Cestodes Flashcards
Tapeworms General morphology
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
Taenia saginata Distribution
1) Worldwide, particularly in Islamic countries
2) Wherever beef is eaten raw or insufficiently cooked
Taenia saginata Infectious Stage
Ingestion of raw or poorly cooked beef containing encysted larvae
Taenia saginata Adult
- 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
Taenia saginata egg
- Round to slightly oval
- 35-45 um in diameter
- Thick striated shell
- 6 hooked oncosphere
Taenia saginata Disease
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
Taenia saginata Diagnostic Stage & Treatment
Diagnosis
- Recovery and examination of gravid proglottids or scolex
- Egg is indistinguishable from T. saginata and T. solium
Treatment
- Prazinquantel or niclosamide
Taenia solium (pork tapeworm) Distribution
1) Worldwide
2) Most common in countries where raw or insufficiently cooked pork is eaten: Mexico, South America, Balkan states, and Slavic countries
Taenia solium Adult
- 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
Taenia solium Disease
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
Taenia solium Diagnostic Stage & Treatment
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
Hymenolepis nana Distribution
1) Worldwide
2) Occurs frequently in children in the tropics and subtropics
Hymenolepsis nana Infectious Stage
Ingestion of egg if primarily from human stool. Rodents may be involved
Hymenolepis nana Adult
1) Matures in several weeks and is approx 40 mm.
2) Scolex has four suckers, short rostellum with hooks
3) Rarely seen in stool
Hymenolepis nana egg
- Round to oval
- 30 - 50 um
- Colorless thin shell
- Six hooked oncosphere has two polar thickenings from which arise polar filaments
Hymenolepis nana Disease
1) Asymptomatic
2) Heavy infection may have abdominal pain, nausea, vomiting, weight loss, nervousness, headaches, and diarrhea
Hymenolepis nana Diagnostic Stage
Diagnosis
- Recovery and identification of eggs in feces
Treatment
- Praziquantel and niclosamide
Hymenolepis diminuta Distribution
1) Worldwide in normal rat host
2) Human cases are accidental and rare
Hymenolepis diminuta Transmission
Accidental ingestion of infected arthropod (intermediate host)
Hymenolepis diminuta Adult
- 90 cm in length
- Scolex has 4 suckers and a small unarmed rostellum
Hymenolepis diminuta egg
- 60-80 um in diameter
- Outer bile stained shell
- Contains 6 hooked oncosphere and clear area btwn oncosphere and shell.
- No polar filaments
Hymenolepis diminuta Disease
Usually asymptomatic
Hymenolepis diminuta Diagnostic Stage & Treatment
Diagnosis
- Recovery and identification of eggs
Treatment
- Niclosamide
Dipylidium caninum Distribution
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
Dipylidium caninum Infectious Stage
Eggs are ingested by arthropod where cysticercoid larval stage forms
Dipylidium caninum Adult
- 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
Dipylidium caninum egg
- Egg packet (group of eggs) may be found in stool
- Each egg measures 25-40 um and contains a six-hooked oncosphere
Dipylidium caninum Disease
1) Indigestion and appetite loss
2) May have migration of proglottids from anus
Dipylidium caninum Diagnostic & Treatment
Diagnosis
- Recovery and identification of characteristic egg packets or proglottids
Treatment
- Niclosamide
Diphyllobothrium latum Distribution
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
Diphyllobothrium latum Transmission
Ingestion of poorly cooked or pickled freshwater fish (pike, perch, salmon, trout, white fish, grayling, ruff, borbot) which contain encysted pleuricercoid larvae
Diphyllobothrium latum adult
- 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
Diphyllobothrium latum egg
- 75 um x 45 um
- Operculum or lid at one end
- Abopercular knob at other end
- Similar in appearance to egg of Paragonimus westermani
Diphyllobothrium latum Disease
1) Single worm infection usually asymptomatic
2) Cause intestinal obstruction, diarrhea abdominal pain or anemia
3) 1% of infected persons develop megaloblastic anemia
Diphyllobothrium latum Diagnostic Stage & Treatment
Diagnosis
- Recovery and identification of typical operculated eggs or proglottids in feces
Treatment
- Praziquantel or niclosamide
Echinococcus granulosis Distribution
1) Worldwide, particularly common in sheep and cattle raising countries
2) Parasitic infection in dogs and similar animals
Echinococcus granulosus Transmission
Ingestion of Eggs
Echinococcus granulosus adult
- 3-6 mm in length
- Only 3-4 proglottids
- Canine host may be infected by several hundred worms that survive up to 20 months
Echinococcus granulosus egg
Resembles Taenia eggs
Echinococcus granulosus Hydatid
- 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
Echinococcus granulosus Disease
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
Echinococcus granulosus Diagnostic Stage & Treatment
Diagnosis
- History of association with dogs in an endemic area
- Detection of slow growing tumor mass
Treatment
- Surgical removal of cyst
Taenia saginata Common Name
Beef tapeworm
Taenia solium Common Name
Pork Tapeworm
Hymenolepis nana Common Name
Dwarf Tapeworm
Hymenolepis diminuta Common Name
Rat Tapeworm
Diphyllobothrium latum Common Name
Fish Tapeworm
