Class Lec_Parasitology_

1. General Parasitology, Malacology & Platyhelminthes
Department of Livestock Science & Veterinary Medicine
Bangabandhu Sheikh Mujibur Rahman Science & Technology University
Gopalganj

2.  Parasitology: It is the branch of biological
Science, which deals with the parasites and
their hosts.
 This discipline includes several approaches to
the study of parasitic organism: such as
phylogeny, morphology, ecology, epidemiology,
life-history, physiology, chemotherapy, serology,
immunology and biochemistry.

3. Animal Association
►Parasitism: It is a condition of life, normal &
necessary for an organism, which lives on or in
a larger organism belongs to different species
and that nourishes itself at the expense of the
larger organism (Host) by inflicting some degree
of injury of the host.
►Example: Neoascaris vitulorum in calves

4. Mutualism
► It is a condition of life in which the both
partners benefit from the association and the
relationship is not obligatory.
►Example: Small fish of several families, feed on
small organisms and parasites on the bodies of
large fish.
Small fish get food and the larger fish are
relieved of unwelcome guests on their bodies.

5. Symbiosis
►Symbiotic relationships include those associations in
which one organism lives on another and get
benefitted. Symbiotic relationships must be obligate
i.e., necessary for the survival of the organisms
involved.
►Example: Relationship between cattle and bacteria
within their intestines. The cattle benefit from the
cellulase produced by the bacteria, which facilitates
digestion; the bacteria benefit from having a stable
supply of nutrients in the host environment.

6. Commensalism
►Commensalism is the condition in which the commensal,
benefits from its relationship with the host, but the host is
neither benefited nor is harmed.
►Example: Cattle egrets foraging in fields among cattle
or other livestock. As livestock graze on the field, they
cause movements that stir up various insects. As the
insects are stirred up, the cattle egrets following the
livestock catch and feed upon them. The egrets benefit
from this relationship because the livestock have
helped them find their meals, while the livestock are
typically unaffected by it.

7. Predation
►Predation is a short-term relationship in which large species
(Predator) benefits at the expense of the other organism
(smaller one), the prey.
►Example: Tiger (the predator) kills the deer (prey) and does
not subsist on it while it is alive.
Phoresis
 Phoresis means “to carry”. This term is capable to two
organisms which are merely travelling together and neither is
physiologically dependent on each other.
 Usually the phoront is smaller than the other and is
mechanically carried in or on the larger species (host)

8. Parasite
►The term “Parasite” refers to an organism, which is
metabolically dependent on another large organism
belongs to different species.
AV Dogiel stresses “Parasites are those animals,
which use other living animals as their environment
and source of food at the same time relinquishing to
their hosts, partly or completely, the task of
regulating their relationship with the external
environment”.

9. Classification of Parasites
• Ectoparasites: The parasites that are attached to the outer
surface of their hosts or superficially embedded in the body
surface are called ectoparasites e.g. Tick, Lice, Mite
• Endoparasites: When the parasites live inside the body of
their host are called endoparasites e.g. Hook worm of man.
• Facultative parasites: The parasite which has retained the
power of independent non-parasitic life, but may become
parasitic under certain circumstances are known as Facultative
parasites. e.g. Maggots of blow flies.
• Obligatory parasites: The parasites which have become fully
dependent on parasitic life and cannot survive apart from their
hosts are known as Obligatory parasites. e.g. Tape worm of
man.

10. • Permanent parasites: When an organism is parasitic in the
body of the host from early life until maturity or sometimes
the entire life is known as permanent parasites. e.g. Fasciola
gigantica
• Temporary parasites: When an organism is parasitic only
during a part of its life cycle is known as temporary parasite.
e.g. Tick
• Periodic parasites: Parasites which visit their host only at the
time when need food are called periodic parasites. e.g.
Mosquito
• Accidental/Incidental parasites: When a parasite establishes
itself in the body of a host in which it does not live is known as
Accidental/Incidental parasite. e.g. Mecistocirrus digitatus in
goats.

11. • Aberrant parasites: Parasites which follow an unusual route of
migration in their host’s bodies and usually become
encapsulated and die are called Aberrant parasites. e.g. Any
parasite
• Stenoxenous parasites: The parasite which has a narrow host
range is known as Stenoxenous parasite. e.g. Eimeria bovis can
infect cattle only.
• Euryxenous parasites: The parasites which has a large/wide host
range is known as Euryxenous parasite. e.g. Trichostrongylus
axei can infect cattle, sheep, goats, horse, rabbit, man etc.
• Hyperparasite: A hyperparasites is an organism which parasitizes
another parasites. e.g. Nosema dollfusi (protozoa) is a
hyperparasite of the larval stage of flatworm, Bucephalus
cuculus, which in turn is a parasite of American oyster.

12. Host
Host is defined as an organism, which is physiologically larger than a
parasite, belongs to a different species and provides protection and
supply nutrition to the parasites. e.g. Cattle is the definite host of
Fasciola spp.
Classification of Host
► Final/Definite host: The host in which parasite reaches its sexual
maturity and reproduces itself is known as final/definite host. e.g.
Moniezia expansa in goats.
► Intermediate host: The host which harbours the larval stage of
parasites for development but not to reach sexual maturity. e.g. Snail
(Lymnea auricularia) is the intermediate host of Fasciola gigantica
► Reservoir host or Carrier host: When a host harbour a parasite until its
sexual maturity but tolerate the infection of the parasite which is
specially harmful to another animal is called Reservoir or Carrier host.

