This document discusses helminths, which are elongated worms that can infect humans. It focuses on two phyla: Platyhelminthes (flatworms) and Nematoda (roundworms). Specifically, it describes the characteristics and life cycles of two tapeworm species, Taenia saginata and Taenia solium. T. saginata has a two-host life cycle involving humans and cattle, while T. solium can cause both intestinal tapeworm infections and cysticercosis in humans through a pig intermediate host. The document provides detailed information on the morphology, reproduction, and larval stages of these cestode species.

1. HELMINTHOLOGY
DR VARSHA SATWIK

2. ◦ HELMINTHS are elongated flat or round worm measuring few millimeters to meters
◦ Eukaryotic multicellular & bilaterally symmetrical
◦ Two PHYLA
◦ PHYLUM PLATYHELMINTHS (FLAT WORMS) 3 classes
◦ 1.Class : Cestoidea (Tape worms)
◦ 2.Class : Trematoda ( Flukes )
◦ 3. Class : Monogenea (ectoparasite of fishes do not infect man)
◦ PHYLUM NEMATHELMINTHS (NEMATODES )

3. PLATYHELMINTHS
NEMATHELMINTHS
◦ Shape : Flattened leaf like or tape like segmented Elongated cylindrical unsegmented
◦ Body cavity : Absent Present
◦ Alimentary canal: Incomplete or absent Present
◦ Sexual differentiation : Hermaphrodite sexes separate
◦ Sexes not separate Diecious
◦ Monoecious

4. DIFFERENCES BETWEEN
CESTODES TREMATODES
NEMATODES

5. CLASSIFICATION OF HELMINTHS BASED ON
HABITAT

6. CESTODES
◦ CESTODES : PHYLUM - PLATYHELMINTHS CLASS – CESTOIDEA SUBCLASS –
EUCESTODA. TWO ORDERS – PSEUDOPHYLLIDEA & CYCLOPHYLLIDEA
◦ Several GENERA. Based on Habitat INTESTINAL CESTODES. SOMATIC / TISSUE
CESTODES
◦ MORPHOLOGY OF CESTODES : 3 forms
◦ ADULT WORM : Found in INTESTINE of MAN
◦ SHAPE – Long Segmented Flattened dorsoventrally known as Tape Worms
◦ SIZE – Few millimeters to several meters
◦ Hymenolepis nana smallest tape worm (1-4 cm)

7. ADULT WORM OF CESTODE

8. ◦ EGGS :
◦ Based on reproduction HELMINTHS classified as
◦ OVIPAROUS :
◦ After fertilization adult worm lay EGGS ( cestodes ,trematodes & intestinal nematodes except
Strongyloides)
◦ VIVIPAROUS :
◦ Some higher helminths do not have egg stage. After fertilization directly discharge LARVAE
(eg Tissue Nematodes eg Filarial worms Dracunculus & Trichinella )
◦ OVOVIVIPAROUS :
◦ Lay EGG CONTAINING LARVA that immediately hatches out (eg Strongyloides)

9. ◦ LIFE CYCLE
◦ CESTODES : TWO HOSTS Definitive Host
◦ Intermediate Host
◦ Except Hymenolepis only one host – man
◦ Diphyllobothrium 3 hosts One definitve – man
◦ Two intermediate hosts first Cyclops second Fish
TREMATODES : THREE HOSTS One Definitive host Man
Two Intermediate hosts –First Snail & Second Aquatic plant or
fish
Except Schistosomes needs Two hosts Definitive host Man &
Intermediate host Snail
NEMATODES : One host (Man) except Filarial worms (Two hosts Definitive host Man &
intermediate host Mosquito ) Dracunculus need two hosts Definitive host – Man &
Intermediate host - Cyclops.

10. ◦ BODY STRUCTURE : 3 parts Head or Scolex Neck Strobila ( body or trunk)
◦ 1.Head or scolex - Organ of attachment
Cyclophyllidean cestodes – scolex bear 4 cup like muscular suckers (acetabula) T.solium & H.nana
scolex has a beak like apical protrusion called as ROSTELLUM armed with hooklets (ARMED TAPE
WORMS)
Pseudophyllidean cestodes – scolex doesnot possess suckers but a bears a pair of longitudinal groove
called as BOTHRIA by which attaches to small intestine.
2.Neck - Next to head is NECK from which segments (PROGLOTTIDS) arise.
3.Strobila – Body surrounded by body wall known as TEGUMENT. No. of segments (proglottids)
Length varies based on no. of segments. THREE type of PROGLOTTIDS
IMMATURE : Male & Female organs are not differentiated.
MATURE : Contain Male & Female organs in the same segment.
GRAVID : Following fertilization uterus gets filled with eggs Other organs are atrophied.

