It sounds like the plot out of a horror movie. An alien invader creeps into the East Coast. It is aggressive and voracious, and though only about the size of a poppy seed, it grows to the size of a pea upon feeding on its victims’ blood. The female lays eggs and can reproduce without a male. Before long, it begins spreading across the country inexorably.
The alien invader is the Asian longhorned tick, first discovered in the United States in 2017 and now found in 18 states, according to the Centers for Disease Control and Prevention.
Craig Prior, BVSc, CVJ, a board member and former president of the Companion Animal Parasite Council and a practice consultant, noted that perhaps the most significant recent news about parasites is that the Asian longhorned tick (Haemaphysalis longicornis) is on the move.
“It’s a nasty tick,” Dr. Prior said. “It really doesn’t care where it lives.
The Asian longhorned tick lives on short grass, and cases reported last year in North Carolina detailed how a couple hundred thousand exsanguinated five cows.”
Michael Dryden, DVM, MS, Ph.D., a groundbreaking parasitology researcher and an emeritus professor at Kansas State University’s College of Veterinary Medicine, said the tick was first recognized in the United States at a feed farm in New Jersey.
“It’s probably been in the U.S. since 2010,” said Dr. Dryden, widely known in the veterinary parasitology community as “Dr. Flea” and “Tick Daddy,” the latter bestowed on him by veterinary students. “It was misidentified for a while. It’s native to Southeast Asia and got introduced to the East Coast.
“It is a separate and unique tick and is essentially born pregnant. It is parthenogenetic, and only one male has been identified in the U.S.
“Now it’s as far west as Missouri and Arkansas. In Long Island, it is now the No. 1 tick, displacing the Lone Star and Lyme ticks.
“Expansion to the West Coast is inevitable,” Dr. Dryden said. “They can feed on dozens of mammalian hosts — any mammal — and birds. The USDA considers it established.”
The good news is that killing the tick is no harder than with other species.
“It’s a common tick in Japan and has been studied there,” he said. “Japan does a good job evaluating products. We already knew these [established] products would kill them.”
The Threat to People
Dr. Prior noted that as humans encroach on nature, moving closer to the habitat of tick-carrying animals, people will be exposed to the diseases ticks carry.
“We’ve seen tick ranges expanding as deer learn to live around humans a lot more easily,” he said. “Our exposure to ticks is getting greater. Lyme disease is getting closer. The presence of Lyme is exploding.”
When the Companion Animal Parasite Council predicted that the Ixodes genus of tick, which carries Lyme disease, would move into Kentucky, it got pushback, Dr. Prior said.
“When we asked if they had looked for it, they said, ‘Well, no.’ So they looked, doing tick surveillance on roadkill. The tick was already there.
“Parasites are dynamic and ever-changing.”
In 2019, a CAPC study found that dogs are a sentinel for human Lyme disease.
“If it’s present in dogs, humans are at risk, too,” Dr. Prior said. “So protecting your pet is protecting your family.”
Fighting Back
A lot has changed in the world of parasite control since 1995, when Ciba Animal Health introduced the oral treatment Program (lufenuron) for managing fleas in dogs and cats.
Brian Herrin, DVM, Ph.D., a veterinary parasitologist and assistant professor at Kansas State, noted a recent trend of manufacturers combining products to treat and prevent fleas, ticks and heartworm disease.
“Many companies are coming out with one-stop shops,” he said. “These products can control the main parasites. Some also control endoparasites — roundworm, hookworm. They include an expanded, wider breadth of what can be controlled.
“Anything to try to increase compliance is good. One pill instead of two is a plus for our clients.”
There was a time when flea bombs were a pet owner’s best option.
“Now we have such good products for dogs and cats that those chemical sprays aren’t needed,” Dr. Herrin said.
Flea bombs aren’t necessary in most cases, he said.
“When there are fleas in the house, there is an environmental burden of flea life stages in the house,” Dr. Herrin said. “The best thing to do is make sure the pet is on a good preventive product for at least three months. Then vacuum wherever pets spend a lot of time.”
While there are many choices for parasite prevention, topicals are still the No. 1 seller in the veterinary industry, Dr. Prior said.
“They provide a range of flea- and tick-control options for our clients,” he said.
THE ISOXAZOLINE BREAKTHROUGH
Veterinary parasitologists say the isoxazoline class of synthetic chemicals has revolutionized the treatment of external parasites over the past five to seven years.
“They are incredibly effective and safe,” said Dr. Michael Dryden, a longtime parasitology researcher and an emeritus professor at Kansas State University’s College of Veterinary Medicine. “They are far beyond anything we’ve ever seen. They’re not comparable.”
The prominent players in the isoxazoline class are the products Bravecto, NexGard, Simparica and Credelio.
An August 2021 news release from the U.S. Food and Drug Administration warned veterinarians and pet owners about the potential for neurological adverse events in cats and dogs treated with products in the isoxazoline class.
The agency said that although the products “can and have been safely used in the majority of dogs and cats, pet owners should consult with their veterinarians to review their patients’ medical histories and determine whether a product in this class is appropriate for their pet.”
The news release reported that isoxazoline products have been associated with muscle tremors, ataxia and seizures in some dogs and cats. It noted that while most dogs and cats haven’t had neurologic adverse reactions, seizures might occur in animals with no previous history.