Cestodes

Question 1

Tapeworms General morphology

Answer 1

Scolex: Organ of attachment at the anterior end of the organism
Proglottids
1) Individual segment in a chain of segments
2) Each contains male and female reproductive organs
3) Classed as immature, mature, and gravid
4) Gravid is at the end of the strobila and contains the fully developed uterus full of eggs
Strobila: entire chain of proglottids
Rostellum: can be armed (with hooklets) or unarmed; this is the area around the attachment device on the scolex
The uterine structure is used as a main criteria for identification

Question 2

Taenia saginata Distribution

Answer 2

1) Worldwide, particularly in Islamic countries
2) Wherever beef is eaten raw or insufficiently cooked

Question 3

Taenia saginata Infectious Stage

Answer 3

Ingestion of raw or poorly cooked beef containing encysted larvae

Question 4

Taenia saginata Adult

Answer 4

• May live up to 25 years and grow to approx 25 ft in length
• Scolex has 4 weak developed suckers and an unarmed rostellum
• Proglottid is longer than it is wide and has an eccentric uterine pore. It has 15-20 branches on each side

Question 5

Taenia saginata egg

Answer 5

• Round to slightly oval
• 35-45 um in diameter
• Thick striated shell
• 6 hooked oncosphere

Question 6

Taenia saginata Disease

Answer 6

1) Usually very few symptoms
2) Rarely causes obstruction.
3) Diarrhea, hunger pains, weight loss, and appendicitis
4) Most common complaint is proglottids crawling from the anus. This may be first clue that a patient has a tape worm

Question 7

Taenia saginata Diagnostic Stage & Treatment

Answer 7

Diagnosis
- Recovery and examination of gravid proglottids or scolex
- Egg is indistinguishable from T. saginata and T. solium
Treatment
- Prazinquantel or niclosamide

Question 8

Taenia solium (pork tapeworm) Distribution

Answer 8

1) Worldwide
2) Most common in countries where raw or insufficiently cooked pork is eaten: Mexico, South America, Balkan states, and Slavic countries

Question 9

Taenia solium Adult

Answer 9

• Matures to adult form in 5-12 weeks.
• May live up to 25 yrs and grow to 6-10 ft in length.
• Usually only single worm present but individuals can have multiple worms
• Scolex has four suckers with an armed rostellum and two rows of hooks
• Proglottids have 7-13 lateral uterine branches on each side
• Less than 100 proglottids
• Gravid proglottids break off from main strobila and passed in stool

Question 10

Taenia solium Disease

Answer 10

Two Infections:
- Adult = slight irritation at site of attachment, vague abdominal symptoms
- Cysticercosis - systematic infection, involve any organ
Serious complications: invasion of spinal cord, brain, and eye

Question 11

Taenia solium Diagnostic Stage & Treatment

Answer 11

Diagnosis
- Adult worm recovery and examination of gravid proglottids
- Cysicercosis surgical removal of parasite and microscopic examination for presence of suckers and hooks on scolex
Treatment
- Adult worm: Praziquantel or niclosamide
- Cysticercosis: Surgical removal where possible

Question 12

Hymenolepis nana Distribution

Answer 12

1) Worldwide
2) Occurs frequently in children in the tropics and subtropics

Question 13

Hymenolepsis nana Infectious Stage

Answer 13

Ingestion of egg if primarily from human stool. Rodents may be involved

Question 14

Hymenolepis nana Adult

Answer 14

1) Matures in several weeks and is approx 40 mm.
2) Scolex has four suckers, short rostellum with hooks
3) Rarely seen in stool

Question 15

Hymenolepis nana egg

Answer 15

• Round to oval
• 30 - 50 um
• Colorless thin shell
• Six hooked oncosphere has two polar thickenings from which arise polar filaments

Question 16

Hymenolepis nana Disease

Answer 16

1) Asymptomatic
2) Heavy infection may have abdominal pain, nausea, vomiting, weight loss, nervousness, headaches, and diarrhea

Question 17

Hymenolepis nana Diagnostic Stage

Answer 17

Diagnosis
- Recovery and identification of eggs in feces
Treatment
- Praziquantel and niclosamide

Question 18

Hymenolepis diminuta Distribution

Answer 18

1) Worldwide in normal rat host
2) Human cases are accidental and rare

Question 19

Hymenolepis diminuta Transmission

Answer 19

Accidental ingestion of infected arthropod (intermediate host)

Question 20

Hymenolepis diminuta Adult

Answer 20

• 90 cm in length
• Scolex has 4 suckers and a small unarmed rostellum

Question 21

Hymenolepis diminuta egg

Answer 21

• 60-80 um in diameter
• Outer bile stained shell
• Contains 6 hooked oncosphere and clear area btwn oncosphere and shell.
• No polar filaments

