L2: Equine Intestinal Parasitism

1. Large/small strongyles

2. Ascarids

3. Tapeworms

What intestinal parasites are clinically important in horses?

1. Strongylus vulgaris

2. Strongylus edentatus

3. Strongylus equinus

What are the different species of large strongyles?

Strongylus vulgaris

Which large strongyle is most common?

true, however, anthelmintic resistance is causing a resurgence in large strongyles

T/F: It is rare to see large strongyles in herds with deworming protocols in place

Colic due to verminous migration to the cranial mesenteric artery → fatal infarct

What are the clinical implications from large strongyles?

Liver

S. edentatus and S. equinus migrate through what organ?

Cyathostomes (owners called them 'redworms')

Small strongyles are also known as what?

Inflammation/thickening of the intestinal wall leads to impaired nutrient absorption (weight loss), fluid absorption (diarrhea), and intestinal motility (colic)

What are the clinical implications of small strongyles?

small

which are more common, large or small strongyles

L3, L4

Small strongyles can encyst as late ________ and mature to _________

true

T/F: There is always a significant population of encysted larvae awaiting development in mucosa as compared to adult parasites in the bowel lumen

false; since there is such a large population can be encysted

T/F: You can rely on FEC to determine the presence of cyathostomes

Parascaris equorum

The equine roundworm is ___________________

1. Young horses/foals

2. Immunocompromised adults

Parascaris equorum affects what groups of horses?

Colic due to non-strangulating small intestinal obstruction

What is the clinical implication of Parascaris equorum?

deworm mare prior to foaling and deworm foal shortly after birth

how should horses be dewormed if pregnant?

true

T/F: There is significant resistance to commonly use anthelmintics for Parascaris equorum

Anoplocephala perfoliata

The primary equine tapeworm is what?

acquired or age

there is no ___ or ___ resistance to anoplocephala perfoliata

Ileocecal valve

Anoplocephala perfoliata classically affects what?

true

T/F: The clinical implications of anoplocephala perfoliata is questionable

1. Ileal impactions

2. Ileal hypertrophy

3. Ileocecal intussusception

Anoplocephala perfoliata could contribute to other diseases of the ileocecal valve such as what?

praziquantel

how are we treating equine tapeworms

Oxyuris equi

The equine pinworm is what?

Eggs are deposited around anus and tailhead

What are the clinical implications of oxyuris equi?

Itchy tailhead

What is the clinical sign of oxyuris equi infection?

Gasterophilus spp.

Bots

1. Generally, not clinically significant

2. Alerts you that parasite control program may be ineffective

3. With severe infection, gastric irritation may be result

What are the clinical implications of gasterophilus sp.?

Dictyocaulus arnfieldi

Equine lungworm

Donkey

What is the natural host for Dictyocaulus arnfieldi?

true

T/F: Horses have to be housed with donkeys to become infected with Dictyocaulus arnfieldi

Parasitic bronchitis

Dictyocaulus arnfieldi causes _________________ in horses

1. Traditional anthelmintic medications (has proven efficacy but there is resistance)

2. Natural anthelmintic treatments (no evidence for efficacy)

What are the options for treating for equine parasites?

1. Benzimidazoles

2. Pyrimidines

3. Macrocyclic lactones

4. Isoquinolones

What are the classes of common equine intestinal parasite anthelmintic drug classes?

Quest plus with moxidectin + praziquantel

what is the most efficacious and least resistant drug?

1. Fenbendazole (Panacur, Safe-guard)

2. Oxibendazole

What are the common benzimidazoles used in horses?

1. Fenbendazole with a double dose for 5 days

2. Moxidectin (quest)

If you need to treat for encysted cyathostomes, what are your treatment options?

Interfere with parasite's energy metabolism

What is the MOA of benzimidazoles?

interfere with parasites energy metabolism

mechanism of benximidazoles

1. Safe dewormer

2. Known resistance

What are the clinical implications of benzimidazoles?

1. Pyrantel pamoate (strongid)

2. Pyrantel tartrate (Strongid-C 2x)

What are common pyrimidines used in horses?

true; it promotes resistance

T/F: You should avoid using pyrantel tartrate (Strongid-C 2x)

Tapeworms

A double dose of pyrantel pamoate is effective in the treatment for what?

Paralyzes the parasite

What is the MOA of pyrimidines?

1. Safe dewormer

2. Known resistance

What are the clinical implications of pyrimidines?

1. Ivermectin

2. Moxidectin

What are the common macrocytic lactones used in horses?

