Class Cestoda: The tapewormsClass Cestoda: The tapeworms

• Exclusively endoparasitesExclusively endoparasites

• Body covered by a tegumentBody covered by a tegument

• Body consists of an anterior scolex, followed Body consists of an anterior scolex, followed by a short neck and then a strobila by a short neck and then a strobila composed of a series of “segments” or composed of a series of “segments” or proglottids.proglottids.

• Digestive track absent.Digestive track absent.

Scolex, anterior holdfast organ

Neck, region of growth

Strobila made up of individual proglottids.

Three types of proglottids: immature, mature and gravid.

SEM of a Scolex

Diversity of scolexes.

Adult TapewormsAdult Tapeworms

You will be responsible for 2 orders of You will be responsible for 2 orders of tapeworms!tapeworms!

• Phylum PlatyhelminthesPhylum Platyhelminthes

– Class: CestoideaClass: Cestoidea

• Subclass EucestodaSubclass Eucestoda

–Order PseudophyllideaOrder Pseudophyllidea

–Order CyclophyllideaOrder Cyclophyllidea

Life CyclesLife Cycles

• Adult tapeworms live in the intestine of Adult tapeworms live in the intestine of vertebrates specifically the small intestine.vertebrates specifically the small intestine.

• Eggs pass in the feces of vertebrate host.Eggs pass in the feces of vertebrate host.

• Larval stage in egg = onchosphere.Larval stage in egg = onchosphere.

• It is spherical and has 6 hooks (hexacanth).It is spherical and has 6 hooks (hexacanth).

Generalized Pseudophyllidean Life CycleGeneralized Pseudophyllidean Life CycleAquatic Life CycleAquatic Life Cycle

Adult in Vertebrate Small IntestineAdult in Vertebrate Small Intestine

Uterine pore

Eggs released; later chains of spent proglottids

Eggs are usually operculated and Eggs are usually operculated and unembryonated when laid. unembryonated when laid.

The oncosphere develops in the egg and The oncosphere develops in the egg and a free swimming larva the Coracidium a free swimming larva the Coracidium

hatches.hatches.

The first larval stage the The first larval stage the CoracidiumCoracidium

CoracidiumCoracidium

The free swimming coracidium is eaten The free swimming coracidium is eaten by 1by 1stst intermediate host usually an intermediate host usually an

aquatic arthropod!aquatic arthropod!

CopepodCopepod

In the copepod the second larval stage In the copepod the second larval stage (PROCERCOID)(PROCERCOID)

Frontal glands

Cercomer posterior end

22ndnd IH is a vertebrate of some kind IH is a vertebrate of some kind (usually cold blooded)(usually cold blooded)

The 3The 3rdrd type of larva that develops in the type of larva that develops in the 22ndnd IH is the PLEROCERCOID IH is the PLEROCERCOID

The cercomere is lost and a scolex develops (no proglottids)!

Life cycle of Ligula intestinalis

Generalized Cyclophyllidean Life CycleGeneralized Cyclophyllidean Life CycleTerrestrial Life CycleTerrestrial Life Cycle

Adults live in the small intestine of Adults live in the small intestine of vertebrates.vertebrates.

Eggs passed not by uterine pore but Eggs passed not by uterine pore but instead by short chains or terminal instead by short chains or terminal proglottids that split open to release proglottids that split open to release

eggs!eggs!

Only one IH can be vertebrate or Only one IH can be vertebrate or invertebrate depending on species of invertebrate depending on species of

tapeworm!tapeworm!

• The type of larval stage that develops varies The type of larval stage that develops varies depending on species of tapeworm!depending on species of tapeworm!

– CysticercoidCysticercoid– CysticercusCysticercus

• StrobilocercusStrobilocercus

– CoenurusCoenurus• HydatidHydatid

• Alveolar hydatidAlveolar hydatid

CysticercoidCysticercoid

• Anterior vesicle with Anterior vesicle with scolex invaginated; scolex invaginated; solid posterior with solid posterior with tail-like region; in tail-like region; in arthropods!arthropods!

