1. NUTRITION AND EXCRETION OF
PARASITES
Part 3: TREMATODE, CESTODE, ACANTHOCEPHALA

2. MONOGENEAN

3. MONOGENEAN
 The mouth and buccal funnel often have associated
suckers.
 Behind the buccal funnel a short prepharynx is
followed by a muscular and glandular pharynx.
 This powerful sucking apparatus draws food into the
system.
 In Entobdella soleae the pharynx can be everted and
the pharyngeal lips closely applied to a host’s skin.

4.  Pharyngeal glands secrete a strong protease that erodes
host epidermis, and the worm sucks up the lysed
products.
 Posterior to the pharynx may be an
esophagus, although it is absent from many species.
 The esophagus may be simple or have lateral branches
and may have unicellular digestive glands opening into it.

5.  In most monogenes the intestine divides into two
lateral crura, which are often highly branched and
may even connect along their length.
 If the crura join near the posterior end of the body, it is
common for a single tube to continue posteriorly for
some distance.
 There is no anus.

6. The range of form of the
monogenean alimentary canal.
m – mouth; ph - pharynx;
int- intestinal caeca.
haptors

7. Longitudinal section through the anterior of the monogenean Polystoma
integerrimum, showing the upper alimentary tract and associated glands
Host tissue Buccal cavity
Oral sucker
Pharynx muscles
Pharynx
Food material
Intestine Gland cells
Esophagus
Vitellaria

8.  Feeding habits among Monogenoidea vary along
taxonomic lines:
- members of subclass Polyonchoinea (including families
such as Gyrodactylidae and Dactylogyridae) feeding
mainly on epidermal cells and secretions,
- members of subclass Heteronchoinea typically feeding
on blood
 In Polyonchoinea, the gut epithelium usually consists of a
single layer of one cell type.

9.  In blood-feeding heteronchoineans, host hemoglobin is
taken up by endocytosis
 As a result of digestion, hematin accumulates in gut
epithelial cells, from which it is eventually released and
regurgitated.
 The protein is taken into a cell by pinocytosis and
digested

10.  Hematin is subsequently extruded by temporary
connections between the reticular system and the gut
lumen.
 Indigestible particles are eliminated through the mouth in
all monogenes
 Can absorb neutral amino acids through its
tegument, suggesting the possibility that direct absorption
of low–molecular weight organic compounds could
supplement its blood diet

11. SURFACE MORPHOLOGY OF MONOGENEAN
These microvilli may
function to spread and
mix secretions of the
different types of head
glands.

12. DIGENEAN
Chinese liver fluke,
Clonorchis sinensis

13. DIGENEAN
 Feeding and digestion in trematodes vary with nutrient type
and habitat within their host.
 Two patterns of feeding predominate: blood feeding and
feeding on tissues and mucus.
 For example, two lung flukes of frogs, Haematoloechus
medioplexus and Haplometra cylindracea, feed predominately
on blood from the capillaries.
 Both species draw a plug of tissue into their oral sucker and
then erode host tissue by a pumping action of their
strong, muscular pharynx.

14.  Other trematode species characteristically found in the
intestine, urinary bladder, rectum, and bile ducts feed
more or less by the same mechanism, although their food
may consist of less blood and more mucus and tissue
from the wall of their habitat, and it may even include gut
contents.
 In contrast S. mansoni, living in blood vessels of the
hepatoportal system and immersed in its semi fluid blood
food, has no necessity to breach host tissues, and, not
surprisingly, this species has neither pharynx nor
muscular esophagus.

