Download UNIT 8: Introduction to Parasitology

UNIT 8: Introduction to Parasitology
Parasitology is a study of the phenomenon of parasites and parasitism. Parasite is
defined as “an animal/ organism or a plant which lives in or upon another animal/
organism (technically called the ‘host’) and draws its nutrition directly from it”.
Animal Association/ relationship
In a broader sense any interaction between two organisms is considered as symbiosis
(living together). And so, the science of parasitology seems largely a study of
symbiosis.
Depending on the degree and type of interdependence of the symbionts, symbiosis can
be divided into different categories as:
1. COMMENSALISM: (Com mensa lat. - sharing table): it is an association where
an organism, the COMMENSAL, derives benefit (nourishment) from another
(host) without harming the benefactor (Host).
E.g., Entamoeba gingivalis in mouth
2. MUTUALISM: it’s an association of two partners where both are benefited by
each other.
E.g., Ciliates in ruminants
3. PHORESIS ("traveling together" or "to carry"): it is a temporary relationship with
no metabolic dependence. A smaller organism, termed the PHORONT, is carried
mechanically by a HOST. For instance, bacteria, fungus, cysts, or eggs on insect
legs or even passively within an arthropod gut.
4. PREDATION: it is usually a short term relation between the two individuals in
which member, the PREDATOR, is benefited and the other, the PREY, is harmed;
usually killed.
E.g., cats and mice
5. PARASITISM: it is a relation in which an organism (the parasite) lives in or on
the host and is metabolically dependent on another organism, the HOST.
Types of parasites
Endoparasites: Endoparasite is one which lives inside the organ/tissues/ body cavity
or body fluids of a host.
Examples: all helminth and protozoa parasites of mammals and birds, larva of some
insects.
Ectoparasites: Ectoparasite is one which lives on the surface of the host.
Example: most insects and arachnids
Obligatory parasite: Obligatory parasite is one which must spend at least a part of its
life as parasite with its host to survive and complete it life cycle.
Example: most of the helminthes and protozoa.
Facultative parasite: facultative parasite is one which is not normally parasitic but
can become so, at least for a time, when it is accidentally ingested or enter the body
orifice or a wound on the body of the host.
Example: when the flesh fly Sarcophaga dux lays its larva in wound on the skin of a
man.
Accidental/incidental parasite: it is one which enters or attaches to the body of a
species of host which is different from its normal host.
Example: ingestion of infective eggs of Toxocara canis by man leading to viscera
larva migrans.
Permanent parasite: permanent parasite is one which lives its entire life within or on
its host.
Example: Trichinella spiralis, Sheep ked (Melophagus ovinus)
Temporary or intermittent parasite: It is one which only visits its host to feed on it
and then leaves.
Example: mosquitoes, bed bugs
Hyperparasites: it is one which parasitizes. It’s a parasite within a parasite.
Example: malaria in mosquitoes; tapeworm larvae in fleas. ‘
Zoonotic parasite: Zoonotic parasites are those parasites which are transmissible
from animals to man (anthropozoonoses) or from man to animals (zooanthroponoses)
or both ways (amphixenoses).
Types of hosts
1. DEFINITIVE OR FINAL HOST- A host in which a parasite reaches sexual
maturity and reproduces.
Example: Cattle, buffaloes, sheep and goats are definitive hosts for Fasciola hepatica.
2. INTERMEDIATE HOST – it is one in which early develop of parasite occurs to
produce usually infective stages of it without reaching to maturity.
Example: snails in the life cycle of Fasciola hepatica.
3. PARATENIC OR TRANSPORT HOST – it is one which picks up the infective
stage of a parasite either from the intermediate host or directly from the
atmosphere without any development of the parasite; but parasite continues to live
and is infective to next host.
Example: A mouse is the paratenic host for Toxocara canis, T. cati or Toxascaris
leonina.
4. VECTORS – vector is usually a blood-sucking arthropod which transmits the
parasite from the infected vertebrate animal to another susceptible vertebrate
animal.
a. BIOLOGICAL VECTOR- biological vector is one which transmits the
parasite after some biological development of the parasite to make it
infective for a susceptible host.
Example: Mosquitoes involved in the transmission of various filarial
roundworms and malarial parasites.
b. MECHANICAL VECTOR – it is one which transmits the parasite in a
short time as such without undergoing any developmental or biological
change.
Example: Tabanid flies transmit Trypanosoma evansi.
5. CARRIER HOST- it is a vertebrate animal which had suffered from an infection
and in later stage carries the infective organisms in its body without showing any
clinical signs.
