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Worm Control News
April, 2010
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Refugia: What It Is, Why It's Important
At Horsemen's Laboratory,
helping horse owners understand the most effective way to use fecal egg counts (FECs) is part of
our mission; as such, we're constantly on the lookout for new information and
research we can share with our customers.
Parasites
have been fought tooth and nail with multiple classes of deworming medications
for decades, with the goal to have a worm-free horse. But, what we once
considered our ultimate goal might be our undoing, if we don't change the way
things are done.
The goal
now is to maintain a 'dewormer sensitive' worm population, and keep the numbers
of worms within reasonable levels, instead of shooting for a 100% worm-free
horse. It can be a difficult concept to wrap your brain around, but if, for
example, you have a horse has a manageable intestinal worm population of 1,500, and 1,497
of those are sensitive to deworming medication, there are still plenty of
'dewormer sensitive' worms to pass along their genes to offpring, keeping the
entire worm population under control. This is what's referred to as 'refugia.'
However, if
those 1,497 sensitive worms are all wiped out with dewormer, that only leaves
the 3 'resistant' worms to pass along their genes; their offspring will be
resistant, and will continue to produce resistant worms, and any sensitivity to
dewormer has been lost, likely forever.
Refugia is
Latin for refuge, and can be defined as 'an area that has escaped ecological
changes...[providing] a suitable habitat.' It's that 'safe habitat' factor that
parasitologists feel will be our saving grace when it comes to equine parasite
resistance, by keeping a population of worms that continues to be sensitive to
currently available dewormers, allowing us to keep parasite populations under
control.
When
parasites are exposed to dewormers over and over again, they experience a
pressure to either develop resistance to frequently used dewormers, or die. In
a 'survival of the fittest' dynamic, the worms sensitive to deworming
medication are killed, and the ones that survive are the ones that have
developed a resistance to the medication. However, those are the ones that are
passing their genes on to their larvae; this means the offspring are more
likely to also be resistant to the dewormer.
In the
concept of equine parasite refugia, we use fecal egg counts (FEC) to determine
how much of a parasite load, and what type of parasites, our horses are
carrying, then target the worms with the correct type of dewormer. When FEC
testing is done both before and after deworming, it's called a fecal egg count
reduction test (FECRT), since it allows us to note the difference (if any) in
the egg count, and determine a further course of action.
The goal in deworming is no longer to eradicate
every parasite and leave a horse worm-free; the goal today is to create a
manageable parasite load with refugia, where some worms that are still
sensitive to dewormers pass their genes along so that the entire worm
population remains responsive to deworming medications, preventing a harmful
over-infestation.
Coming
next month: Q&A with a special guest expert.
Return to the April issue of Worm Control News
Visit the Horsemen's Laboratory Web site
Worm Control News is written and produced by KempEquine.com.
Copyright 2010 Horsemen's Laboratory. Please contact us at hlab@horsemenslab.com for reprint permission. Linking to Worm Control News is acceptable, and we would appreciate notification of links so we can acknowledge them in future issues.
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