strobila
>Anapolytic
do not shed
segments
>Apolytic
(gravid)
Shed
segments
>Scotch
tape
swab/peri-
anal
Pore
>Uterine pore
Median
ventral
surface
>Genital
pore
Lateral
margin of
proglottid
Intermedi
ate host
2 IH
>Crustaceans
(coracidium)
>Copepod
(procercoid)
>Fresh water
fish
(plerocercoid)
1 IH
>Lower
forms of
mammal
>Anthropod
• Species that utilize humans as definitive
hosts
o Dibothriocephalus latus
o Taenia saginata
o Hymenolepis diminuta
• Species that utilize humans as both
intermediate and definitive hosts
o Taenia solium
o Hymenolepis nana
• Species that utilize humans as a possible
intermediate host ONLY
o Echinococcus spp.
pf3
pf4
pf5

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CESTODES

General information

  • Flat and ribbon-like body
  • White or yellowish
  • Dorsoventrally flattened
  • Few mm to several meters
  • Sexes are not separated
  • Adult tapeworms live in the small intestine, attached to the mucosa.
  • Tapeworms do not have a digestive system.
  • Body cavity and alimentary cavity are absent.
  • Excretory and nervous systems are present.
  • Complete reproductive systems are present in every proglottid.
  • Cestodes body parts: o Scolex – anterior attachment organ o Neck o Proglottids/strobila ▪ Immature – new segments - Male and female organs are not differentiated. ▪ Mature – contain either one or two sets of both male and female reproductive organs. - Male and female organs have become differentiated (male organs appear first) ▪ Ripe or gravid – filled with eggs. - May become detached in the intestine and pass out with a stool in a process called apolysis. - Other organs have become atrophied or disappeared.
  • Types of cestodes: o Order Pseudophyllidea – possess a scolex bearing grooves called bothria. o Order Cyclophyllidea – have four muscular, cup-shaped suckers on the scolex. Points of difference s Pseudophyllid ean cyclophyllid ean trematode s Ova No coracidium Coracidium (embryonat ed ova) Meracidiu m (embryona ted ova SHOCE – lahat may eova Larval stage >Coracidium (egg) > 1 st^ IH: procercoid >Plerocercoid or sparganum >Cysticerco id >Cysticercu s hydatid Strobila >Anapolytic do not shed segments >Apolytic (gravid) Shed segments >Scotch tape swab/peri- anal Pore >Uterine pore Median ventral surface >Genital pore Lateral margin of proglottid Intermedi ate host 2 IH >Crustaceans (coracidium) >Copepod (procercoid) >Fresh water fish (plerocercoid) 1 IH >Lower forms of mammal >Anthropod
  • Species that utilize humans as definitive hosts o Dibothriocephalus latus o Taenia saginata o Hymenolepis diminuta
  • Species that utilize humans as both intermediate and definitive hosts o Taenia solium o Hymenolepis nana
  • Species that utilize humans as a possible intermediate host ONLY o Echinococcus spp.

