Equine Science Update
Reports from the world of equine research.
Written by Mark Andrews. Published online 28.08.10
© Copyright Equine Science Update 2010
© Copyright Equine Science Update 2010
Not all bad news about dewormers
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At a time when there are plenty of reports of increasing resistance to dewormers, it’s encouraging to receive some good news for a change.
Research carried out by Dr Craig Reinemeyer and others at East Tennessee Clinical Research Inc., has revealed some positive findings.
In separate studies they examined the efficacy of dewormers against Oxyuris equi, and against macrocyclic lactone resistant Parascaris equorum.
Oxyuris equi (equine pinworm) rarely causes serious problems for the horse, but does cause irritation when the female lays the sticky eggs on the skin around the anus of the host. It has been assumed that most routine dewormers will control it.
However, anecdotal reports that anthelmintic treatments were not as effective against Oxyuris equi as expected prompted Dr Reinemeyer’s study.
Twenty-one horses with naturally-acquired Oxyuris equi infections were divided into three groups. One was treated with pyrantel pamoate (at 13.2mg/kg -the dose used for tapeworms); one group received ivermectin (200mcg/kg) and the third group was left untreated.
Fourteen days later, post mortem examination of large intestinal contents showed that both anthelmintics produced a significant reduction in numbers of O. equi. Pyrantel pamoate was 91.2% effective, and ivermectin 96.0% effective, against the adult worms. Both products were more than 99% effective against the fourth-stage O. equi larvae.
Unlike O. equi, Parascaris equorum does cause serious problems, especially in foals, in which heavy infections can lead to intestinal obstruction or rupture.
Recent reports have recorded an increasing problem of reduced efficacy of macrocyclic lactone anthelmintics (such as ivermectin) against these parasites.
In a study of experimentally infected foals, Reinemeyer and colleagues found that pyrantel pamoate administered at 13.2mg/kg was effective against a macrocyclic lactone -resistant (ML-R) isolate of Parascaris equorum.
Mean ascarid egg counts were reduced by 98.8% two weeks after treatment - compared with a reduction of only 47% two weeks after ivermectin (200mcg/kg). Post mortem examination of intestinal contents showed that the paste formulation of pyrantel pamoate was 97.3% effective against the MLR P. equorum.
It is reassuring to know that these drugs were effective under the specific conditions of the study. But that’s not to say that they will always remain so., or that the results are representative of all worm populations The advice to treat for worms only when necessary and to monitor the effectiveness of any treatment still stands.
For more details see:
Efficacy of pyrantel pamoate and ivermectin paste formulations against naturally acquired Oxyuris equi infections in horses.
Reinemeyer CR, Prado JC, Nichols EC, Marchiondo AA.
Vet Parasitol. (2010) 171:106-110. (published online 2010 Mar 3.)
Efficacy of pyrantel pamoate against a macrocyclic lactone-resistant isolate of Parascaris equorum in horses.
Reinemeyer CR, Prado JC, Nichols EC, Marchiondo AA.
Vet Parasitol. (2010) 171:111-115. (published online 2010 Mar 4.)
Research carried out by Dr Craig Reinemeyer and others at East Tennessee Clinical Research Inc., has revealed some positive findings.
In separate studies they examined the efficacy of dewormers against Oxyuris equi, and against macrocyclic lactone resistant Parascaris equorum.
Oxyuris equi (equine pinworm) rarely causes serious problems for the horse, but does cause irritation when the female lays the sticky eggs on the skin around the anus of the host. It has been assumed that most routine dewormers will control it.
However, anecdotal reports that anthelmintic treatments were not as effective against Oxyuris equi as expected prompted Dr Reinemeyer’s study.
Twenty-
Fourteen days later, post mortem examination of large intestinal contents showed that both anthelmintics produced a significant reduction in numbers of O. equi. Pyrantel pamoate was 91.2% effective, and ivermectin 96.0% effective, against the adult worms. Both products were more than 99% effective against the fourth-
Unlike O. equi, Parascaris equorum does cause serious problems, especially in foals, in which heavy infections can lead to intestinal obstruction or rupture.
Recent reports have recorded an increasing problem of reduced efficacy of macrocyclic lactone anthelmintics (such as ivermectin) against these parasites.
In a study of experimentally infected foals, Reinemeyer and colleagues found that pyrantel pamoate administered at 13.2mg/kg was effective against a macrocyclic lactone -
Mean ascarid egg counts were reduced by 98.8% two weeks after treatment -
It is reassuring to know that these drugs were effective under the specific conditions of the study. But that’s not to say that they will always remain so., or that the results are representative of all worm populations The advice to treat for worms only when necessary and to monitor the effectiveness of any treatment still stands.
For more details see:
Efficacy of pyrantel pamoate and ivermectin paste formulations against naturally acquired Oxyuris equi infections in horses.
Reinemeyer CR, Prado JC, Nichols EC, Marchiondo AA.
Vet Parasitol. (2010) 171:106-
Reinemeyer CR, Prado JC, Nichols EC, Marchiondo AA.
Vet Parasitol. (2010) 171:111-