6. RESERVOIR HOST – it is a vertebrate animal which may or may not be the
natural host of a parasite and possess parasitic infection without any clinical
manifestation that serves as sources of infection to other susceptible hosts.
Types of life cycle
Direct life cycle: direct life cycle of a parasite does not involve any intermediate host
between parasite and its host.
Example: Strongylid nematodes
Indirect life cycle: indirect life cycle of a parasite involves necessarily one or more
intermediate hosts or vector(s) to complete its life cycle.
Example: Fasciola hepatica.
Simple life cycle: it is the one where a parasite simply multiplies by binary fission
both in its vertebrate host and its insect vector for its propagation.
Example: Trypanosoma spp.
Complex life cycle: it is one where there is an alteration of both asexual and sexual
processes of reproduction in the life cycle of a parasite.
Example: all helminth parasites
A. Helminth Parasites
“Helmins or helminthes (Grk): a Worm.
Helminth means a worm and usually applied to parasitic and non-parasitic species
belonging to the following three phyla:
1. Phylum: Platyhelminthes
2. Phylum:Nematohelminthes
3. Phylum: AAcanthocephala
Phylum: Platyhelminthes
The worms are usually bilaterally symmetrical; dorso-ventrallly flattened and
commonly called flatworms. These are either leaf-like or oval/globular (fluke
parasites) grouped under a Class- Trematoda, or a very long elongate tape-like
(tapeworms) grouped under two classes- Eucestoda (true tapeworms) and
Cotyloda (fish tapeworms). All flatworms are hermaphrodite and most of the
species are parasitic.
a. Class: Trematoda: has only one sub-classDigenea of veterinary importance
which contains species of flukes of variety shape and sizes (0.16 mm to 5.7 cm
long). Most fluke parasites are hermaphrodite but blood flukes, classified under
the family Schistosomatidae, are unisexual and elongate. All types of flukes
possesss a powerful oral sucker surrounding the mouth. Besides, some flukes have
a ventral sucker near middle or in upper half of the body, while others have a
muscular sucker towards the posterior end. Life cycle of all trematodes is indirect
involving one or more intermediate hosts. In all cases, the first or the only one
intermesdiate host is a species of snail. The second intermediate host, if any, may
be an ant, grasshopper, fish, dragon fly, snail, frog or some crustaceans.
Trematodes lay usually operculated eggs, while a few others lay spinosed eggs
(blood flukes) or with a long filament at either ends. The different early
developmental stages inside the snail are:
i. Miracidium: enter the snail soon after hatching out from an egg.
ii. Sporocysts
iii. Redia and
iv. Cercaria
The cercaria stage comes out of the snsail and encysts either on vegetation or inside a
second intermediate host. Thus, the infective stage so developed is called
metacercaria. Mode of infection of an animal with most flukes occur either through
ingestion of metacercaria stage encysted on the vegetation or by eating second
intermediate host harbouring metacercarial stages, or through skin penetration by
cercariae in case of blood flukes.
Life Cycle
The life cycle of Fasciola hepatica is typical of the order.
Fasciola hepatica can infect a wide variety of mammalian hosts, particularly sheep
and cattle. It requires snails of the genus Lymnaea as intermediate hosts. The most
common is L. truncatula, an amphibious snail with a world-wide distribution.
Mature adults live in the bile ducts of livers in their mammalian hosts. Eggs are laid
in the bile ducts, pass to the small intestine then out in the feces of the host. The first
stage, a miracidium (A), develops within each egg, which hatches and releases the
mature, motile, ciliated miracidium. Hatching of eggs takes less than two weeks at
optimal temperatures between 220C and 260C. Development is negligible below
100C.
Hatched miracidia are short-lived because they do not feed. They must find a suitable
snail intermediate host within 24 hours of hatching or they die. Miracidia swim, using
their cilia, and seek out snails by chemotaxis. They adhere to snails and penetrate their
soft tissues using an enzyme and a cone-shaped papilla at the anterior end. The
miracidium loses its cilia and continues to develop into the sporocyst stage (B), which
is a sac containing germinal cells. Each germinal cell grows and divides eventually
becoming a redia (C). These first generation rediae burst through the wall of the
sporocyst and migrate to the hepato-pancreas of the snail. A second generation of
"daughter" rediae may develop from germinal cells in the first, parent generation.
