Parasitology exam 2 review - pt 1? Cestodes

What do cestodes look like/what are some characteristics? 

They are flattened, dorsoventral + segmented ribbon like body. They have no digestive tract - absorbs nutrients through skin. They have an Indirect life cycle (ALWAYS needs an intermediate host(1 exception?). 

What are cestodes?

Tapeworms!

Which is usually are more damaged by tapeworm/cestodes, the IH or the DH? Why/How? What can it cause in humans?

The IH usually is effected the most.

Why/How: Larval (metacestode) stages develop in: tissues/organs (liver, lungs, muscle, brain, etc.), 

can cause: 

• Cysts (hydatid)(Fluid filled sac), pressure, or even fatal disease depending on the location (e.g., neurocysticercosis in humans, hydatid disease from Echinococcus).

Tapeworm of the horse – how many species are there?  What is the IH? 

3 different ones. 

• Anoplocephala perfoliata: Which lives in the small + large intestines and the cecum. 

• Anocplocephala magna: Lives in the stomach and small intestines.

• Paranoplocephala mamilana: Lives in the stomach and small intestines. Only occasionally affects horses. (Called the dwarf tapeworm!!**)

The IH of equine tapeworms is the grain mite. 

What are some zoonotic tapeworms (including the one that causes hydatid cycts)

Taenia solium and saginata(Humans can be the IH), Echinococcus (Causes hydatid cysts in humans. E granulosus (dog - sheep cycle) + E. multilocularis (dog - rodent cycle), Diphyllobothrium latum (Broad fish tapeworm, 1st IH: aquatic crustaceans, 2nd IH: fish).

What is a spurious infection?

A false infection - Parasite eggs found in feces from ingestion of infected tissue, not due to the host actually being infected. EX: dog eats cow poop -> we find a specific worm only found in cows -> these worms will not grow due to being in the wrong host.

What are the cestodes/tapeworms in *only* dogs? (Dogs are the DH)

Diplydium, Teania pisiforms (think piss on fire hydrant..?). T. hydatigena, and T. ovis, and Echinococcus granulosus

What are the names of the larval stages in Taenia?

T. pisiforms: Cysticercus pisiforms

T. hydatigena: Cysticercus tenuicollis

T. ovis: cysticercus ovis

T. Taeniaeformis (Cysticercus fasciolaris).

What are the three genus’s of cestode that the DH is BOTH dogs and cats? 

Diplydium, Echinococcus and Mesocestoides. However E. granulosus effects Dogs, and E. multilocularis effects cats, and Mesocestoides effects both. 

What are the cestodes that the DH is only cats?

Taenia taeniaeformis (Hydatigera taeniaeformis) and Echinococcus granulosus.

What are the cestodeds/tapeworms that the DH is mice?

Hymenolepis nana, and H. diminuta.

What is unique about H. nana? **

It is the only tapeworm that does NOT have an IH!!**

What are the tapeworms of Ruminants?

Moniezia benedini (only cows), Moniezia expansa (cows, sheep, and goats), and Thysanosoma actinoides (No known IH).

What are the two pseudotapeworms? 

Spirometra spp. (Zipper tapeworm), and Diphyllobothrium latum (The broad fish tapeworm).

What is the difference between true tapeworms (Eucestoda), and pseudotapeworms (Cotyloda? 

True: Terrestrial life cycle, one intermediate host, suckers on scolex, non-operculated eggs, single larval stage (e.g. cysticercus). 

Pseudo: Aquatic life cycle, two intermediate hosts, bothria on scolex, operculated eggs, three larval stages (coracidium → procercoid → plerocercoid). 

What are the two subclasses of phylum Platyhelminthes class Cestoda?

Eucestoda (The true tapeworms) and Cotyloda (The pseudo-tapeworms).

What is the metacestode stage, what are the different stages?