13. ► Paratenic or transport host: When the infective stage of a
parasite enters the body of a host and does not undergo any
development but continues to stay alive and be infective to a
definite host is known as paratenic or transport host. e.g.
Earthworm (Lambricus spp.) acts as a paratenic host of
Ascaridia galli.
► Reservoir host or Carrier host: When a host harbours a
parasite until its sexual maturity but tolerate the infection of
the parasite which is specially harmful to another animal is
called Reservoir or Carrier host. e.g. Dog acts as reservoir host
of Entamoeba spp. of Man.

14. Vector
Vector may be defined as an arthropod, mollusk
or other agents that transmit disease or
parasites from one vertebrate host to another.
e.g. Anopheles spp. is the vector of Malaria.
Vector may be biological or mechanical

15. History of Parasitology
►Parasites infecting man can be dated back to 1250 to 1000 BC
since mummies of 20th Egyptian Dynasty contained eggs of
Schistosoma haematobium in the kidneys.
►Egyptian medical scroll Papyrus Ebers refers to worms like
tapeworm, roundworm, ectoparasites (fleas, flies) and
mosquitos.
►Aristotle (384-322 BC) the father of Zoology in his Historia
Animalium recorded tapeworms, cylindrical worm as ascarids.
►Hippocrates (450-357 BC) father of Medicine knew about
pinworm of horse.

16. ►Little progress was made between 1200 & 1650 AD.
Dibothriocephalus latus by Dunus in 1592, Fasciola
hepatica by De Bries in 1379, Sarcoptes scabiei by
Hauptman in 1657.
►The greatest contributions up to 1800 were made by
Rudolphi in late 1700’s and Zeder in late 1800’s.
►Carolus Linnaeus (1707-1778) in his Systema naturae
classified worms into 5 classes – Nematoda,
Treamatoda, Cestoda, Acanthocephala & Cystica.

17. The most outstanding contributions in Parasitology are
listed below:
 Jean de Clamorgan rediscovered Dictyophyma renale in
1550
 Ruysch observed Strongylus equinus in the arteries of a
horse in 1665
 Leeuwenhoek described the oocysts of Eimeria in
1674, scientific and anatomical study of Ascaris
lumbricoides in 1682
 Wepfer stated that Gid of sheep and goats was caused
by Multiceps multiceps in 1675
 Hartmann first observed Echinococus in dogs in 1694

18. ►Mongin described the first case of Loa loa infection thus
establishing the concept of filarial disease in 1770
►Owen described Trichinella spiralis in human muscle in 1835
►Valentin first described Trypanosomes from fish in 1841
►Gros described Entamoeba histolytica in man in 1849
►Bilharz discovered Schistosoma haematobium, Hymenolepis nana
and Heterophyse heterophyse in 1851
►Malmsten described the first parasitic ciliate of man Balantidium
coli in 1857
►Patrick Manson observed the development of Wuchereria
bancrofti in the body of mosquito, Culex quinquefasciatus in 1878
►Charles Laveran discovered the malaria organism Plasmodium
malariae in the RBC of man in 1880.
►Thomas and Leuckart worked out the first life history of Fasciola
hepatica in 1883

19. ► Smith and Kilbourne discovered the causative agent of Texas cattle
fever Babesia bigemina in RBC in 1889
► Bruce discovered that the Tsetse (wmwm) fly Glossina morsitans
served as vector of T. brucei in 1895
► Forde discovered Trypanosoma gambiense, the causetive agent of
Gambian sleeping sickness in 1901
► Chagas proved that Triatoma megista is the vector of Trypanosoma
cruzi (Chagas’s Disease) in 1909
► Fantham described Trypanosoma rhodesiense causing Rhodesian
sleeping sickness in 1910
► Kleine and Taute in Germany completed the life cycle of Trypanosoma
gambiense in 1911
► Stoll reported “Self cure” in sheep infected with Haemonchus
controtus in 1928
► O’Roke demonstrated the dipteran Simulium venustum transmits the
Leukocytozoon anatis in 1934

20. Zoological Nomenclature
►Aristotle (384-322 BC) father of Zoology indicated that
animals may be grouped together according to their
characters
►Carolus Linnaeus (1707-1778) laid the real basis for modern
clasification and nomenclature of animal. He divided the
Animal Kingdom down to species and gave each species a
distinct name in his Systema naturae (1758)
►The International Congress of Zoology held at Cambridge,
United Kingdom in 1898 set up an International Commission
on Zoological Nomenclature (ICZN) as permanent body

21. Rules deal with all scientific names and provide
an essence as follows:
►Zoological and botanical name are distinct
►No two genera in the Animal Kingdom may bear the same
name and same applies two species in a genus
►Scientific name must be either Latin or Latinized and
preferably printed in Italic
►The genus name should be single word and begin with capital
letter
►The species name should be single or compound word
beginning with a small letter

