"Refugia".
Have you heard of it?
In simple terms, "Refugia" is the proportion of a
parasite population that remains susceptible to a
deworming drug.
Parasites in refugia are not exposed to a deworming
treatment.
Since we choose not to deworm certain animals,
these parasites are in "refuge" from the drug.
Resistance to dewormers occurs when parasites are
able to survive treatment with a drug that was
previously effective at killing them.
This becomes a problem for your animals when
resistant parasites outnumber the parasites
still vulnerable to a particular dewormer.
Eventually a product can become ineffective at
treating parasites on your farm.
Refugia is one tool you can use to help slow the
development of resistance on your farm.
This is a simplified example of how to use a
dewormer to maintain Refugia in order to help
slow the development of parasite resistance in a
herd.
Within every herd, grazing animals harbor a
mix of parasites that are either susceptible or
resistant to a dewormer.
Let's assume that each circle represents a
parasite in an animal's digestive tract.
The blue circles are parasites that are
susceptible to a dewormer and the red circles are
parasites resistant to the same dewormer.
Assume that every animal in this herd is treated
with a de-wormer.
The only parasites that remain are those resistant
to the dewormer.
The next deworming treatment won't be
effective at controlling these parasites.
Now let's take the same herd and this time, select
only half of the animals for deworming.
After treatment, susceptible parasites
remain within untreated animals.
These parasites will dilute the population of
resistant parasites that are also still present.
Fewer resistance genes will be passed to the
next generation of parasites.
This will help delay or even prevent the
establishment of a completely resistant
parasite population within the herd.
Refugia can come from sources other than
untreated animals.
For example, the eggs and larvae that are already on
the pasture but not within the animals when they're
treated, are called "environmental" refugia.
Another example is the life stages of parasites,
such as larval stages in the animal, that are
unaffected and therefore survive deworming
treatment.
Once these larvae mature to adult parasites, they
become another source of refugia.
Remember, while refugia may help delay the
development of resistance, sick and heavily
parasitized animals should be treated.
Work with your veterinarian to decide
which animals to deworm and when.
Timing and frequency of deworming on an individual
farm will vary depending on species and geographic
location.
Using refugia as part of your parasite control
program is one way to help keep deworming products
effective for as long as possible.
END