Beware of Dog Parks: Canine Parasite Has Evolved Resistance to All Treatments

Dog Park

Hookworms have evolved to evade all FDA approved medications veterinarians use to kill them.

Hookworms are one of the most common parasites plaguing the companion animal world.

They use their hooklike mouths to latch onto an animal’s intestines, where they feast on tissue fluids and blood. Infected animals can experience dramatic weight loss, bloody stool, anemia and lethargy, among other issues.

Now they’ve become multiple-drug resistant, according to new research from the University of Georgia.

Right now, U.S. veterinarians rely on three types of drugs to kill the hookworms, but the parasites appear to becoming resistant to all of them. Researchers from the UGA College of Veterinary Medicine first reported this concerning development in 2019, and new research, published recently in the International Journal for Parasitology: Drugs and Drug Resistance, provides deeper insight into where the problem started and how bad it’s since become.

Hookworm Eggs

Hookworm eggs are seen under a microscope. Credit: University of Georgia

For the present study, the researchers focused on current and former racing greyhounds. Dog racetracks are particularly conducive to spreading the parasite due to the sandy ground of the facilities, an ideal breeding ground for hookworms. Because of the conditions, all the dogs are dewormed about every three to four weeks.

After analyzing fecal samples from greyhound adoption kennels, three veterinary practices that work with adoption groups and an active racing kennel, the researchers found the parasites were highly prevalent in the breed. Four out of every five greyhounds tested came up positive for hookworms. And the ones that tested negative are probably also infected, said Ray Kaplan, the study’s corresponding author and a former professor of veterinary parasitology at UGA.

Hookworms Puppy Intestines

Hookworms are visible within the intestine of a deceased puppy. Credit: University of Georgia

Hookworms can sometimes “hide” in tissues, where they won’t reproduce and shed eggs until the infection worsens and leaks into the dog’s intestines.

But perhaps more alarming, the team saw that the dogs still had high levels of infection with hookworms even after they were treated for them.

The study marks the first demonstration of widespread multiple-drug resistance in a dog parasite reported in the world.

Parasite mutations

In situations where there are a lot of dogs infected with a lot of parasites, such as on racing dog breeding farms and kennels, there are many more opportunities for parasites to develop rare mutations allowing them to survive the dewormer treatments. If dewormers are applied frequently, the newly emerging resistant worms will survive and pass on the mutation that helped them sneak past the drug to their offspring.

With repeated treatments over time, most of the drug-susceptible worms at the farm or kennel will be killed, and the resistant worms will then predominate.

Compounding the problem, veterinarians don’t typically test animals after treatment to ensure the worms are gone, so the drug-resistant worms go unnoticed until the dog has a heavy infection and starts showing signs of hookworm disease.

“Personally, I would not take my dog to a dog park. If your dog picks up these resistant hookworms, it’s not as easy as just treating them with medication anymore.”
Ray Kaplan, professor of veterinary parasitology

The researchers found that almost all the fecal samples tested positive for the mutation that enables hookworms to survive treatment with benzimidazoles, a broad-spectrum class of dewormers used in both animals and humans. Although a molecular test does not yet exist to test for the resistance to the other two types of drugs, other types of testing by the team showed that the hookworms were resistant to those drugs as well.

“There’s a very committed greyhound adoption industry because they are lovely dogs,” said Kaplan. “I used to own one. But as those dogs are adopted, the drug-resistant hookworms are going to show up in other pet dogs.”

Hookworms Microscopic Hooks

Hookworms get their name from their hook-shaped mouths shown here under a microscope. Credit: University of Georgia

One possible breeding ground for a potential drug-resistant hookworm outbreak is also the place many dog owners use to exercise their animals: dog parks.

“Personally, I would not take my dog to a dog park,” Kaplan said. “If your dog picks up these resistant hookworms, it’s not as easy as just treating them with medication anymore. Until new types of drugs are available, taking your dog to a dog park has to be considered a risky activity.”