CysticercusCysticercus

• Central cavity; fluid-Central cavity; fluid-filled; invaginated filled; invaginated scolex; in reptiles or scolex; in reptiles or mammals, rarely mammals, rarely birds!birds!

CysticercusCysticercus

StrobilocercusStrobilocercus

• Strobiloceroid-a Strobiloceroid-a simple cysticercus simple cysticercus in which some in which some strobilation occurs strobilation occurs in the cyst.in the cyst.

CoenurusCoenurus

• Bladder with multiple Bladder with multiple scolices; in mammals; scolices; in mammals; hydatid cyst a special hydatid cyst a special case!case!

Hydatid CystsHydatid Cysts

Secondary brood cysts

Hydatid CystsHydatid Cysts

Alveolar hydatid cyst in a mouse - cyst metastasizes from the liver to fill the body cavity

Alveolar Hydatid CystsAlveolar Hydatid Cysts

PseudophyllideaPseudophyllidea

Diphyllobothrium latumDiphyllobothrium latum

• Broad fish tapewormBroad fish tapeworm

• Fish eating mammalsFish eating mammals

• Scandinavia, Baltic States, Russia, Great Scandinavia, Baltic States, Russia, Great Lakes, West coast of N. AmericaLakes, West coast of N. America– unusualunusual

• 9 million people infected9 million people infected

• 10 meters long10 meters long

• 1 million eggs per day1 million eggs per day

Life cycle of Diphyllobothrium

latum

The broad fish tapeworm

Coracidium

Procercoid

Plerocercoid

Pike and salmon common hosts Paratenic host

Pathology and SymptomsPathology and Symptoms

• Attaches to small intestineAttaches to small intestine

• Pathogenicity variesPathogenicity varies– AsymtomaticAsymtomatic– Abdominal discomfort, diarrhea, nauseaAbdominal discomfort, diarrhea, nausea– Megaloblastic Anemia (caused by loss of Megaloblastic Anemia (caused by loss of

vitamin B12)vitamin B12)• Worms absorb vitamin B12Worms absorb vitamin B12

• Disrupt host ability to absorb B12Disrupt host ability to absorb B12

• FinlandFinland

Diagnosis and TreatmentDiagnosis and Treatment

• Look for ___________________in feces.Look for ___________________in feces.

• PraziquantelPraziquantel

EpidemiologyEpidemiology

• How do you get infected with How do you get infected with Diphyllobothrium latumDiphyllobothrium latum??

• What else should we be concerned about?What else should we be concerned about?

• Fish pondsFish ponds

Life Cycle ofLife Cycle of Spirometra Spirometra ((DiphyllobothriumDiphyllobothrium)) mansonoides mansonoides

Adult tapeworm occurs in the small intestine of a cat the definitive host.

 

Frog second intermediate host containing the plerocercoid

Spirometra Spirometra ((DiphyllobothriumDiphyllobothrium)) mansonoides mansonoides

Unusual causes a great increase in size of a mammalian second intermediate host (mice).

SparganosisSparganosis

Human Infections ofHuman Infections of Spirometra Spirometra ((DiphyllobothriumDiphyllobothrium) ) mansonoides mansonoides

A few cases in the US have involved finding plerocercoids in the eyes.

 

Parasite is rare - only about 40 cases of human sparganosis have been reported in the U.S.

Human Infections ofHuman Infections of Spirometra Spirometra ((DiphyllobothriumDiphyllobothrium) ) mansonoidesmansonoides

SparganosisSparganosis• DiseaseDisease• Humans infected with Humans infected with

plerocercoidplerocercoid– Ingest copepodIngest copepod– Eating raw meat with Eating raw meat with

plerocercoidsplerocercoids• Plerocercoid transfers to Plerocercoid transfers to

humanhuman

– Frog or snake flesh Frog or snake flesh poultice poultice

• Pluerocercoid moves into Pluerocercoid moves into human tissuehuman tissue

SparganosisSparganosis

• Seriousness depends onSeriousness depends on– Where plerocercoid establishesWhere plerocercoid establishes– NumberNumber– If reproduction occursIf reproduction occurs

• Removed by surgeryRemoved by surgery