Download - 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.