Once a tapeworm egg is ingested by the IH it develops into a metacestode stage, or larval tapeworm. The metacestode may take one of several forms: cysticercoid (usually insects, athropods are the IH), cysticercus (vertebraes), coenurus, hydatid cyst, or tetrathyridium. These larval stages differ in their choice of host, their structure, their predilection site, and their pathogenicity to the intermediate host. 

What are the IH for Taenia and Dipylidium?

Taenia: K9: Rabbit/ Hare (think hunting dogs) Feline: Mice/ Rats. (Cysticercus)

Diplydium: Fleas (cystercercoid).

 Taenia eggs contain what in them?

They contain a single oncosphere (literally a “growth ball”) with three pairs of hooks (six total). The oncosphere is often called a hexacanth embryo. The eggs of the taeniids are very similar to those of Echinococcus and Multiceps species. 

Which have Taenia looking eggs? (Dipylidium or taenia?)

Taenia…?

What do Dipylidium eggs look like?

Egg are in “packets” and have embryo inside

What do the tapeworm eggs of ruminants look like?

Moniezia spp: Square or triangle shaped eggs with a three-layered eggshell; the innermost lining is a pyriform (pear shaped) apparatus. 

Thysanosoma actinoides: Eggs of this tapeworm occur in packets of 6 to 12 eggs, with individual eggs measuring 19 × 27 μm. These eggs do not possess a pyriform apparatus. The eggs can be found on standard fecal flotation procedures

Which tapeworm doesn’t require an intermediate host?

Hymenolepis nana 

DH: humans + rodents (Mice, Rats, Gerbils, Hamsters, Dogs, + Humans)

Pseudotapeworms – Where are the IH found and therefore the parasite?

IH: aquatic crustaceans + musculature of fish + reptiles. Pseudotapeworms are found in the gastrointestinal tract of the IH host. 

What is the broadfish tapeworm?

Diphyllobothrium latum

• Located in the small intestines

• IH 1: aquatic crustaceans

• IH 2: Fish

Host: Cats, Dogs, + Humans

Parts of the tapeworm?

Scolex: tapeworm's attachment device (head)

Neck: region of growth

Strobila: tapeworm segment (proglottids)

What is a cysticercus?

• Metacestode stage: In Mammalian/vertebrates IH host

• Cyst form of a tapeworm in tissue. Fluid-filled bladder with a single invaginated scolex (“bladder worm”). 

• This is the classic “bladder worm.” One scolex means one adult tapeworm develops if ingested by the final host.

• Usually in Taenia spp.

Cysticercoid

• Metacestode stage: In Arthropod(insects, fleas, mites) IH host usually. 

• Solid body with an invaginated scolex (no fluid-filled bladder); the larva is small and compact. 

• **Because arthropods are small, the larva must remain small and compact — hence the cysticercoid form.**

• Typically in Hymenolepis, Dipylidium.

What is a coenurus?

• Metacestode stage: In herbivore IH usually (Sheep, rabbits, etc)... 

• Large fluid-filled bladder containing many invaginated scolices (multicephalic cyst). 

• Think of coenurus as “one cyst with many heads.” Each scolex can become an adult worm in the final host.

• Usually in Taenia multiceps and T. serialis

What is a hydatid cyst?

• Metacestode stage: Sheep, cattle, and other herbivores (E. granulosus); rats, mice, and voles (E. multilocularis); humans (both)

• Very large fluid-filled cyst. May form daughter cysts internally or externally

• This is the most complex and dangerous metacestode form. Can be very harmful to humans

• Usually in Echinococcus granulosus, E. multilocularis.

What is a tetrathyridium?

• Metacestode stage: Reptiles, amphibians, small mammals. (Mesocestoides [which has tetrahyridium as its metacestode stage] has 2 IH hosts.)

• Elongated, worm-like larva with a scolex that is invaginated or evaginated; not a simple cyst. 

• Unlike the other cystic forms, the tetrathyridium is motile and elongated — more like a miniature tapeworm.