22. ►When a new genus is proposed the type must be indicated
►A family name is denoted by adding IDEA to the stem of the name
of genus and subfamily name by INAE
►Genera are grouped together into families, families into order,
orders into classes and classes into phyla
Example: Kingdom: Animalia
Phylum: Platyhelminthes
Class: Trematoda
Order: Digenea
Family: Fasciolidae
Genus: Fasciola
Species: Fasciola gigantica

23. Taxon Ending Example
Class a Nematoda
Order ida Rhabditida
Sub order ina Strongylina
Super family oidea Strongyloidea
Family idae Strongylidae
Sub family inae Strongylinae

24. Geographic Distribution of Parasites
► Some parasites are more prevalent in the
tropical/developing countries than that of temperate
countries
► The presence or absence of a number of biological,
chemical and physical factors in the environment
affects directly or indirectly the distribution and
densities of parasites

25. • The development and survival of free living stages of
parasites are greatly influenced by the temperature and
humidity
• Intense/severe dry heat or direct sun light may destroy
larval forms of parasites
• Low temperature and humidity may arrest the
development of ova and larvae of helminths
• Topography may also influence the distribution of
parasites
1. Climate

26. 2. Flora
►Vegetation that serves as food and shelter
for hosts, both definite and intermediate
hosts, greatly influences the parasite
population
►This is particularly evident in case of
helminth parasites
e.g. Various aquatic molluscan hosts of
digenetic treamatodes (Fasciola spp.,
Paramphistomum spp., Schistosoma spp.
etc)

27. 3. Fauna
a. Availability of intermediate host
 When a parasite requires an intermediate host, its
distribution is greatly influenced by the availability of
intermediate host
 The availability of intermediate host largely depends
on its ecological conditions such as suitable
temperature, humidity, food, vegetation and natural
enemies.
e.g. Fasciola hepatica is absent in Bangladeh due to
unavailability of the intermediate host Lymnaea
truncatula

28. b. Availability of definite host and host range
– Population densities of definite, and transport
hosts affect the parasitic densities and
distribution
– Parasite can not survive in an area where the
susceptible host are unavailable
– Availability of hosts is important for the
distribution of parasites
– Parasites is more widely distributed when it
has a large host range. e.g. Trichostrongylus
axie has cosmopolitan distribution due to
large host range

29. Habits and Ecology of the Host
►The habits of the host may allow it to come in
contact with the infected materials thus
completing the life cycle of parasite for its
survival
e.g. In temperate countries, the habit of people
eating raw/insufficiently cooked food expose to
tapeworms.
Hindus are never exposed to tapeworm (Taenia
saginata) due to their religious restriction on
eating beef.

30. Host specificity
Host specificity may be defined as the natural
adaptability of parasite to a certain species of host or
group of hosts
►Factors that influence the host specificity are:
– Close evolutionary relationship: Host and parasites have
evolved closely thus allowing the parasite to adopt itself with
the host environment
– Physiological condition: Hosts’ food, blood & lymph
compositions and pH in the digestive system influences the
parasites to adopt
– Resistance of the host: Immunity of the host can injure
parasites for it elimination.

31. Organ specificity
► Certain parasites are usually or
exclusively parasitic to certain organs
only
– This is due to oxygen tension, availability
of composed food and pH and texture of
the organ
► e.g. Fasciola hepatica inhibits the bile duct
of the liver only of its definite host.

32. Immunity against parasitic infection
►The state of resistance to an antigen is called
immunity.
►The term immunity is applied to the condition arising
from the defensive response of the host against the
invasion by the parasite.
►Resistance: A host is resistant when its physiological
condition prevents the establishment and survival of a
parasite within its body.
►Susceptibility: When a host is capable of being
infected by a specific parasite then it is known as
susceptible.

33. Classification of Immunity
►Innate Immunity
►Natural Immunity
►Acquired Immunity
(a) Active Acquired Immunity
(i) Natural active acquired immunity
(ii) Artificial active acquired immunity
(b) Passive Acquired Immunity
(i) Natural passive acquired immunity
(ii) Artificial passive acquired immunity
►Age resistance
(i) Inverse age resistance

34. Innate Immunity
►Innate Immunity refers to immune response
where a host is permanently resistant against
the infectivity of a parasite and the host is not
affected previously with the pathogens
►This type of immunity is complete one and can
not be broken down by any condition.
►The anatomical and physiological features make
the host unsuitable for a certain types of
parasites.
e.g. Man has innate immunity against Moniezia
expansa, a type of tape worm of ruminants.

35. Natural Immunity
►When the immunity is programmed in the
host cell DNA is called natural immunity
►The host is resistance against the infection
of a parasite but this can be broken down
under certain condition such as stress,
malnutrition or heavy infective doses etc.
e.g. Sheep is naturally resistant to
Neoascaris vitulorum infestation.

