Problems with equine parasite control Flashcards
Diagnostics for equine internal parasites. (3)
Clinical examination
* Signs are often nonspecific.
Signalment, anamnesis, clinical signs – alone not sufficient.
Diagnosis is Supported by laboratory tests.
Parasites and colic.
Parasites can predispose to colic /cause colic in many ways.
Often very difficult to determine their role in colic case.
Detecting the presence of a widespread parasite in a horse with colic does not prove a causal relationship.
If suspected – treat with anthelmintics once the colic has resolved.
Diagnosing clinical disease cannot rely on egg counts or larval cultures. Why?
Parasites are more or less present in all horses.
Eggs or larvae in feces do not = parasitic disease.
False-negative egg counts are not uncommon.
Migrating or encysted larvae do not produce eggs and thus are not detected in fecals.
Small redworm blood test diagnoses cyathostomin infection in horses.
No direct relationship between actual egg count and size of the worm burden.
Describe fecal egg counts.
FEC is Cornerstone of the diagnostics.
- Quantitive (eggs per gram)
- Should be interpreted with +/- 50%
- McMaster technique (most common), Stoll, Wisconsin methods used too. Involves Flotation of eggs.
Most important purposes:
1. Clinical diagnosis of parasitism in a single horse.
2. Identification of horses as high, medium and low egg shedders for selective deworming.
3. Screening for anthelmintic efficacy (FECRT)
FECRT = Faecal egg count reduction test tests for sensitivity!
Purpose of FEC in foals: (3)
To decide whether to primarily treat for Parascaris or Cyathostomines.
Detecting Parascaris worm burden.
Monitoring resistance.
Diagnostic tests for larval cyathostominosis.
Do the red bloodworm test:
- ELISA test that detects IgG specific to 3 cyathostomin antigens
- Ideal time to test is yearly between Sept-Dec.
- If ideal time is missed, you can still test until April.
- Confirmation of larval cyathostimiasis diagnosis.
- You should not test for 4 months from last moxidectin.
Typical patient 1-4 y horse with diarrhea/loose feces and hypoproteinemia → suspect larval cyathostominosis.
Typical patient 1-4 y horse with diarrhea/loose feces and hypoproteinemia → suspect what?
larval cyathostominosis
small red worms
Risk assessment for cyathostomin infection and decision making.
Diagnostic testing methods for tapeworms.
Is Challenging because of the physiologic characteristics.
Eggs are released in clumps, Unevenly distributed in feces and Often within intact tapeworm segments so
Egg counts are not useful.
If routine egg count test is positive → likely to have a significant tapeworm burden!
If an increased quantity of feces analyzed → more likely to find tapeworm eggs. The Routine McMaster technique requires 4g of feces vs traditional Tapeworm detection methods, 30-40g of feces.
Serum or saliva tapeworm testing is the Most reliable.
For example, Laboklin using ELISA.
Ideal time to to start deworming foals.
from 2 months old onwards
Diagnostic testing frequency for tapeworms.
UK-Vet deworming guidelines (Rendleet al.,2019) categorically state that “The traditional approach, to routinely treat for tapeworms annually or 6-monthly without diagnostic testing, is obsolete.”
“Treatment should only be administered to adult horses in response to positive serum or salivary antibody testing.”
Test every 6 months.
Allows detection of horses with tapeworm infections and Confirms diagnosis in horses with clinical symptoms.
Results can be: low, borderline or moderate/high.
The test cannot be used to monitor anthelminitic efficacy, and do not test for 4 months from last treatment.
describe Macrocyclic lactones:
ivermectin, moxidectin
Used against Small and large Strongyles, Gasterophilus spp., S.westeri etc.
Moxidectin only in horses >4 months old, for encysted cyathostomines
No effect on tapeworms.
Image about resistance.
horse indications for Pyrantel embonate use (3)
Cyathostomins
Parascaris equorum
Double dose for tapeworm
Image about resistance.
Describe Fenbendazole indications in horses.
Very safe and First choice for Parascaris equorum.
Only for nematodes, no effect in tapeworms.
Widespread resistance though, esp. amongst cyathostomes.
Problems with interval treatment?
Interval treatment has been used since the 1960s.
Main objective was to control S.vulgaris (most pathogenic). Used 3-4 times a year or even every 2 months. “Dose and move” strategy was used.
