Date post: | 19-Feb-2017 |
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CESTODES : general properties
• Flat worms, tape-like, Segmented parasites
• Length range from mm to meters
• Scolex (Head) provided with suckers, Hooks +/-
• Adult worms are in Gastrointestinal tract
• Digestive tract is absent, absorb
nutrients from body wall
• Hermophrodites, Reproductive system,
Excretory & Nervous systems present
• complete chain of segments known as strobila,
Segment – Proglottid
• Life span – 5 to 25 years
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Important Cestodes
Taenia saginata : Beef tapeworm
Taenia solium : Pork tapeworm
Echinococcus granulosus : Dog tape worm
Taenia asiatica : Asian tapeworm (morphology close to T.saginata; life cycle similar to T.solium))
Diphyllobothrium latum : Fish tape worm
Hymenolepis nana : Dwarf tape worm
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1. Spherical
2. Bile stained (yellowish-Brown)
3. Striated wall
4. Size 30-40 micron in diameter
5. With embryo – oncosphere
6. THREE pairs of hooklets
Eggs of T.solium and T. saginata
are indistinguishable
Larva of T. saginata - cysticercus bovis Larva of T. solium - cysticercus cellulosae
Cysticercus larva
T.saginata T.solium
Length (meters) 3 to 10 (upto 25) 2 to 5 (upto 7)
Suckers 4 4
Rostellum &
Hooklets
Absent Present
Proglottids 1000 to 2000 1000
Eggs production
/proglottid
100000 50000
Mode of Transmission
Ingestion of raw or under cooked
Beef (T.saginata) or Pork (T.soilum)
with encysted larval stage
- cysticercus
Humans develop intestinal infection with adult worms after ingestion of
contaminated pork or may develop cysticercosis after ingestion of
T. solium eggs (making humans intermediate hosts).
1. Humans ingest raw or undercooked pork containing cysticerci (larvae).
2. After ingestion, cysts evaginate, attach to the small intestine by their
scolex, and mature into adult worms in about 2 mo.
3. Adult tapeworms produce proglottids, which become gravid;
they detach from the tapeworm and migrate to the anus.
4. Detached proglottids, eggs, or both are passed from the
definitive host (human) in feces.
5. Pigs or humans become infected by ingesting embryonated eggs
or gravid proglottids (eg, in fecally contaminated food).
Autoinfection may occur in humans if proglottids pass from
the intestine to the stomach via reverse peristalsis.
6. After eggs are ingested, they hatch in the intestine and
release oncospheres, which penetrate the intestinal wall.
7. Oncospheres travel through the bloodstream to striated muscles
and to the brain, liver, and other organs, where they develop into
cysticerci. Cysticercosis can result.
• All species of Taenia cause Taeniasis (Intestine) and
• T.solium cause Taeniasis (Intestine) & cysticercosis (extra-intestinal)
Signs and Symptoms : • Most people – Asymptomatic or mild symptoms.
• Tapeworms can cause digestive problems
including abdominal pain, loss of appetite, weight
loss, diarrhea and upset stomach.
• Most visible symptom - passing of proglottids
• RARE - tapeworm segments become lodged in the
appendix (appendicitis), or the bile ducts
(cholangitis) • Infection with T. solium tapeworms can result in
human cysticercosis, - cause seizures and muscle
or eye damage.
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Laboratory Diagnosis : Stool Examination
1. Macroscopic examination :
Proglottids
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2. Microscopic examination :
Eggs
T.Solium <12 uterine
branches
and
T. saginata, >12 uterine
branches
Bile stained
30-35 Microns in diameter
are radially-striated.
The internal oncosphere contains
six refractile hooks.
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Treatment :
AntiHelminthic Drugs :
praziquantel or niclosamide
Prevention : Food Safety : Adequate safe cooking of beef or pork destroys cysticerci.
Freezing (-10°c for 9 days) or long period and salting is lethal to
cysticerci.
Cysticerci do not survive temperatures below -10o c and above 60o c.