36. Acquired Immunity
 The immunity which is developed within the host after
infestation or contact with the parasites is called acquired
immunity.
 It is often incomplete and may be broken down under certain
condition such as stress, heavy infective doses and
malnutrition.
(a) Active acquired immunity: The immunity which is developed
by the host themselves producing antibodies against the
invading parasites.
(i) Natural Active Acquired Immunity: Produced through
previously affected by low grade infection
(ii) Artificial Active Acquired Immunity: Produced through
artificial infestation of low infective doses or attenuated
infective stages of parasites. e.g. Immunity produced by
Dictyocaulus viviparus (Lungworm) in cattle

37. (b). Passive Acquired Immunity: When the
antibodies are not produced by the host, but are
received by it either from its mother through
colostrum, milk, placental blood or by
mechanical transfusion.
(i). Natural Passive Acquired Immunity: When the
resistant mother passes antibodies on to their
young against the parasite either through
placental circulation or colostrum/milk.
(ii). Artificial Passive Acquired Immunity: When
the antibodies are transferred mechanically to
the susceptible host via artificial means.

38. (b). Passive Acquired Immunity: When the
antibodies are not produced by the host, but are
received by it either from its mother through
colostrum, milk, placental blood or by mechanical
transfusion.
(i). Natural Passive Acquired Immunity: When the
resistant mother passes antibodies on to their
young against the parasite either through
placental circulation or colostrum/milk.
(ii). Artificial Passive Acquired Immunity: When
the antibodies are transferred mechanically to
the susceptible host via artificial means.

39. Age Resistance/Immunity
►It is a type of natural immunity in which the older
hosts are more resistant than the younger to parasitic
infestation. e.g. Older sheep is resistant than the lamb
to Moniezia expansa (Tapeworm).
►Inverse age resistance: It is a natural Resistance which
refers to the lack or loss of susceptibility of young
hosts compared to older to parasitic infestation. e.g.
Young cattle are less susceptibility to Babesia bigemina
than older one.
►Premunition: When naturally acquired active
resistance persists only so long as the parasite
provokes it and continues to survive in the host. e.g.
Taenia solium or T. saginata

40. Mechanism of Immunity
►Immunity production involves phagocytosis by
macrophages and production of specific
antibodies
►Phagocytes engulf the invading organisms
(parasites) and lysozyme tries to dissolve or
destroy the organisms
► Thus, this may carry the organisms to the
organs for further production of antibodies and
leading to immunity against the organisms

41. Factors associated with Immunity
►Immunity depends upon
– The production of specific antibodies
– Phagocytic activities of the macrophages
– Resistance body tissues
– Other non-specific factors such as body
temperature, action of digestive juices,
impermeability of the skin, physical well being etc

42. Parasitic immunity involves the following factors
1. Extra haemopoetic factors:
►Genetic difference: Within a single species, difference in
susceptibility to parasitic infection occur due to genetic
variation. e.g. Negroes are less susceptible to Necator
americanus than white
►The body integuments:
– Skin is an effective barrier and has the self sterilizing
properties
– Secretion of sebaceous glands, lactic acid from sweat and
high osmotic pressure play a role in the immune system of
the body
– Mucus: In the mucosa the cilia of the epithelium, flushing
action of tears and urine help to remove undesirable
infective materials
– Body temperature: High body temperature accounts for
combating many pathogens. e.g. Birds are less susceptible to
infection than man due to high body temperature
– Metabolic or Physical wellbeing: Better nourished animals
are less susceptible to diseases than malnourished animals.

43. 2. Humoral factors
► Lysozymes: This is an enzyme found in the tissue
cells, blood serum, glandular secretions and which is
capable of destroying many invading organisms
► Antibodies: It destroy the invading organism
(parasites) , their development or more rarely
neutralize their toxic products. Antibodies are 5 types
as IgA, IgG, IgM, IgD, IgE. IgE is more prevalent during
parasitic infection.
3. Cellular factors: This comprises phagocytosis by
macrophages, leukocytes.

44. Factors that break down the resistance
►Inadequate nutrition
►Concurrent infection with other parasites, bacteria and
viruses
►Stress from journey, overwork or climatic changes
►Heavy infective dose may break down the existing
immune status against this parasite.

45. Source of Infection
►The source of infection of parasitic infestation may be:
– An infected definite host
– Reservoir host
– Intermediate host
– Transport host
– Contaminated food and water

46. ►The way through which the parasite leaves from the host body
are:
– Faeces: When the parasites inhibit the digestive
system
– Nasal secretion/Sputum: When the parasites live in
the respiratory system
– Urine/Genital secretion: When the parasites inhibit
in the genito-urinary system
– Blood/Lymph: Through the withdrawal of
blood/lymph mechanically or by blood sucking
arthopods for transmission to a susceptible host
– Skin and Tissue: The skin and subcutaneous tissues
provide a means of exit from the body and are
readily accessible to insect vector

47. Mode of Transmission of Parasitic Diseases
►The infective stages of parasites may pass from infected host to
susceptible host only by
– Direct contact
– Various developmental stages either as free living form
– The intermediate host before becoming infective
1. Transmission by Direct Contact
 This implies the intermediate transmission of infective stages
from one host to another. e.g. Tritrichomonas foetus (protozoa)
is transmitted by direct contact (coitus)
 Lice and Mites also transmitted directly

48. 2. Transmission through Mouth and Food
– The infective stages of parasites may be present in
feed or it gains access to food from contaminated
soil and water and enter into the host through
ingestion
– Aquatic plants and grass may contain the encysted
cercariae of trematodes
– Vegetable may be contaminated with soil, water
containing cysts, ova and larvae of parasites
– The infective larval stage of may be present in meat,
fish, crustaceans and molluscas.

