Worm control and Anthelmintic resistance Flashcards
The main nematode species causing disease (PGE) in British sheep are ____
Teladorsagia circumcincta Trichostrongylus spp. Nematodirus battus Haemonchus contortus Cooperia spp.
less important worms in sheep
Nematodirus spp Oesophagostomum venulosum Chabertia ovina Bunostomum trigonocephalum Strongyloides papillosus
main worm in cattle
Ostertagia ostertagi
other worms in cattle
Cooperia spp.
Trichostrongylus spp
Nematodirus helvetianus
lungworm in cattle
Dictyocaulus viviparus
most important horse worm
strongyles (“redworms”)
2 groups of strongyles
non/migratory
migratory strongyles
large
Strongylus vulgaris; Strongylus edentatus;
Strongylus equinus
non-migratory strongyles
Triodontophorus, spp. (Large)
Cyathostomins (or trichonemes) - includes 4 genera and over 40 species (Small)
Poteriostomum, Oesophagodontus (Small)
treatment failures
under dosing - Underestimation of bodyweight
Inadequate maintenance of equipment
Poor treatment techniques
Failure to follow manufacturer’s instructions
Use of incorrect drug for target worms
Re-introduction of animals onto heavily contaminated pasture
ANTHELMINTIC RESISTANCE
anthelminitic resistance
the parasite can tolerate anthelmintic doses which are normally lethal
the ability to do so is heritable
how does resistance appear
resistance alleles pre-exist in most worm populations even before anthelmintics are ever used
when the anthelmintic is used worms with resistance alleles are favoured
resistance develops slowly at first, then more rapidly as allele freq increases
resistance in sheep nematodes
reported worldwide
BZ resistance widespread in UK
some “triple” resistant Teladorsagia circumcincta
resistance in horses
Benzimidazole resistance now widespread in cyathostomins
Resistance to pyrantel and macrocyclic lactones still uncommon
Large strongyles (Strongylus spp.) are now rarely found and so little or no resistance reported
clinical failure due to resistance
unlikely to be clinical failure of the anthelmintic until thev allele frequency approaches 50% and the frequency of resistant parasites is > 20%
drench test
A quick indicator of anthelmintic efficacy
FEC on 10 faecal samples post treatment
The time after treatment depends on the anthelmintic used
Faecal Egg Count Reduction Test
Estimation of efficacy by comparing FEC before and after treatment with untreated controls
Resistance indicated if treatment does not reduce FEC by >95%
SCOPS guidelines
- Work out a control strategy with your vet or advisor
- Use effective quarantine strategies
- Test for AR on your farm
- Administer anthelmintics effectively
- Use anthelmintics only when necessary
- Select the appropriate anthelmintic for the task
- Adopt strategies to preserve susceptible worms
- Reduce dependence on anthelmintics
- Work out a control strategy with your vet or advisor
cost effective, reliable and sustainable plan
- Use effective quarantine strategies
Treat with two products in different groups sequentially (not together)
Hold off pasture for 24-48 hours
Turn out on to dirty pasture
- Test for AR on your farm
Test particularly where pour-on products are used
Use either post treatment Wormer Test (WT) or Faecal Egg Count reduction Test (FECRT)
Larval identification to determine species involved
- Administer anthelmintics effectively
Weigh or dose for the heaviest in the group
Check the dosing/pour-on gun
Use correct techniques especially with pour-on products
- Use anthelmintics only when necessary
Dosing of adult cows is not normally required
Indoor calves are usually worm-free at turnout
Provide low risk pasture at the start of grazing season
use strategic preventative treatments if pasture infectivity is high risk
Move mid season to low risk pastures
Monitor by FEC to optimise timing of treatments
- Select the appropriate anthelmintic for the task
Use narrow spectrum products where possible
Avoid ‘off-target’ use such as combination products
Rotate products where appropriate
- Adopt strategies to preserve susceptible worms
Reduce selection pressure and preserve wormer susceptibility
Leave some calves undosed
Dose on contaminated pasture and delay the move to clean pasture
- Reduce dependence on anthelmintics
Use grazing management to reduce the parasite challenge
Alternation of cattle and sheep grazing
Use of new leys and aftermaths
resistance in cattle nematodes
resistance much less common than with sheep nematodes
most ML-resistance in cooperia spp.
few reports in UK