ORDER PSEUDOPHYLLIDEA

Dibothriocephalus latus

  • Old name: Diphyllobothrium latum
  • Common name: broad fish tapeworm
  • General morphology: o Eggs ▪ ovoid ▪ Possess an operculum for the escape of the embryo. ▪ Not infective to man o Larva ▪ First stage: Coracidium - Ciliated oncosphere that develops from egg in water ▪ Second stage: Procercoid - Spindle-like solid body with cephalic invagination - Found inside the cyclops (1st IH) ▪ Third stage: Plerocercoid - Head is invaginated in the neck - Found in the freshwater fish (2nd^ IH) o Adult ▪ The scolex is elongate, spoon- shaped / almond shaped / spatulate and characterized by two longitudinal grooves called bothria. ▪ Gravid proglottids contain a rosette-shaped uterus ▪ Color: yellowish grey ▪ Measurement: 3-10 m in length ▪ Lifespan: 5- 15 years
  • Intermediate hosts: o 1 st^ IH: freshwater crustaceans (copepods), also known as cyclops or diaptomus o 2 nd^ IH: freshwater fish, pike, trout, salmon, perch
  • Infective stage: Plerocercoid
  • Diagnostic stage: eggs and proglottids
  • Method of diagnosis: Stool examination
  • Mode of transmission: ingestion of uncooked fish
  • Pathogenesis: o Vitamin B12 deficiency o Megaloblastic anemia o Pernicious anemia
  • Treatment: o Drug of choice: praziquantel o Niclosamide Spirometra spp.
  • The larvae are called sparganum
  • General morphology: o sparganum is a wrinkled, whitish, ribbon-shaped organism
  • Intermediate hosts: o 1 st^ IH: Copepods o 2 nd^ IH: fish, reptiles, amphibians
  • Definitive host: Dogs and Cats
  • Infective stages: o Procercoid o Plerocercoid
  • Laboratory Diagnosis: surgical removal of sparganum
  • Mode of transmission: drinking water containing copepods infected with the procercoid larval stage
  • Pathogenesis: o Sparganosis o Ocular sparganosis o Cerebral sparganosis – characterized by seizures.
  • Treatment: o Surgical removal o Praziquantel ORDER CYCLOPHYLLIDEA Taenia solium
  • Common name: pork tapeworm
  • General morphology: o Egg ▪ Infective to man as well as pigs ▪ Thick brown striated embyophore surrounding a hexacanth embryo o Adult ▪ Armed scolex is muscular and bears a double crown of prominent hooks ▪ Number of proglottids: below 1000
  • Hydatid sand o granular material, consisting of free protoscolices, daughter cysts, and amorphous material. o Found in adult cysts.
  • General morphology o Egg ▪ Ovoid in shape ▪ Resemble Taenia ova ▪ Hexacanth embryo with 3 pairs of hooks ▪ Infective to: man (larva), cattle, sheep, and other herbivorous animals. o Larva ▪ Larval stage: Hydatid ▪ Man harbors the larval form. ▪ Found within the hydatid cyst developing inside the intermediate host. ▪ Represents the structure of the scolex of the future adult worm. o Adult ▪ Scolex bears 4 suckers and a protrusible rostellum with 2 circular rows of hooks ▪ Adult worms usually possess three proglottids (Occasionally 4) ▪ Adult worms are small (3-6 mm in length)
  • Intermediate hosts: o Sheep – pastoral cycle o Wolves – sylvatic cycle o Other: pig, cattle, horse, goat
  • Definitive hosts: dog, wolf, fox, jackal
  • Infective stage: embryonated egg
  • Diagnostic stage: hydatid cysts
  • Method of diagnosis: o Imaging techniques like CT scans o Antibody and Antigen detection
  • Mode of transmission o Adult worms acquired by sheep dogs or stray dogs o Scavenging or preying on sheep or wild herbivores o Transmission on humans occur by accidental ingestion of eggs passed by dogs or cats.
  • Pathogenesis: o Symptoms may vary on the location of the cyst. o Necrosis of surrounding tissues o Eosinophilia o Alveolar cysts usually occur in the liver of humans. o Most common site of involvement is the liver. o Echinococcus granulosus cyst: uniocular hydatid cyst o Echinococcus moltilocularis : alveolar cyst
  • Treatment: o Albendazole is better absorbed than mebendazole. o Chemotherapy o PAIR – Percutaneous, Aspiration, Injection, and Reaspiration. Hymenolepis species
  • Genus derived from the membranous character of the egg shell “hymen”
  • 3 testes in each mature segment (HYPERMENolepis)
  • Uterus is sac-like and transverse
  • Eggs possess two membranes’ outer membrane is thin and transparent.
  • Larval stage: cysticercoid
  • Small bladder containing the invaginate head proximally and a solis, elongated portion as a caudal appendage. Hymenolepis nana
  • Common name: Dwarf tapeworm
  • Common parasite of house mouse
  • Seen most frequently in children.
  • Smallest tapeworm that parasitizes human intestine.
  • May or may not require an intermediate host.
  • Man can harbor both the adult and larval stages of the parasite.
  • Exception to the rule that “helminths do not multiply inside the body of the definitive host.
  • 2 cycles: o Direct – IS = embryonated egg ▪ Host ingests eggs that hatches in the duodenum o Indirect – IS = cysticercoid larva ▪ Accidental ingestion of infected arthropod intermediate host like rice and flour beetles.
  • General morphology: o Egg ▪ Spherical or oval ▪ Outer membrane is thin transparent and colorless. ▪ Inner embryophore encloses an oncosphere with 3 pairs of lancet shaped hooklets ▪ Intermembranous space is filled with yolk granules and 4-8 polar filaments emating from little knobs at either end of the embryophore. o Adult ▪ Armed scolex has four suckers and a rostellum with one circle of hooks. ▪ Rostellar hooklets of scolex are shaped like tuning forks. ▪ Found in the ileum ▪ Delicate strobila ▪ 25 - 45 mm ▪ Worms may be present in large numbers from 1k-8k. ▪ Short life span (2 weeks) ▪ Up to 200 proglottids ▪ Transverse uterus ▪ 3 testes
  • Infective stages: o Cysticercoid larva in grain beetles o Embryonated egg
  • Diagnostic stage: eggs (polar filaments)
  • Method of diagnosis: stool examination
  • Mode of transmission: o Ingestion of grain products contaminated by infected insects. o Hyper infection because of eggs - Pathogenesis: o Abdominal pain o Diarrhea o Headache o Anorexia o Dizziness - Treatment: o Drug of choice: Praziquantel o Niclosamide o Nitazoxanide Hymenolepis diminuta
  • Common name: rat tapeworm
  • Common parasite of rats and mice.
  • 2 hosts: o Larval stage: cysticercoid is passed in fleas. o Adult stage in rats and mice and accidentally in humans (especially children who ingest fleas)
  • Arthropod intermediate hosts may be found in precooked cereals.
  • General morphology o Egg ▪ Larger than H. nana ▪ Outer shell is yellowish in color. ▪ Inner embryophore has 2 knob- like thickenings ▪ No polar filaments o Adult ▪ Unarmed scolex bears four suckers and a small rostellum without hooks. ▪ Larger than H. nana ▪ Measures 60cm in length ▪ Proglottid: 800 – 1000
  • Intermediate host: anthropods (flour moths and flour beetles)
  • Infective stage: cysticercoid larvae in flour beetles
  • Diagnostic stage: eggs
  • Method of diagnosis: stool examination
  • Mode of transmission: o Human infection occurs through accidental ingestion of intermediate host containing cysticercoid larva.
  • Pathogenesis

o Cysticercus ▪ Taenia

  • Pseudophyllidean o Dibothriocephalus latus o Spirometra spp. ( sparganum ) ▪ Sparganum mansoni ▪ Sparganum proliferum
  • Cyclophyllidean o Taenia spp. ▪ Taenia saginata ▪ Taenia solium o Hymenolepis spp. ▪ Hymenolepis nana ▪ Hymenolepis diminuta o Dipylidium caninum o Echinococcus granulosus