The consequences 

Dogs don’t have to ingest the worms to become infected. Hookworm larvae live in the soil and can also burrow through the dog’s skin and paws. And female dogs can pass the parasite on to their puppies through their milk.

If that’s not scary enough, dog hookworms can also infect humans.

The infection doesn’t manifest in the same way in people, but after the worms penetrate the skin, they cause a red, very itchy rash as they travel under the skin. As the number of drug-resistant worms grows, they’ll also pose a risk to humans.

Previously, doctors would treat patients with an ointment that contains a dewormer along with a corticosteroid. “Unfortunately, that’s not going to work against these drug-resistant hookworms,” Kaplan said.

But hope isn’t entirely lost.

Kaplan and Pablo Jimenez Castro, lead author of the study and a recent doctoral graduate from Kaplan’s lab, found in another recent study that these multiple-drug resistant dog hookworms do appear to be susceptible to emodepside, a dewormer currently only approved for use in cats in the U.S. But use of this cat drug on dogs should only be performed by a veterinarian, as it requires veterinary expertise and supervision.

Based in part on Castro’s work, the American Association of Veterinary Parasitologists recently formed a national task force to address the issue of drug resistance in canine hookworms.

Reference: “Multiple drug resistance in hookworms infecting greyhound dogs in the USA” by Pablo D. Jimenez Castro,
Abhinaya Venkatesan, Elizabeth Redman, Rebecca Chen, Abigail Malatesta, Hannah Huff, Daniel A. Zuluaga Salazar, Russell Avramenko, John S. Gilleard and Ray M.Kaplan, 2 September 2021, International Journal for Parasitology: Drugs and Drug Resistance.
DOI: 10.1016/j.ijpddr.2021.08.005

Co-authors on this study include Abigail Malatesta, a veterinary student from Tuskegee University, Hannah Huff, currently a veterinary student at the University of Georgia, and researchers from the University of Calgary in Canada.

13 Comments on "Beware of Dog Parks: Canine Parasite Has Evolved Resistance to All Treatments"

  1. If you heat the dog’s intestines to 350F for thirty minutes, they will all die.

  2. Richard James Samuelson | September 30, 2021 at 4:28 am | Reply

    That’s the worst bunch of bull crap I’ve heard jumbled up into one short article since there was going to be a cow fart tax!

  3. What about diatomaceous earth, or bentonite clay? Garlic?

  4. That sounds like a Trumpeter solution for dogs and humans , I will boil my dogs intestines, and for COVID drink bleach lol !! I will keep my dog away from other dogs ,

  5. Let’s heat Due Donem’s intestines to 350 for 30 minutes. It’ll cure the world of her!

  6. Headline said there are no treatments left to try, but then you said there’s an option used in cats. Why did you leave the truth to the very END of the article? And if there truly is no treatment, then deciding if the dog park is worth the trade off is something I can personally weigh.

  7. It’s a timing thing .took a yr to get
    rid of my rottweilers hook. If your intrested email me.

  8. Sounds like the Greyhound racing community created this problem by unnecessary worming and not rotating the medication used for treating hooks. Also sounds like they, UGA, are prematurely sounding the alarm as this is a very small demographic of a specialized breed kept in a very limited and confined area that family dogs will never be exposed to. There are several reasons for not taking your dog to public or county funded dog parks, possible treatment resistant hook worms is a small factor in all that. These parks are a petei dish for disease as they are not properly cleaned and kept up neither by those who bring ygeir dogs or the entity that holds or runs them, not to mention people bring dogs that shouldn’t be in multi dog situations to start with.

  9. Scoobie Squires | September 30, 2021 at 9:48 am | Reply

    Asking for a friend, Are there by chance, any human cases of this drug resistant hookworms”?!? 🤔🤔😳😯😟😣

  10. Or maybe one or two day on deworming drug is not enough. Maybe it takes lots more application. Maybe they are real nasty. Maybe thy eat cartiledge and cause bone decay. Maybe they cause autoimmune disease? my doctor says the body attacks itself for no reason? Lets all just say b and be done with it.

  11. HoW do you heat a dogs intestines to 350* without KiLlInG them?

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