Lecture Notes in Medical Technology: Lecture #5: THE CESTODES OR TAPEWORMS

General characteristics

1. They are ribbon like parasites, segmented, flattened dorso–ventrally and varies from a few millimeter to several meters.

a. Composed anteriorly of an attenuated structure called scolex, whose main function is for attachment.

b. Neck which follows the scolex and is the site of proliferation.

c. Strobila or body which consists of segments differentiated into immature, mature and gravid proglottids.

(1) The immature segment lies proximal to the neck and is composed of immature reproductive organs.

(2) The mature or middle segment contains the well–developed reproductive organs.

(3) The distal most portions are the gravid segment which is characterized by its uteri filled with eggs.

2. They are hermaphrodites (monoecious).

3. Adults are attached to the intestinal wall by means of suckers or by hooks found at the posterior portion.

4. There is no special digestive tract; nutrition is mainly derived from absorption of digested materials thru its integument.

5. Excretory system is as primitive as that of trematodes.

6. Nervous system is confined primarily to the scolex.

7. Genital organs are elaborately developed in each proglottid. The testes are usually multiple and are distributed throughout the median plane of each mature proglottid; the ovary is commonly a bilobed organ posterior to the equatorial plane of each proglottid.

8. The eggs are essentially spherical, non–operculated, almost fully embryonated when they escape from mother proglottid except for the Pseudophyllideans wherein the eggs are ovoidal, operculated and immature when lay.

9. Requires at least one intermediate host for transmission, except for D. latum where two intermediate hosts are required and H. nana where no intermediate host is needed.

The definitive host becomes infected with the adult tapeworm from ingestion of the mature larva in its intermediate host tissue. Man is the definite host of most tapeworms to which he is susceptible. Exceptions are E. granulosus and Multiceps sp. of which the dog is the usual definitive host and man an intermediate host; also Taenia solium, of which man maybe an intermediate host as well as the only definite host.

10. Infection is generally by encysted larva.

Classification of Cestodes

1. Pseudophyllidean

a. Diphylobotrium latum – Broadfish tapeworm

b. Diphylobotrium mansoni (spirometra mansoni)

2. Cyclophyllidean

a. Taenia solium – pork tapeworm

b. Taenia saginata – beef tapeworm

c. Hymenolepis nana – dwarf tapeworm

d. Hymenolepis diminuta – rat tapeworm

e. Dipylidium caninum – dog tapeworm

f. Echinococcus granulosus – hydatid tapeworm

g. Raillietinia sp.

DIFFERENCE BETWEEN THE TWO TYPES OF CESTODES

PSEUDOPHYLLIDEAN CYCLOPHYLLIDEAN

# of host 2 1

Needs water in L.C. needed not needed

Stages of eggs immature, operculated mature,

non–operculated

Type of larval stage solid bladder or cystic

Hatching occurs in water occurs after ingestion

by intermediate host

Embryo coracedium or ciliated larva oncosphere, hexacanth

(free swimming) embryo (non–ciliated)

Scolex spatulate or spoon–like with quadrates or globular

Sulci or bothria mid–ventrally with4 cuplike muscular

& mid–dorsally suckers; rostellum may

be armed or unarmed

with hooklets open

at the margin of the

segment

Method of egg via uterine pore by apolysis

dissemination (detachment and

disintegration of

gravid segment)

DIPHYLLOBOTHRIUM LATUM / DIBOTHRIOCEPHALUS LATUS

Common name: Broad tapeworm or breadfish tapeworm

Disease: Diphyllobothriasis or fish tapeworm infection

Sparganosis

Infective stage: Adult and larva (sparganum)

1^st Intermediate Host: Copepods (Diaptomus vulbaris, D. gracilis, Cyclops)

2^nd Intermediate Host: Fresh water fish

Life Cycle

Adult

Egg

************ TAENIA SOLIUM ***********

Common name: Pork tapeworm

Disease: Taeniasis solium

Cysticercosis cellulosae

Adult worm

Ova

Life cycle

************ TAENIA SAGINATA ************

Common name: Beef tapeworm

Disease: Taeniasis saginata or beef tapeworm infection

Adult worm

Life cycle

Same as in T. solium except that the intermediate host is the cattle and the larval stage is called the cysticercus bovis.

Difference between T. solium & T. Saginata

************ DIPYLIDIUM CANINUM ************

Common name: Double–pored dog tapeworm

Disease: Dipylidiasis or dog tapeworm infection

Adult

Eggs

Intermediate host: Flea (Ctenocephalides sp.) – for dog and cat

Pulex – for man, an accidental host

Life cycle

************ HYMENOLEPIS NANA ************

Common name: Dwarf tapeworm

Disease: Hymenolepiasis nana

Adult is small measuring up to 25–40 mm in length; the minute scolex is rhomboidal, has 4 hemi–spherical suckers and rostellum, armed with 20–30 spines in 1 ring; long slender neck; very short, narrow immature proglottids, those more distal in position become increasingly wider and broader; the distal end of the strobila.

Eggs are spherical or sub–spherical, hyaline, measuring 30–47u and contains an oncosphere which is enclosed in an inner envelope with 2 polar thickening, from each of which arise 4–8 polar filaments; within the oncosphere are 3 pairs of lancet–shaped hooklets.