introduction to tapeworms

Class Cestoidea – Tapeworms – Chap. 20 & 21

Tapeworms are entirely endoparasitic.

Adults inhabit the ________________________________of vertebrate definitive hosts.

Life cycles involve larval development in 1 or 2 intermediate hosts.

Of the two subclasses, cestodes of medical and veterinary importance occur in the SUBCLASS EUCESTODA

General Tapeworm Morphology

Tapeworms are polyzoic and consist of 3 regions:

a.

b.

c.

General Tapeworm Morphology

1. Scolex - anterior attachment structure

Is is NOT a __________________________

Structures for attachment differ in the 2 important orders:

• Order Pseudophyllidea - scolex contains slit-like suckers called ____________________________

• Order Cyclophyllidea - scolex contains ______________________________ and a central domed area called the _____________________________ with or without hooks

Scolex is an important taxonomic structure.

2. Neck - undifferentiated region posterior to scolex

General Tapeworm Morphology

3. Strobila - linear series of segments or proglottids

Proglottids are continuously formed posterior to the neck region in a process called strobilization.

As new proglottids are formed, the older proglottids move posteriorly and become sexually mature.

• immature proglottids –

• mature proglottids –

• gravid proglottids -

General Tapeworm Morphology

• Gravid proglottids cont:

Male and female organs in gravid proglottids degenerate as the uterus fills with eggs.

Gravid proglottids often detach from the strobila:

- disintegrate during passage through the digestive tract releasing eggs in the feces

- or are released intact in the feces.

Tapeworm Tegument

Structure of the tapeworm tegument is similar to that of trematodes.

1. Syntegument - outer anucleate syncytial cytoplasmic layer containing mitochondria and secretory bodies. Major difference involves the presence of _____________________________ on the surface

• microvilli-like projections but with a dense core • increase absorptive area. • Glycocalyx covers the microtriches.

Tapeworm Tegument

2. Cytotegument - nucleated cell bodies lying beneath the tegumental muscles and connected to syntegument.

Tapeworm Tegument

Microtriches showing the dense core

Tapeworm tegument

Functions of the Tapeworm Tegument

1. Because tapeworms lack a digestive tract, _________________________________ are absorbed through tegument.

 2. Tegument protects the tapeworm from host

______________________________________

This is especially important as adults live in the small intestine where digestive enzymes occur.

3. Tegument protects the tapeworm from _____________________________________________.

This is important in larval forms that live in many habitats in host body.

Parenchyma

System of loose cells filling space in the proglottid.

Many parenchymal cells contain _____________________________________ - a characteristic structure in tapeworms.

These are circular structures consisting of concentric rings.

Possible functions are (1) ___________________________________________

(2) ______________________________________________

Calcareous corpuscles are best seen in living specimens.

Reproductive Organs

Tapeworms are _________________________________- each proglottid is a reproductive individual with both male and female organs.

Male system develops first

Structures begin to form in the immature proglottids and are fully developed in mature proglottids.

Structures are:

many testes (# varies from 3 to 100's)

vasa efferentia

vas deferens (often highly coiled)

cirrus sac with cirrus

common genital pore

Reproductive Organs

Female system - structures form and become functional in mature proglottids.

Structures are:

1 ovary

vitellaria - scattered or compact

Mehlis' gland

uterus (contains eggs in branches)

vagina (carries sperm to ootype)

  common genital pore

Most of the female organs disappear in gravid proglottids except for the egg-filled uterus.

Taxonomy of the Class Cestoidea

Contains 13 orders but only 2 orders contain tapeworms of medical and veterinary importance.

Order Pseudophyllidea

Order Cyclophyllidea

Order Pseudophyllidea - Chapter 21

Contains some of the largest tapeworms known - lengths of 10-30 feet are common

Characteristics of the order:

 1. scolex contains

_______________________________ - slit-like adhesive organs

Order Pseudophyllidea - Chapter 21

Characteristics of the order cont:

2. male and female genital openings are separate and located midventrally in the proglottid

3. __________________________ are scattered throughout the proglottid

4. gravid proglottid is not shed; eggs are released through ________________________________

♂♀

Uterine pore

Order Pseudophyllidea

Characteristics of the order cont:

5. life cycles are complex involving 3 hosts: 

first intermediate host - ____________________

second intermediate host - _______________________

definitive host - _________________________

Two species of medical importance

Diphyllobothrium latum

Common name - the BROAD FISH TAPEWORM

broad - indicates that the proglottids are wider than long

fish - indicates that the definitive host is infected by eating raw or poorly cooked fish

DISTRIBUTION - _________________distribution (not tropical)

Occurs in northern Europe, Asia, and North America

In North America, it is common in the Arctic and the Great Lakes Region

In Wisconsin?

Adult of Diphyllobothrium latum

Scolex with bothria

Little difference between mature and gravid proglottids

• proglottids are ________________________

• uterus is _____________________________

Strobila reaches length of 30 feet

Adult of Diphyllobothrium latum

Eggs are shed from gravid proglottids through uterine pore (difficult to see)

- up to 1,000,000 eggs released/day

- egg in feces is diagnostic - has ________________________________ and _______________________________________

Adult of Diphyllobothrium latum

DEFINITIVE HOSTS - _________________________________________________

Common hosts include bears, dogs, cats, foxes, mink, raccoons, walruses, seals, and humans.

