Parasites, Part II
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Transcript Parasites, Part II
Internal Parasites, Part II Control
INAG 120 – Equine
Health Management
November 16, 2011
Deworming Protocols
Rotational Purge Deworming:
Goal is to keep the load of eggs and
larvae to a minimum
Done every 8-12 weeks via oral paste
Kills adult and/or larval stages of
worms inside the horse before they
start producing eggs
Drawbacks of Purge Deworming
If other horses in same area not
dewormed when needed, environmental
reduction won’t work
Some parasite eggs can live as long as 30
years in the soil!
Immature worms mature worms =
migration through intestinesand other
tissues = damage!
Success depends on timing
Many purge dewormers don’t kill bots
Myths: Vets must tube-worm for it
to be effective
Only way to guarantee that all the
drug is given
Old dewormers were irritating or badtasting
Myth: Toxicity will build over time
in my horse
Organophosphates (used in 60’s and
70’s) did cause problems
Major concern with modern
dewormers:
Ascarid impaction in foals
Myth: Dewormers aren’t safe for
use in broodmares
If drug label says it’s safe for mares:
Manufacturer must TEST it for FDA
approval
Requires 2 years of demonstrated efficacy
The Pfizer Babies of CSU
Praziquantel study
in France
Quest?
Myth: Diatomaceous Earth is just
as effective as chemical dewormers
Herbs and other compounds are not
required to be tested (not FDAcertified)
No scientific evidence supports use as
dewormer
Myth: Rotational deworming will
prevent development of resistance
Rotational deworming started about
40 years ago
Reason was NOT resistance
Earlier dewormers were not broadspectrum
Purge Deworming Drugs
How they work
Classes & Brand Names
Benzimidazoles (Panacur Pack)
Tetrahydropyrimidines (Pyrantel Pamoate)
Heterocyclic compounds (Piperazine)
Macrocyclic lactones (Ivermectin/Moxidectin)
Isoquinoline-Pyrozines (Praziquantel)
Safety and efficacy
Dewormer Products
All must be approved by FDA
Rigorous testing required
Must be proven safe and effective
Must remove at least 90% of target
parasites
Most are broad-spectrum
Don’t require refrigeration but can be
damaged by excessive heat
How do they work?
Nematocides
Death by starvation
Death by paralysis
Worms can’t store energy
Must eat continuously
Most parasites will die within 24 hours if
eating process is interrupted
Paralysis blocks ability to stay in gut
Benzimidazoles
Interfere with metabolism on a cellular
level
Bind to a particular structure, thereby blocking
energy metabolism
Because of mechanism of action, can also
kill eggs
Available in granules, paste and suspension
More effective when given several days in a
row
Panacur Powerpac
5 Days of Panacur
(Fenbendazole) at 2x dosage
Kills everything
Good for new horses coming into
your herd as treatment
Good for all horses moving to new
area where there were no horses in
the past
Pancur Powerpac
Panacur Powerpac
Benzimidazoles
Generic
Name
Brand Name
Safety Level
Fenbendazole
Panacur,
Safeguard
100X
Oxfendazole
Benzelmin
10X
Oxibendazole
Anthelcide EQ
60X
Benzimidazoles
Effective control of following
parasites:
Strongyloides (except benzelmin)
Ascarids
Large strongyles
Pinworms
NOT Bots
NOT Small Strongyles
Exception is Panacur PowerPak
Tetrahydropyrimidines
Say that 5 times fast…
Mimic activity of acetylcholine (a
neurotransmitter that causes muscle
contraction)
With tetrahydropyrimidines, contraction is
permanent rigid paralysis of parasite
Fastest activity of any deworming product
Only affect adult parasites (not larval stages)
Parasites bounce back quickly
Paste, suspension, and pelleted forms
Tetrahydropyrimidines
Generic
Name
Brand Name
Safety Level
Pyrantel Pamoate
Exodus, Rotectin-P,
Equi-Cide, PSI’s
suspension, LiquiCare P, Strongid
Paste
20X
Pyrantel tartrate
Strongid C (2X),
Continuex (2X)
--
Tetrahydropyrimidines
Effective against the following parasites:
Ascarids
Large Strongyles
Small Strongyles
Pinworms
NOT effective for Bots
NOT effective for Strongyloides
Effective for tapeworms when given at twice the
normal dosage
Heterocyclic Compounds
Only one used in horses (Piperazine)
Depolarizes muscle membranes –
resistant to acetylcholine
Worms become paralyzed
Limited to adult parasites
Available only in powder and liquid
(stomach tube), pelleted
Brand name: Piperazine (1X safety
factor!)
Macrocyclic Lactones
Act on parasite’s nerve and muscle
cells
Normal transmission of stimuli
disturbed
Flaccid paralysis inability to feed or
swallow nutrients
Most potent killers! But, slow to act
Ability to kill external parasites
Lice, mites, ticks
Macrocyclic Lactones
Generic
Name
Ivermectin
Moxidectin
Brand Name
Zimecterin,
Rotation 1,
Ivercare,
Equell
Quest, Quest
Plus,
ComboCare
Safety Level
60X
3X - 5X*
Macrocyclic Lactones
Effective against the following
parasites:
Strongyloides
Ascarids**
Large Strongyles
Small Strongyles (adult only –
ivermectin; all stages - moxidectin)
Bots
Pinworms
Isoquinoline-Pyrazines
New kid on the block
NO ACTIVITY AGAINST NEMATODES!