49. 3. Transmission through skin penetration
– The infective stages of parasites may penetrate the host’s
skin by its own effects. e.g. Cercariae of Schistosoma spp.
Infective larvae of Hook worms.
– Infective stages of parasites may be introduced into hosts
body by arthropod vectors through biting. e.g. Babesia spp.
Theileria spp. By Tick vectors, Malaria by female Anopheles
mosquitoes.
– Infective phases may also be introduced into the body
mechanically during injection or vaccination by using the
same syringe & needle.

50. 4. Transmammary Transmission
– The infective stages of parasites may enter into the
young/offspring through milk from the infected
mother/dam.
e.g. Toxocara vitulorum infection in Buffalo calves
5. Transplacental/Intra-uterine transmission/Pre-natal
Infection
– Infective stage of parasites enter into the body of
young through foetal circulation.
e.g. Ancylostoma caninum (Hook worm) in dogs.

51. Effects of Parasitism on the Host and Parasites
1. Utilization of host’s food
 Utilization of host’s nutrients to a detrimental point by the
parasites is the first type of damage
 Depletion of hosts nutrient by the parasites through absorption
which have serious consequence
 Tapeworms absorb simple sugar, amino acids, vitamin B12, some
constituent of yeast diet and other nutrients.
e.g. Diphyllobothrium latum in man cause anaemia by absorbing
vitamin B12.
2. Removal of host’s blood & tissue fluids
 Blood sucking parasites sucks sufficient amount of blood causing
fluid loss due to secretion of anticoagulent. e.g. Haemonchus
controtus of cattle can remove 0.05 ml blood per day from the
body

52. 3. Destruction of host’s tissues
– Some parasites injure the host tissues during entering the
host’s body
– Other inflicting tissue damage after have successfully entered
the host’s body
– Some others induce histo-pathological changes by eliciting
cellular immune response
► The nature of tissue damage is given bellow:
– Ingestation and lyses of the epithelial cell lining of host’s large intestine
causing ulceration. e.g. Entamoeba histolytica
– Destruction of cells (Lung alveoli) while migrating through it. e.g. Ascaris
lumbricoides larvae in man.
– Tear off/bite off and ingestion of the host tissues. e.g. Strongylus vulgaris
in horse.
– The cercariae of some parasites penetrate the host’s skin causing
“Swimmer itch” in man. e.g. Schistosoma spp.

53. 4. Mechanical interference
(a) Blood and lymphatic vessels, bite ducts or alimentary canal. e.g.
(i) Blood vessel – Dirofilaria immitis in dogs
(ii) Lyphatic canal – Wuchereria bancrofti in man
(iii) Bile ducts – Fasciola gigantica in cattle
(iv) Alimentary tract – Ascaris lumbricoides in man
(b) Causes pressure atrophy of different organs. e.g.
(i) Coenurus cerebralis (Gid disease) in the brain of goats
(ii) Hydatid cyst (Echinococus granulosus) in the liver of cattle.

54. 5. Abnormal growth of host’s tissues/Tissues change
– The egg of Schistosoma nasalis cause hyperplasia of nasal mucosa of
cattle
– Development of tumors – Cysticerci of Taenia taeniaeformis causing
tumor in the liver of rats
– Hyperplasia may turn into malignant tumors. e.g. Paragonimus
westermanii cause cancer/metaplasia in the lung of tigers
– Hypertrophy is commonly associated with intracellular parasites. e.g.
Plasmodium vivex cause enlargement of Red Blood Cell (RBC) in man
6. Secretion/Excretion of various harmful substances into the host
– Irritating parasitic secretions incite an allergic reaction in host’s body. e.g.
Swimmer itch/cercarial dermatitis in man caused by the cercariae of
Schistosoma spp. through skin penetration
– Nodules in the small intestine of cattle caused by the larvae of
Oesophagostomum radiatum that induces inflammatory reaction

55. 7. Introduce other pathogenic bacteria, virus, rickettsia &
protozoan parasites into the host
– Borrelia anserina causing Spirochaetosis in birds by Argus
persicus tick
– Viral lymphocytic chorio-meningitis in Guineapigs caused by
Trichinella spiralis
– Rickettsia connori causing Q-fever in man is introduced by
the tick Dermacentor andersoni
– Histomonas meleagridis causing Black Head disease in
Trukey is introduced by caecal nematode Heterakis
gallinarum

56. Adaptations of Parasites
1. Adaptation to feed & attachment with the host:
– Powerful, strong and large buccal capsule with teeth to affect blood
sucking of parasites from the body of the hosts. e.g. Hookworms
(Ancylostoma caninum) in dogs
– Remarkable structural and functional changes in the mouth parts
characteristic of blood sucking insects to suck blood or tissue fluid of
the host. e.g. Mosquitoes (Anopheles spp.)
– Loss of entire digestive system in tapeworms (Cestode) which have
adapted in absorbing body fluid from the host’s through cuticle. e.g.
Moniezia expensa in ruminants
– The suckers and hooks are the characteristics structure of flukes and
tapeworm primarily used for attachment to the host but also help in
getting food