11. ◦ FEMALE REPRODUCTIVE ORGANS : present on ventral side
◦ Bilobed ovary Oviduct. Ootype Vagina Uterus. Vitelline gland (vitellaria) Mehlis gland
◦ MALE GENITAL ORGANS : present on dorsal side
◦ Testes. Vas deferens
◦ NERVOUS SYSTEM : rudimentary consists of brain like structure (central ganglion lateral & rostellar
ganglia connected by central nerve ring.) present in scolex from which longitudinal nerve arises & pass
through all segments & joined by transverse nerves in each segment.
◦ EXCRETORY SYSTEM : Excretory canals are built up of FLAME CELLS & CANAL CELLS.
◦ NO CIRCULATORY SYSTEM & NO BODY CAVITY
◦ BODY WALL (TEGUMENT) : made up of outer MICROVILLUS like structure called as
MICROTHRIX
◦ Middle BASAL PLASMA MEMBRANE & inner MUSCULAR LAYER ( outer circular & inner
longitudinal muscle coats
◦

12. MATURE PROGLOTTIDS A – PSEUDOPHYILLIDEAN
CESTODES
B – CYCLOPHYLLIDEAN CESTODES

13. ◦ EGGS :
◦ Released in uterus following fertilization & fill the gravid proglottids.
◦ Pseudophyllidean cestodes : Eggs - ovoid operculated surrounded by single layer called EGG SHELL.
◦ Inside – EMBRYO containing THREE PAIRS OF HOOKLETS Membrane lining the embryo is
CILIATED.
◦ Cyclophyllidean cestodes : Eggs – round to oval covered by TWO LAYERS
◦ OUTER EGG SHELL- filled with yolk material
◦ INNER THICK – radially striated EMBRYOPHORE

14. EGGS : A – Pseudophyllidean cestodes B – Cyclophyllidean cestodes C
– Cyclophyllidean cestodes after loss of egg shell

15. ◦ LARVA : Embryonated eggs undergo further development to form larva
◦ CYCLOPHYLLIDEAN CESTODES :
◦ Larvae contain bladder like sacs :
◦ Cysticercus : Larval stage of Taenia
◦ Hydatid cyst : Larval stage of Echinococcus
◦ Coenurus : Larval satge of Multiceps
◦ Cysticercoid : Larval stage of Hymenolepis

16. LARVAE OF CYCLOPHYLLIDEAN CESTODES
A - CYSTICERCUS BOVIS B – CYSTICERCOID C- CYSTICERCUS CELLULOSAE.
D – COENURUS E- HYDATID CYST

17. ◦ CYSTICERCOID :
◦ Entire larva is solid & small bladder worm containing invaginated scolex . Characteristic of Tape worm.
◦ COENURUS :
◦ Larval stage in form of bladder worm containing many invaginated scolices.
◦ CYSTICERCUS :
◦ True bladder worm Resting stage of larva in the Intermediate host where it develops into bladder worm.
Consists of hollow vesicle with invaginated scolex on its wall & central cavity which contains fluid .From
this SCOLEX head of adult worm sprouts.
◦ This is CYSTICERCUS PROPER consists of BLADDER with one SCOLEX seen in Taenia saginata &
Taenia solium .Scolex remains invaginated within cyst wall & seen with naked eyes as milk white spots.
CYSTICERCUS BOVIS & CYSTICERCUS CELLULOSAE

18. ◦ HYDATID CYS T : ECHINOCOCCUS
◦ Bladder which multiplies by BUDDING & forms many daughter & grand daughter bladders.
◦ On wall of these cysts BROOD CAPSULES are produced inside which lye SCOLICES as in
ECHINOCOCCUS GRANULOSUS .
◦ Each scolex gives rise to one adult worm from larva.

19. CYCLOPHYLLIDEAN CESTODES
◦ TAENIA SPECIES CAUSE TWO TYPES OF MANIFESTATIONS IN HUMANS
◦ INTESTINAL TAENIASIS
◦ CYSTICERCOSIS.
◦ CLASSIFICATION : ORDER : CYCLOPHYLLIDEA
◦ FAMILY : TAENIDAE
◦ SPECIES : T.saginata (Beef tapeworm) causes intestinal taenisis in man
◦ T.solium (pork tape worm) causes both intestinal taeniasis & cysticercosis .
◦ HISTORY : CYSTICERCOSIS IS AN ANCIENT DISEASE
◦ First described in pigs by Aristophanes & Aristotle in 3rd century BC .Noticed in humans by Parunoli in
1550 . NEUROCYSTICERCOSIS was first reported in a coolie from Madras died due to seizuresby
Armstrong 1888. In 1912 Krishnaswamy reported cases of muscle pains & subcutaneous nodules with
abundant cysticerci in muscles, heart & brain through autopsy.