15. THE RANGE OF FORM OF THE DIGENEAN
ALIMENTARY CANAL.
A) Gastromata – one ventral mouth and
intestine in shape of sac/ bag
B) Protostomata – anterior
mouth, pharynx, esophagus, caecum/
intestine (braching into 2)
C) Complex Protostomata – extensive
barching of caecum/ intestine –
intestinal diverticulum
int – intestinal caeca; m – mouth; oes – esophagus; o.s – oral sucker;
ph – pharynx; v.s – ventral sucker

16.  A frog lung fluke, Haplometra cylindracea, has pear-shaped
gland cells in its anterior end,
 and a nonspecific esterase is secreted from these cells through
the tegument of the oral sucker, beginning the digestive
process even before food is drawn into the ceca.
 The liver fluke, Fasciola hepatica, by contrast, feeds on both
tissue and blood and completes digestion of the blood meal
intracellularly in the gasnodermis, passing waste iron to the
excretory canals to be voided.
 In Fasciola, a curious gastrodermal cell cycle has been
identified, which is related to the various phases of ingestion
and digestion of food

17.  Trematodes can absorb small molecules through their
tegument.
 Schistosoma mansoni takes in glucose only through its
tegument
 Schistosomes absorb glucose both by diffusion and by a
carrier-mediated system

18. SURFACE MORPHOLOGY OF DIGENEAN

19.  Schistosomes ingest large quantities of host blood via the
mouth and digest haemoglobin readily;
 The schistosome gut is typically delineated by the
presence of the black pigment, haematin, which is the
result of this digestion.
 In certain species they secrete some digestive enzymes:
proteases, dipeptidases, an aminopeptidase, lipases, acid
phosphatase, and esterases.

20. The proteases of schistosomes vary in their occurrence

during the life cycle and may thus have stage-specific
functions;
the haemoglobinase itself is only expressed in the
developing schistosomulum and adult worm,
 This adult protease is highly antigenic and is useful in the
diagnosis of schistosomes in subclinical human cases as
a prelude to chemotherapy.

21. Schistosome proteases may be expressed in a stage specific manner.

22. PART 3: CESTODES
 Cestodes lack any trace of a digestive tract and therefore
must absorb all required substances through their external
covering.
 All nutrient molecules must be absorbed across the tegument.
 Mechanisms of absorption include active transport, mediated
diffusion, and simple diffusion.
 Whether pinocytosis is possible at the cestode surface has
been the subject of some dispute, but plerocercoids of
Schistocephalus solidus and Ligula intestinalis are capable of
this process.
 Cysticerci of Taenia crassiceps are capable of
pinocytosis, and the process is stimulated by presence of
glucose, yeast extract, or bovine serum albumin in the
medium
Generalized diagram of a tapeworm.
scolex (a), neck (b), and strobila (c).

23. TEGUMENT
Longitudinal section through immature proglottid
of Hymenolepis diminuta, showing nature of
tegumentary cortical region.

24. ACQUISITION OF NUTRIENTS
 Glucose is the most important nutrient molecule to fuel
energy processes in tapeworms.
 The tapeworm transports carbohydrates by both carrier-
mediated systems and by diffusion
 Glycerol and glucose enter by separate carriers but both
depend on sodium ion concentration.
 Fatty acid transport is similarly complicated and separate
systems,

25. POSTULATIONS
1) Choice of organics molecules
- Only micromolecules are absorbed
- Complex proteins and macromolecules – not absorbed
- The only carbohydrates that most cestodes can absorb
are glucose and galactose, and although some
tapeworms can absorb other monosaccharides and
disaccharides.

26. - On the surface of tegument there are numerous
fingershaped tubes called microtriches
- Microtriches are similar in some respects to
microvilli found on gut mucosal cells and other
vertebrate and invertebrate transport epithelia, and
they completely cover the worm’s surface, including
its suckers
- Microtriches serve to increase absorptive area of
the tegument.

27. Posteriorly directed microtriches on the
surface of a proglottid of Hymenolepis
diminuta

28. 2) Tegument may possess some enzymes to digest some food particles
- Hymenolepis diminuta synthesizes digestive
phosphohydrolases, hydrolysing phosphate esters, monoglyceride
hydrolases and ribonucleases, all of which function in a digestive
capacity at the tegumental surface.
- The tapeworm can also bind host digestive enzymes, such as
amylases, where upon enzyme activity may become enhanced
- Conversely, tapeworms can bind and inhibit host enzymes (e.g.
trypsin, chymotrypsin) and this is possibly one adaptation for parasite
survival in an enzymatically hostile environment.

