TREATMENT AND CONTROL METHODS IN

PARASITOLOGY

Part 2: Control Methods1

INTRODUCTION

The success of control measures against any disease is

dependent on:

- a knowledge of its aetiology (causative agent)

- natural history epidemiology, including its mode of

transmission,

e.g. whether it is vector-borne, water-borne, or

transmitted by orofaecal, aerosol or venereal methods.

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CONTROL OF PARASITIC DISEASES

Concepts of eradication, elimination, and control of

parasitic diseases

Education

Environmental modification and cultural control

Role of government, foundations and aid organisations

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CONCEPTS OF ERADICATION, ELIMINATION, AND CONTROL

OF PARASITIC DISEASES

Eradication indicates that the parasite no longer exists

anywhere in the world.

Therefore is no need to maintain treatment regimes or

control programmes.

By contrast, if a parasite is merely controlled, then it

continues to exist, though its incidence and prevalence,

morbidity and mortality in particular areas will reduced as

consequence of the ongoing control measures.

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There are no example of successful parasite eradication

campaigns.

In many developed countries, may human parasites have

been eradicated as a consequence of the rise in living

standards, effective waste disposal, and improved

hygiene.

Improved meat hygiene inspection and concern over

zoonotic diseases have lead to the virtual elimination of

helmiths such as Enchinococcus granulosus and Taenia

saginata. 5

Control of any disease by the reduction of parasite load or

vector population, thus reducing transmission, implies

recognition that there is likely to be a continuing problem

and hence commitment.

The objective is to reduce the disease to a level at which

it is acceptable to the community or the stockholder by

reducing morbidity to levels commensurate with

socioeconomic development or livestock productivity.

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EDUCATION

Parasitic infections tend to have their most severe impact

upon those who are poorly educated

But the risk of infection can often be reduced by simple

changes in behaviour

Education is a key feature of parasitic control

programmes

For example: if people understand that the large cysts

that grow inside them result from eating and drinking

substances that are contaminated with dog faeces, then

theoritically it should be relatively easy to reduce the

incidence of hydatid disease.

HOW?7

BY MAKING THEM REASSESS THEIR RELATIONSHIP WITH DOG!

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Educational materials leaflets, posters, radio and television programmes.

Avoid scientific terminology, employing illustrations and photographs

Some example of country that has good success:

1) China

- So called „barefoot doctors‟

- Dispense simple treatment and verbal guidance to isolated communities.

- Health messages often delivered via teachers

- Health clinics provide opportunity to talk to women in the communities.

* Women – often have a strong influence on the behaviour of all members in the family

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2) Finland

- During 1800s, hydatid disease was effectively controlled

for many years through the provision of educational

pamphlets.

- Legislation and more effective treatments became

available

- By 1960s – the disease had been eliminated from the

country.

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Example of failure – Africa

- Insecticide-treated bed-nets

are effectively at preventing

malaria, provided that they use

it correctly

- As a consequence, aid

agencies in parts of Africa

distribute free bed-nets and

instruct them how to use it.

- However the level of infant

mortality still remains high.

- WHY? 11

The bed-nets are not always appropriate for the way

people actually live.

Such as burden to hang and disassemble the net

everyday.

The net traps heat difficult to sleep.

Risks – fire, safety of the children

They sleep outside of the house at night

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ENVIRONMENTAL MODIFICATION AND CULTURAL CONTROL

Until the development of effective drugs and pesticides,

environmental modification and cultural control were the main

means of combating parasites, pests and diseases.

It was seldom understood why certain practices were effective

but experience taught us to do or not to certain things at

certain times of the year.

In countries with seasonal climates, the risk of infection is often

most pronounced at certain times of year and sometimes

possible to predict when or whether a parasite will be particular

problem and take appropriate action. 13

Relatively simple environmental modifications can reduce the risk of exposure to many parasites diseases.

Example:

1)increasing the water flow rate in the irrigation channels and removing plant growth

- unsuitable environment for the snails that acts as the intermediate hosts of schistosomes

2) concrete farm yards and animal pens

- easy to keep clean of faeces

3) solid hut or house walls and ceiling

- Do not provide hiding places for the hemipteran bug vectors of Trypanosoma cruzi

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For ruminant parasitic species pasture and grazing management.

Grazing management has an important role in parasite control.

The aim of grazing management is to have vulnerable sheep exposed to fewer larvae on pasture.

The result will be that fewer drenches will need to be used.

At the same time grazing management provides nutrition to allow sheep to better deal with parasites.

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Grazing paddocks alternately with sheep and cattle can

exploit the fact that most of the common worms of sheep

do not readily infect cattle, and vice-versa.

The best method for alternate grazing of sheep and cattle

is a 6-monthly interchange, with the sheep and cattle

being swapped in January and July.