Question 22

Hymenolepis diminuta Disease

Answer 22

Usually asymptomatic

Question 23

Hymenolepis diminuta Diagnostic Stage & Treatment

Answer 23

Diagnosis
- Recovery and identification of eggs
Treatment
- Niclosamide

Question 24

Dipylidium caninum Distribution

Answer 24

1) Commonly found throughout the world in dogs and cats
2) Can be found in humans as well including in the US
3) Infection occurs mostly in children

Question 25

Dipylidium caninum Infectious Stage

Answer 25

Eggs are ingested by arthropod where cysticercoid larval stage forms

Question 26

Dipylidium caninum Adult

Answer 26

- Matures in 3-4 weeks - 10-70 cm in length - Scolex has four suckers and an armed rostellum - Proglottids possess a double set of genital pores

Question 27

Dipylidium caninum egg

Answer 27

- Egg packet (group of eggs) may be found in stool - Each egg measures 25-40 um and contains a six-hooked oncosphere

Question 28

Dipylidium caninum Disease

Answer 28

1) Indigestion and appetite loss 2) May have migration of proglottids from anus

Question 29

Dipylidium caninum Diagnostic & Treatment

Answer 29

Diagnosis - Recovery and identification of characteristic egg packets or proglottids Treatment - Niclosamide

Question 30

Diphyllobothrium latum Distribution

Answer 30

1) Temperate regions where eating of freshwater fish is quite common 2) Great lakes of both Canada and US, Asia, Chile, and Argentina, and many parts of Europe

Question 31

Diphyllobothrium latum Transmission

Answer 31

Ingestion of poorly cooked or pickled freshwater fish (pike, perch, salmon, trout, white fish, grayling, ruff, borbot) which contain encysted pleuricercoid larvae

Question 32

Diphyllobothrium latum adult

Answer 32

- 30+ ft and up to 3,000 proglottids - Scolex is almond shaped, 2-3 mm x 1 mm - Scolex has 2 deep dorsoventral suctorial grooves demarcated by lateral folds - Two slit-like grooves or suckers that run longitundinally almost length of scolex - Proglottid have segments broader than long - Proglottid have rosette-like, coiled uterus centrally located

Question 33

Diphyllobothrium latum egg

Answer 33

- 75 um x 45 um - Operculum or lid at one end - Abopercular knob at other end - Similar in appearance to egg of Paragonimus westermani

Question 34

Diphyllobothrium latum Disease

Answer 34

1) Single worm infection usually asymptomatic 2) Cause intestinal obstruction, diarrhea abdominal pain or anemia 3) 1% of infected persons develop megaloblastic anemia

Question 35

Diphyllobothrium latum Diagnostic Stage & Treatment

Answer 35

Diagnosis - Recovery and identification of typical operculated eggs or proglottids in feces Treatment - Praziquantel or niclosamide

Question 36

Echinococcus granulosis Distribution

Answer 36

1) Worldwide, particularly common in sheep and cattle raising countries 2) Parasitic infection in dogs and similar animals

Question 37

Echinococcus granulosus Transmission

Answer 37

Ingestion of Eggs

Question 38

Echinococcus granulosus adult

Answer 38

- 3-6 mm in length - Only 3-4 proglottids - Canine host may be infected by several hundred worms that survive up to 20 months

Question 39

Echinococcus granulosus egg

Answer 39

Resembles Taenia eggs

Question 40

Echinococcus granulosus Hydatid

Answer 40

- Usually by 5th month of infection, wall of hydatid cyst has become differentiated into laminated non-nuclear layer and inner nucleated germinal layer - Secondary cysts may form budding off from inner germinal layer - Individual scoleces escaped from inner walls of cyst - hydatid sand

Question 41

Echinococcus granulosus Disease

Answer 41

1) Size of cyst and organ location will greatly influence the outcome 2) 60-70% of cases in humans involve liver 3) Cysts in vital organs of bone cause severe damage 4) During life cycle of cyst, small leaks of fluid can occur that sensitize patient so if a later larger leak occurs or cyst burts, a very severe allergic reaction can occur or even anaphylactic reaction 5) Release of cyst tissue may lead to abscess formation or development of additional young cysts at secondary sites

Question 42

Echinococcus granulosus Diagnostic Stage & Treatment

Answer 42

Diagnosis - History of association with dogs in an endemic area - Detection of slow growing tumor mass Treatment - Surgical removal of cyst

Question 43

Taenia saginata Common Name

Answer 43

Beef tapeworm

Question 44

Taenia solium Common Name

Answer 44

Pork Tapeworm

Question 45

Hymenolepis nana Common Name

Answer 45

Dwarf Tapeworm

Question 46

Hymenolepis diminuta Common Name

Answer 46

Rat Tapeworm

Question 47

Diphyllobothrium latum Common Name

Answer 47

Fish Tapeworm