Worm control and Anthelmintic resistance

Question 1

The main nematode species causing disease (PGE) in British sheep are ____

Answer 1

Teladorsagia circumcincta
Trichostrongylus spp. 
Nematodirus battus 
Haemonchus contortus 
Cooperia spp.

Question 2

less important worms in sheep

Answer 2

Nematodirus spp 
Oesophagostomum venulosum 
Chabertia ovina 
Bunostomum trigonocephalum 
Strongyloides papillosus

Question 3

main worm in cattle

Answer 3

Ostertagia ostertagi

Question 4

other worms in cattle

Answer 4

Cooperia spp.
Trichostrongylus spp
Nematodirus helvetianus

Question 5

lungworm in cattle

Answer 5

Dictyocaulus viviparus

Question 6

most important horse worm

Answer 6

strongyles (“redworms”)

Question 7

2 groups of strongyles

Answer 7

non/migratory

Question 8

migratory strongyles

Answer 8

large
Strongylus vulgaris; Strongylus edentatus;
Strongylus equinus

Question 9

non-migratory strongyles

Answer 9

Triodontophorus, spp. (Large)
Cyathostomins (or trichonemes) - includes 4 genera and over 40 species (Small)
Poteriostomum, Oesophagodontus (Small)

Question 10

treatment failures

Answer 10

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

Question 11

anthelminitic resistance

Answer 11

the parasite can tolerate anthelmintic doses which are normally lethal
the ability to do so is heritable

Question 12

how does resistance appear

Answer 12

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

Question 13

resistance in sheep nematodes

Answer 13

reported worldwide
BZ resistance widespread in UK
some “triple” resistant Teladorsagia circumcincta

Question 14

resistance in horses

Answer 14

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

Question 15

clinical failure due to resistance

Answer 15

unlikely to be clinical failure of the anthelmintic until thev allele frequency approaches 50% and the frequency of resistant parasites is > 20%

Question 16

drench test

Answer 16

A quick indicator of anthelmintic efficacy
FEC on 10 faecal samples post treatment
The time after treatment depends on the anthelmintic used

Question 17

Faecal Egg Count Reduction Test

Answer 17

Estimation of efficacy by comparing FEC before and after treatment with untreated controls
Resistance indicated if treatment does not reduce FEC by >95%

Question 18

SCOPS guidelines

Answer 18

1. Work out a control strategy with your vet or advisor
2. Use effective quarantine strategies
3. Test for AR on your farm
4. Administer anthelmintics effectively
5. Use anthelmintics only when necessary
6. Select the appropriate anthelmintic for the task
7. Adopt strategies to preserve susceptible worms
8. Reduce dependence on anthelmintics

Question 19

1. Work out a control strategy with your vet or advisor

Answer 19

cost effective, reliable and sustainable plan

Question 20

2. Use effective quarantine strategies

Answer 20

Treat with two products in different groups sequentially (not together)
Hold off pasture for 24-48 hours
Turn out on to dirty pasture

Question 21

3. Test for AR on your farm

Answer 21

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

Question 22

4. Administer anthelmintics effectively

Answer 22

Weigh or dose for the heaviest in the group
Check the dosing/pour-on gun
Use correct techniques especially with pour-on products

Question 23

5. Use anthelmintics only when necessary

Answer 23

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

Question 24

6. Select the appropriate anthelmintic for the task

Answer 24

Use narrow spectrum products where possible
Avoid ‘off-target’ use such as combination products
Rotate products where appropriate

Question 25

7. Adopt strategies to preserve susceptible worms

Answer 25

Reduce selection pressure and preserve wormer susceptibility
Leave some calves undosed
Dose on contaminated pasture and delay the move to clean pasture

Question 26

8. Reduce dependence on anthelmintics

Answer 26

Use grazing management to reduce the parasite challenge
Alternation of cattle and sheep grazing
Use of new leys and aftermaths

Question 27

resistance in cattle nematodes

Answer 27

resistance much less common than with sheep nematodes
most ML-resistance in cooperia spp.
few reports in UK