Germinal cells in these daughter rediae develop into the final cercarial stages
(D). Cercariae are, in fact, immature flukes with tails used for swimming. They attach
to plants such as grass blades, lose their tails and encyst as metacercariae (E), the
infective stages for their final mammalian hosts.
(
) Following ingestion of metacercariae by the final host, they excyst in the
small intestine (F), migrate through the gut wall, cross the peritoneum and penetrate
the liver capsule (G). The immature flukes tunnel through the liver parenchyma for 6
to 8 weeks, then enter the small bile ducts, then migrate to the larger ducts and
occasionally the gall bladder.
(
) Eggs laid by adult flukes pass down the bile ducts through the
gastrointestinal tract and exit the host in feces, completing the cycle.
The prepatent period is 10 to 12 weeks, and the minimal period for completion of one
entire life cycle of Fasciola hepatica is 17 to 18 weeks
CLASS: TREMATODA: common trematodes in animals
Family: Dicrocoelidae e.g., Dicrocoelium dendriticum in liver of ruminants and other
mammals
Family: Heterophyidae e.g., Heterophyses heterophyses in the small intestine of dog,
cat and man.
Family: prosthogonimidae e.g., Prosthogonimus ovatus (Oviduct fluke) in the bursa of
fabricious and oviduct of domestic fowl.
Family: Opisthorchiidae e.g., Opisthorchis tenuicollis in the bile ducts of dogs and
cats, Clonorchis sinensis in the liver of man
Family: Fasciolidae eg., Fasciola hepatica (liver fluke) and Fasciola gigantica in the
liver of sheep and cattle, Fascioloides magna in the liver of cattle and horse,
Fasciolopsis buski in the small intestine of man and pigs.
Family: Paragonimidae e.g., Paragonimus westerman (lung fluke) in the lungs of
dogs and cats and tiger.
Family: Paramphistomatidae e.g, Paramphistomum cervi and Cotylophoron
cotylophoron (rumen fluke) in the rumen of cattle.
Family: Schistosomatidae e.g., Schistosoma indicum, S.nasalis, Ornithobilharzia
bomfordi (Blood flukes) in the blood vessels.
Class: Eucestoda: the members of this class are elongate, tape-like with flat body
without a body cavity. The body is divided into a scolex followed by a short
unsegmented neck and in general, the remainder of the body called strobila, which
consists of a number of segments called proglottids. All species of cestodes have
indirect life cycle except Hymenolepis nana. The intermediate host may be orbatid
mites, mollusks, ants, beetles, earthworms, houseflies, fleas or lice amongst
invertebrates, or there may be a species of vertebrate host viz., cattle, buffalo, sheep,
goat and other ruminants, pigs, rabbit, ungulates, rats, and sometimes man.
The eggs of tapeworms develop inside an intermediate host to a variety of
metacestode stages which are the infective stages viz., cysticercoid, Cysticercus,
strobilacercus, coenurus, hydatid and tetrathyridium. The infection of animal occurs
either by ingestionof the whole invertebrate intermediate host or by eating raw or
undercooked flesh of a vertebrate intermediate host containing infective
metacestodes.. Class Eucestoda has six orders of importance.
Class: Cotyloda: These are primarily tapeworms of fish. The only tapeworms of
interest under this class are Diphyllobothrium latum and Spirometra spp. of man, dog,
cat and some fish-eating mammals. Life-cycle is indirect usually having two
intermediate hosts and with larval stages developing in two different intermediate
hosts. These are called procercoid and plerocercoid respectively. Infection of the
final host occurs by eating raw or undercooked fish or any other second intermediate
host harbouring the infective stage (plerocercoid).
Life cycle of Taenia solium
www.humanillnesses.com/.../T-Ty/Tapeworm.html retrieved on 15 September 2008
CLASS: EUCESTODA: common parasites
ORDER: ANOPLOCEPHALIDEA
Family: Anoplocephalidae e.g., Anaplocephala perfoliata, Paranaplocephala
mimmillana in horse
Family: Thysanosomidae e.g., Stilesia hepatica in the bile ducts of ruminants,
Thysanosoma actinoides in the bile ducts and pancreatic duct of ruminants
ORDER: DAVAINEIDEA
Family: Davaineidae e.g., Davainea proglottina, Raillietina tetragona, and Cotugnia
diagnophora in the small intestine of fowl.
ORDER: DILEPIDIDEA
Family: Dilepididae e.g., Amoebotaenia sphenoides in the small intestine of domestic
birds
Family: Dipylidiidae e.g., Dipylidium caninum in the small intestine of dogs and cats.
