Intestinal Infections by Cestodes Flashcards
Morphology of Diphyllbothrium latum (Fish tapeworm) scolex
- It is the largest tape worm
- Formed of scolex, neck, stroblia.
- Scolex (head):
- Spoon-shaped.
- It carries two slit-like longitudinal (bothria), on dorsal and ventral sides
Morphology of strobila in D.latum
- Strobila :
- It consists of 3,000-4,000 proglottids (segments.
- Testes are numerous minute follicles situated laterally in the dorsal plane.
- The female reproductive organs are along the midline ventrally.
The ovary is bilobed . The large rosette-like uterus Lies convoluted in the center.
• The fertilized ova develop in the uterus and are discharged periodically through the uterine pore
Habitat of S.latum
Small intestine of humans
Morphology of D.latum egg
🥚:
- Ovoid, about 65 μm by 45 μm, with a thick, light brown shell .
- It has an operculum at one end and often a small knob at the other.
- The freshly passed egg contains an immature embryo
Which disease is cause by D.latum?
Diphyllobothriasis
Who is the definite host in D.latum?
- Man
2. fish eating animals ( eg. Cats or dogs)
What is the 1st intermediate host in D.latum ?
Fresh water copepod (small aquatic crustacean), mainly of genera Cyclops
What is the infective stage in humans from D.latum?
plerocercoid larva
What is the 2nd intermediate host in D.latum ?
Salmon ( fresh water fish )
Fish with plerocercoid larva of D. latum can act also as _______ if they have been eaten by another fish
paratenic host
How infection of D.latum is transmitted?
Human & fish-eating animals are infected by ——-> eating infected fishes either raw or improperly cooked (smoked or pickled) containing the plerocercoid larva
Clinical features of D.latum
- Intestinal symptoms:
* digestive disturbance, nausea, vomiting, loss of appetite, diarrhea - Mechanical intestinal obstruction
- Macrocytic anemia:
* the parasite competes with the host for vitamin B 12 leading to deficiency of this vitamin. In severe cases, patients may exhibit neurologic sequelae of vitamin B 12 deficiency
Laboratory diagnosis of fish tapeworm
- Detection of eggs in feces
2. Blood picture for anemia
What is the infection caused by the plerocercoid larva ( sparganum ) of Diphyllbothrium mansoni (Spirometra)?
Sparganosis
How humans are infected by Sparganosis?
This adult worm lives in the small intestine of animals ( dogs)
Man acts as an accidental host and is infected by:
- Ingestion of cyclops containing procercoid larva.
- Ingestion of plerocercoid larva present in uncooked meat of fishes, birds or frogs.
- Local application of raw flesh of infected animals on skin or mucosa (as a poultice).
* The solid larvae migrate to subcutaneous tissue, become encysted and develop into nodules known as spargana
How to diagnose Sparganosis?
By surgical removal of the nodules and demonstration of the worm
Describe the egg structure in both Taenia saginata and Taenia solium?
- 🥚 :
- Eggs of both species are indistinguishable
- Spherical, 30–40 μm in diameter
- Thin hyaline embryonic membrane around it, disappears after release
- The inner embryophore is radially striated
- Fully developed hexacanth embryo (oncosphere)
- The eggs of T. saginata are infective only to cattle and not to humans, whereas the eggs of T. solium are infective to pigs as well as to humans
The larval stage of Taenia is called ?
cysticercus
What is the larve of T.saginata called ?
Cysticercus bovis
What is the larva of T.solium ?
Cysticercus cellulosae
Definite host in T.Saginata & T.solium
Humans
Intermediate host in T.saginata
Cattles ( that harbor the larval stage of the worm)
Infective stage in T.saginata
- Cysticercus bovis (larval stage) is the infective stage to man, while eggs are infective to cattles only.
- Humans are infected by consuming inadequately cooked beef containing cysticercus bovis .
Intermediate host in T.solium
Pig & man
Infective stage of T.solium
—> Cysticercus cellulosae (larva) and eggs
- Humans are infected by consuming inadequately cooked pork containing cysticercus cellulosae resulting in intestinal taeniasis
- Humans can also be infected by ingestion of eggs resulting in cycticercosis disease
Clinical findings in T.saginata & Solium
- Diarrhea and sometimes Intestinal obstruction may occur by a rolled mass of worms
- Loss of weight as the parasite consumes much of patient’s food
- Migration of segments out of anus causes perianal irritation and itching
Laboratory diagnosis of T.saginata & Solium
- Microscopic stool examination for Eggs (eggs of T. saginata and T. Solium are similar).
- The Proglottids (segments) passed in feces are for species identification.
What happens in the presence of cysticercus cellulosae in human tissues ?
Cysticercosis
How Cysticercosis infection occur ?
Infection occurs after ingestion of the T.solium eggs through:
- Contaminated food or water.
- Autoinfection: patients having adult worm may be complicated with cysticercosis (external) along contaminated fingers from anus to mouth, or (internal) by reversed peristalsis.
• Symptoms depend on number, size & site of larvae
Disease of Hymenolepis nana (Dwarf tapeworm)
Hymenolepiasis
Adult worm morphology in H.nana
- H. nana is the smallest intestinal cestode that infects man.
- It is 5–45 mm in length. Scolex has 4 suckers and a retractile rostellum with a single row of hooklets
Symptoms depend on number, size & site of larvae in Cysticercosis
Mention these symptoms
- Subcutaneous mass
- Muscle Rounded masses & Myositis
- Cerebral Headache, seizures with no fever
- Ocular blurred vision
Egg morphology in H.nana
- Spherical or ovoid, 30–40 μm in s
- It has a thin colorless outer membrane and inner embryophore enclosing the hexacanth oncosphere.
- The space between 2 membranes 4–8 thread like polar filaments arising from 2 knobs on the embryophore.
- Immediately infective
Definite host in H.nana
- Human ( more common in children)
- Rats
- Mice
Mode of transmission in H.nana
ingestion of the food and water contaminated with eggs
What is the internal autoinfection of H.nana ?
may also occur when the eggs released in the intestine hatch there and the embryo penetrates the intestinal villus and develops into the cysticercoid larva and adult worm later
External auto infection in H.nana
occurs when a person ingest own eggs by fecal oral route
Clinical picture of H.nana
- Mild infection: no symptoms
- Heavy infection:
1. Intestinal irritation, enteritis with abdominal pain, anorexia, vomiting and diarrhea .
2. Nervous manifestations (due to absorption of toxic metabolic products) dizziness, insomnia & convulsions.
How to diagnose H.nana ?
Direct microscopy :
* Demonstration of characteristic eggs in feces
Morphology of Dipylidium caninum (Dog tape worm)
• The adult worm in the intestine is about 10–70 cm long
• Scolex:
has 4 prominent suckers and a retractile rostellum with up to 7 rows of spines
• Mature proglottid :
has 2 genital pores, one on either side, hence the name Dipylidium (dipylos—2 entrances)
• Gravid proglottids :
contain egg capsules and are passed out of the anus of the host singly or in groups
Disease caused by D.caninum
Dipylidiasis.
*Common tapeworm of dogs and cats, it accidentally cause human infection
Definite host in D.caninum
- Dogs
- Cats
- And rarely man
Intermediate host in D.caninum
Fleas
Infective stage of D.caninum
cysticercoid larva
Mode of transmission in D.caninum
Human acquires infection by ingestion of flea harboring cysticercoid larva
Clinical features of D.caninum
Usually symptomless
although small particles (egg capsules) that look like rice will be seen in the stool
How to diagnose D.caninum?
Stool examination:
* Finding the gravid segments or egg capsule in the stool
