December 20, 2019

The U.S. Food and Drug Administration continues to work with stakeholders to address antiparasitic resistance in livestock (cattle, sheep, goats, swine, and poultry) and horses. In an on-going effort to help maintain the effectiveness of approved antiparasitic drugs, the FDA has produced two videos on antiparasitic resistance; released the results of a survey of the U.S. veterinary community about antiparasitic drug use and antiparasitic resistance in grazing animals; and asked animal drug companies to add information about antiparasitic resistance to the labels of all approved antiparasitic drugs for livestock and horses.

Parasite infections are a health and welfare concern for livestock and horses. Therefore, effective antiparasitic drugs are vital to the animal health industry in the U.S. However, parasites are becoming increasingly resistant to drugs that were generally effective against them in the past. In these situations, after an animal is treated with an antiparasitic drug, the susceptible parasites die and the resistant ones survive to pass on resistance genes to their offspring.

Although antiparasitic resistance in animals doesn’t directly affect the health of people in the U.S., it’s a growing animal health threat in this country and can result in production losses in food-producing animals. Heavy parasite infections can cause diarrhea, weight loss, anemia (low level of red blood cells), and death in animals. Antiparasitic resistance also poses a significant threat to the sustained effectiveness of antiparasitic drugs.

Science shows that antiparasitic resistance can’t be stopped. Parasites will continue to evolve and develop resistance; however, this natural process may be slowed down. The FDA’s strategy to address antiparasitic resistance aims to promote the sustainable use of antiparasitic drugs in livestock and horses to help slow the development of antiparasitic resistance in these animals. This, in turn, will help ensure that antiparasitic drugs remain effective for as long as possible.

Within the last two years, the FDA has accomplished the following to spread awareness about antiparasitic resistance:

Produced two videos for animal producers and owners on antiparasitic resistance.

• Antiparasitic Resistance in Cattle, Small Ruminants, and Horses in the U.S., which discusses how to detect antiparasitic resistance and what to do about it.
• Using Refugia to Manage Parasites in Cattle, Sheep, Goats, and Horses and Reduce Resistance to Dewormers, which explains the concept of refugia and how it helps reduce antiparasitic resistance.

Released the results of a survey of the U.S. veterinary community about antiparasitic drug use and antiparasitic resistance in grazing animals. 

The survey, which focused on cattle, sheep, goats, and horses, collected information for the first time from U.S. veterinarians and veterinary parasitologists to find out: 

• Their current level of awareness of and concern about antiparasitic resistance in grazing animals;
• Which strategies they commonly use to detect, monitor, and/or manage parasites and antiparasitic resistance; and
• Their opinions about the best ways to ensure the safe and effective use of antiparasitic drugs.

The FDA hopes the survey results will facilitate dialogue between animal drug companies, researchers, regulators, educators, and animal owners regarding ways to minimize the development of antiparasitic resistance.

In July 2018, the FDA presented part of the survey results at the annual meeting of the American Association of Veterinary Parasitologists. 

Requested that animal drug companies voluntarily revise the labels of drugs intended to treat certain internal parasites in livestock and horses to add information about antiparasitic resistance.

The requested labeling changes specifically affect anthelmintics used in livestock and horses. Anthelmintics, often called dewormers, are antiparasitic drugs that treat certain internal parasites, such as roundworms. Resistance to dewormers is particularly concerning in grazing species (cattle, sheep, goats, and horses), but it is also a problem in swine and poultry. The new labeling information emphasizes these important points:

• Any use of a dewormer can result in the development of antiparasitic resistance.
• Proper dosing is critical to the safe and effective use of a dewormer.
• End-users should work with their veterinarian to monitor herds and flocks to determine the extent of antiparasitic resistance on a particular farm.
• Dewormers should be used as only one part of an overall internal parasite control program.

The FDA made this request in December 2018 to all drug companies with approved dewormers (both over-the-counter and prescription) for livestock and horses. So far, over one-third of the companies have added the new labeling statements to their products.

The agency will continue working with the veterinary and animal health communities to find ways to maintain the effectiveness of antiparasitic drugs in livestock and horses in the U.S. For more information about the FDA’s efforts to address antiparasitic resistance, please see the FDA’s webpage on Antiparasitic Resistance.