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Cropping

- The timing and duration of cropping is ideal for preparing

paddocks that are virtually free of worm larvae.

- This is because most larvae are removed with the crop,

remaining larvae die because they are exposed to the

sun and there is no contamination with worm eggs since

the early autumn.

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Preparation of 'Safe' Pastures.

- 'Safe' pastures are those with low numbers of infective

larvae.

- Worm control can be greatly improved and drenching

frequency reduced by preparing 'safe' pastures for the

most susceptible animals in the flock.

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95% in pasture

PARASITE POPULATIONS –

RARELY IN THE HOST

5% in host

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BIOLOGICAL CONTROL

Biological control is an ecological method designed by

man for lower a pest or parasite population to keep these

populations at a non harmful level.

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STEP 1. Accurate identification of the pest species and confirmation of the pest as a target for biological control.

STEP 2. Surveys for natural enemies (generally insects, mites, nematodes and diseases) are conducted in the area of origin of the pest

STEP 3. Determine host-specificity of potential control organisms to assess impact on targets and nontargets and environmental safety.

STEP 4. Following approval from federal and state regulatory officials, biological control agents are shipped to a domestic quarantine facility where they are examined to confirm species identity and to determine whether they are free of parasites and diseases.

STEP 5. These agents are tested in field plots to determine that the agents do reduce densities of the target pest and do not have adverse effects on nontargets. Once this small scale testing is completed, appropriate natural enemies can be mass-reared to high numbers and released at field sites established by county biologists.

STEP 6. Once released, each biological control agent is evaluated for establishment, spread, impact on the target species, and impact on nontargetspecies. Careful, long-term evaluation studies provide scientific data that are used to improve current and future programs. Additional releases may be made in an augmentative manner in systems where long-term stability of the natural enemies is not feasible.

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AGENTS FOR BIOLOGICAL CONTROL

These organisms include

1) Micro-arthropods

- Biological control of insects may include predators (e.g. spider) parasites, parasitoids, (insect parasites of insects)

2) Protozoa

- Some protozoa such as Haemogregarina, Nosema, Babesia and Theileria are pathogenic for some parasites like "ticks"

3) Predacious nematode

- Steinernema (Neoaplectana) carpocapsae has shown some success against mosquitoes on an experimental level.

4) Virus

- Some potential candidate has been identified by not much known about them.

5) Bacteria

- Bacillus thuringiensis are among the most widely used antagonists in biological control of insects.

- After ingestion, target insects are killed by a gut toxin which is released from crystal proteins in the bacterial spores

6) Fungi22

NEMATOPHAGOUS-FUNGI

Fungi that exhibit anti-nematode properties have been

known for a long time.

They are divided into three major groups based on their

morphology and types of nematode-destroying

apparatus

1. Predacious Fungi

2. Endo-parasitic Fungi

3. Egg-parasitic Fungi

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PREDACIOUS FUNGI

Produce specialized nematode-trapping structures

(adhesive knobs, networks, rings etc.) on the mycelium

The trapping activity of the fungus was influenced by the

motility of the infective larvae & there is no specificity for

the parasitic species

E.g Arthobotrys spp. (A. oligospora)

- Cooperia oncophora

- H. contortus or Ostertagia circumcincta

Monacrosporium spp

Duddingtonia flagrans

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Predatory fungus

Arthrobotrys anchonia

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(A) Formation of the fungal trap (white

arrow) after 6 h of the fungus/larva

interaction

(B) fungal trap in anastomosis (white

arrow), forming the scattered

adhesive three-dimensional network

trap and septate conidium of the D.

flagrans fungus (black arrow)

(C) scattered adhesive three-dimensional

network traps (white arrow)

(D) fungal hyphae of the control

without Ancylostoma spp. L3

(E) Ancylostoma spp. L3 in the control

without fungus

(F) Ancylostoma spp. L3 captured, after

8 h of interaction with the fungus, at

the cephalic portion (white arrow) and

at the middle of the body (black

arrow) by traps in the anastomosis

process (dashed white arrow).

Maciel A. S., Araujo J. V., Campos A. K., Benjamin L. A., Freitas L. G., 2009. Scanning electron microscopy

of Ancylostoma spp. dog infective larvae captured and destroyed by the nematophagous fungus Duddingtonia

flagrans. Micron 40(4): 463 – 470.

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ENDO-PARASITIC FUNGI

These invade nematodes either by penetration of cuticle from

sticky spores adhering to the cuticle or following ingestion of

spores which lodged in the gut.

Inside the host, they develop an infectious thallus which

absorbs the body contents.

Endoparasitic fungi have no extensive hyphal development

outside the body of the host except fertile hyphae such as

evacuation tubes or conidiophores that release the spores.

