Define prophylaxis
Preventing high levels of parasite infection by reducing transmission, therefore reducing the incidence of disease
What are the 3 strategies for anthelmintic control?
- Interval dosing - treatment at regular intervals based on egg reappearance period
- Strategic dosing - treat when the parasite number is highest to disrupt seasonal cycle of transmission
- Targeted dosing - treat on the basis of diagnostic indicators
Define anthelmintic resistance
When parasites usually killed by a specific drug at a specific dose are no longer killed by it - it is a heritable trait
Describe the resistance in the following:
BZs
LEV
MLs
BZs = extensive resistance LEV = Resistance evident MLs = Resistance emerging
Which 2 groups of parasites are most resistant?
Nematodes
Trematodes
What is the role of genomic windows?
- Shows part of the genome that are inherited
- Allow markers to localise regions of the genome that are under selection/inherited
What influences the development of drug resistance?
- a parasites biology
- the selection pressure exerted on a parasites population
- proportion of the parasites population ‘in refuge’ - untreated
What increases the selection pressure on a parasites population?
Frequent use of drugs
When should resistant be suspected in:
- therapeutic treatment
- prophylactic treatment
- Failure to treat animals with disease so clinical signs persist post treatment
- When faecal egg count remains high or clinical signs persist following treatment
How can resistance be diagnosed?
Faecal egg count reduction test
- FEC: 10-14 days after Tx, use large groups, compare post-treatment groups with control of drug-treated groups
When analysing a faecal egg count reduction test, how is an effective anthelmintic concluded?
> 95% reduction in mean FEC compared to controls
Why may drugs appear to ‘fail’?
- 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- activity of drug is reduced (stored inappropriately or out of date)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
What are non-drug based approaches?
- Grazing management
- Breeding animals resistant to infection
What does SCOPS stand for?
Sustainable control of parasites in sheep
What are the 8 key points of SCOPS?
- engage with a veterinarian or advisor
- Quarantine strategies
- Test for AR
- Give drugs effectively
- Only use drugs when necessary
- Select an appropriate wormer
- reduce dependence on anthelmintics
- Use strategies to preserve susceptible worms on farm