Adults show low host specificity.

Life Cycle of Diphyllobothrium latum

1. Adult tapeworm occurs in the ___________________________of carnivore or human definitive host.

2. Eggs are shed in the feces into water.

3. Eggs embryonate in water and a ___________________________ hatches from each egg after several weeks.

Life Cycle of Diphyllobothrium latum

Coracidium consists of outer ciliated embryophore and inner oncosphere containing six hooks

embryophore

oncosphere

Life Cycle of Diphyllobothrium latum

4. Free-swimming coracidium is eaten by ________________ 1st intermediate host.

5. In copepod's midgut, embryophore ruptures and _________________________uses its 6 hooks to penetrate midgut.

Oncosphere migrates to the copepod hemocoel.

6. In the hemocoel, the oncosphere elongates to become the _________________________

Life Cycle of Diphyllobothrium latum

7. Infected copepod is eaten by a ___________________ 2nd intermediate host

(Almost any fish including minnows will work)

8. Procercoid burrows through the fish gut and migrates to the muscles where it transforms into a ________________________(scolex and neck)

Life Cycle of Diphyllobothrium latum

9. Larger fish - northern pike, walleye, perch, salmon, trout - eat smaller infected fish.

Plerocercoid will live in these fish but undergoes no further development

These fish are ________________________ and increase chances of reaching the definitive host.

Life Cycle of Diphyllobothrium latum

10. Carnivore or human definitive host is infected by eating raw or poorly cooked fish containing plerocercoids.

Worms attach to the wall of the small intestine and become sexually mature in 1 to 2 weeks

Life Cycle Stages of Diphyllobothrium latum

Copepod first intermediate host containing the procercoid

Fish second intermediate host containing the plerocercoid

Diphyllobothrium latum infections

Fish in the Great Lakes are common second intermediate hosts and are heavily parasitized with plerocercoids - up to 50-75% prevalence

Bears are common definitive hosts due to their fish-eating habits.

Dogs and cats become definite hosts when fed scraps of fish.

Diphyllobothrium latum infections

Humans become infected by ____________________________________________________

- gefilte fish (Scandanavian)

- sushi and sashimi (Japanese)

- cerviche (Latin American)

Pathology of Diphyllobothrium latum

Human infections cause:

1. ___________________________________________ (diarrhea, nausea, intestinal cramps).

2. some cases result in ____________________________________

  - adult D. latum absorbs high levels of __________________

  - lack of this causes decreased rbc production and anemia

Parasite is never life threatening.

Diagnosis & Treatment of Diphyllobothrium latum

DIAGNOSIS - ID egg in feces - egg has distinct operculum and abopercular knob

TREATMENT – drugs ___________________________________ are effective in eliminating adult tapeworms

Diphyllobothrium mansonoides

Causative agent of a human disease called ______________________________________

- disease results when humans become ___________________ ________________________________________________

- old name for plerocercoid was sparganum - hence the name sparganosis

  - humans are NEVER definitive hosts

Diphyllobothrium mansonoides

Adult tapeworm is morphologically similar to D. latum.

Life Cycle of Diphyllobothrium mansonoides

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

 2. Eggs are shed in water and a __________________________ hatches.

 3. Coracidium is eaten by _______________________ and procercoid develops.

Life Cycle of Diphyllobothrium mansonoides

4. Copepod is eaten by second intermediate host - can be almost ___________ ________________________. Common hosts are fish, frogs, snakes, and mice.

 5. Plerocercoid (= sparganum) occurs primarily in the ___________________________________________

6. Cat becomes infected by eating infected second intermediate.

Life Cycle Stages of Diphyllobothrium mansonoides

Plerocercoid beneath the skin (subcutaneous location) in a mouse second intermediate host

Procercoid in copepod first intermediate host

Human Infections of Diphyllobothrium mansonoides

Humans can serve as accidental hosts of the _______________________

Humans are infected by 3 methods:

1. _____________________ _______________________ _______________________ _______________________

Procercoid penetrates intestinal wall and migrates into the subcutaneous regions as the plerocercoid.

Human Infections of Diphyllobothrium mansonoides

2. __________________ ____________________________________________________________

Plerocercoid migrates to subcutaneous tissues and undergoes no further development.

Human Infections of Diphyllobothrium mansonoides

3. __________________ _______________________________________________________________

Plerocercoid crawls out of this host into human.

Human Infections of Diphyllobothrium mansonoides

A few cases have

involved finding plerocercoids in the __________________ from this method of infection.

Human Infections of Diphyllobothrium mansonoides

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

Parasite is diagnosed and treated by _____________________________________________________

Diphyllobothrium mansonoides

Unusual occurrence is the production of a chemical called __________________ ________________________________

This chemical acts much like _______________________________ and causes a great increase in size of a mammalian second intermediate host (mice).

This hormone, however, does not effect humans.