PSEUDOPHYLLIDEAN TAPE WORMS Flashcards
What about Pseudophyllidean tape worms?
Possess false or slit-like grooves called bothria
Adult pseudophyllidean tape worms in Intestine
Diphyllobothrium latum: Fish Tapeworm
Pseudophyllidean tape worm general morphology
*Head or scolex:
=Bears 2 slit-like grooves
=Bears 4cup-like suckers
*uterus
=No branching, Convoluted uterine tubes assume the form of rosettes
*Uterine pore
=present
*Common genital pore
=Ventral; in the midline
*eggs
=Operculated; gives rise to ciliated larvae
Larval development proceeds in two intermediate hosts:
First larval stage is called PROCERCOID
Second larval stage is called PLEROCERCOID
Larval stages: Plerocercoid in Man
Sparganum mansoni
Sparganum proliferum
Common Name of Diphyllobothrium latum?
*Fish Tapeworm
*Broad Tapeworm
Diphyllobothrium latum Adult worm Morphology:
・Yellowish grey in color
・Dark central markings in the strobila are due to the egg-filled uterus
・Measures 3 to 10 meters in length
・Life-span is for a period of 5 to 15 years
・Scolex is spoon-shaped or spatulate
・Scolex bears 2 slit-like grooves called bothria(1 on the dorsal surface and 1 on the ventral surface)
・Scolex has no rostellum and no hooklets
・Neck is thin and unsegmented and is much longer than the head
・3,000 to 4,000
・A mature segment is filled with male and female
reproductive organs
・Terminal segments shrink and becomes empty as eggs are constantly discharged
・Dried up segments break off from the body in chains and are passed out in the host’s feces
・Uterus at the center of the segment appears in the form of a rosette
Diphyllobothrium latum Ova Morphology
*Passed out in the host’s feces in large numbers
*Oval
*Bile stained
*Contains abundant granules and unsegmented ovum
*Inconspicuous operculum at one end and a small
knob at the other end
*Does not float in saturated solutions of common salt
*A single egg gives rise to a single larva
**Not infective to man
Diphyllobothrium latum larva Morphology
*Passed first in water and then in the respective intermediate hosts
3 stages
– First stage larva
Coracidium
Ciliated oncosphere that develops from egg in water
– Second stage larva
Procercoid
Spindle-like solid body with cephalic invagination
Found inside the cyclops (the first intermediate host)
– Third stage larva
Plerocercoid
Head is invaginated in the neck
Found in the fresh water fish, the second intermediate host
Diphyllobothrium latum Life Cycle
①The adult worm is attached to the mucosal lining of the small intestine
⓶Eggs are released from the uterine pore
③The eggs must lie dormant in the water for approximately 8-12 days or longer to complete embryonic development
④The hexacanth embryo is covered by a ciliated embryophore and is called a coracidium
⑤Soon after hatching, the motile coracidium must be ingested by a FW copepod
⑥In the digestive tract of the copepod, the ciliated
embryophore is shed and the naked hexacanth larva bores through the intestinal wall into the hemocoel
⑦The hexacanth embryo metamorphoses into an elongated procercoid larva.
The prominent cercomer, containing the 6 larval hooks, projects posteriorly.
⑧When the infected copepod is ingested by a plankton-feeding FW fish, the procercoid penetrates the intestinal wall and
migrates to the body muscles.
⑨Here it develops into a long, solid, pseudosegmented plerocercoid larva with an adult scolex at one end.
*The plerocercoid of D. latum is coiled and at times encapsulated, or more commonly, lying free in muscle tissue.
*When it invades the muscles of the body wall, encapsulation
rarely occurs.
*However, when it settles in or on the viscera,
encapsulation is common.
**Infection of the definitive host results from the
ingestion of plerocercoids in poorly cooked,
steamed, smoked, pickled, or raw fish.
Upon entering the small intestine of the definitive
host, it attaches to the mucosa and begins to
grow
What is the infective form and diagnostic form of Diphylloborithium latum?
INFECTIVE FORM: Plerocercoids
DIAGNOSTIC FORM: Unembryonated eggs passed in feces
Diphyllobothrium latum Symptoms
*Rarely is more than a single worm found in an infected human, and many victims display few if any symptoms.
*There may be abdominal pain, weight loss, weakness, and nervous disorders. (attributable to the patient’s reaction to the parasite’s metabolic wastes, to degenerating proglottids or to irritation of the intestinal mucosa.)
*Occasionally, the worm is found in the upper portions of the jejunum, in which case it can compete successfully with the
host for ingested vitamin B12.
Summary of Diphyllobothrium latum:
*Final Host
Man, dog, cat
Small intestine
*1st I.H.
Cyclops or Diaptomus
*2nd I.H.
Fresh water fish, pike, trout, salmon, perch
*Mode of Infection
Ingestion of imperfectly cooked infected fish or roe containing plerocercoid larvae
*Infection
Diphyllobothriasis
G.I. disturbances and anemia
*Diagnosis
Microscopic examination of feces for the characteristic operculated eggs
Other Pseudophyllideans Found in Humans: Sparganosis
*When procercoids of some species are accidentally ingested (e.g. swallowing copepods while drinking water) they can migrate from the gut and develop into plerocercoids.
*It can cause some rather severe pathology.
*Another pseudophyllidean is LIGULA INTESTINALIS, found in the body cavity of carp, suckers, and shiners – causes substantial changes in host behavior.
*Adult worms often occur with mergansers (fish eating ducks
