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.
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?
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 ________________ 1 st 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 ___________________ 2 nd 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.