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May 01, 2021

Seresto collars come under greater scrutiny

Elanco defends product, experts remain comfortable with their use
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Recent reports from pet owners of adverse events attributed to a popular brand of flea and tick collars have gained national attention.

The manufacturer has defended the collars as safe and effective, and veterinary experts say they have seen no cause for alarm. Meanwhile, federal regulators remind the public that these types of adverse event reports do not necessarily show a product was the cause of harm.

Seresto collars, developed by Bayer and now manufactured and sold by Elanco Animal Health, contain two pesticides: imidacloprid, which is a neonicotinoid, and flumethrin, which is a pyrethroid. The collars are regulated by the Environmental Protection Agency, which regulates most flea and tick products applied to a pet’s skin or fur, such as collars and spot-on products.

Pet owner placing a flea and tick collar on a dog
A flea and tick collar on a dog

On March 2, USA Today and the Midwest Center for Investigative Reporting published findings that the EPA has received more than 75,000 incident reports involving Seresto collars since they were first introduced in 2012. Those reports included 1,700 deaths of pets and about 1,000 incidents of harm to humans.

Elanco characterized the media coverage as misleading, pointing out that more than 25 million of the collars have been sold in the U.S. and that the products have been reviewed by more than 80 regulatory authorities around the world. The company added that data generated for the product’s registration and obtained through postmarket surveillance indicate the product is safe and effective and argued that there was no medical or scientific basis for a recall.

Yet, on March 17, the U.S. House Subcommittee on Economic and Consumer Policy called for Elanco Animal Health to “immediately institute a temporary recall of all Seresto flea and tick collars, following reports that the collars may have killed thousands of pets and may have caused injuries to many more pets as well as humans.” Subcommittee Chair Rep. Raja Krishnamoorthi of Illinois said in a letter to Elanco CEO Jeff Simmons that members of the subcommittee believe the numbers of injuries and deaths are much greater than reported because most consumers would not know to report the incidents to the EPA.

The subcommittee also called for Elanco to provide plans for recalls and refunds, copies of all complaints and administrative or legal actions regarding allegations of harm to people or animals associated with the collars, copies of communications involving product safety, and U.S. sales figures.

“Elanco is cooperating with the Subcommittee’s request and looks forward to explaining how the media reports on this topic have been widely refuted by toxicologists and veterinarians,” the company response states. “Elanco believes that any further reporting on these matters should be based on the relevant science and facts.”

Many illness reports anecdotal

Although Elanco states that postmarket surveillance indicates Seresto collars are safe, pet owners have posted online in the past few years that they blame the collars for problems ranging from vomiting, loss of appetite, and rashes to seizures, dizziness, weakness, and death. Some owners took to registering their complaints with the EPA as well.

Experts note that anyone can file an incident report with the EPA, which also receives incident reports from pesticide makers and the National Pesticide Information Center. Agency officials track incident reports through the EPA Incident Data System, review reports to determine when regulatory action is needed, and use that information during reviews of active ingredients in pesticides to ensure they pose no unreasonable risks to human health or the environment. When a product is the subject of a high number of reports, EPA officials ask product registrants for more information or to further investigate the incidents, according to an agency statement from EPA spokesperson Ken Labbe. He also said the EPA cannot confirm or refute claims that the agency has received an unusually high number of incident reports related to Seresto collars, compared with the numbers of reports for other pesticides applied to pets. But agency officials take each incident report seriously.

“Some incidents are well-investigated and reported in such a way as to establish a strong link between the adverse effect and the exposure,” the EPA statement says. “On the other hand, many other reports do not include enough facts to clearly demonstrate causation.

“Many of the reports are anecdotal, with no indication of whether the user followed label use instructions or used a product appropriate for the pet type and size. Generally, however, there is no process for verifying the information in reports.”

Elanco Animal Health spokesperson Keri McGrath provided a statement that the adverse event reports are raw data, not reliable medical information vetted by pharmacovigilance experts. Some of the reports involving Seresto collars describe incidents in which the collars were clearly unrelated to the pet’s ailments, according to the statement. McGrath cited as an example a report filed about a Seresto collar placed on a dog a few months before its arthritis became debilitating, leading to the dog’s euthanasia.

The company statement also indicates the reported rate of all adverse events related to Seresto collars is 0.3%, and more than 90% of those incidents relate to minor effects such as skin issues at the application site.

Most illnesses minor

Dr. Renee Schmid, who is a veterinary toxicologist and senior consulting veterinarian for the Pet Poison Helpline, said hotline operators had received about 400 calls involving Seresto collars since January 2015. The vast majority involved pets that ingested collars, typically dogs that ate their collars or chewed a housemate’s collar.

About 60% developed clinical signs, and about 90% of those with clinical signs vomited, she said. Some also developed diarrhea or mild lethargy.

“Overall, the majority of pets had only mild signs,” she said. “Serious signs were not common.”

Dr. Schmid and colleagues at the hotline consider the low concentration of flumethrin to be safe in dogs and cats and unlikely to cause more than mild gastrointestinal upset if ingested, she said. Imidacloprid also has a wide safety margin, she said. Differences in receptor binding properties make insects more vulnerable than mammals to imidacloprid.

“Both of these products really have a nice safety margin,” she said.

Some pets and people can have higher sensitivities to a pesticide, she said. But, based on the toxicological profile of the Seresto collars and calls to the hotline, she said, “We feel very comfortable with this particular product and its use in animals.”

Counterfeits may be contributing to reports

Dr. Adriano Vatta is an associate professor of parasitology at the Louisiana State University School of Veterinary Medicine and secretary-treasurer of the American Association of Veterinary Parasitologists. He and his wife, Dr. Ruey Stocking, who owns Red Barn Cat Clinic in Richland, Michigan, have had good experiences using the collars to protect their outdoor cats from ticks.

Dr. Vatta said some cats wearing Seresto collars may develop skin irritation, but he wondered whether counterfeit collars might be linked with many of the reports to the EPA. He also said collars stored improperly, applied incorrectly, or used past their expiration dates could cause problems.

“There are apparently a lot of counterfeit collars out there that people order online and that either have no effect or are potentially very toxic,” he said. “And I’ve seen one of these collars that are counterfeit, because a client of my wife’s brought one in, and she had to explain that it was counterfeit.”

Elanco Animal Health announcements also indicate counterfeit products have been sources of adverse event reports and encourage people to buy from authorized retailers.

Dr. Vatta sees an opportunity to encourage pet owners to buy parasite control products through their veterinarians.

“If there’s a problem with the product, they have recourse to the veterinarian, who then has recourse to the company to help address the problem,” he said.