This type of fungi is obligate parasite of nematodes, with very

limited capacity to develop outside the prey and density

dependent

E.g Drechmeria coniospora

Harposporium anguillulae27

Conidia attached to tail region of nematode.

Diagram of Drechmeria showing

salient features.

Shows conidia of fungus attached to

buccal (mouth) region of the

nematode. Some spores have

germinated and you can see faintly the

sinuous hyphae of the parasite tracing

through the body of the victim.

Massive reproductive growth of

conidiophores and conidia

of Drechmeria bursting through the

cuticle of the host.

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EGG-PARASITIC FUNGI

These have the ability to attack the egg stage and may have a role in the control of animal parasites which have a long development and/or survival time in the egg stage in the environment outside host

May be defined as fungal parasites of cyst and root-knot nematodes

The fungus was shown to be able to degrade the egg shell enzymatically and infect the eggs

E.g Paecilomyces lilacinus

- Ascaridia galli and Parascaris equorum

Verticillium chlamydosporium

- Toxocara canis 29

Paecilomyces

(A) Eggs of Ascaridia galli in Petri dishes of the

control group (white arrows).

(B) (B–D) Destroyed A. galli egg (white arrows)

after interaction with the hyphae and

chlamydospores of Pochonia

chlamydosporia fungus (black arrows)

F.R. Braga, J.V. Araújo, J.M. Araujo, L.N. Frassy, A.O. Tavela, F.E.F. Soares, R.O. Carvalho, L.M.

Queiroz and J.H. Queiroz. 2012. Pochonia chlamydosporia fungal activity in a solid medium and its

crude extract against eggs of Ascaridia galli. Journal of Helminthology 86(03): 348-352.

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INTEGRATED PARASITE MANAGEMENT (IPM)

In livestock production

Goal is not to create parasite-free animals.

It is normal for sheep and goats to have parasites.

Goal is to prevent clinical disease and production losses

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Good Management

Use of Clean or Safe Pastures

Pasture Rest and Rotation

Grazing Strategies

Multi-species Grazing

Alternative Forages

Healthy Soil

Nutritional Management

Zero Grazing

Genetics33

GOOD MANAGEMENT

Internal parasite control starts with good management

and common sense.

Sheep should not be fed on the ground.

Feeders which cannot easily be contaminated with feces

should be utilized for grain, hay, and minerals.

Water should be clean and free from fecal matter.

Pastures and pens should not be overstocked.

When new sheep are acquired they should be isolated

from the rest of the flock for 30 days and aggressively

dewormed to prevent the introduction of drug-resistant

worms. 34

USE OF CLEAN OR SAFE PASTURES

Clean or safe pastures are pastures which are not contaminated with the worm larvae that affect sheep.

Examples of clean pastures include:

- pastures that have not been grazed by sheep or goats for the past 6 to 12 months;

- pastures which have been grazed by horses or cattle; pasture fields in which a hay or silage crop has been removed;

- pasture fields which have been rotated with field crops; and

- pastures than have been recently established or renovated

While burning a pasture will remove worm larvae, there are no pasture treatments that will effectively eliminate or reduce worm larvae.

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PASTURE REST AND ROTATION

It is a common misconception that rotational grazing

helps to control internal parasites in sheep.

Intensive rotational grazing may actually contribute to

parasitic problems.

This is because rotating large groups of sheep and lambs

through small paddocks concentrates livestock and

infective parasite larvae onto the same small area.

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Researchers in the Netherlands found that it takes three months of rest for an infected pasture to return to a low level of infectivity.

Researchers at Langston University (Oklahoma) determined that a 65-day rest period was sufficient (for goats).

Rotational grazing is an effective management tool for managing parasites, but only if pasture rest periods are long enough (i.e. 60 days or more).

On the other hand, better nutrition provided by rotational grazing may offset the effects of higher parasite loads on the pasture.

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GRAZING STRATEGIES

Approximately 80 percent of the worm larvae can be

found in the first two inches of grass.

Therefore, sheep grazing taller forages will have fewer

parasite problems.

Sheep should not be allowed to graze forages shorter

than 2 inches in height.

Sheep that browse also have fewer parasite problems.

Another grazing strategy is to wait until the dew has lifted

from the grass or grass has dried after a rain.

Dry conditions force parasites to stay at the base of the

plants where they are less likely to be consumed by the

livestock.38

MULTI-SPECIES GRAZING

Sheep (and goats) are generally not affected by the same

internal parasites as cattle and horses.

Consequently, pastures grazed by cattle and horses are

safe(r) for sheep (and goats) and conversely.

Sheep can be co-grazed with cattle and/or horses.

A leader-follower system can be utilized or pastures can

be alternated between sheep and cattle and/or horses.

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There are numerous other benefits to multi-species

grazing.

Each species has different grazing behavior that

complements one another.