57. – Incomplete intestine (absent of anus) in trematodes (flukes)
which only can intake liquid food through mouth. e.g.
Fasciola gigantica in cattle
– The acanthocephalid worms and ticks are attached with the
body of their host by toothed proboscis and hypostome
– The other ectoparasites such as lice, sheep ked and
hippoboscid insects are enable to attach the external surface
of the hosts with the help of claws

58. 2. Loss or reduction of organs:
– Parasitic insects such as lice and fleas have lost their wings but
they can move rapidly by means of their limbs
– Retention of locomotory organs such as cilia. e.g. miracidium of
trematodes that bear cilia and made contact with snail host
– Parasitism tends to cause simplification of structure
3. Reproductive adaptations:
– Represent the method by which the parasites meet the risk of loss
of relatively large numbers of its offspring
– One method is to increase the production of eggs which may be
affected by
(i) Increase size of the ovary. e.g. When tapeworms & trematodes
mature, ovaries occupying the whole body
(ii) Increased egg production by a single ovary. e.g. A female
Ascaris lumbricoides may produce 2,000,000 eggs per day and
Ancylostoma duodenale produce 25,000 eggs per day

59.  Parasites which have less risk of destruction of
offspring may produce fewer eggs.
e.g. Female warble fly (Hypoderma lineata
produced 500-800 eggs and sheep ked
(Melophagus ovinus) produce 10-15 larvae in
their life time
 Reproductive adaptation is the method by
which the parasite increases the number of
individuals derived from each fertilized eggs.
e.g. A single oocyst of Eimeria tenella may
produce 1,800,000 individuals by sexual
multiplication within 4-5 days.

60. Principles of Control of Helminth Infection
1. Reducing contamination
2. Avoiding infestation of the host
3. Treating the host/Reservoir of contamination
Reducing contamination
Desiccation:
 First & second stage larvae of nematodes are
readily destroyed by drying out on soil and pasture
 Eggs and third stage larvae are somewhat more
resistant
 The longer the pastures are kept free of airmails,
the greater is the mortality amongst all the free
living stages

61. Nutrition of the host
– A well nourished animal is more resistant to infection than a
poorly nourished animal
– Good feeding thus encourages high productivity in two ways,
by providing nutrients for growth and by assisting the host to
destroy its own intake of parasites
Immunity
– Initial infestations commonly lead to development of some
degrees of immunity
– Older animals with immunity may cause safely graze areas
dangerous for young animals

62. Alternative host
– The larvae of certain gastrointestinal parasites
can develop in different hosts. e.g. Toxocara axei
of cattle will develop in horse and vice-versa,
but the effects of cross infection are usually not
as severe
– Proportionately fewer larvae develop in the
alternate host. Other larvae will not develop at
all in the alternative host
– Thus, horse can be used to reduce
contamination of pastures of cattle and vice-
versa.

63. Alternate Husbandry
 In some countries, animals are stabled in winter months and
graze pastures during other seasons. Under such management
the husbandry alternates with seasons. Winter quarters are
vacant, they can be thoroughly cleaned at leisure
 Another “alternative husbandry” system is grazing during early
growth, followed by intensive fattening on feed lots. These
systems of alternate husbandry provide an excellent means of
improving parasite control
 The aim should be to reduce the contamination of both
environments as well as possible by treatment of all just before
they are moved from one environment to the other and
thorough cleaning or complete spelling of the alternate quarters
while vacant

64. Stable Management
 Stable should be constructed with a view to keep the animals
away from their own faeces or to regular removal of faeces
 Cleaning twice a week is usually sufficient, as eggs and larvae are
thus removed before larvae can reach the infective stage
Destruction of Intermediate host
 This is not often practical for animals that are grazed over
extensive pasture areas
 Fluke-bearing snails can be controlled to some extent in
restricted areas by drainage or use of molluscicides

65.  But, snails can survive many months under quite dry conditions
and their rate of reproduction is such that if a few escape
destruction, populations quickly reach previous levels again
Avoiding infestation of the host
Hours of Grazing:
 Larvae are mostly found in the surface layers of the soil. They
ascend pasture and herbage stems in responses to light when
moisture conditions are suitable, particularly when early
morning dew is present
 Keeping animals stabled until the dew has evaporated, will
therefore, avoid much infestation

66. Low-Lying Pastures
 Rain tend to wash faeces and larvae from slopes down to lower
grounds resulting in local areas of heavy contamination
 Usually the combination of moisture and manure promotes
better growth of pasture attracting the animals to these
locations
 These grazing areas can be highly dangerous and their grazing
should be restricted, if possible, to the times when the grass and
herbage are dry.
Moist Areas
 In dry period, animals tend to congregate beside surface water,
small streams, ponds and irrigation canals where they can drink
and where moisture may provide some green growth

67.  Their faeces are concentrated on these area, where
because of the moisture, a high proportion of larvae
develop and survive
 These areas should be avoided as much as possible.
Overgrazing
 Overgrazing of pasture to the extent that animals are
grazing at soil level, increases the intake of larvae
which are mostly in the surface layers of the soil
 Much infestation can be avoided by limiting grazing,
removing the animals to fresh pastures before risk of
soil intake is reached.