Personal Hygiene : Autoinfection or ingestion of egg is limited by good personal hygiene and
hand washing, after toilet use
Public Health measures : Inspection of Slaughter House, Examination of Food Handlers,
Proper excreta disposal system
Pathogenesis & Presentation
Invasive oncospheres (embryos) in the eggs are
liberated by the action of gastric acid and intestinal fluids
- actively cross intestinal wall, enter the bloodstream,
and are carried to the muscles and other tissues.
At small terminal vessels, they establish and encyst as
cysticerci , reaching their definitive size of about
1 cm in 2–3 months.
Clinical manifestations depend on
the affected organ; neurocysticercosis and ophthalmic
cysticercosis are associated with substantial morbidity.
Signs and symptoms :
• Cysts in the muscles:
– Cysts in the muscles generally do not cause symptoms. Able to feel lumps under your skin. The lumps sometimes become tender.
– Subcutaneous cysticercosis presents as small, movable, painless nodules that are most commonly noticed in the arms or chest
– After a few months or even years, the nodules become swollen,tender, and inflamed, and then they gradually disappear
• Cysts in the eyes: Ophthalmic cysticercosis
– Although rare, cysts may float in the eye and cause blurry or disturbed vision. Infection in the eyes may cause swelling or detachment of the retina.
Neurocysticercosis (cysts in the brain, spinal cord):
Symptoms of neurocysticercosis depend upon where
and how many cysts are found in the brain.
Seizures and headaches are the most common symptoms.
However, confusion, lack of attention to people
and surroundings, difficulty with balance,
excess fluid around the brain (called hydrocephalus)
may also occur.
The disease can result in death.
Laboratory Diagnosis : • Biopsy or fine-needle cytology of a subcutaneous
nodule helps to confirm the diagnosis of cysticercosis
infection.
• *An Enzyme-Linked Immuno blot (EITB) assay was
developed for immunodiagnosing human
cysticercosis.
• Calcified larvae in the subcutaneous and muscle
tissues can be identified by an X-ray examination
• CT scan and MRI can detect the lesions
• Patients may have higher IgE level in their serum
• A finding of eosinophils in the cerebrospinal fluid
suggests the diagnosis of neurocysticercosis.
• PCR tests have been developed to detect T.
solium DNA in CSF
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In cases where two or more cysts are present, this assay is very
sensitive, 100% and 95%, using serum or CSF, respectively, and is
essentially 100% specific for either sample.
Typical antibody reactions immunoblot for cysticercosis
CDC immunoblot for cysticercosis. Cysticercosis-specific antibodies
react with 7 glycoproteins derived from T. solium cysts.
molecular masses of 7 diagnostic glycoproteins are expressed in kDa
A positive result - any one of 7 cysticercosis-specific proteins.
MANAGEMENT
• OCULAR CYSTICERCOSIS: the cysts are removed surgically
• SUBCUTANEOUS CYSTICERCOSIS - Excisonal biopsies are performed
• NEURO CYSTICERCOSIS
ALBENDAZOLE & PRAZIQUANTEL are relatively successful as treatments.
• Supporting therapy with CORTICOSTEROIDS and anti-epileptic drugs
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The focus of initial therapy is control of seizures, edema,
intracranial hypertension, or hydrocephalus, when one of
these conditions is present.
Anthelminthic therapy, because it kills viable cysts and
provokes an inflammatory response, may actually increase
symptoms acutely.
Co-administration of corticosteroids that cross the
blood brain barrier (e.g. dexamethasone) is used to
mitigate these effects
Several studies suggest that albendazole
(conventional dosage 15 mg/kg/day in 2 divided doses for 15
days) may be superior to praziquantel
(50 mg/kg/day for 15 days) for the treatment of
neurocysticercosis.
Human echinococcosis (hydatidosis, or hydatid disease)
Echinococcus granulosus , E. multilocularis
• Human echinococcosis is caused
by the larval stages genus Echinococcus
• More than 1 million people are affected with
echinococcosis
• Humans are infected through ingestion of parasite eggs in
contaminated food, water or soil, or through direct contact
with animal hosts.