For example, sheep prefer to eat weeds and short,

tender grasses and clover, while cattle prefer to eat taller

grasses.

Cattle may offer some protection from predators. 40

ALTERNATIVE FORAGES

Some pasture plants have anthelmintic properties, such

as those containing condensed tannins.

Research has shown that sheep grazing tannin-rich

forages have lower fecal egg counts than animals grazing

traditional grass pastures.

The tannins may also decrease the hatch rate of worm

eggs and larval development in feces.

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Forage species which contain high levels of condensed

tannins include Sericea lespedeza, birdsfoot trefoil, and

chicory.

Sericea lespedeza is a warm, season legume.

Birdsfoot trefoil is a long-lived perennial legume.

Chicory is a low-growing, leafy perennial.

Generally speaking, trees and shrubs contain higher

levels of tannins than pasture grasses, and tropical

legumes contain more condensed tannins than temperate

legumes

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HEALTHY SOIL

Earthworms have been shown to ingest worm eggs and larvae, either killing them or carrying them below the soil surface.

Certain types of fungi will trap and kill parasitic larvae.

Dung beetles ingest and disperse manure, thus keeping eggs and larvae from developing.

Anything that is done to maintain soil health and promote these types of organisms will aid in parasite control.

Scientists are examining the possibility of feeding nematophagous fungi to livestock to kill larvae in manure piles.

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NUTRITIONAL MANAGEMENT

Supplemental feeding should not be overlooked as a means to control parasites.

Sheep and lambs on a higher plane of nutrition mount a better immune response to internal parasites than animals whose nutritional status is compromised.

Animals on low protein diets are more susceptible to infection because they produce less IgA(immunoglobulin).

Higher levels of protein have been shown to improve the pregnant ewe's immune response to parasites after lambing.

Lambs receiving protein supplementation have reduced fecal egg counts. 44

ZERO GRAZING

Keeping sheep and/or lambs in confinement (i.e. "zero grazing") is a means of reducing parasitism and preventing reinfection.

Under a zero grazing situation, sheep and/or lambs do not have access to any vegetation for grazing.

They are housed in a bedded barn, dirt lot, or facility with slotted floors.

Feed should be fed off the ground in feeders.

Watering containers should be kept free from fecal matter.

Slotted floors offer the best protection against internal parasites because sheep generally do not come into contact with their feces.

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GENETICS

Genetics is probably the best long term weapon against

internal parasites in sheep.

Some sheep breeds are more resistant and resilient to

internal parasites.

They include the Florida (or Gulf Coast) Native and the

hair sheep breeds: St. Croix, Barbados Blackbelly (and its

derivatives), and Katahdin.

In Malaysia – Kalahari Red, Boer etc.

Grazing resistant breeds of sheep with susceptible

breeds, may act to “sweep” pastures and reduce

contamination to susceptible animals.46

Regardless of the breed raised, producers can also breed

sheep which are less resistant to parasites by culling ewes that

are persistently affected by parasites and favoring parasite

resistant ewes and rams in their selection programs.

Both fecal egg counts and FAMACHA© scores can be used to

identify sheep with resistant and susceptible genetics.

In New Zealand, it is possible to select rams that shed 60 to 70

percent fewer parasite eggs than historical averages.

Scientists are currently looking for genetic markers for worm

resistance so that a DNA test could be used to show producers

which of their animals are resistant to internal parasites.

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FAMACHA©• Developed in South Africa in

response to the emergence of severe anthelminticresistance

• A system to assess Haemonchus contortus(barber pole worm) infection in sheep and goats and the need for dewormingindividual animals

• Named for its originator:

Dr. Francois “Faffa” MAlan CHArt

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FAMACHA©

Clinical Category

Eye Lid Color

Packed Cell

VolumeTreat?

1 Red > 28 No

2 Red-Pink 23-27 No

3 Pink 18-22 ?

4 Pink-White 13-17 Yes

5 White < 12 Yes

Treat adults at scores 4 and 5*Treat lambs and kids at categories 3, 4, and 5

*South Africa recommends goats be treated at categories 3, 4, and 5

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ROLE OF GOVERNMENT, FOUNDATIONS AND AID

ORGANIZATIONS

Depends on co-ordinated national or even international responses which only can be achieved through the active cooperation of governments.

Require stability within the country and a suitable infrastructure for distribution of funds, communication and travel for expert personnel.

Can be organized through:

- national government

- local government

- combination

Only government have the power to pass and enforce legislation. 50

Legislation can be an effective tool:

- can force local authorities to provide safe water and

sanitation

- make it an offence to import pets or domestic animals

without a certificate

- require farmers to dispose of dead animals appropriately.

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Role of different organizational levels of health services in sleeping sickness

control.(After World Health Organization, 1986.)

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