ORDER: HYMENOLEPIDIDEA
Family: Hymenolepididae e.g., Hymenolepis nana in man
ORDER: TAENIIDEA
Family: Taeniidae e.g., Taenia multiceps and Echinococcus granulosus in dogs
CLASS: COTYLODA
ORDER: DIPHYLLIDEA
Family: Diphyllobothriidae e.g., Diphyllobothrium latum, Spirometra ranarum in
dogs and man.
Phylum: Nemathelminthes
Class: Nematoda: the nematode worms are commonly called roundworms because
of their cylindrical forms generally with their both endsa somewhat pointed. The body
is not segmentesd and the sexes are separate. The lengths of nematodes vary from
about 2 mm (Strongyloides stercoralis) to upto 400 cm (Dracunculus medinensis).
The female worms are generally longer than males. Eggs are laid by gravid females
either as embryonated or unembryonated. A group of nematodes called the filarial
worms lay first immature larval stage called microfilaria in body fluids and tissues of
the host. Thus, female laying unembryonated eggs are called oviparous, embryonated
eggs as ovo-viviparous; or larvae called as viviparous.
Most of the nematodes have early free living developmental stages in their life cycle
viz., first stage larva (L1), second stage larva (L2) and third stage larva (L3). The last
one always matures to become the infective stage. Nematodes having direct life
cycle, have all the three larval stages developing outside the host in open whilein
nematodes having indirect life cycle, these stages develop inside the intermediate
host. Infection of the final host takes place generally by ingestion of the infective egg
(Ascarid worm) or L3 stage (Strongylid worm) or through skin penetration by L3 stage
(hookworms) or by transplacental and/or transcolostral route (Toxocara spp.); or
htrough ingfestion of invertebrate intermediate/paratenic host. In addition to this, a
group of filarial nematodes, laying microfilariae in circulating blood, lymph,
subcutaneous tissues, etc are transmitted by blood sucking insect vectors viz.,
mosquitoes, houseflies, etc. There is one specialized nematode, Trichenella spiralis,
which has no period of free existence and the transmission occurs through eating raw
or underccoked flesh of infected animals harbouring encysted infective larvae.
Life cycles of Nematodes
AInfected DH with
Adult nematode
Egg
L1
L2
L3
L3
Susceptible DH
L4
L5
(Adult Stage)
Egg
CLASS: NEMATODA: Common parasites
ORDER: ASCARIDIDA
Family: Ascarididae E.g., Ascaris suum in pigs, Parascaris equorum in horses,
Toxascaris leonina and Toxocara canis in dogs
Family: Oxyuridae e.g., Oxyuris equi in horses.
Family: heterakidae: Heterakis gallinarum and Ascaridia galli in small intestine of
fowl.
ORDER: RHABDITIDA
Family: Strongyloididae e.g., Strongyloides papillosus in the small intestine of
ruminants.
ORDER: STROGYLIDA
Family: Strongylidae e.g. Strongylus vulgarus in the mesenteric vessel of equines
Family: Trichonimatidae E.g., Chabertia ovina and Oesophagostomum columbianum
in abomasum of sheep
Family: Stephanuridae e.g., Stephanurus dentatus (kidney worm of swine) in the
kidney of pigs
Family: Syngamidae e.g., Syngamus trachei in trachea of fowls
Family: Ancylostomatidae e.g., Ancylostoma caninum in dogs, Bunostomum
phlebotomum in cattle
Family: Trichostrongylidae e.g., Trichostrongylus axei and Haemonchus contortus in
abomasum of sheep
Family: Dictyocaulidae e.g., Dictyocaulus filaria in bronchi of sheep, and goats
ORDER: SPIRURIDA
Family: Thelaziidae e.g., Spirocerca lupi in the esophagus of dogs
Family: Filariidae e.g., Dirofilaria immitis in the pulmonary artery of dogs and cats
Family: Onchocercidae e.g., Onchocerca armillata in the aortic walls of cattle.
ORDER: ENOPLIDA
Family: Trichinellidae e.g., Trichinella spiralis in small intestine of man, pigs and rats
Family: Trichuridae e.g., Trichuris ovis in the caecum and upper colonof sheep, goat
and cattle.
Family: Dioctophymidae e.g., Dioctophyma renale renale in the kidney of dogs and
other wild carnivores.
Phylum: Acanthocephala
The phylum contains a group of parasitic worms which are cylindrical and closely
resemble to the nematodes. They are commonly called ‘thorny headed worms.
The life cycle is indirect involving an intermediate host which is usually an arthropod.