29. 3) Exchange of proteins (in the form amino acids) between
parasite and the host cells
- Amino acids are also actively transported and accumulated
- Presence of other amino acids in the ambient medium
stimulates efflux of amino acids from the worm; therefore, the
worm pool of amino acids rapidly comes to equilibrium with
amino acids in the intestinal milieu.
- Purines and pyrimidines are absorbed by facilitated diffusion
 Amino acid and purine/pyrimidine transport are complex
processes: there are six separate amino acid carriers; four
transporting neutral amino acids, one for acidic and one for
basic amino acids; and at least three purine/pyrimidine carriers
with multiple binding capacity.

30. EXCRETION AND OSMOREGULATION OF CESTODES
 In many families of cestodes the main excretory canals run the
length of the strobila from the scolex to the posterior end.
 These are usually in two pairs, one ventrolateral and the other
dorsolateral on each side
 Most often the dorsal pair is smaller in diameter than is the
ventral pair
 The canals may branch and rejoin throughout the strobila or
may be independent.
 Usually a transverse canal joins the ventral canals at the
posterior margin of each proglottid.

31. DIAGRAM SHOWING THE TYPICAL ARRANGEMENT
OF DORSAL (D) AND VENTRAL (V) OSMOREGULATORY CANALS.

32.  The dorsal and ventral canals unite in the scolex, often with
some degree of branching.
 Posteriorly, the two pairs of canals merge into an excretory
bladder with a single pore to the outside.
 When the terminal proglottid of a polyzoic species
detaches, the canals empty independently at the end of the
strobila.
 Rarely the major canals also empty through short, lateral
ducts.
 In some orders, such as Pseudophyllidea, canals form a
network that lacks major dorsal and ventral ducts.

33.  Embedded throughout the parenchyma are flame cell
protonephridia, whose ductules feed into the main canals.
 The flagella of a flame cell provide motive force to the fluid in
the system.
 Protonephridia of tapeworms show the weir construction.
*weir – is formed by rods from both the terminal flagellated cell

34. DIAGRAM OF TERMINAL ORGAN OF FLAME CELL PROTONEPHRIDIUM
IN HYMENOLEPIS DIMINUTA.
The flame is composed of
approximately 50 - 100
flagella.

35.  The excretory ducts are lined with
microvilli thus suggesting that the
duct linings serve a transport
function.
 Therefore, functions of the
system might include active
transport of excretory wastes and
ionic regulation of the excretory
fluid.
Low-magnification electron micrograph of
 Fluid from the excretory canals of excretory duct of Hymenolepis diminuta
H. diminuta contains showing beadlike microvilli (MV).
glucose, soluble proteins, lactic
acid, urea, and ammonia but no
lipid.

36.  The principal end products of cestode energy
metabolism, short-chain organic acids, are probably
excreted through the tegument, either by diffusion.
 Osmoregulation is another function of the tegumental
surface.
 With little ability to regulate their body volume in media of
differing osmotic concentrations,

37.  Hymenolepis diminuta can osmoregulate between 210
and 335 mOsm/L in a balanced salt solution if 5 mM
glucose is present.
 The worms rapidly lose water at pH 7.4 and 300 mOsm/L
without glucose.
 Water balance in H. diminuta is closely related to
excretory acid concentration and pH of the medium.

38. ACANTHOCEPHALA: THORNY-HEADED WORMS
 Acanthocephala is a small group of obligate parasites that
utilize arthropods and vertebrates in a conserved two-host
life cycle.
 Inhabit the intestine of fishes, amphibians, reptiles
(rarely), birds, and mammals, in which they occasionally
cause serious disease.
 The acanthocephalan body consists of an anterior
proboscis, a neck, and a trunk

39. Examples of different types of acanthocephalan proboscides
(a) Octospiniferoides australis; (b) Sphaerechinorhynchus serpenticola; (c) Oncicola spirula; (d)
Acanthosentis acanthuri; (e) Pomphorhynchus yamagutii; (f) Paracanthocephalus rauschi; (g)
Mediorhynchus wardae; (h) Palliolisentis polyonca; (i) Owilfordia olseni.

