Hookworms -- a common parasite in animals -- have become resistant to multiple deworming drugs used to kill them, a new study finds.
Veterinarians typically use three types of drugs to kill hookworms, and all three have lost their effectiveness, researchers report.
Moreover, as more hookworms survive, they'll be a threat to people, too, according to the study.
One possible breeding ground for a potential drug-resistant hookworm outbreak is dog parks.
"Personally, I would not take my dog to a dog park," said study co-author Dr. Ray Kaplan, a former professor of veterinary parasitology at the University of Georgia.
"If your dog picks up these resistant hookworms, it's not as easy as just treating them with medication anymore," he said in a university news release. "Until new types of drugs are available, taking your dog to a dog park has to be considered a risky activity."
For the study, Kaplan's team looked at current and former racing greyhounds. Race kennels are conducive to spreading hookworm because of the sandy ground, and the dogs are dewormed about every three to four weeks.
Of the dogs tested, 4 out of every 5 had hookworms. But even the dogs that tested negative likely were infected, Kaplan said, because hookworms can hide in tissues, until the infection worsens.
The researchers also found the dogs still had high levels of hookworms even after they were treated.
In areas where hookworms are common, it is easy for them to develop mutations that protect them against the drugs used to kill them. With repeated treatments, most of the drug-susceptible worms will be killed, and the resistant ones will predominate, the researchers noted.
And making the problem worse, veterinarians usually don't test for hookworm after treatment, so drug-resistant worms go unnoticed until the dog starts showing signs of infection with hookworm disease.
"There's a very committed greyhound adoption industry because they are lovely dogs," Kaplan said. "I used to own one. But as those dogs are adopted, the drug-resistant hookworms are going to show up in other pet dogs."
Dogs don't have to ingest the worms to become infected. Hookworm larvae live in the soil and can also enter through the dog's skin and paws. And female dogs can pass the parasite to their puppies through their milk.
In people, the infection can penetrate the skin and cause a red, very itchy rash.
There is still one possible solution: Hookworms appear susceptible to emodepside, a dewormer only approved for use in cats. Using this cat drug on dogs should only be done by a veterinarian, the researchers said.
The study was published recently in the International Journal for Parasitology: Drugs and Drug Resistance.
For more on hookworm, see the U.S. Centers for Disease Control and Prevention.
SOURCE: University of Georgia, news release, Sept. 22, 2021