This document summarizes key information about cestodes (tapeworms). It describes the morphology, lifecycles and transmission of Taenia saginata, Taenia solium, and Echinococcus granulosus. T. saginata causes intestinal taeniasis in humans through ingestion of undercooked beef containing the larval stage. T. solium can cause intestinal taeniasis or cysticercosis depending if the person is a definitive or intermediate host. E. granulosus causes cystic hydatid disease in humans through ingestion of food contaminated by dog feces containing eggs.

1. CESTODES
DR. SUMESH KUMAR DASH
PG RESIDENT,
DEPARTMENT OF MICROBIOLOGY,
IMS & SUM HOSPITAL.

2. MORPHOLOGY
 In their life cycle, they exist in three morphological
forms: 1) Adult worm 2) Egg 3) Larva
Adult Worm Usually found in the intestine of men and
animals
Shape Long, segmented, flattened dorsoventrally, tape
like worms hence also called as tapeworms.
Size Cestodes vary from few millimeter to several meter.
Hymenolepis nana (smallest tapeworm;1–4 cm),
Diphyllobothrium (Longest10 meters or more)
Body Structure Adult worm consists of three parts:
1. Head or scolex (Organ of attachment)
2. Neck (Segmented / Proglottids)
3. Strobila (Body or trunk)

3. TAENIA SAGINATA
 Habitat: Small intestine (jejunum and ileum) of humans,
 Manifestations: Intestinal taeniasis
 Host: Men (Definitive)
Cattle (Intermediate)
 Infective stage:
Cysticercus bovis (larval stage) is the infective stage to men while eggs are infective to
cattle.
 Mode of transmission:
Man acquires the infection by ingestion of undercooked beef containing encysted
larval stage (cysticercus bovis)

4. INTESTINAL TAENIASIS
 Both T. Saginata and T. Solium can cause intestinal taeniasis.
 Often, it is asymptomatic.
 Patients become aware of the infection most commonly by noting the passage of
proglottids in their feces.
 The proglottids are often motile, and patients may experience perianal discomfort (or
pruritus) when these are discharged.
 Mild abdominal pain or discomfort, nausea, loss of appetite, weakness, weight loss,
headache and change in bowel habit (constipation or diarrhoea) can occur.
 Occasionally obstruction by the migrating proglottids can result in appendicitis or
cholangitis.

5. Laboratory diagnosis
 Stool examination - Detects eggs,
proglottids
 Taenia specific coproantigen detection in
stool - ELISA
 Antibody detection in serum - ELISA
 Molecular method - PCR

6. Treatment
 Praziquantel (drug of choice): Single dose of (10 mg/kg) is highly effective
 Niclosamide (2 g) is also effective but is not widely available.

7. TAENIA SOLIUM
 Habitat: Small intestine (Adult worm)
Muscle, brain and eyes (Larva)
 Manifestations: Cysticercosis
Intestinal taeniasis
 Host: Man acts as both definitive and intermediate host.
 Infective stage: Eggs of T. solium.
 Mode of transmission: Firstly man acquire the infection by
1. Ingestion of contaminated food or water with eggs of T. solium and
2. Autoinfection (Eggs excreted from men reinfect the same individual)
 External autoinfection: Due to unhygienic personal habit, e.g., contaminated
finger
 Internal autoinfection: Due to reverse peristaltic movements by which the gravid
segments throw the eggs back into the stomach (equivalent to swallowing of the

8. CYSTICERCOSIS
 Clinical spectra of the disease depend upon the localization of the cyst.
 Though it is discovered from any site of the body but the common sites are central
nervous system (CNS),subcutaneous tissue, skeletal muscle and eyes.
 Neurocysticercosis (NCC): Most common parasitic CNS infection of man and the
most common cause of adult onset epilepsy throughout the world
 Ocular cysticercosis: Can involve eye lids, conjunctiva and sclera. Common
symptoms like proptosis, diplopia, loss of vision and slow growing nodule with focal
inflammation.
 Subcutaneous cysticercosis: It is frequently asymptomatic but may manifest as
palpable nodules
 Muscular cysticercosis: Manifest as muscular pain, weakness or pseudohypertrophy

9. Laboratory diagnosis
 Radiodiagnosis - CT scan and MRI
 Antibody detection in serum or CSF -
ELISA
 Antigen detection in serum or CSF -
ELISA
 Lymphocyte transformation test
 Histopathology of muscles, eyes,
subcutaneous tissues or brain biopsies
 FNAC of cyst
 Modified Del Brutto diagnostic criteria

10. Treatment
ANTIPARASITIC
 Albendazole (15 mg/kg per day for 8–28 days)
 Praziquantel (50–100 mg/kg daily in three divided doses for 15–30 days)
SYMPTOMATIC TREATMENT
SURGERY
 Open craniotomy to remove cysticerci is rarely required nowadays
 Indicated for ocular and spinal and ventricular lesions because anti parasitic drugs
can provoke irreversible inflammatory damage.

