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7 Cards in this Set

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What is the definition of anthelmintic resistance?
1. When the normal concentration or dose of a product no longer reduces the numbers of parasites as it used to. Basically, a greater concentration of the drug is required to reach the same efficacy that the original lower concentration attained.
More parasites are surviving the same dose.
What is "Accumulation of Resistance"?
It is the process in which parasites become resistant to drugs. It has 3 parts.
A. Establishment: This is a random event which makes the parasite more resistant to the anthelmintic.
B. Development: This is where we use a selective agent (an anthelminitic) that kills the susceptible parasites, but leaves the resistant ones to survive and reproduce.
C. Emergence: This is the part where we notice that the parasites are now resistant to the anthelmintic that we have always used.
What is the "polygenic nature of resistance"?
There is usually more than one gene involved in the parasites ability to form resistance to a certain anthelmintic.
How is resistance measured?
Fecal egg count reduction tests. If with normal doses of the anthelmintic, the reduction in egg count (need a before and after fecal) is less than 95% than there is said to be resistance.
This can be misleading though as some anthelmintics stop egg production but do not kill the adults which gives you a false efficacy. Need to retest in a couple of week to make sure the egg counts are still reduced.
Labs do LD50's. There is also a Critical Test.
What are some selection pressures for resistance?
Parasitic genetics: recessive genes.
The number of genes necessary to become resistant. (the fewer needed, the faster the resistance).
The more fit the parasite, the more likely it will survive.
Generation time of the parasite
Direct vs indirect (harder to become resistant) life cycle
Host quarantined or not?
REFUGIA status?
What are some mechanisms of resistance?
1. Changes in the target site structure/shape, etc.
2. Metabolism
3. Access
4. Amplification of genes
What are some ways to manage the rate of resistance?
1. Use fewer slow release anthemlintics as they encourage the concentration of recessive alleles due to an increase in half life.
2. Avoid underdosing. Dose for the larger of the flock.
3. Maintain refugia!
4. Only treat those that need it.
5. Combinations of anthelmintics or complimentary methods help also.