1. ECOLOGY OF PARASITES
1 Part 2: Problems and obstacles
Parasite adaptations

2. A PARASITE’S ECOLOGICAL NICHE
 A parasite’s ecological niche includes resources provided by the living body of
another species as well as abiotic conditions encountered by transmission stages
such as eggs, cysts, spores, and juveniles.
 The digestive tract thus providing numerous microenvironments.
- A trip through the gut could be described also in terms of different symbionts
encountered along the way,
- from Entamoeba gingivalis in the mouth,
- to fourth-stage juvenile Ascaris lumbricoides in the stomach,
- to Taenia saginata (or many other helminths) in the small intestine,
- to Dientamoeba fragilis, Entamoeba coli, Endolimax nana, and Trichuris trichiura
in the large intestine, and
- finally to pinworms (Enterobius vermicularis) crawling around the anal orifice
 The blood system
 Coelom – body cavity
 In special cells – e.g microphage
 Organ – e.g lungs, liver, brain etc 2

3. IN THE ALIMENTARY CANAL
1) Total darkness
2) pH: 1.5 to 8.4
3) Many enzymes – digestive enzymes are also
capable of digesting and destroying the parasites.
4) Physiological, chemical and mechanical changes
5) Low level of oxygen
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4. TOTAL DARKNESS
 No light inside the host.
 Can be problematic to parasites.
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5. PH PROBLEM
 Mouth: pH 6.7 (5.6 – 7.5)
 Stomach:
- pH 1.49 – 8.38 (human)
- pH 3.26 – 6.24 (mice)
- pH 2.0 – 4.1 (cattle)
- pH 1.05 – 3.6 (sheep)
 Duodenum:
- pH 6.7 (human) – acidic
- pH 8.2 – 8.9 (cat, goat) – alkaline
 Implication  from mouth  stomach  duodenum 
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small intestine  CHANGES IN PH.

6. ENZYMES AND CHEMICAL PROBLEMS
 Food processing occurs in distinct phases, from
- chewing and salivary amylase action of the mouth,
- to the acid pH and proteolytic enzyme reactions of the
stomach,
- to more neutral pH and numerous amylases, proteases,
lipases, and nucleases working in the small intestine,
- to reclamation of water in the large intestine and
- subsequent elimination of solid wastes.
 Chemical – Different subtracts ingested by the host can
be problematic to the parasites.
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8. PHYSIOLOGICAL AND MECHANICAL CHANGES
 All these changes – fast and continuous can be problematic to
parasites
 Physical
- Change in the habitat/ hosts
 E.g filarial worms – mosquitoes  human
 Mechanical
– Peristalsis
 continuous and expansion of the alimentary tract – pushes food –
esophagus – stomach – small intestine – large intestine
- Food and water flow
 can be problematic to parasites
 will sweep away the parasites present in the alimentary tract
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9. LOW LEVEL OF OXYGEN
 The low level of oxygen in the alimentary tract can be
problematic to parasites.
 Low oxygen level for survival in the hosts.
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10. PARASITE ADAPTATIONS
 Physiological Adaptations
 Behavioral Adaptations
 Structural and Functional Adaptations
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11. PHYSIOLOGICAL ADAPTATIONS
1) Parasite reproduction
 Among animals, parental care is one factor that tends to increase the
chance of an offspring surviving.
 Parasites, on the other hand, exhibit little parental care, although
viviparity, or live birth, such as occurs in some nematodes and
monogeneans, can be considered a more “caring” approach than
indiscriminate scattering of eggs.
 Parasites exhibit a variety of mechanisms that function to increase
the reproductive potential of those individuals that do succeed at
finding a host.
 These mechanisms often take the form of asexual reproduction and
hermaphroditism. 11

12.  Asexual reproduction often occurs in the larval or sexually immature
stages as either polyembryony or internal budding.
 Hermaphroditism is the occurrence of both male and female sex
organs in a single individual.
 It sometimes eliminates the necessity of finding an individual of the
opposite sex for fertilization if gonads of both sexes function
simultaneously and self fertilization is mechanically possible.
 Reproductive encounters result in two fertilized female systems.
 The specific manifestations of asexual reproduction and
hermaphroditism, however, differ depending on the group of 12
parasites.