40. Scanning electron micrographs of
Leptorhynchoides thecatus
Note some of the major anatomical
Quadrigyrus nickoli, illustrating basic features of acanthocephalans.
acanthocephalan morphology. P, proboscis; H, hook; N, neck;
(a) Female; (b) male. T, trunk

41. ACQUISITION AND USE OF NUTRIENTS
 Have no gut and obtain all nutrient molecules through
their body surfaces and is facilitated by a syncytial
epidermis and a lacunar system of circulatory channels.
 Lacunar system refers to a network of fluid-filled channels
in the body wall.
 The acanthocephalan surface is physiologically
comparable although morphologically quite different from
the platyhelminths.

42.  Acanthocephalans can absorb at least some
triglycerides, amino acids, nucleotides, and sugars.
 The surface of Moniliformis moniliformis contains
peptidases, which can cleave several dipeptides, and the
amino acid products are then absorbed by the worm.
 In several other species, lysine is absorbed across the
metasomal tegument, especially the anterior portion, and
accumulates in nuclei and the outer muscle belt.

43. Tegument of Moniliformis moniliformis
(a) Diagram of transverse section to show layers. The felt-fiber zone contains many vesicles and mitochondria with
poorly developed cristae. Lacunar canals are in the radial fiber zone.
(b) Electron micrograph showing the major features of the striped zone. The worm is coated with a finely filamentous
surface coat (SC). Numerous surface crypts (C) appear as large scattered vesicular structures with elements
occasionally appearing to course to the surface of the helminth. The crypts are separated by patches of moderately
electronopaque material (*), giving the zone its striped appearance under the light microscope. Mitochondria
(M), glycogen particles, microtubules, and other cytoplasmic details are evident in the inner portion of the striped zone.
Bundles of fine cytoplasmic filaments (f) extend between this region and the deeper cytoplasm of the body wall

44. Organization of lacunar system in Macracanthorhynchus hirudinaceus
(a) Midmetasomal region; (b) region near neck, with presomal lacunar system not
indicated; (c) near posterior end of metasoma. DLC, dorsal longitudinal channel;
HC, hypodermal canal (in radial fiber zone); MLC, medial longitudinal channel;
PRC, primary ring canal; RC, radial canal; SRC, secondary ring canal; VLC, ventral
longitudinal channel.

45.  The uptake started in the anterior half of the proboscis
 M. moniliformis has an absolute dependence on host
dietary carbohydrate for growth and energy metabolism as
an adult.
 The worm can absorb glucose, mannose, fructose, and
galactose, as well as several glucose analogs.
 M. moniliformis can grow and mature in the host fed a diet
containing fructose as the sole carbohydrate source.

46.  Absorption of glucose is through a single transport
locus, whereas transport of mannose, fructose, and
galactose is mediated both by the glucose locus and the
fructose site.
 Maltose and glucose-6-phosphate (G6P) are absorbed
also, but first they are hydrolyzed to glucose by enzymes
in or on the tegumental surface.

47.  Acanthocephalans also accumulate a variety of nonorganic
molecules, including heavy metals.
 M. moniliformis took up more lead and cadmium than their rat
hosts, concentrating both mainly in female worms, the lead especially
in eggs.
 Acanthocephalan species parasitizing fish take up so much heavy
metal—up to 200 times as much as their hosts—that the worms are
potentially useful as bioindicators of pollution
 At least 16 different elements are taken up.
 In some cases worms compete with one another and with their fish
hosts for these substances.

48. EXCRETORY SYSTEM
 Excretion in most species appears to be effected by diffusion through
the body wall.
 However, members of Oligacanthorhynchidae, one family in class
Archiacanthocephala, are unique in possessing two protonephridial
excretory organs.
 Each comprises many anucleate flame bulbs with tufts of flagella and
may or may not be encapsulated, depending on species.
 In males these organs are attached to the vas deferens and empty
through it;
 In females they are attached to the uterine bell and empty into the
uterus.

49.  Acanthocephalans show little ability to
osmoregulate, swelling in hypotonic, balanced saline or
sucrose solutions and becoming flaccid in hypertonic
solutions.
 They take up sodium and potassium, swelling in
hypertonic solutions of sodium chloride or potassium
chloride at 37°C.
 In balanced saline they lose sodium and accumulate
potassium against a concentration gradient.