Important forms of the disease in humans :
1. cystic echinococcosis (hydatid disease or hydatidosis)
Echinococcus granulosus
2. alveolar echinococcosis.
E. multilocularis
LIFE CYCLE :
• Dogs ingest the organs of other animals that contain hydatid cysts.
• The cysts develop into adult tapeworms in the dog.
• Infected dogs shed tapeworm eggs in their feces
• Sheep, cattle, goats, and pigs ingest tapeworm eggs in the contaminated ground; once ingested, the eggs hatch and develop into cysts in the internal organs.
• The most common mode of transmission to humans is by the accidental consumption of soil, water, or food that has been contaminated by the fecal matter of an infected dog.
• Echinococcus eggs that have been deposited in soil can stay viable for up to a year.
• The definitive host becomes infected by ingesting the cyst-containing organs of the infected intermediate host. After ingestion, the protoscolices evaginate, attach to the intestinal mucosa , and develop into adult stages in 32 to 80 days.
sheep, goat, swine, cattle, horses, camel
ingesting the
cyst-containing
organs of the
infected
intermediate host
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• Consumption of contaminated food & water with eggs of the parasite of an infected dog.
• Embryo : oncosphere or hexcanth larva
hatch in small intestine, Penetrate gut mucosa, enter the circulation
• Via Blood stream carried to various organs and settle down any organ: Most common organ is LIVER, other include Lungs, Heart, Brain
• Larva start to grow & forms cystic cavity:HYDATID CYST
• Inner wall contain germinal layer gives rise to Brood capsule and inside protoscolices develop
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Mode of transmission and life cycle in Humans
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Brood capsules detached,
are called as daughter cysts
Cyst enlarges 1-5 cm per
year; becomes symptomatic
at 10 cm
Cyst-growth leads to loss of
function of the organ in which
it is situated
• The same life cycle occurs with
E. multilocularis (1.2 to 3.7 mm),
with the following differences:
the definitive hosts are foxes, and to a lesser extent
dogs, cats, and wolves; the intermediate host are small
rodents.
Mortality rate is high 50 to 70 % as patients live in
remote areas where health care facilities are not easily
available
Clinical Pesentation :
development of one or more hydatids located liver and lungs,
and less frequently in the bones, kidneys, spleen, muscles,
central nervous system, and eyes.
Liver : Abdominal pain, nausea and vomiting
Lungs : chronic cough, chest pain and shortness of breath.
Alveolar/Hepatic echinococcosis - an asymptomatic
incubation period of 5–15 years & slow development of a
primary tumour-like lesion which is usually located in the liver.
Clinical signs include weight loss, abdominal pain, general
malaise and signs of hepatic failure. May spread to spleen,
lungs, brain
Complications caused by rupture of cysts, Immunologic
reactions - anaphylaxis, due to release of antigenic
material
Laboratory Diagnosis
- Imaging techniques - CT scan, ultrasonography, and MRIs, are used to detect cysts.
- After cyst detection - Serology tests may be used to confirm the diagnosis - ELISA, Immunofluorescent assay.
- Pulmonary cysts - routine chest x-ray
- Examination of the cyst fluid [Hydatid sand]
shows typical invaginated scolices & is diagnostic
- CASONI’s test : Intradermal Skin test -Antigen derived from hydatid fluid is injected
- CBC may detect eosinophilia
Treatment
• Medical : mebendazole and albendazole, are the only
anthelmintics effective against cystic echinococcosis.
• Albendazole is the drug of choice against this disease
because its degree of systemic absorption and
penetration into hydatid cysts is superior to that of
mebendazole.
• Surgical Care : surgical excision of cysts. presurgical
use of albendazole in echinococcus infestations reduced
risk of recurrence
• percutaneous treatment of the hydatid cysts
• puncture-aspiration-injection-reaspiration (PAIR) therapy
– hepatic cyst therapy. • ultrasound-guided percutaneous puncture of the cyst
• aspiration of cystic fluid
• injection of a scolicidal solution
• reaspiration of the solution