Dogs get hookworms through three main routes: swallowing infective larvae from contaminated soil, larvae burrowing directly through the skin (usually the paws), and nursing puppies ingesting larvae passed through their mother’s milk. Of these, skin penetration and oral ingestion from the environment are the most common in adult dogs, while transmission through milk is the leading cause of infection in newborn puppies.
Swallowing Larvae From the Environment
When an infected dog passes stool, hookworm eggs land in the soil and hatch into microscopic larvae. These larvae go through several stages of development in the dirt before reaching an infective stage. A dog that sniffs, licks, or eats contaminated soil, grass, or feces can swallow these larvae directly. Once inside, the larvae travel to the small intestine, latch onto the intestinal wall with hook-like mouthparts, and begin feeding on blood.
Dogs that spend time in areas with poor sanitation, dog parks with heavy foot traffic, or kennels with contaminated runs are at higher risk. The larvae thrive in warm, moist, shady soil, which is why hookworm infections are more common in humid climates and during warmer months. Concrete or dry, sun-baked ground is far less hospitable to the larvae.
Larvae Burrowing Through the Skin
Hookworm larvae don’t need to be swallowed to cause infection. They can penetrate a dog’s skin on contact, most often through the soft tissue between the toes or on the belly. A dog lying on contaminated ground or walking through infested soil gives larvae an entry point. Once through the skin, the larvae enter the bloodstream and travel to the lungs, where they’re coughed up, swallowed, and ultimately reach the small intestine to mature into adults.
This route of infection often leaves a telltale sign: red, itchy bumps between the toes. If your dog is licking or chewing at its paws and you notice irritated skin in the interdigital spaces, hookworm larvae may be the cause.
Transmission From Mother to Puppies
This is the route that makes hookworms so dangerous to very young dogs. A mother dog can harbor dormant hookworm larvae in her muscles and other tissues for months or even years without showing symptoms. During pregnancy, hormonal shifts triggered by estrogen, progesterone, and prolactin reactivate these dormant larvae. The larvae migrate to the mammary glands, and nursing puppies swallow them with every meal.
The puppies receiving these larvae have no immune defenses against them. Because hookworms feed on blood, even a moderate infection can cause life-threatening anemia in a puppy within days. This is why veterinary guidelines recommend deworming puppies starting at just 2 weeks of age, with treatments repeated every 2 weeks until routine parasite prevention begins. Waiting until symptoms appear can be too late for small puppies with limited blood volume.
What Happens Inside the Dog
Regardless of how the larvae get in, the destination is the same: the small intestine. Adult hookworms anchor to the intestinal lining and feed on blood, creating small wounds that continue to bleed even after the worm moves to a new feeding site. This constant blood loss is what drives the most serious consequences of infection.
Puppies with heavy infections develop anemia quickly. You might notice pale gums, weakness, dark tarry stool (which indicates digested blood), and failure to gain weight. Adult dogs with strong immune systems may tolerate a low-level infection with minimal symptoms, but a sudden heavy exposure can still cause anemia, weight loss, diarrhea, lethargy, and a dull coat. Coughing sometimes occurs when larvae are migrating through the lungs before being swallowed.
Signs to Watch For
The symptoms of hookworm infection overlap with many other conditions, so a stool test is the only reliable way to confirm it. That said, certain combinations of signs point strongly toward hookworms:
- Dark, tarry diarrhea rather than the bright red blood you’d see with a colon problem
- Pale gums indicating anemia
- Weight loss or failure to thrive in puppies despite normal appetite
- Red, itchy bumps between the toes from larvae entering through the skin
- Lethargy and weakness that worsens over days
Vets diagnose hookworms by examining a stool sample under a microscope to identify eggs, or through newer tests that detect parasite DNA or specific proteins in the feces. In early infections or cases with only a few worms, standard stool tests can miss the diagnosis, which is why some veterinary parasitologists recommend combining microscopic examination with antigen or DNA-based testing for the most accurate results.
How Dogs Get Reinfected
One of the frustrating things about hookworms is how easily reinfection occurs. Treating an active infection kills the adult worms in the intestine, but dormant larvae hiding in the dog’s muscle tissue can reactivate later, especially during pregnancy or periods of immune stress. A dog that’s been successfully treated can also pick up new larvae the next time it walks through contaminated soil.
This is why the Companion Animal Parasite Council recommends year-round broad-spectrum parasite prevention for all dogs, not just seasonal treatment. For adult dogs not on continuous prevention, quarterly deworming is the minimum recommendation. Puppies need more aggressive treatment: deworming every 2 weeks starting at 2 weeks old, then monthly until 6 months of age.
Hookworms Can Spread to People
Dog hookworm larvae can also infect humans, though they typically can’t complete their life cycle in a human body. Instead, the larvae burrow into exposed skin and tunnel just beneath the surface, creating intensely itchy, raised, reddish tracks. This condition, called cutaneous larva migrans, most often affects the feet, legs, or anywhere bare skin contacts contaminated ground. Symptoms usually develop within 10 to 15 days of exposure, though onset can sometimes be delayed for weeks.
In rare cases, the larvae migrate deeper into the body, reaching the lungs or intestinal tract. Picking up after your dog promptly, avoiding walking barefoot in areas where dogs defecate, and keeping your dog on regular parasite prevention all reduce the risk to your family.
Reducing Environmental Risk
Because hookworm larvae develop in soil contaminated by infected stool, the single most effective environmental step is cleaning up after your dog promptly, ideally within 24 hours. Larvae need time to develop in the soil before they become infective, so removing stool quickly breaks the cycle. Keeping your yard well-drained and exposed to sunlight also helps, since larvae survive best in moist, shaded areas. In kennels or dog runs, hard surfaces like concrete are much easier to decontaminate than grass or dirt.
For dogs that frequent shared spaces like dog parks or boarding facilities, consistent monthly parasite prevention is the most practical line of defense. No amount of environmental management can eliminate every larva, but combining regular deworming with good sanitation dramatically lowers the odds of infection.