Praziquantel

Both ivermectin and moxidectin are paired with ______________ to broaden spectrum to include tapeworms

Make sure to dose by accurate weight

What is important to keep in mind when dosing moxidectin?

1. Foals/weanlings (<6 months) or miniature horses/donkeys

2. Debilitated horses or horses with impaired BBB (neurological disease)

Moxidectin is not recommended in what groups of horses?

Disrupts the parasites neuromuscular activity (this is why you cannot give this medication to horses with neurological disease)

What is the MOA of macrocylic lactones?

Quest plus (moxidectin + praziquantel)

Which drug has the least resistance, so care should be taken when using it?

1. Pyrantel pamoate

2. Praziquantel

What are your options for treating tapeworms?

Tapeworms

Praziquantel is the only isoquinoline used in horses and is only effective for treatment of what?

Impair the suckers and stimulates the worm's motility

What is the MOA of isoquinolones?

1. Attempt to LIMIT parasite infections instead of eliminating infections

2. Minimize risk of disease

3. Parasite control measures should target managing contamination of the environment and maintaining drug efficacy against the parasites

What are the overall goals of parasite control programs?

Environmental management

Parasite control measures should first target ____________________

1. Low number of horses/acre (stocking density)

2. Manure removal from any housing space

3. Mow and harrow pasture periodically

What is included in targeting environmental management for parasite control measures?

Strategic

Anthelmintic medications should always be used in a ______________ way

1. Base on fecal egg counts for each horse

2. Base on the age of the horse, reproductive status, and the clinical signs

3. Tailored to target appropriate parasites and their unique characteristics (rational deworming)

How do you strategically use anthelmintic medications for deworming?

1. To determine the shedding status of the horse at the time of sampling

2. To evaluate the anthelmintic efficacy

3. To determine the parasite type (particularly in foals and weanlings)

What are the indications for using a McMaster fecal egg count?

Fecal egg count reduction test

Done after the horse is dewormed to assess parasite reduction or the efficacy of anthelmintic

McMaster fecal egg count

This test is valuable in horses with clinical signs of GI disease to assess if parasites may be the cause

1. Does not accurately reflect the burden of adult strongyles or ascarids (it's looking at eggs)

2. Does not detect immature or larval stages of parasites and/or encysted cyathostomes

3. Tapeworm infections are not identified by this technique

4. Pinworm eggs are usually missed

What are the limitations of the McMaster fecal egg count?

1. 1 to 2 times/year in the spring and fall

2. Ideally on all horses on the property

3. On new additions before they are added to the herd

When designing a parasite control program, consider performing a FEC...

if stocking density is high or if other environmental management measures are not performed

when should you increase the frequency of FECs

A. <200 epg

B. 200-500 epg

C. > 500 epg

How many eggs are classified as:

A. Low shedders

B. Moderate shedders

C. High shedders

If the horse is a high shedder (>500 epg)

When should you deworm based off the McMaster fecal egg count?

20%, 80%

____ of horses shed _________ of total amount of eggs

1-2 times

because of the 20/80 rule, you may only be deworming ___ times per year

1. Sheather's flotation

2. Scotch tape test

3. Modified Baermann

Other than McMasters fecal egg count, what are other parasite identification techniques?

quantitative

sheathers float is not what?

1. Strongyles

2. Ascarids

3. +/- tapeworms

Sheather's flotation can be used to identify what?

Pinworms

The scotch tape test is used to identify what?

Modified baermann

What test should you use to identify lungworms?

ELISA on saliva

Other than a flotation, what else can be used to diagnose tapeworm infections?

1. Age of the horse(s)

2. Reproductive status

3. Clinical signs

4. Herd size and movement on/off farm

When designing a deworming program, what should you consider?

Egg reappearance period (ERP)

Time interval between the last effective anthelmintic treatment and the resumption of significant shedding of strongyle eggs

Egg reappearance period (ERP)

Shortening of the ________ is a precursor to the development of resistance

Three years

For mature horses, you should evaluate for resistance at least every ____________ using the FECRT

1 to 2

For mature horses, anthelmintic treatments should consist of _________ yearly treatments

true

T/F: You should focus anthelmintic treatments during seasons of peak transmission (usually spring and fall) for mature horses

false; ascarid populations not measured

T/F: FEC are effective for young horses

Beginning at 2 to 3 months of age, should be treated 4x over first year

How often should young horses be treated with anthelmintics?

on clean pasture

where should weaned foals be placed?