WELCOMEI'm a great believer in luck, and I find

the harder I work the more I have of it.

Thomas Jefferson (1743 - 1826)

Md. Abdullah Al MamunAssistant Professor, Department of

Parasitology, Bangladesh Agricultural University, Mymensingh-2202,

Bangladesh.

Class lectureDVM

Level 2, Semester 1

INTRODUCTION•• ParasitologyParasitology is the branch of biological is the branch of biological science which deals with the parasites and science which deals with the parasites and their hosts.their hosts.

•• This discipline includes several approaches This discipline includes several approaches to the study of parasitic organism; such as, to the study of parasitic organism; such as, phylogeny, morphology, ecology, phylogeny, morphology, ecology, epidemiology, life history, physiology, epidemiology, life history, physiology, chemotherapy, serology, immunology, and chemotherapy, serology, immunology, and biochemistry.biochemistry.

ANIMAL ASSOCIATION

• Parasitism: Parasitism is a condition of life, normal and 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 to the host.

• Example: Neoascaris vitulorum in calves.

MUTUALISM• Mutualism 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 larger fish. Small fish get food and the larger fish are relieved of unwelcome guests on their bodies.

SYMBIOSIS• Symbiotic relationships include those

associations in which one organism lives on another and get benefited. 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.

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.

• Predation: Predation is a short term relationship in which larger species (the 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 applicable to two organisms which are merely traveling together and neither is physiologically dependent on each others.

• Usually the phoront is smaller than the other and is mechanically carried in or on the larger species (host).

PARASITE• The term “Parasite” refers to an organism

which is metabolically dependent on another larger organism belongs to different species.

• According to V. A. Dogiel stresses “Parasitesare 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”.

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.

• Permanent parasite: 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 parasite. e.g. Fasciolagigantica.

• Temporary Parasites: When an organism is parasitic only during a part of its life cycle, is known as temporary parasite. eg. Tick, Lice.

• Periodic Parasite: 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 goat.

• Aberrant parasite: 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 parasite: The parasite which has a narrow host range is known as stenoxenousparasite. e g. Eimeria bovis can infect cattle only.

• Euryxenous parasite: The parasite which has a large/wide host range is known as euryxenousparasite. e g. Trichostrongylus axei can infect cattle, sheep, goat, horse, rabbit, man etc

• Hyperparasite: A hyperparasite 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.

HOST• Host is defined as an organism which is

physiologically larger than a parasite, belongs to a different species and provides protection and supply nourishment to the parasites. e.g. Cattle is the definite host of Fasciola sp.

Classification of Host: Hosts are classified as follows

• Final/Definite host: The host in which parasite reaches its sexual maturity and reproduces itself is known as final/ definite host. Eg. Moniezia expansain goat.

• Intermediate host: The host which harbours the larval stage of parasites for development but not to reach sexual maturity is known as intermediate host.Example: Snail (Lymnea auricularia) is the intermediate host of Fasciola gigantica.

• 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.

• Example: Eathworm (Lambricus sp.) 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.

• Example: Dog acts as reservoir host of Entomoeba sp of man

Vector

• Vector may be defined as an arthropod, mollusk or other agents that transmit disease or parasites from one vertebrate host to another.Example: Anopheles sp is the vector of Malaria.Vector may be biological or mechanical

The important thing is not to stop questioning.

Albert Einstein

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 Zoologyin his Historia Animalium recorded tapeworms, cylindrical worm as ascarids

• Hippocrates (450-357 BC), father of Medicineknew about pinworm of horse

• Little progress was made between 1200 and 1650 A.D. 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 Systemanaturae classified worms into five classes-Nematoda, treamatoda, cestoda, Acanthocephala and cystica

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 goat was caused by Multiceps multiceps in1675

• Hartmann first observed Echinococus in dog in 1694

• Mongin described the first case of Loa loainfection 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 Heterophyseheterophyse 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

• Smith and Kilbourne discovered the causative agent of Texas cattle fever, Babesia bigemia in RBC in 1889

• Bruce discovered that the Tsetse fly, Glossinamorsitans served as vector of T.brucei in 1895

• Forde discovered Trypanosoma gambiense, the causative agent of Gambian sleeping sickness in 1901

• Chagas proved that Triatoma megista is the vector of Trypanosoma cruzi (Chagas’sdisease) in 1909