• Typically in Mesocestoides spp.

What is the tapeworm of dogs that causes CNS signs in sheep? Why do they? Whats the IH of this tapeworm, and what is the common name? Is it zoonotic?

Taenia multiceps

• Lesions that occupy lots of space within the brain + spinal cord producing neurological signs in infected sheep

  • IH: sheep

  • Common name: Coenurus-producing tapeworm

    • Not zoonotic!

What is the Zipper tapeworm? What are the IH’s?

Spirometra spp. (mansonoides)

• nonproliferative form (benign plerocercoidosis) and are associated with the presence of a single larva

  • 1st IH: Copepod

  • 2nd IH: Frog, snake, or rodent (2nd IH)

    • Humans can be accidental hosts → sparganosis (larval infection)

How do you prevent/treat tapeworms in dogs and cats?

Treatment:

• Praziquantel (Droncit®)

• Epsiprantel

• Fenbendazole (for some species)

Prevention:

• Control fleas (for Dipylidium caninum)

• Prevent hunting/ingesting prey (for Taenia spp. and Spirometra)

• Practice good sanitation and deworm routinely

What is the life cycle of true tapeworms?

Adult stage: Lives in the small intestine of DH, attaching with suckers or hooks on the scolex. It absorbs nutrients directly through its tegument (no digestive system).

Egg production: Mature (Gravid) segments (proglottids) are filled with eggs and are passed with the feces to the outside environment singly or in chains. Each egg contains an oncosphere (hexacanth embryo) — a larva (or larva’s depending on species) with six hooks. These proglottids rupture in the external environment and release thousands of hexacanth embryos, or eggs, to the outside environment

Ingestion by IH: To continue the life cycle, the egg must be ingested by a suitable intermediate host, either an invertebrate or vertebrate while grazing or eating contaminated food or water. In the gut, the oncosphere hatches and penetrates the intestinal wall.

Metacestode stage: Within this host, the egg develops into a metacestode stage, or larval tapeworm. The metacestode may take one of several forms: cysticercoid, cysticercus, coenurus, hydatid cyst, or tetrathyridium. These larval stages differ in their choice of host, their structure, their predilection site, and their pathogenicity to the intermediate host.

Ingestion by definitive host: The definitive host becomes infected by ingesting the intermediate host containing the metacestode stage. The “juvenile,” or developing, tapeworm emerges from the metacestode stage, attaches to the lining of the small intestine, and begins to produce the strobila, which is composed of proglottids.

Sometimes the metacestode, or larval stage of the tapeworm, is more pathogenic to the intermediate host than the adult or mature tapeworm is to the definitive host.

What are the two Acanthocephalans that we are concerned with in veterinary medicine?

Macracanthorhynchus hirudinaceus (pigs) and Oncicola canis (dogs)

Acanthocephalan of pigs? What is IH?

Macracanthorhynchus hirudinaceus

• IH: dung beetle

• DH: pig

  • Located in the small intestinal mucosa

Acanthocephalan of dogs? What is IH?

Oncicola canis (dogs) 

• IH: Dung beetle

• DH: Dog

  • In the small intestinal mucosa.

Trichuris vulpis - DH, transmission, where it lives? 

• DH: dogs

• Transmitted by ingestation of eggs

• Lives in colon, cecum, + rectum

What are strongyloides

Threadworms.

Free-living and parasitic forms

Ancylostoma caninum - Causes what? transmission? zoonotic? 

• Causes anemia in puppies/kittens

• Transmammary, skin penetration

  • zoonotic

Gravid?

Bearing eggs/mature

Mollusk?

Snail

Hermaphrodite?

Both male + female organs

Trematode?

Fluke

Cestode?

Tapeworm

Cysticercus vocab? 

cyst of a tapeworm in tissue

Proglottid?

Tapeworm segment

Scolex?

Tapeworm attachment device (head).