11. PREVENSION
 Adequate cooking of beef or pork viscera
 Exposure to temperatures as low as 56°C for 5 minutes
 Refrigeration at 4C for 30days
 Effective fecal disposal to prevent infection to cattle and pigs.
 Treatment and prevention of human intestinal infections.

12. ECHINOCOCCUS
 Echinococcus causes hydatid disease in man.
 There are four species of Echinococcus known to infect humans:
 E. granulosus: Causes cystic hydatid disease
 E. multilocularis: Causes alveolar hydatid disease
 E. vogeli and E. oligarthrus: Cause polycystic hydatid disease.

13. ECHINOCOCCUS GRANULOSUS
Also called as dog tapeworm.
Habitat
 The larval form (hydatid cyst) is found in liver and other viscera of man and other
herbivores.
 The adult worms reside in dog’s intestine.
Morphology
 Adult Worm It is much smaller than other cestodes.
 Eggs Similar to Taenia eggs.
 Larva The larval form of E. granulosus is called as hydatid cyst.

14. Hydatid cyst (Larva)
 Unilocular, subspherical, shape and size varies from few
millimeters to more than 30 cm (usual size 5–8 cm)
 Appears as fluid filled bladder like cyst
 Cyst wall consists of three layers:
1. Pericyst (outer layer, host derived): Consists of fibrous
tissue and blood vessels produced by the host cellular
reaction
2. Ectocyst (middle layer, parasite derived): It is a tough
elastic, glycan rich acellular hyaline layer of variable
thickness (1 mm). It resembles the white of a hardboiled
egg.
3. Endocyst (inner layer, parasite derived): Germinal layer,
22–25 µm thickness.

15. Hydatid fluid
 It is clear, colorless to pale yellow h It has a pH of 6.7
 It contains sodium chloride, sodium sulfate, sodium phosphate and succinates.
 It is antigenic, toxic and anaphylactic
Hydatid sand
 Some of the brood capsules and protoscolices break off and gets deposited at the
bottom as granular deposit to form the hydatid sand.
Fate of the hydatid cyst
 Spontaneous resolution may happen to few cysts.
 Rupture of the cyst may either lead to: − Formation of secondary cysts

16. Life cycle
Host
 Dogs and other canine animals (Definitive host)
 Sheep and other herbivores (Intermediate host)
 Man (Accidental intermediate host) (dead end).
Mode of transmission
 Men (and other intermediate hosts) acquire the infection by ingestion of food
contaminated with dog’s feces containing E. granulosus eggs.
Infective from
 Eggs / Cyst

18. Clinical features
 Infection usually occurs in childhood but gets manifested in adult life.
 Most common site of location of the cyst is liver (60–70%, right lobe) or lung (20–30%)
but may be found in any organs like spleen and kidney (3–5%), brain and heart (1–1.5%)
and rarely bones
 Many cases are asymptomatic and infection is detected only incidentally by imaging
studies
Symptoms occur due to
 Pressure effect of the enlarging cyst leads to palpable abdominal mass, hepatomegaly,
abdominal tenderness, portal hypertension and ascites
 Obstruction by daughter cyst may erode into the biliary tree or a bronchus and enter into
the lumen to cause cholestasis and dyspnea.
 Secondary bacterial infection can cause pyogenic abscess formation in the hydatid cysts.

19. Laboratory diagnosis
 Hydatid fluid microscopy (direct mount or staining with acid
fast stain) - detects brood capsules and protoscolices
 Histological examination (H & E) - demonstrates cyst wall
and attached brood capsules
 Antibody detection - IHA, LAT, IFA, ELISA, Western blot
 Antigen detection—ELISA, CIEP, LAT
 Imaging methods - X-ray, USG (demonstrates Water lily
sign), CT scan, MRI
 Molecular method - PCR
 Skin test (Casoni test)

20. Treatment
Therapy for cystic echinococcosis is based on the considerations like–size, location, and
manifestations of cysts and overall health of the patient.
PAIR (puncture, aspiration, injection and re-aspiration)
 Alternate method recommended instead of surgery.
 Higher cure rate, less recurrence rate, less complications and hospitalization compared to
surgery
Surgery
 Though surgery is the definitive method of treatment, it should be reserved for cases where
PAIR is contraindicated or Secondary bacterial infection or Advanced disease
Antiparasitic agents
 Albendazole is the drug of choice, given to prevent recurrence and to reduce the size of the
cyst before surgery or PAIR

21. Prevention
 Administering praziquantel to infected dogs.
 To improve personal hygiene to reduce contamination of food and water with dog’s
feces
 Vaccinating the sheep
 Limitation of stray dogs population