• Fantham described Trypanosomarhodesiense 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 contortus in 1928

• O’ Roke demonstrated the dipteran Simuliumvenustum transmits the Leukocytozoonanatis in 1934

Zoological Nomenclature• Aristotle (384-322 BC) father of Zoology

indicated that animals may be grouped together according to their characters

• Carolus Linnaeus (1707-78) laid the real basis for modern classification 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 in 1898 set up an International Commission on Zoological Nomenclature as permanent body

The 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

• When a new genus is proposed the type must be indicated

• A family name is denoted by adding IDAE to the stem of the name of genus and subfamily name by INAE

• Genera are grouped together into families, families into orders, orders into classes and classes into phyla

Example: Kingdom: AnimaliaPhylum: PlatehelminthesClass: TrematodaOrder: DigeneaFamily: FasciolidaeGenus: FasciolaSpecies: gigantica

Taxon Ending ExampleClass a NematodaOrder ida Rhabditida

Sub order ina StrongylinaSuper family oidea StrongyloideaFamily idea Strongylidae

Sub family inae Strongylinae

Geographic Distribution of Parasites

• Some parasites are more prevalent in tropical/developing countries than that of temperate countries.

• The presence or absence of a number of biological, chemical and physical factors in the environment affect directly or indirectly the distribution and densities of parasites.

1. Climate• 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

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

• Example: Various aquatic molluscan hosts of digenetic treamatodes (Fasciola sp, Paramphistomum sp, Schistosoma sp etc) survive only where plants in the water and deciduous trees on the banks are abundant

3. Faunaa. 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.

• Example: Fasciola hepatica is absent in Bangladesh because unavailability of the intermediate host Lymnaea truncatula

b. Availability of definite host and host range

• Population densities of definite, and transport hosts affect the parasitic densities and distribution

• Parasites can not survive in an area where the susceptible host are unavailable.

• So availability of host is important for the distribution of parasites

• Parasite is more widely distributed when it has a large host range.

• Example: Trichostrongylus axie has cosmopolitan distribution due to large host range

4. Habits or 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

Example: In temperate countries, the habit of people eating raw/insufficiently cooked food expose to tapeworms.

• Hindus are never exposed to tapeworm (Taeniasaginata) due to their religious restriction on eating beef.

Host specificityHost 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:a) Close evolutionary relationship: Host and parasites have evolved closely thus allowing the parasite to adapt itself with the host environmentb) Physiological condition: in the host such as, composition of host’s food, blood & lymph and pH in the digestive tract,c) Resistance of the host: Immunity of the host is such that it can injure the parasite for its elimination.

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 & texture of the organ

• Example: Fasciola hepatica inhabits the liver only of its definite host.

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

Classification of immunity• Innate immunity• Natural immunity• Acquired immunity

a) Active acquired immunityi) Natural active acquired immunityii) Artificial active acquired immunity

b) Passive acquired immunityi) Natural passive acquired immunityii) Artificial passive acquired immunity

• Age resistancei) Inverse age resistance

Innate Immunity• Innate immunity refers to immune response

where a host is permanently resistant against the infectivity of a parasite and is not affected prior contact with the pathogens

• This type of immunity is complete and can not be broken down by any condition

• The anatomical and physiological features make the host unsuitable for a certain types of parasites.

• Example: Man has innate immunity against Moniezia expansa, a tape worm of ruminants

Natural immunity• When the immunity is programmed in the

host cell DNA is called natural immunity• The host is resistant against the infection of a

parasite but this can be broke down under certain condition such as stress, malnutrition or heavy infective doses etc.

• Example: Sheep is naturally resistant to Neoascaris vitulorum infection

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

own production antibodies against the invading parasites is known as active acquired immunity

i) Natural active acquired immunity It is natural when produced through previous low

grade infection. e.g. Immunity of birds to Ascaridia galli

ii) Artificial active acquired immunityIt may also artificial when produced through

artificial infestation of low infective doses or attenuated infective stages of parasites. e.g. Immunity produced in Dictyocaulus viviparusin cattle

b) Passive acquired immunityWhen 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 immunityWhen the resistant mother passes antibodies on

to their young against the parasite either through placental circulation or colostrum/milk is called natural passive acquire immunityii) Artificial passive acquired immunity

When the antibodies are transferred mechanically to the susceptible host via artificial means is called artificial passive acquired immunity

Age resistance/immunity• It is a type of natural immunity in which the older

hosts are more resistant than the younger to parasitic infestation. eg. older sheep are resistant than lambs to Moniezia expansa

Inverse age resistance: It is a natural resistance which refers to the lake or loss of susceptibility of young hosts compared to older to parasitic infestation. eg. Young cattle are less susceptible 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 is called premunition eg. Premunition in case of Taenia solium or T. saginata.

