Dog parasite is developing resistance to treatments: Hookworms have evolved to evade all FDA approved medications veterinarians use to kill them

Hookworms are a common parasite that plagues companion animals.
They attach themselves to animals' intestines with their hook-like mouths. Here they feast on blood and tissue fluids. Among other problems, infected animals may experience weight loss, bloody stool and lethargy.

According to University of Georgia research, they are now multi-drug resistant.

The U.S. vets currently use three types of drugs against hookworms. However, the parasites seem to be resistant to all three. This alarming development was first discovered by researchers at the UGA College for Veterinary Medicine in 2019. New research published in the International Journal for Parasitology: Drugs and Drug Resistance provides deeper insight into the origins of the problem and the extent to which it has progressed.

The researchers studied greyhounds that were racing at the time of the study. The sandy ground at dog racetracks makes them a breeding ground for hookworms. All dogs must be dewormed every three to four week due to the harsh conditions.

The researchers discovered that the parasites are highly prevalent in greyhounds after analysing feces from three veterinary practices who work with adoption groups, a greyhound adoption kennel and an active racing dog kennel. Hookworms were found in four out of five greyhounds. Ray Kaplan, the study's co-author and former UGA professor of veterinary parasitology, stated that the negative ones are likely also infected. Sometimes hookworms "hide" in tissues. They don't reproduce and then shed eggs until the infection becomes worse and leaks into the dog’s intestines.


Worse, however, was the discovery that hookworm infection was still present in the dogs even after treatment.

This is the first time that multiple-drug resistance has been demonstrated in a dog parasite.

Parasite mutations

Parasites can develop rare mutations in situations where there is a lot to deal with, such as racing dog breeding farms or kennels. The newly developed resistant worms can survive if dewormers are used frequently and will pass the mutation to their offspring.

Repeated treatments will kill most drug-susceptible parasites in the farm or kennel, and resistant worms will take over.


The problem is compounded by the fact that veterinarians rarely test animals for worms after treatment. This means that drug-resistant worms can go unnoticed until the dog develops hookworm disease or has a severe infection.

Researchers found that nearly all fecal samples were positive for the mutation that allows hookworms to survive treatment using benzimidazoles. This broad-spectrum dewormer is used in humans and animals. While a molecular test is not available to determine if hookworms are resistant to these drugs, the team performed other testing.

Kaplan stated that there is a dedicated greyhound adoption market because they are wonderful dogs. "I used to have one. The drug-resistant hookworms will soon be found in other pets dogs as these dogs are adopted.

Dog parks are a common place where dog owners exercise their dogs. This could be a breeding ground for drug-resistant hookworm.

Kaplan stated, "Personally, I wouldn't take my dog to the dog park." It's difficult to treat resistant hookworms if your dog gets them. You should not take your dog to the dog park until new drugs are developed.

The consequences

Dogs don’t need to ingest the hookworms in order to get infected. Hookworm larvae live in soil and can burrow through skin and paws of dogs. Female dogs can also pass the parasite to their puppies by drinking their milk.

Dog hookworms can also infect humans if this isn't scary enough.

Although the infection isn't the same in everyone, once the worms have penetrated the skin, it causes a red, itchy rash. They pose a threat to humans as they become more resistant to drugs.

Doctors used to treat patients with an ointment containing a dewormer and a corticosteroid. Kaplan stated, "Unfortunately that's going to not work against these drug resistant hookworms."

However, hope is not lost.

Pablo Jimenez Castro and Kaplan, the lead author of this study, and a recent graduate from Kaplan’s lab, discovered in another study that multiple-drug resistant hookworms are susceptible to emodepside. This dewormer is currently only approved for cats in the U.S. This cat drug should be used only by veterinarians. It requires expertise and supervision.

Castro's research was a major inspiration for the American Association of Veterinary Parasitologists to create a task force in the United States to tackle the problem of canine hookworms drug resistance.

Abigail Malatesta (a Tuskegee University veterinary student), Hannah Huff (currently a University of Georgia veterinary student), and researchers from Calgary, Canada, are co-authors of this study.