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Timely topic: August 2014

Should I consider using LongRange™ dewormer for parasite control in small ruminants?

The answer is a clear NO! This product should not be used
in small ruminants for routine parasite control. This article
will address the reasons why this is so.


by Dr. Ray Kaplan
Professor of Parasitology
Department of Infectious Diseases
College of Veterinary Medicine
University of Georgia
Athens, Georgia

LongRange

LongRange™, a relatively new product from Merial Ltd. is gaining wide scale use in cattle, for which the product was developed. I often receive questions about whether this product would be good to use to control parasites in small ruminants. 

LongRange™ contains the drug eprinomectin, which is also found in the cattle pour-on product Eprinex®. Eprinomectin is in the same family of drugs as ivermectin (Ivomec®). This family of drugs, the macrocyclic lactones (or MLs), also includes the drugs doramectin (Dectomax®) and moxidectin (Cydectin®). 

All of these drugs are very closely related to each other and kill parasites in the same basic way. Likewise, when worms become resistant to one of these drugs, they are also resistant to the others. The one exception to this is moxidectin, which will still kill worms resistant to the other drugs in this group for a limited time.  But we have seen that once worms have resistance to any of the ML drugs, that use of moxidectin will fairly rapidly lead to resistance to that drug as well.

So – where does LongRange™ fit in?  LongRange™ is a new and novel formulation of eprinomectin whereby the drug is present in the tissues for a very long period after it is injected. This is achieved through clever and creative formulation chemistry. What happens when LongRange™ is injected is that a biogel forms at the injection site. This biogel then slowly degrades over time, and as it degrades it releases the drug into the tissues. 

This product was developed for use in beef cattle, and all studies so far studying the pharmacology, safety, and effectiveness of the product have been performed in cattle.  Furthermore, the species of worms that primarily infect cattle are different than those that infect small ruminants. 

beef cattle
LongRange™ was developed for use in beef cattle.

Since the long action is based on the formation of a biogel followed by slow breakdown and release of the drug, the pharmacology could very well differ among different types of animals. This is especially relevant to goats, as we know that goats metabolize drugs much more rapidly than do cattle or sheep. Thus, it is quite possible, even probable that the drug levels achieved in goats will be below those necessary for full effectiveness. And that is even assuming the worms are susceptible to the ML drugs.

However, we know that ivermectin resistance in Haemonchus contortus (barberpole worm) is extremely common, being present on the overwhelming majority of goat farms. And as mentioned above, if worms are resistant to ivermectin they will also be resistant to eprinomectin. Thus LongRange™ would also be ineffective on those farms. On the few farms where the level of resistance to ivermectin/eprinomectin is low, LongRange™ would most likely be pretty effective – at first.  However, this effectiveness would be very short-lived. 

This is because the treatment with Longrange™ would kill all of the drug-susceptible worms for about 120 days, but the few resistant worms on the farm would still infect the animals. As a result, over the long period where the drug is present in the tissues, only eggs from resistant worms will be shed onto the pasture.

Haemonchus contortus
Haemonchus contortus (image by Ray Kaplan)

Thus, as the drug-susceptible infective larvae already on pasture at the initial time of treatment die of old age, they are replaced only by the resistant worms in the LongRange™- treated animals. This will then select out the most-resistant portion of the worm population. The outcome would be that after 1 or 2 uses you would then have a highly drug-resistant population of worms that no longer could be killed with these drugs.

Furthermore, moxidectin (Cydectin®) resistance in Haemonchus is becoming fairly common on goat farms. As mentioned above, moxidectin is more potent than eprinomectin; thus, if the worms are resistant to moxidectin, eprinomectin will not kill them. On these farms even the first dose of LongRange™ would be virtually ineffective.

In conclusion, if you are one of the few lucky farms without ivermectin resistance, you likely won't be for long if LongRange™ is used. And if you already have high-level ivermectin or moxidectin resistance, which is quite common, the product will be ineffective on day one.  So – what is one to do when dewormers no longer seem to work well ???  That is a topic for another article, but there is a great deal of information on the ACSRPC web site that addresses this issue.

The one place where LongRange™ might serve a useful purpose is for the prevention of meningeal worm (P. tenuis) where this worm is a significant concern (particularly in camelids). Since on many small ruminant and camelid farms, ML drugs no longer kill Haemonchus anyway, it could be used as a narrow spectrum drug just for meningeal worm.  But someone will need to be brave to find out because as mentioned above there is no safety data. And one must be aware that if used for that purpose, that other strategies and other families of drugs will need to be used to treat and control gastrointestinal worms.


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