Mechanism of Immunity

• Immunity production involves phagocytosis by macrophages and production of specific antibodies

• The 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

Factors associated with ImmunityImmunity 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

Parasitic immunity involves the following factors1. Extra haemopoetic factorsa) 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 whites

b) 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

c) Mucus: In the mucosa the cilia of the epithelium, flushing action of tears and urine help to remove undesirable infective materials

d) Body temperature: High body temperature accounts for combating many pathogens eg. Birds are less susceptible to infection than man due high body temperature

e) Metabolic or physical well being: Better nourished animals are less susceptible to diseases than malnourished animals

2. Humoral factors• Lysozymes: This an enzyme found in the

tissue cells, blood serum, glandular secretions and capable of destroying many invading organisms

• Antibodies: Antibodies destroy the invading organism (parasites), their development or more rarely neutralize their toxic products. Antibodies are five types ,IgA, IgG, IgM, IgD, IgE. IgE is more prevalent during parasitic infection.

3.Cellular factors: This comprises phagocytosis by macrophages, leukocytes

Factors that break down 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.

Source of InfectionThe source of infection of parasitic infestation may

be:• An infected definite host• Reservoir host• Intermediate host• Transport host• Contaminated food and water

The way through which the parasite leaves from the host body are:

• Faeces: When the parasites inhabit the digestive system.

• Nasal secretion / sputum: When the parasites live in the respiratory system.

• Urine / genital secretion: When the parasites inhabit in the genito-urinary system.

• Blood / lymph: must be withdrawn mechanically or by blood sucking arthropods for transmission to a susceptible host.

• Skin and tissues: The skin and subcutaneous tissues provide a means of exit from the body and are readily accessible to insect vector.

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

forms • The intermediate host before becoming infective.

1. Transmission by Direct contact• This implies the intermediate transmission of

infective stages from one host to another• Example: Tritrichomonas foetus is transmitted

by direct contact (coitus) • Lice and mites also transmitted directly

2. Transmission through mouth or 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, fishes, crustaceans and molluscas

3. Transmission through skin penetration• The infective stages of parasites may penetrate

the host’s skin by its own effects. e. g Cercariaeof Schistosoma sp, Infective larvae of Hook worms

• Infective stages of parasites may be introduced into hosts body by arthropod vectors through biting. e g. Babesia sp, Theileria sp by tick vectors, Malaria by female Anophelesmosquitoes

• Infective phases may also be introduced into the body mechanically during injection or vaccination by using the same syringe and needle

4.Transmammary transmission

• The infective stages of parasites may enter into the young /offspring through milk from the infected mother /dam

• Example: Toxocara vitulorum infection if buffalo calves

5. Transplacental/Intra-uterine transmission/ pre natal infection

• Infective stage of parasites enter into the body of young through foetal circulation

• Example: Ancylostoma caninum in dogs

Effects of Parasitism on Host and Parasites

1. Utilization of hosts 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 consequences

• Tape worms absorb simple sugar, amino acids, vitamin B12, some constituent of yeast diet and other nutrients

• Example: Diphyllobothrium latum in man cause anemia by absorbing vitamin B12

2. Removal of host’s blood and tissue fluids• Blood sucking parasite sucks sufficient amount

of blood and cause fluid loss due to secretion of anticoagulant

• Example: Haemonchus contortus of cattle can remove 0.05 ml blood per day from the body

3. Destruction of host’s tissues• Some parasites injure the host tissues during

entering• Other inflicting tissue damage after have

successfully entered• Some others induce histo-pathological

changes by eliciting cellular immune response

The nature of tissue damage is given below• Ingestion 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. Eg. Ascarislumbricoides larvae in man.

• Tear off /bite off and ingestion of the host tissues. eg. Strongylus vulgaris in horse

• The cercariae of some parasites penetrate the host’s skin causing “Swimmer itch” in man. e. g Schistosoma sp.