Effective only against tapeworms
Disrupts worm’s outer layer worm
can’t maintain fluid balance
Generic name: Praziquantel
Brand names: Equimax, Quest
Plus, ComboCare Gel, and
Zimectrin Gold
Purge Deworming Sample Adult
Horse Program (Maryland):
February: Deworm with Ivermectin +
Praziquantel to kill bots and Tapeworms
April: Deworm with Moxidectin to kill
encysted strongyles
August: Deworm with Ivermectin or
Ivermectin + Praziquantel to kill bots
and tapeworms
October: Deworm with Oxibendazole
December: Deworm with Ivermectin to
kill bots
Problems with rotational
deworming as we know it
Reasons for deworming often not
known
Drug chosen may not be effective
against parasite present in horse
Don’t discriminate between horses in
different parts of the country (i.e.
Florida vs. New York)
Horses vary widely in susceptibility to
parasites
How should we deworm, then?
Target parasites
Tapeworm – once a year, during spring or
autumn (more often for known problems)
Bots – must enter host prior to winter, deworm
late autumn/early winter
Large strongyles
Most horse owners have unknowingly
eradicated large strongyles already
Treat all horses at intervals of 6 months for 18
months
Small strongyles present greatest problem today
Targeting small strongyles
Objective of control
NOT to “kill worms”
Prevent contamination of environment
with eggs
Kill female worms before they reproduce
Environmental factors
All horses pass strongyle eggs at a
predictable time post-treatment
Infectivity of eggs is dependent upon
environmental factors
Targeting small strongyles…
Environmental factors…
Northern states:
Hatching and development during spring,
summer and autumn
Autumnwinter favorable for persistence!
Southern states:
Hatching and development during autumn
and spring
Summer: development and survival poor;
winter ok
Targeting small strongyles…
Host factors
Individual horses differ!
Routine deworming may be unnecessary for
some horses in a herd
Categorize horses
Perform quantitative fecal examinations
Anthelmintic Issues
FECRT (Fecal Egg count Reduction Testing)
Know expected egg reappearance periods for
the different compounds
Determining Strongyle
Contaminative Potential
Requires fecal egg counts!
If horses haven’t been dewormed recently:
20-30% = high egg counts
30-50% = low egg counts
Less than 150 eggs per gram = Low
Contaminators
Greater than 500 EPG = High
Contaminators
Examine fecal samples 4 weeks after
expiration of egg reappearance period
Expected Egg Reappearance
Periods
Anthelmintic
Expected Egg
Strongyle
Reappearance contaminative
Period
Period
Benzimadazoles 4 weeks
8 weeks
Pyrantels
4 weeks
8 weeks
Ivermectin
8 weeks
12 weeks
Moxidectin
12 weeks
16 weeks
Sample Schedule for Deworming
October – Moxidectin and Praziquantel for ALL horses
November, December, January, February –
NOTHING (too cold)
March – FEC, identify contaminators
Ivermectin to all horses
April – NOTHING
May – FECRT
Strongid to moderate and high contaminators from
March
Recheck fecal in 10-14 days
June – Strongid to high contaminators
July, August – NOTHING (too hot)
September – Strongid to moderate and high
contaminators
Slow Rotation
A recommendation by some
parasitologists
Rotate annually:
Moxidectin – year one
Strongid – year two
Ivermectin – year three
Panacur – year four
Deworming Protocols
Daily Dewormer:
Prevents damage done by immature
worms migrating through internal
organs
Few worms will survive to maturity
few to no worm eggs in manure
decreased likelihood of reinfestation of
environment
Drawbacks of Daily Deworming
Active ingredient does not kill bots
You will have to give an ivermectin twice
per year!
Light infestation may lead to natural
immunity, dailies may prevent that
Not “natural” care even though no
studies have shown any toxic effects
Accumulation over time?
Daily Dewormer Schedule
Spring Thaw: Ivermectin or Moxidectin to
kill bots
Spring – early summer: daily dewormer
June 1: if tapeworms are a problem,
double-dose of pyrantel pamoate or
praziquantel
June 2 – killing frost: daily dewormer
Killing frost day: Ivermectin or moxidectin
to kill bots
Day after – spring thaw: Daily dewormer
Anthelmintic Resistance
Drug resistance = ability of worms in
a population to survive a treatment
that once was effective against the
same population
Same drug
Same dose
Same parasite
VERY common
Resistance
High mutation rate among some
worms
1. Small number of resistant worms
present
2. Deworm – kills off non-resistant
worms
3. Resistant worms survive and
reproduce, population grows
Does resistance exist in horse
populations?
Small strongyles = most problematic
internal parasites in horses
Wide range of symptoms
Rough hair coat
Poor growth
Suboptimal performance
Life-threatening chronic diarrhea, colic, and
severe weight loss
Most effective control = deworming
medications
Some small strongyles are resistant to
dewormers!
Does resistance exist in horse
populations?
Resistance to Panacur on 90% of the farms tested
20% of farms - resistance to Strongid
No evidence of resistance to Ivermectin on any farm
Few farms were tested
Ivermectin resistance may exist elsewhere
Ivermectin-resistant parasites have been found in
sheep and goats
Continue using ivermectin, moxidectin, and even
pyrantel – check for resistance in your herd
No benefit to rotating dewormers with each treatment
Slow rotation recommended: one class per year
Management to control
Parasites
Pasture Management!
Remove feces from
congregation areas
Drag pastures
regularly to break up
manure
Do not overstock
pasture!
Rotational grazing
Biological vacuum cleaners
Compost manure before spreading