The larva in the egg hatches in the intermediate host and then encysts as ‘Cystacanth’
in the haemocoel of the arthropod. One to threee months are required for the
cysaccanth to become infective stage. Usually, the definitive hosts become infected by
ingesting the arthropods, and reaches adult stage in 5-12 weeks. The adult
acanthocephalan parasites chiefly occur in aquatic vertebrates like fish and birds
besides some mammals.
Family: Oligacanthorhynchidae
Genus: Macrocanthorhynchus
Macrocanthorhynchus hirudinaceus occurs in the small intestine of domestic pigs and
wild boars. The male is upto 10 cm and the female is upto 15 cm or more long.
B. PROTOZOA
Protozoa are thought to be very primitive (not well-organized) in nature because they
are unicellular. Hence, called protozoa (proto- first, zoa- animal).
But they are highly organized and very specialized within a single cell itself.
Salient features of protozoa
1. unicellular
2. microscopic (10 µm to 200 µm)
3. eukaryotic
Most parsitic protozoa have a distinct nucleus. There are some species which have
two similar (e.g., Giardia, Hexamita) or two dissimilar nuclei (e.g., Balantidium coli).
Reproduction is either asexual (simple binary fission) or by both asexual and sexual
processes. Sporogony is a process of spore formation by asexual division inside the
zygote/cyst or oocyst formed by gametogony. The resultant sporozoites are the
infective stages in all cases. Most protozoa are free-living while a few are parasites of
animals and man.
Direct life cycle:
a. Simple (by binary fission) e.g. flagellates
b. Complex (by alternation of asexual and sexual generations) like Coccidia
Indirect life cycle:
a. Involvement of insect vectors e.g., mosquitoes in the life cycle of members of
family Plasmodidae (malarial parasites), and involvement of arachnid vectors
e.g., Ixodid ticks in the life cycle of Babesia and Theileria species.
b. Involvement of mammalian host(s) in the life cycle of Sarcocystis and
Toxoplasma.
Life cycle stages of protozoa:
The stages of parasitic protozoa that actively feed and multiply are frequently called
trophozoites.
Cysts are stages with a protective membrane or thickened wall. Protozoan cysts that
must survive outside the host usually have more resistant walls than cysts that form in
tissues.
C. ARTHROPOD PARASITES
Phylum: Arthropoda
Arthropod (Greek: Arthros- Joint and podos- foot). The members of the phylum
Arthropoda therefore have jointed–legs. Arthropods are segmented animals. The
anterior group of segments forms the head, the middle group the thorax, and the
posterior group the abdomen. The appendages on the body are typically paired. The
sexes are separate.
Arthropods of veterinary importance
Class: Insecta includes all insects of which only a few are parasites of mammals and
birds.
Class: Arachnida includes ticks and mites as parasites of mammals and birds.
Class: Pentastomida. Only Linguatula serrata is important as a parasite.
ARTHROPODA
INSECTA
ARACHNIDA
ACARI
Astigmata
Diptera
(Flies)
Prostigmata
Phthiraptera
(Lice)
Siphonoptera
(Fleas)
Mesostigmata
Metastigmata
Some typical characteristics of parasitism
1. High reproductive potential (i.e. multiple fission in Apicomplexa;
hermaphroditism of trematodes; parthenogenesis in Strongyloides spp.; i.e.
strobilation of tapeworms for high ova output; and overall high ova/larval output
of many worms)
2. Often unique morphological or physiological specializations, loss of structures,
etc.
a. loss of digestive tract of tapeworms
b. loss of wings of fleas and lice
c. loss of many sensory structures of nematodes
d. development and refinement of a TEGUMENT; a living external layer of
digeneans, cestodes and acanthocephala that allows digestion and other
functions across body surface
e. development of special holdfast organs, including hooks, suckers, teeth,
clamps, cutting plates, spines
f. production of anti-coagulants in leeches and hookworms
3. Often special site specificity
4. Usually, but not always, non-lethal to host
5. Generally more numerous than hosts
6. Generally much smaller than host (if larger, then termed a predator)
7. Often have evolved methods of evading host immune system
a. Antigenic variation of trypanosomes
b. Tough tegument of acanthocephalans
c. Intracellular habitat of coccidia and Trichinella larvae
d. Antigen acquisition of schistosomes
e. Suppression of eosinophil or neutrophil migration to the site of the parasite
f. Encystment
g. Ability to cleave antibodies or consume complement
h. Ability to trigger certain arms of the immune response, which may in turn
damage host tissue enough to facilitate parasite invasion
Harmful effects of parasites on their host
All parasites have different types of effects on their hosts. Some are innocuous, some
are mildly pathogenic, and others are moderately harmful, while a few others are
highly pathogenic and fatal. Variability in the degree of harmful effects amongst
various parasites is related to their number, invasive power, virulence, propensity of
release of toxic products and their localization in the body of their hosts, besides many
other intrinsic and extrinsic factors in their surroundings within and outside of their
hosts like, general health conditions, age, breed, sex, nutritional level, concurrent
infections, inclement weather, etc. Precisely, the following types of harms
(pathological conditions) are caused by different types of parasites.