13. 13

14.  Schizogony, or multiple fission, is asexual reproduction
characteristic of some parasitic protozoa
 In schizogony the nucleus divides numerous times before cytokinesis
(cytoplasmic division) occurs, resulting in simultaneous production of
many daughter cells.
 Simple binary fission is also asexual reproduction.
 It is common among familiar free-living protozoa such as
Paramecium species as well as some amebas, including parasitic
ones.
 As with any process in which numbers double regularly, rapid fission
can result easily in millions of offspring after only a few days.
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15. Simple binary fission
Schizogony, or multiple fission
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16.  Trematodes and some tapeworms reproduce asexually
during immature stages.
 The juveniles (metacestodes) of several tapeworm
species are capable of external or internal budding of
more metacestodes.
 The cysticercus juvenile of Taenia crassiceps, for
instance, can bud off as many as a hundred small bladder
worms while in the abdominal cavity of a mouse
intermediate host.
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17.  Each new metacestode develops a scolex and neck, and
when the mouse is eaten by a carnivore, each scolex
develops into an adult tapeworm.
 The hydatid metacestode of Echinococcus granulosus is
capable of budding off hundreds of thousands of new
scolices within a fluid-filled bladder.
 When such a packet of immature worms is eaten by a
dog, vast numbers of adult cestodes are produced.
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18.  Perhaps the most remarkable asexual reproduction in all
zoology is found among trematodes, a large and
successful group of parasites commonly called flukes.
 These animals produce a series of embryo generations,
each within the body of the prior generation.
 This is an example of polyembryony, in which many
embryos develop from a single zygote.
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19.  Trematode eggs hatch into miracidia, which enter a first
intermediate host, always a mollusc, and become sac like
sporocysts.
 Sporocysts may give rise to daughter sporocysts, which,
in turn, may each produce a generation of rediae.
 These then become filled with daughter rediae, which
finally produce cercariae.
 And many flukes give birth to thousands of eggs each
day.
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20. Some life cycles of digenetic trematodes.
(1) Diplostomum flexicaudum
(2) Trichobilharzia physellae
(3) Alaria mustelae
(4) Fasciola hepatica
(5) Metorchis conjunctus
(6) Proterometra dickermani
(7) Stichorchis subtriquetrus 20
(8) Caecincola parvulus

21.  With hermaphroditism, a parasite evidently solves the problem of
finding a mate.
 Many tapeworms and trematodes can fertilize their own eggs
 This method, although not likely to produce many unusual genetic
recombinations, guarantees offspring.
 Tapeworms also undergo continuous asexual production of segments
(strobilization) from an undifferentiated region immediately behind the
scolex, or attachment organ.
 These segments, called proglottids, are each the reproductive
equivalent of a hermaphroditic worm, at least in the vast majority of
tapeworm species, because each contains both male and female
reproductive organs.
 Each fertilized female system in each proglottid eventually becomes
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filled with eggs containing larvae.

22.  The result of this combination of asexual reproduction,
hermaphroditism, and self-fertilization is a true tapeworm
egg factory.
 Whale tapeworms of the genus Hexagonoporus, for
example, are 100-foot reproductive monsters consisting
of about 45,000 proglottids, each with 5 to 14 sets of male
and female systems.
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23.  Parasites often increase reproductive potential through
production of vast numbers of eggs.
 A common rat tapeworm, Hymenolepis diminuta, for
example, produces up to 250,000 eggs a day
 During a period of slightly over a year, a single tapeworm
can thus generate a hundred million eggs.
 If all these eggs reached maturity in new hosts, they
would represent more than 20 tons of tapeworm tissue. 23

24. Female nematodes are also sometimes prodigious egg
layers;
- E.g - A single Ascaris lumbricoides can produce more
than 200,000 eggs a day for several months, and over the
course of their lifetimes
- Members of the filarial genus Wuchereria bancrofti may
release several million young into their host’s blood.
 Such high reproductive potential, of course, ensures that
such parasites will become medical and veterinary
problems when host populations are crowded and
transmission conditions are favorable.
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25. 2) Secretion of certain enzymes
 Parasite secrete pepsin if the environment gets too acidic
to neutralize the acidity environment
 E.g – Hymenolepis diminuta, Taenia taeniaformis
 Secrete anti-enyzmes
 E.g – Ascaris spp.
- 2 anti enzymes – Anti-trypsin
- Anti-chemotrypsin
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26. 3) Can undergo anaerobic metabolism
- In the absence of oxygen, certain species of
parasite can undergoes an anaerobic metabolism.
- E.g – In tapeworms
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27. 4) Thermoregulation
- Induction of certain protein to enhance the transmission
- E.g Fillarial worms – Brugia pahangi
- Mf – the most abundant protein  small heat shock
proteins
- The synthesis of small Hsps by Mf may be an adaptive
response to the potentially hostile environment of the
mammalian blood stream.
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28. BEHAVIORAL ADAPTATIONS
 Behavior is an important tool for animal survival this is
also true for parasites
 Behavior can be used to enhance their chances for
success
 There are numerous examples of parasite attributes that
presumably increase a species’ chances of encountering
new hosts.
 These attributes often influence an intermediate host in
some way, making it more susceptible to predation by a 28
definitive host.