20. TAENIA SAGINATA
◦ GEOGRAPHICAL DISTRIBUTION : world wide
◦ HABITAT : Adult worm lives in small intestine upper jejunum of man.
◦ MORPHOLOGY :
◦ ADULT WORM: HEAD (SCOLEX) NECK & STROBILA
◦ White & semitransparent 5-10 meters in length may be 24 meters.
◦ SCOLEX : 1-2 mm in diameter Quadrate in outline & has 4 circular suckers may be pigmented . Not provided
with rostellum or hooklets & moves against peristaltic movements in host intestine.
◦ NECK : Narrow from which PROGLOTTIDS arise .
◦ STROBILA (PROGLOTTIDS) : segments 3 : IMMATURE MATURE. GRAVID
◦ No. varies from 1000-2000 Length of gravid segment is 3-4 times its breadth. Gravid proglottid while crawling
out of anal orifice oviposts in perianal skin.
◦ Life span of adult worms is 10 years.
◦

21. CARMINE STAINED
SCOLEX
A- T.SAGINATA
B- T.SOLIUM C- ADULT WORMOF TAENIA
SPS

23. ◦ EGGS : LIBERATED BY RUPTURE OF RIPE PROGLOTTIDS.
◦ CHARACTERISTICS OF EGGS –
◦ Spherical & brown in color (bile stained)
◦ 31 – 43 u in diameter
◦ Thin outer transparent shell represents remnant of yolk mass
◦ Inner embryophore is brown thick walled & radially striated
◦ Contains an onchosphere with 3 pairs of hooklets
◦ Doesnot float in saturated salt solution of common salt
◦ Eggs are resistant & can remain viable for 8 weeks
◦ INFECTIVE TO CATTLE

24. EGGS OF TAENIA SPECIES
A- saline mount B – schematic diagram

25. ◦ LIFE CYCLE :
◦ DEFINITIVE HOST : MAN
◦ INTERMEDIATE HOST : CATTLE , COW, BUFFALO HARBOURS THE LARVAL FORM
◦ INFECTIVE STAGE : CYSTICERCUS BOVIS (LARVAL STAGE) INFECTIVE TO MAN
◦ EGGS INFECTIVE TO CATTLE
◦ HUMAN CYCLE :
◦ MODE OF TRANSMISSION : Man gets infection by ingestion of undercooked beef containing encysted
larval stage (cysticercus bovis)
◦ Larva transforms to adult: Larva hatched out in small intestine , scolices exvaginate & anchor to intestinal wall
by suckers & gradually develop into adult worms.
◦ Adult worms become sexually mature in 10-14 weeks
◦ Fertilization occurs (self or cross fertilization within the segments) & EGGS formed & released in feces. EGGS
ARE INFECTIVE TO CATTLE
◦ Sometime older gravid segments break off & released in feces. They are quite mobile & migrate in feces.

26. ◦ CATTLE CYCLE :
◦ MODE OF TRANSMISSION : Eggs ingested by cows & buffaloes while grazing the field.
◦ Eggs transform to larvae : In duodenum striated walls ( embryophore) rupture releasing ONCHOSHERE .
Penetrate the gut wall with hooks & enter portal vessels or mesenteric lymphatics & further reaching systemic
circulation they further reach liver right side of heart , lungs , left side of heart.
◦ Onchosphere are filtered from circulating blood into muscular tissues & settle down.
◦ Muscles commonly selected are tongue, neck shoulder cardiac muscles.
◦ Onchosphere loose their hooks on reaching destination. Cells in centre are liquefied & in 8 days each
onchosphere form oval vesicle increasing in size containing its larva referred to as CYSTICERCUS.
◦ 60 -70 days required for an ONCHOSPHERE to metamorphise into CYSTICERCUS BOVIS.
◦ HUMANBEINGS ARE INFECTED THROUGH EATING UNDERCOOKED BEEF CONTAINING
CYSTICERCI.

27. LIFE CYCLE OF TAENIA SAGINATA

28. TAENIA SOLIUM
◦ LIFE CYCLE
◦ Human beings are infected through eating undercooked pork containing cysticerci.
◦ TAENIA SOLIUM CAUSES INTESTINAL TAENIASIS
◦ LIFE CYCLE OF TAENIA SOLIUM IS SAME AS TAENIA SAGINATA EXCEPT
◦ Intermediate host is PIG (called as PORK WORM)
◦ Men harboring adult worm excrete eggs in feces which can infect same individual as AUTOINFECTION
◦ In PIGS development time is SHORTER 7-9 weeks.
◦ Causes CYSTICERCOSIS LIFE CYCLE IS DIFFERENT.
◦ HOST : MAN acts as both DEFINITIVE & INTERMEDIATE HOST
◦ INFECTIVE STAGE : EGGS of Taenia solium
◦ MODE OF TRANSMISSION : MAN acquires infection by (1) Ingestion of contaminated food or water containing eggs of
T.solium (2) AUTO INFECTION : (a)External autoinfection- unhygienic habit contaminated fingers (b) Internal autoinfection
– Due to reverse peristaltic movements by which gravid segments throw eggs back into stomach (equivalent to swallowing of
eggs)