1. Compete with the host for food including vitamins (e.g., Ascarid roundworms,
tapeworms like Diphyllobothrium latum)
2. Decrease utilization and absorption of nutrients (e.g., Haemonchus contortus
in sheep).
3. Reduction in feed intake by animals.
4. Increase in the passage of food without proper digestion through the digestive
tract of animals.
5. Changes or reduces the absorptive surface of the intestine. E.g.,
Oesophagostomum spp in sheep, Coccidia in poultry)
6. Alterations in the efflux and influx of water and ions into the bowel.
7. Removal of hosts’ body fluid including blood. E.g., Hookworms, blood
sucking insects, ticks, etc.
8. Destruction of the hosts’ tissue mechanically or by pressure of the growing
size of the parasite (Hydatid cysts).
9. Cause mechanical obstruction of the gut lumen, air passages, ducts, blood
vessels, etc. (E.g., Ascarids, liver fluke, blood fluke).
10. Produce toxic substances causing haemolysis, histolysis, neurotoxin,
anticoagulants, toxic metabolites, toxicity due to dead worms in the body of
the host, etc
11. Host’s tissue reactions against parasites like inflammation, haemorrhage,
necrosis, fibrosis, excess mucous production, hyperplasia, hypertrophy,
paralysis, ulceration, anaemia, fever, etc.
12. Some parasites carry other pathogenic organisms (E.g., Heterakis gallinae
transmits Histomonas meleagridis; Metastrongylus apri carries swine
influenza virus)
GENERAL PRICIPLES OF PREVENTION AND CONTROL
There are some essential prerequisites on which principles of prevention and control
of a parasitic infection can be formulated. Mainly, the following information is
necessary before developing strategy for prevention and control of parasitic diseases.
1. Nature of infection(s), whether it is ubiquitous, endemic or sporadic.
2. Type of life cycle of disease causing parasite(s) in the area of operation, and
involvement of any intermediate host/vector(s), if any, and their breeding places.
3. History of the infection in a herd/flock of animals/birds in the area. Geo- and agroclimatic data and rainfall in the area.
4. Hygienic status of livestock farms maintained in the area.
5. Nutritional level of animals and the sources of their feed and potable water.
The term prevention of a disease is used when efforts are made to prevent healthy
animals from infection by adopting the following methods.
1. Keeping animals in hygienic and in dry surroundings
2. Avoiding access of susceptible animals to various sources of infection including
contact with diseased animals.
3. Providing balanced and clean drinking water.
4. Removing spots/places of breeding of intermediate hosts/vectors including their
killing by using molluscicides/ insecticides.
5. Proper maintenance of slaughter houses and effective disposals of offals/ blood
accessible to stray animals.
6. Proper investigation of new animals before introducing in the herd/flock.
7. Use of sterilized equipment for mass vaccination, artificial insemination, feeding,
watering, storing, etc.
8. Frequent screening of animals to detect any latent/carrier case and its immediate
treatment.
9. Formulating mass drenching schedule for prophylaxis (prevention) according to
the requirement in the area against possible parasitic infection and to remove
infection from sub-clinical or carrier cases, particularly at organized livestock
farms. Also, immuno-prophylaxis may be adopted by vaccinating animals against
infections like lungworms in sheep and theileriosis in dairy animals.
10. Frequent removal of ticks from the body of the animals and their immediate
burning.
11. Newly born and young growing animals should be reared separately from the
adult animals and they should not be allowed to graze on infected pastures.
The term control of a parasitic disease means to minimize the intensity and to prevent
further spread of an existing infection in animals by adopting the following methods.
1. Segregation of clinical cases and their proper treatment (chemotherapy).
2. All apparently healthy animas should be given preventive medication
(chemoprophylaxis).
3. Immunoprophylaxis (vaccination) may be done as stated under prevention, and all
other methods of prevention may be adopted.