29.  Simple host finding behaviors
 Periodic Behaviors
 Host Modifying Behaviors
 Use of intermediate larval stages on intermediate
hosts
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30. SIMPLE HOST FINDING BEHAVIORS
 eg. Entobdella (Monogenea)
- skin parasite of a stingray
- eggs are released and settle to bottom
- larvae emerge from eggs within 3 seconds of sudden
darkness
- then swim vertically upwards
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31. PERIODIC BEHAVIORS
 Parasite keys in on cyclic stimulus
 E.g Filarial Worms
- live in blood
- transmitted by mosquito or fly
- larvae (microfilariae) move to peripheral blood
on periodic basis
- corresponds to “biting hours” of local vector (flies &
mosquitoes)
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32.  E.g Guinea worm (nematode: Dracunculus
medinensis)
- occur in tropical areas; lots of rice fields
- eggs must be laid in water to be able to get to its
intermediate host
- female may contain up to 1 Million eggs each with a
developing larva inside
- larvae must be released in water to complete life cycle
- to do this female moves to part of body likely to be
immersed in water lower legs
- creates an ulcer
- discharges 1000’s of infective larvae 32

33. HOST MODIFYING BEHAVIORS
 an alternative to modifying the parasites own behavior is
to alter the hosts behavior to make it more likely to
complete parasites life cycle
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34. E.g Trematodes of the genus Dicrocoelium,
- Which infect large herbivores such as sheep
- The second intermediate host of Dicrocoelium
dendriticum is an ant.
- A metacercaria lodges in the ant’s brain, making the
insect move to the top of a grass blade, where its
likelihood of being accidentally ingested by a definitive
host is greatly increased.
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35.  E.g The immature stages of some thorny-headed worms
(phylum Acanthocephala)
- Infect freshwater crustaceans of order Amphipoda (side-
swimmers).
- Some acanthocephalan juveniles appear as conspicuous
white or orange spots in the hemocoel of the translucent
amphipods
- Making infected ones stand out from the uninfected.
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36.  E.g Fluke (Leucochloridium)
- Adult in birds; larva in snail
- When infected, snails tend to crawl to tips of
vegetation instead of hiding like normal in snail,
larvae migrate to tentacles of snail
- Larvae are brightly colored with red and green
bands
- makes snails very conspicuous in daytime
- At night the larvae withdraw into the snails body
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37. USE OF INTERMEDIATE LARVAL STAGES ON
INTERMEDIATE HOSTS
 To enhance chances of getting to final host
 simplest life cycle:
- adult parasite  eggs  ingestion by new host
 more complex life cycle:
- adult parasite  eggs  intermediate host  definitive
host
 most complex life cycle:
- flukes have several intermediate states that reproduce
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38. STRUCTURAL AND FUNCTIONAL ADAPTATIONS
 Modification of body structures/ functions
 Reduction in “unnecessary” structures and
enhancement of reproductive capacity
 Usually have a resistant stage in life cycle
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39. MODIFICATION OF BODY STRUCTURES/ FUNCTIONS
1) Structures for penetration and attachment to host
- Attaching itself to the host using special organs
– suckers, hooks, extended lips/labium, bothrium
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40. The mouth of Necator americanus. Ancylostoma duodenale,
Note the two broad cutting 40
plates in the ventrolateral
margins (top).

41. Scanning electron micrographs of
Haemonchus contortus,
Leptorhynchoides thecatus
ventral view of male. 41
Note some of the major anatomical
features of acanthocephalans. P,
proboscis; H, hook; N, neck; T, trunk

42. 42
Scolex of Taenia solium

43. 2) Body thin and long
- E.g tapeworms
- Body can curve according to the current of the food flow
- No resistance
- Prevents being broken up by the food flow/ peristalsis
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44. Taenia solium
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45. 3) Cell membrane
- E.g Entamoeba histolyca
- The cell membrane becomes turgid that will prevents the
entry of enzymes into its cyctoplasm
4) Bury itself deep in the mucosa
- Prevention method from being swept away especially in the
intestine
- E.g Entamoeba histolytica
5) Having a thick layer of body wall
- Prevent the entry of enzymes into the body
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- E.g cuticle/ tegument – in many intestinal nematodes

46. REDUCTION IN “UNNECESSARY” STRUCTURES
1) Reduced sense organs
2) Reduced nervous system
3) Reduced locomotion
4) Reduced digestive system
- Some endoparasites have lost gut entirely
- Some ectoparasites use gut mainly for food storage
(eg. leeches, ticks)
5) Enhancement of reproductive capacity
- Reproductive organs are often the largest, most
apparent organ systems present compare to other organs
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47. USUALLY HAVE A RESISTANT STAGE IN LIFE CYCLE
1) For getting from one host to another which is often in a
different kind of environment
2) If endoparasite - needs to survive trip through digestive
system
3) Formation of cysts
-Numerous parasites, such as juvenile tapeworms
(cestodes) in various tissues, achieve protection from the
host response by envelopment with cystic membrane.
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48. ENCYSTMENT IN PROTOZOA
 Many protozoa can secrete a resistant covering and enter
a resting stage, or cyst
 Cyst formation is particularly common among parasitic
protozoa as well as among free-living protozoa found in
temporary bodies of water that are subject to drying or
other harsh conditions.
 During encystment a cyst wall is secreted, and some food
reserves, such as starch or glycogen, are stored
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49.  In coccidians the cystic form is an oocyst, which is
formed after gamete union and in which multiple fission
(sporogony) occurs to produce sporozoites.
 In eimerian coccidians, oocysts containing sporozoites
serve as resistant stages for transmission to new hosts,
 In haemosporidians (including the causative agents of
malaria, Plasmodium spp.) oocysts serve as
developmental capsules for sporozoites within their insect
host.
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