68. Order of Grazing
 Young, relatively worm-free animals , should be allowed first
access to pastures that are relatively safe before these pasture
are grazed by older animals that would infest the pasture
 Conversely, if an area is known to be heavily contaminated,
grazing by the older animals that have some immunity can
lessen the risk to younger animals grazed on the same pasture
later, providing the infestation of the older animals is not high
enough to maintain or increase the degree of contamination
“Clean” Pastures for Grazing after Treatment
 Areas of pastures should be kept free of animals for some weeks
prior to anticipated treatment
 The animals should be moved to these clean pastures
immediately after treatment

69. Avoiding Camping Ground
 Places where flocks or herds regularly camp at night are
subjected to concentrated deposition of faeces, resulting in
heavy contamination with infective larvae
 Management, especially of migrating flocks, should provide for
regular changes in camping grounds to avoid development of
areas of high contamination where stock are regularly in close
contact with their own faeces and the infective larvae
developing in them.
Treating the Host-Reservoir of Contamination
 Anthelmintic treatment given to destroy or remove parasites
from the host has two objectives, firstly to offset effects of
parasites on the host and secondly to reduce the contamination
of pastures or stables with free living stages

70.  Movement to clean pastures immediately after treatment is
almost as important as treatment itself, because the animals will
soon become re-infested by larvae developing from faeces they
themselves produced before treatment if they remain on the
same pasture.
Strategic Treatments
 Correct timing of treatments in relation to the seasonal
incidence of the parasites is necessary if best results are to be
obtained
 Strategic treatments designed to prevent infestations reaching
problem levels
 These Strategic treatments are based on seasonal incidence of
parasites in normal seasons, and they should be given as a
routine, irrespective of whether animals appear to be infested or
not

71.  The whole aim is to prevent the appearance of signs and loss
from sub-clinical diseases
 Animals must be treated while they are healthy to keep them
healthy.
Tactical Treatments
 These are the treatments , in addition to the above “Strategic
Treatment” that may be needed to obtain proper control in
abnormal years. e.g. if good rains fall for longer into Summer,
favouring Haemonchus, additional treatment may be needed
against this species
 Long wet winters may call for an additional treatment with a
wide-spectrum anthelmintic in late January or early February
 “Worms work by the Winter” and tactical treatments call for
“Drenching by the Weather”.

72. Helminthology
 The name helminth is derived from Greek words
Helmins or Helminthos - means a worm
 It is applied to the parasitic species belonging to the
Phyla:
• Platyhelminthes
• Nemathelminthes &
• Acanthocephala.

73. Phylum: Platyhelminthes
►Flat worms
►Incomplete or absent digestive tract
►No body cavity
►Most species are monoecious/bisexual or
hermaphrodite but a few are dioecious (unisexual)
►Life cycle is direct or indirect (involving an intermediate
host)

74. Phylum: Nemathelminthes
►Round worms, round in cross section
►Body is unsegmented
►Separate sexes
►Complete digestive system
►Life cycle is direct or indirect

75. Phylum: Acanthocephala
►The Acanthocephala or “Thorny Headed Worms” are elongated,
most being cylindrical, tapering at both ends with some
flattened forms
►The main characteristic of the acanthocephala is the protrusible
armed proboscis at the anterior end
►A digestive tract is completely absent and like cestodes and
absorb nutrients through body cuticle
►Life cyle is indirect involving crustacean intermediate hosts in
most cases
►Acanthocephalas have a number of hosts including
invertebrates, fish, amphibians, birds and mammals
►About 1150 species have been described.

76. Platyhelminthes includes three classes
►Class: Turbellaria
 Most turbellaria are free-living in salt and fresh water
 Some are parasitic in crustaceans, molluscs, arachnids
etc
 They have undivided body
 Simple direct life-cycle

77. ►Class: Trematoda
 Flukes
 Mostly Leaf shaped and Unsegmented body
 Life-cycle is direct or indirect
 Digestive system incomplete
 Most species are monoecious but a few are dioecious
►Class: Cestoda
 Tapeworms
 Segmented bodies and each segment containing complete set of
male and female reproductive organs
 No alimentary tract
 Nutrition by absorption through body wall
 Life-cycle is indirect

78. Class: Trematoda
►The bodies of trematodas or flukes are dorso-ventrally flattened,
unsegmented and leaf-like
►The have two suckers, oral sucker and ventral sucker or
acetabulum, these facilitate attachment to the exterior or
internal organs of their hosts
►All the organs are embedded in body parenchyma
►Digestive system is simple with two blind intestinal caeca
►The excretory system flame cell
►Trematodes are monooecious, except Schistosomas which are
dioeceous
►The life histories are direct or indirect

79. ►Trematoda is divided into three Order
Order: Monogenea
 These are medium to fairly large sized trematode between 1-3
cm in length
 They are generally flattened dorsoventrally
 Monogenetic trematodes are usually parasitize poikilothermic
vertebrates
 They cling to the skin or gills of fish, amphibians and reptiles and
have only little or no livestock or medical importance.
Order: Aspidogastrea
 Pyriform to slightly elongate in shape
 Aspidogastra are usually the parasites of fish and sometimes
mollusc and crusaceans.