29. LIFE CYCLE OF TAENIA SOLIUM

30. ◦ CYSTICERCUS BOVIS
◦ LARVAL STAGE OF T.SAGINATA
◦ It develops in striated muscles of cattle.
◦ Its oval measuring 8 mm x 5 mm containing an invaginated scolex.
◦ Can survive in muscles for 2-3 years
◦ Remain viable in meat for 3 months at 0 c & for 2 weeks at -2 c
◦ If exposed to 25% solution of saline it cant survive for few days
◦ Freezing at -20 c for several days can reduce some human infections
◦ THIS LARVAL STAGE DOESNOT DEVELOP IN MAN

31. ◦ CYSTCERCUS CELLULOSAE
◦ LARVAL STAGE OF T.SOLIUM. DEVELOPS IN MUSCLES OF PIG
◦ Its ellipsoid spherical in shape measuring 5mm x 10 mm ,
◦ Yellowish white separated from host tissue by a thin collagenous capsule.
◦ Contains two chambers : Outer one is a bladder like sac filled with 0.5ml of vesicular fluid (may be upto
60 ml in brain) Inner chamber contains the growing scolex with hooklets & a spiral canal.
◦ Racemose cysticerci : In some cases when parasites are lodged in spacious area. They grow & transform
into larger lobulated cysticerci (>20 cm) containing 60 ml of vesicular fluid.
◦ They do not contain scolices within the bladder, resemble metastatic tumor.
◦ Found in brain (fourth ventricle & subarachnoid space ) & cervical spinal cord
◦ Associated frequently with HIV infected patient
◦ Prognosis of racemose cysticerci is poor.

32. Cysticercus cellulosae (surgically removed)

33. ◦ PATHOGENESIS & CLINICAL FEATURES
◦ INTESTINAL TAENIASIS
◦ Seen in T.saginata & T.solium
◦ Asymptomatic – patient passes proglottids in feces.
◦ Proglottids are often motile patients feel perianal discomfort or pruritus.
◦ Mild abdominal pain or discomfort nausea loss of appetite weakness weight loss headache & change in
bowel habbit
◦ Occasionally obstruction by migrating proglottids can result in appendicitis or cholangitis.

34. ◦ CYSTICERCOSIS
◦ Depend on localization of cyst.
◦ Common sites are CNS Subcutaneous tissue Skeletal muscle & Eyes
◦ SUBCUTANEOUS CSTICERCOSIS : asymptomatic but may manifest as palpable nodules.
◦ MUSCULAR CYSTICERCOSIS : Muscular pain weakness or pseudohypertrophy.
◦ OCULAR CYSTICERCOSIS : Involves eyelids , conjunctiva & sclera . Symptoms like proptosis , diplopia , loss of
vision & slow growing nodule with focal inflammation.
◦ NEUROCYSTICERCOSIS : (NCC) accounts for 60-90% cases for cysticercosis 30-50 years age are affected
commonly. Two types based on site of involvement.
◦ 1. PARENCHYMAL : brain parenchyma
◦ 2.EXTRAPARENCHYMAL : meninges , ventricles, spinal cord & subarachnoid space.
◦ ASYMPTOMATIC
◦ MANIFESTATIONS : Seizure Epilepsy Hydrocephalus Increased intracranial pressure Chronic meningitis Focal
neurological deficits Psychological disorders & dementia Cerebral arteritis Basal & ventricular involvement

35. ◦ LABORATORY DIAGNOSIS
◦ INTESTINAL TAENIASIS
◦ 1. Stool examination:
◦ Wet mount concentration techniques
◦ Anal swabs
◦ EGGS PROGLOTTIDS
◦ 2. Taenia specific antigen detection in stool. : ELISA developed to detect Taenia specific antigen in stool
by using polyclonal Taenia antibodies
◦ 3. Molecular methods PCR

36. ◦ CYSTICERCOSIS
1. Radiodiagnosis : CT scan MRI
2. Antibody detection : in serum or CSF – ELISA Western Blot
3. Antigen detection : in serum or CSF Lymphocyte transformation test
4. HISTOPATHOLOGY : of muscles , eyes , subcutaneous tissues or brain biopsies - detect cysticerci
5.FNAC : of cyst & staining with Giemsa stain
6. FUNDOSCPOY of eye : detects larvae
7. Del Bruttos criteria used for diagnosis of NCC