Now we have Anthelmintic resistance!
And No new anthelmintics under development. :(
How are we Dealing with anthelminthic resistance.
The aim is to reduce anthelmintic treatment intensity in order to maintain anthelmintic efficacy for as long as possible.
Using a combination of:
Prescription drugs
Pasture management
Selective anthelmintic treatment (SAT)
Maintaining refugia
Monitoring parasite levels and anthelmintic resistance (FEC, FECRT, ERP).
fecal egg count, Faecal egg count reduction test, egg reappearance periods
Describe Pasture management for parasite control.
Removal of feces from pastures results in Significant reduction of pasture infectivity and Less reinfection of grazing horses.
remove feces 2-3 times/week (optimally)
Is Labor-intensive of course.
Alternatives are:
„Cross-grazing“ with sheep, cattle which significantly reduces pasture larval transmission but the Pastures often remain infective.
Or,
Rotational grazing but this requires knowledge of parasite epidemiology in the local area and the pastures remain Contaminated.
Describe strategic anthelminthic treatment.
Strategic treatment requires knowledge of parasite life cycles, seasonality and climate because they are used to define appropriate times for treating.
Strategic tx is Typically performed without diagnostic testing and is Applied during active grazing season.
Describe Selective anthelmintic treatment (SAT).
Cyathostomins are main concern in general horse population. SAT is Based on the presence of small strongyles.
Rationale for selectivity: find the horses that contaminate the pasture the most. 20% of animals harbor approximately 80% of the parasite population or shed 80% of the total egg output.
Identify and treat the horses who have moderate to high FECs .
High shredders can receive more frequent treatments or can be treated with moxidectin.
Only horses with >200 epg are treated.
AR must be tested as well (FECRT) and Macrocyclic lactones spared whenever possible. Combination products to be avoided.
Low strongyle egg shredders within the herd have <200 EPG.
Moderate shedders have 200-500 EPG.
High shedders >500 EPG.
fecal egg count burden characterization
FEC are usually quite stable:
Low strongyle egg shredders within the herd have <200 EPG.
Moderate shedders have 200-500 EPG.
High shedders >500 EPG.
Egg shedding patterns are much less consistent in horses < 4 years old. Selective therapy is not recommended in these ones.
selective tx described in image
Selective anthelmintic treatment (SAT) - What about parasites other than cyathostomes?
At least at the herd level, presence or absence of large strongyles should be checked.
Use Larval culture and Molecular analysis.
If S.vulgaris is endemic, ivermectin or moxidectin is recommended late autumn.
Tx of Tapeworms – ideally based on saliva/serum testing.
Tx of Gasterophilus spp. - not pathogenic, no treatment needed.
Oxyuris equi treated with control methods not drugs.
How is resistance detected? (3)
FEC – fecal egg count is the Cornerstone of the diagnostics and gives you a Quantitive result (eggs per gram). It Should be interpreted with +/- 50%.
Uses Flotation methods: McMaster, Stoll, Wisconsin.
Then, FECRT – fecal egg count reduction test (% FECR=100[(FECpre−FECpost)/FECpost]). Gold standard.
And finally, ERP – egg reappearance period.
Describe the Fecal Egg Count Reduction Test (FECRT).
Gold standard for detection of resistance.
Evaluates the efficacy of an anthelmintic drug on a parasite by Its ability to reduce fecal egg output after treatment.
Perform FEC Just before anthelmintic drug use and
14 days after treatment.
+/- 42 days after treatment for ivermectin
+/- 56 days after treatment for moxidectin
Describe the Egg Reappearance Period (ERP) (-test).
Number of weeks from treatment until eggs are found in the feces again.
Useful tool to monitor emergence of anthelmintic resistance.
ERP will be shortened before the FECRT shows reduced efficacy on the anthelmintics 2 weeks after treatment!
Refugia =
the portion of a population of parasites that escapes selection with the drug at the time of a treatment event.
Refugia consists of:
* Stages not affected by the treatmen
* All free-living parasite stages on the pasture
* All parasites in animals that were not treated
How is refugia maintained?
Maintenance of an adequate parasite refugia is a valuable source of susceptible genes to dilute resistant genes and reduces the development of anthelmintic resistance.
