Anthelmintic resistance

Question 1

Define prophylaxis

Answer 1

Preventing high levels of parasite infection by reducing transmission, therefore reducing the incidence of disease

Question 2

What are the 3 strategies for anthelmintic control?

Answer 2

1. Interval dosing - treatment at regular intervals based on egg reappearance period
2. Strategic dosing - treat when the parasite number is highest to disrupt seasonal cycle of transmission
3. Targeted dosing - treat on the basis of diagnostic indicators

Question 3

Define anthelmintic resistance

Answer 3

When parasites usually killed by a specific drug at a specific dose are no longer killed by it - it is a heritable trait

Question 4

Describe the resistance in the following:
BZs
LEV
MLs

Answer 4

BZs = extensive resistance
LEV = Resistance evident
MLs = Resistance emerging

Question 5

Which 2 groups of parasites are most resistant?

Answer 5

Nematodes

Trematodes

Question 6

What is the role of genomic windows?

Answer 6

• Shows part of the genome that are inherited

- Allow markers to localise regions of the genome that are under selection/inherited

Question 7

What influences the development of drug resistance?

Answer 7

• a parasites biology
• the selection pressure exerted on a parasites population
• proportion of the parasites population ‘in refuge’ - untreated

Question 8

What increases the selection pressure on a parasites population?

Answer 8

Frequent use of drugs

Question 9

When should resistant be suspected in:

1. therapeutic treatment
2. prophylactic treatment

Answer 9

1. Failure to treat animals with disease so clinical signs persist post treatment
2. When faecal egg count remains high or clinical signs persist following treatment

Question 10

How can resistance be diagnosed?

Answer 10

Faecal egg count reduction test

- FEC: 10-14 days after Tx, use large groups, compare post-treatment groups with control of drug-treated groups

Question 11

When analysing a faecal egg count reduction test, how is an effective anthelmintic concluded?

Answer 11

> 95% reduction in mean FEC compared to controls

Question 12

Why may drugs appear to ‘fail’?

Answer 12

• inadequate dose of drug administered
• activity of drug is reduced (stored inappropriately or out of date)
• Error in method used for FEC or result interpretation
• Calculation errors
• Suspensions not thoroughly mixed before use
• Wrong drug for target species

Question 13

What are non-drug based approaches?

Answer 13

• Grazing management

- Breeding animals resistant to infection

Question 14

What does SCOPS stand for?

Answer 14

Sustainable control of parasites in sheep

Question 15

What are the 8 key points of SCOPS?

Answer 15

1. engage with a veterinarian or advisor
2. Quarantine strategies
3. Test for AR
4. Give drugs effectively
5. Only use drugs when necessary
6. Select an appropriate wormer
7. reduce dependence on anthelmintics
8. Use strategies to preserve susceptible worms on farm