Transcript Worms – A Pain in the Gut - Calhan Veterinary Clinic

Worms – A Pain in the
Gut
Alison Moore DVM, DVSc, DACVIM
National Equine Medical Consultant
IDEXX Canada/Vita-Tech
Markham, Ontario
Why talk about internal parasites?
• Diseases caused by
parasites are on the
increase
• There is resistance to
dewormers
Diseases Caused by Internal
Parasites
• 3 major groups of intestinal parasites
– Roundworms (Parascaris equorum)
– Strongyles (Large strongyles –Bloodworms, small
strongyles)
– Tapeworms
– Each causes it own clinical signs that affect
performance
– Signs are due to migration of larvae
– Subclinical signs – poor absorption of feed and
supplements
Roundworms
• Young horses < 2yrs
of age (< 6months of
age are most
susceptible)
• Pot-belly
• Poor hair coat
• Lethargy
• Coughing /lung
inflammation
• Colic (impactions,
intussusceptions)
Deworming: The Philosophy
Roundworms
• Takes 70 days before
eggs are seen in
manure
• Start deworming at 6
– 8 weeks of age
• Develop immunity
with age
• Eggs survive in
environment for years
Bloodworms – Large Strongyles
• Strongylus vulgaris
• “verminous arteritis”
“thromboembolic
colic”
• Poor-doer
• Weight loss
Bloodworms
• After ingestion, larvae
penetrate the lining of
the small intestine by 7
days post-infection
• Penetrate the arteries of
the cecum and colon
and migrate to the root
of the mesenteric artery
• Develop for 3-4 months
then return to the colon
• May take 6 to 11
months from ingestion
to passing eggs in
manure
Cyathastomes – small strongyles
• Don’t migrate through
body
• Infected larvae are
ingested and can
develop to shedding
adults in 6 – 14 weeks
or can “hibernate for the
winter” or “summer”
depending on climate
• Form cysts in the lining
of the large colon – safe
from dewormers-can
encyst for 2 years
• Difficult to detect in
manure
Cyathastomes
• Emergence of the
hibernating larvae
occurs in the spring in
the north and fall in the
south – very large
numbers
• 12-30°C (25°C optimum
for emergence)
• Severe protein losing
life-threatening diarrhea
• Chronic weight loss,
poor digestion, low
protein
Tapeworms
• Ingest a mite found
on the pasture or in
the stable that is
infected with eggs
• Larvae attach at the
connection of the
small intestine and
cecum (valve)
• Colic
Tapeworms
• Mite activity is
temperature
dependent – increase
in cold dry climate
• Affects all ages
(weanling and older)
• No acquired resistance
• Only 30-50% of
tapeworm infected
horses are positive on
examination of the
manure
• Serum Antibody test
becoming available
Diagnosis of Parasites
• Fecal floatation
• Fecal Egg Count
• Serum Antibody Test
(Tapeworms)
Fecal Egg Count
• Fecal exam only detects eggs from adult females
• Eggs per gram of manure
• 200 or less EPG is a light load – may not need to
deworm (<100 for a foal)
• A parasite-free horse is an anomaly and not a
realistic goal
• Provides vital information about the individual as
well as the parasite status of the herd
Fecal Egg Counts
• 20% of the horses
shed 80% of the
worms
Fecal Egg Count Reduction Test
• Perform a fecal egg count before
administering dewormer then repeat in
14 days
• EPG (pretreatment)-EPG
(posttreatment)/ EPG (pretreatment) x
100 = FECR
• Should be >90% - if not, there is
resistance developing
Dewormers
• 3 major chemical
classes of dewormers:
• Macrocyclic lactone
(Ivermectin (Eqvalan)
moxidectin (Quest)
• Benzimidazole
(fenbendazole
(Panacur)
• Pyrantels (Pyrantel
Pamoate (Strongid – P)
Pyrantel Tartrate
(Strongid –T)
Resistance to Dewormers
• The persistence of benzimidazole-resistant
cyathostomes on horse farms in Ontario over 10
years and the effectiveness of ivermectin and
moxidectin against these resistant strains.Can
Vet J. 2008 Jan;49(1):56-60.
• Macrocyclic lactone-resistant Parascaris
equorum on stud farms in Canada and
effectiveness of fenbendazole and pyrantel
pamoate. Vet Parasitol. 2007 Apr 30;145(34):371-6. Epub 2006 Sep 7.
Resistance to Dewormers
• 21 countries report resistance to
benzimidazoles (Panacur)
• Pyrantel resistance is most prevalent in the US
(especially to Strongid C)
• The more often a horse is dewormed the
greater the chance for resistance
• Frequent rotation may speed the development
of resistance as each generation of worms is
exposed to several different classes of drug
Assessing your horse’s risk for
parasite burden
•
•
•
•
Age, health status
Stable or pasture
Stocking density
Travel to other
climates
• Pasture management
• Deworming practices
Dewormers and parasite group
• Roundworms
–
Treated with ivermectin
(Eqvalan), moxidectin
(Quest), Fenbendazole
(Panacur) or Pyrantel
Pamoate (Strongid P)
• Resistance reported to:
ivermectin and
moxidectin in Ontario
Roundworms
• Goal is to reduce to spread of eggs in the
manure
• Deworm starting at 6 weeks and then
two months later – asses with a fecal egg
count in two months
• Monitor with fecal egg counts – presence
of large numbers of eggs 2 to 4 weeks
after treatment suggests the deworming
is ineffective
Tapeworms
• Treatment with
praziquantel (combined
with ivermectin or
moxidectin in Eqvalan
Gold or EquiMax,
Quest Plus) or double
dose pyrantel pamoate
(Strongid P)
• Spring and/or Autumn
to correspond to
exposure to infected
mites
• Serum antibody test
Strongyles
• Large Strongyles –
adult stages –can use
all class of dewormers,
larvae (moxidectin,
ivermectin or
fenbendazole (twice
dose for 5 days)
• Small strongles – very
susceptible to
resistance
Small Strongyles (Cyathostomes)
• Fecal egg count on individuals
• Low contaminators – deworm twice yearly at
beginning and end of grazing season
• High contaminators – focus of control program –
need treatment throughout grazing season
– resistance reported to pyrantel tartrate
(Strongid C) and Pyrantel pamoate
(Strongid P)
• Ivermectin, moxidectin for adults and L4 larvae
and Moxidectin for the hibernating stage
• Deworm after the fall freeze with Moxidectin or
Ivermectin
• If travelling to Florida, remember the pastures
may be heavily contaminated in the fall and
winter
Deworming Summary
• Roundworms – at 6-8 weeks every two
months – use FEC/RT to determine if
resistance (to ivermectin/moxidectin)
• Tapeworms – Spring and Fall with
Praziquantel combo (Eqvalan Gold) or
double dose Strongid P
• Large Strongyles – twice yearly with any
dewormer – check with FEC
• Small Strongyles (Cyathastomes) – After
fall freeze with Moxidectin/Ivermectin
and again in the spring – monitor with
FEC
Manure Management
• Only about 5-10% of
the parasites are in
the horse
• The remaining 9095% are on the
ground
• Need to reduce
contamination by
removing manure
(vacuuming) if
stocking density is
high
• Compost
Summary
• Parasites can cause debilitating disease
• Resistance to dewormers is a problem (Quest,
Ivermectin, Panacur, Strongid on some farms)
• Utilize Fecal egg counts to determine low and high
shedders
• Use Fecal egg count reduction test to determine
resistance to dewormers
• Manure and pasture management