80. ►Order: Digenea
 Trematodes with two or more asexual generations and
alteration of hosts are known as Digenetic Trematodes
 They are usually flat, elongated, leaf-shaped
 The Body is covered by the cuticle
 They have two suckers, oral sucker and ventral sucker
or acetabulum
 No body cavity
 Mouth leads into a muscular pharynx, short narrow
oesophagus extends from the pharynx to the intestine.

81. ►Order: Digenea (contd.)
 The excretory system is flame cell
 All are monoecious except Schistosomatidae
 The male reproductive organs comprise of testes, vas
efferentia and vas differens
 The female genital organs comprise of a single ovary,
anoviduct, a seminal receptacle, two vitelline glands
and ducts
 In the hermaphroditic trematodes uually slf-
fertilization take place.

82. Life-Cycle
 A series of stages through which an organism passes
between recurrences of a primary stage
 The course of developmental changes in an organism
from fertilized zygote to maturity when another zygote
can be produced
 The set of states a person goes through from birth to
death
Direct Life-Cycle
 A life-cycle in which a parasite is transmitted directly from one
host to the next without an intermediate host or vector of
another species. e.g. Life-cycle of hookworm

83. Indirect Life-Cycle
 A life-cycle which requires one or more intermediate
hosts before the definitive host species is reinfected.
e.g. Life-cycle of Fasciola hepatica
Life-Cycle stages/Developmental stages of
Digenetic Trematode
 (i) Miracidium
 (ii) Sporocyst
 (iii) Redia
 (iv) Cercaria and or
 (v) Metacercaria

84. Miracidium
►The larval stage which hatches out of the developed
egg is the miracidium
►The miracidium is highly motile due to the cilia on its
surface
►In most cases, miracidium comes in contact with
water and swim straight in it
►Without finds a specific snail host it may die within
24-72 hours

85. Sporocyst
►After penetration into suitable intermediate host,
miracidium looses its ciliated covering and turned into
a spherical body – the Sporocyst
►It is a kind of living cyst, tightly packed with germinal
cells

86. Redia
►It is cylindrical in shape
►The body of redia is filled with germinal cells, which gradually
multiply to form germ-balls
Cercaria
►Cercaria is the developmental stage of the digenetic trematodes
that developed from redia
►A typical cercaria has a discoidal body and a long backwardly
projecting tail
►It has an oral sucker encirculing the mouth and a ventral sucker
occupies the centre of the body
►Fully formed cercaria escapes and settle on grass blades or
penetrate the tissues of second intermediate hosts and becomes
metacercaria.

87. Types of Cercaria
►A comprehensive classification of cercariae is made by
Luhe (1909) which are as follows:
1. Lophocercaria:
 A dorsal longitudinal fin-fold is present along the
body. e.g. Sanguinicolidae
2. Gastrotome cercariae:
 Mouth is situated centrally on the ventral surface of
the body
 Presence of very short tail stem
 The entire tail compleax resembles the horns of an ox.
e.g. Bucephalidae

88. 3. Monostome cercariae:
 Only small oral sucker present
 Ventral sucker is absent
 Two or Three eyespots present. e.g. cyclocoelidae
4. Amphistome cercariae:
 A large ventral sucker situated at or near the posterior
extremity of the body
 Oral sucker is small
 Tail is simple and globular. e.g. Paramphistomatidae

89. 5. Distome cercariae:
 Ventral sucker is distant from the posterior extremity of
the body. e.g. Dicrocoelidae
6. Cystocercous cercariae:
 Base of the tail containing a cavity in which the body
can be retracted. e.g. Heliaegus spp.
7. Rhopalocercous cercariae:
 The tail is as wide as the body. e.g. Cercariae isospori,
Fish trematode

90. 8. Leptocercous cercariae:
 The tail is slender, staright and narrow than the body
cavity. It is three types:
(i) Gymnocephalus cercariae:
 An oral and ventral sucker present
 There is a tail with or without a fin-fold
 Anterior extremity is rounded and lack of spine. e.g.
Fasciolidae
(ii) Echinostome cercariae:
 Presence of a head collar with spines near the anterior
extremity of the body. e.g. Echinostomatidae

91. (iii) Xiphidocercous cercariae:
 Occurrence of stylet at the anterior extremity of the
oral sucker
 Poor swimmers. e.g. Plagorchiidae
9. Trichocercous cercariae:
 Tail is provided with spines or bristles. e.g.
Lepocreadium spp. of planktons.
10. Furcocercous cercariae:
 Tail is bifurcated (forked tail)
 They are usually distomes oral sucker and the ventral
sucker (rudimentary). e.g. Schistosamatidae

92. 11. Microcercous cercariae:
 The tail is short and stumpy. e.g. Troglotrematidae
12. Rat-King cercariar:
 Cercariae are arranged in groups having the tip of the
tails united to form a kind of colony. e.g.
Asymphylodera spp.