WASHINGTON – Anti-parasitic resistance is a widespread problem among small ruminants — such as sheep, cattle and horses — but its development can be slowed and its extent limited, according to the Food and Drug Administration's Center for Veterinary Medicine's (CVM) Office of New Animal Drug Evaluation.

The CVM held a public meeting in early March to discuss the current status of anti-parasitic resistance in ruminants and equines in the US. A panel of internationally recognized veterinary parasitologists and pharmacologists gave presentations and focused their discussion on how to monitor anti-parasitic resistance and ways to maximize the effectiveness of anti-parasitic drugs and minimize resistance. CVM issued a report on the panel members’ discussion and findings.

Genetics of the parasite, the biology of the parasite and parasite fitness are factors contributing to the development of anti-parasitic resistance. Management factors contributing to the issue include treating too often, deworming when most parasites are in the host animal rather than in the environment; inadequate quarantine procedures and under-dosing. Finally, whether an anti-parasitic drug is long-acting or short-acting impacts how quickly drug resistance develops.

Adding to the problem is that veterinarians seemed poorly informed about the current status of anti-parasitic resistance in the US, particularly in cattle. CVM said economic losses from decreased production due to anti-parasitic resistance could eventually cost more than the overhead to run diagnostics.

"While veterinarians and producers agree that anti-parasitic resistance is a problem, they, in general, still mistakenly believe that reducing treatment frequency causes negative economic and animal-health consequences," CVM said in its overview report on the meeting. "They need to be shown the financial consequences of anti-parasitic resistance."

The CVM report said part of the solution to the problem is changing the historic pattern of anti-parasitic drug us. But that would require a "dramatic paradigm shift" and extensive re-education of veterinarians and producers, and better education of veterinary students, according to CVM.

"Large animal parasitology classes at many veterinary schools often teach students outdated information," the CVM report stated. "And unfortunately, veterinary parasitologists don’t have the resources or infrastructure to appropriately educate, or re-educate, veterinarians and producers about anti-parasitic resistance and appropriate anti-parasitic drug use.

"But the drug companies that develop and manufacturer these drugs could, and should, embrace this stewardship," CVM added. "It may be helpful if drug companies combined the approval of new anti-parasitic drugs with educational programs to reinforce appropriate use."

Anti-parasitic resistance is inevitable, but its development can be slowed and its extent limited. The CVM compared the current status of anti-parasitic resistance in the US to where Australia and New Zealand were 15 to 20 years ago, suggesting that the US could learn from those countries’ experience in dealing with anti-parasitic drug resistance.

"The US should acknowledge that anti-parasitic resistance is emerging, and by learning from the experiences of other parts of the world, pro-actively approach the issue," CVM reported.