4. Mechanical interferencea) Blood and lymphatic vessels, bile ducts or

alimentary canal can be obstructed by heavy load of parasites, eg.

i) Blood vessel - Dirofilaria immitis in dogii) Lymphatic canal - Wuchereria bancrofti in maniii) Bile duct - Fasciola gigantica in cattleiv) Alimentary tract- Ascaris lumbricoides in man

b) Causes pressure atrophy of different organs, eg.

i) Coenurus cerebralis (Gid disease) in the brain of goat

ii) Hydatid cyst (Echinococus granulosus) in the liver of cattle

5. Abnormal growth of host’s tissues/ Tissue change

• The egg of Schistosoma nasalis cause hyperplasia of nasal mucosa of cattle

• Development of tumors- Cysticerci of Taeniataeniaeformis causing tumor in the liver of rats.

• Hyperplasia may turn into malignant tumers, eg. Paragonimus westermanii cause cancer/ metaplasia in the lung of tigers.

• Hypertrophy is commonly associated with intracellular parasites, eg. Plasmodium vivaxcause enlargement of red blood cell of man

6. Secretion /excretion of various harmful substances into the host

• Irritating parasitic secretions incite an allergic reaction in host’s body.

• Example: “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.

7. Introduce other pathogenic bacteria, virus, rickettsia and protozoan parasite into 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 turkey is introduced by caecalnematode Heterakis gallinarum

Adaptations of Parasite

1. Adaptation to feed and attachment with the host

• Powerful, strong and large buccal capsule with teeth to affect blood sucking of parasites from the body of the hosts, eg. 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, eg. mosquitoes (Anopheles sp)

• Loss of entire digestive system in tapeworms (cestode) which have adapted in absorbing body fluid from the host’s through cuticle, eg. Monieziaexpansa in ruminants

• Incomplete intestine (absent of anus) in trematodes (flukes) which only can intake liquid food through mouth, eg. Fasciola gigantica in cattle.

• 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

• The acanthocephalid worms and ticks are attached with the body of their host by toothed proboscis and the 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

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, eg. miracidium of trematodes that bear cilia and made contact with snail host

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 byi) Increase size of the ovary, eg. When tapeworms and trematodes mature, ovaries occupying the whole bodyii) Increased egg production by a single ovary, eg. A female Ascaris lumbricoides may produce 2,000,000 eggs per day and Ancylostomaduodenale produce 25,000 eggs per day

• Parasites which have less risk of destruction of offspring may produce fewer eggs.

• Example: Female warble fly (Hypoderma lineata) produces 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

• Example: A single oocyst of Eimeria tenella may produce 1,800,000 individuals by sexual multiplication within 4-5 days.

PRINCIPLES OF CONTROL OF HELMINTH INFECTION

1. Reducing contamination2. Avoiding infestation of the host3. Treating the host/ reservoir of

contamination

REDUCING CONTAMINATION

DESICCATION:• First and 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 of the free living stages.

NUTRITION OF THE HOST

• A well nourished animal is more resistant to infestation 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.

• Thus, older animals with immunity may cause safely graze areas dangerous for young animals.

ALTERNATIVE HOST• The larvae of certain gastrointestinal

parasites can develop in different hosts, eg. T. 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 for Cattle and Vice-versa.

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.

STABLE MANAGEMENT

• Stables should be constructed with a view to keep the animals away from their own feces or to regular removal of feces.

• 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.

• 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.

LOW-LYING PASTURES• Rains 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.

• 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.

OVER GRAZING

• Overgrazing of pastures 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.

ORDER OF GRAZING • Young, relatively worm-free animals should be

allowed first access to pastures that are relatively safe before these pastures are grazed by older animals that would infest the pastures.

• 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 treatments.

• The animals should be moved to these clean pastures immediately after treatment.

AVOIDING CAMPING GROUNDS

• 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 effect of parasites on the host and secondly to reduce the contamination of pastures or stables with free living stages.

• 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 pastures.

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.

• The whole aim is to prevent the appearance of symptoms and loss from sub-clinical disease.

• Animals must be treated while they are healthy to keep them healthy.

TACTICAL TREATMENTS• These are treatments, in addition to the above

"Strategic Treatments" that may be needed to obtain proper control in abnormal years. e.g., if good rains fall for longer into the 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 Weather" and tactical treatments call for "Drenching by the Weather".