Medical Parasitology

CESTODES (Tape Worms)

Dr.Durgadas Govind Naik

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

T.solium

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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

T.Solium / T.saginata

12 T.solium – cysticercosis, - eggs

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

3 to 6 mm

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