What are hookworms in puppies? — Why do anemia and weight loss occur?

Infection/ParasitesQ&AMeongsiljang Veterinary Advisory Board

Hookworms in dogs are parasitic worms that cause anemia and weight loss by feeding on blood. This guide covers everything from early warning signs like pale gums and black stools, to diagnosis via fecal testing, deworming treatment, and prevention of reinfection.

What is hookworm infection in puppies?

A veterinarian examining the gum condition of a young puppy.

Hookworm infection in puppies is a parasitic disease in which hookworms attach to the small intestinal mucosa and feed on blood, causing anemia and weight loss. Early diagnosis is key. If you notice pale gums, black stools, or rapid weight loss, have your puppy undergo a fecal examination at a veterinary clinic immediately. Puppies aged 2 to 6 months are especially vulnerable, as rapidly progressing hemorrhagic anemia can be life-threatening. Additionally, hookworms are zoonotic parasites that can cause cutaneous larva migrans in humans, so pet owners should take preventive measures as well.

How do they get infected? — 4 routes

Hookworms (Ancylostoma caninum) are primarily transmitted through two routes: oral infection, where eggs or larvae are ingested, and percutaneous infection, where larvae penetrate the skin. Additionally, transmission through the mother’s milk is a well-known route of infection in puppies. Infection can occur when dogs come into contact with soil, grass, or feces from other dogs on walks, making dog parks and shared walking areas particularly high-risk. Since puppies can be infected in utero or through nursing, they may already harbor the parasite at birth; therefore, even if fecal test results are negative, presumptive treatment is often initiated if clinical signs are suspected.

Main symptom checklist

Because hookworms are blood-sucking parasites, anemia is typically the first sign of infection.

Pale gums: Blood loss from the parasites causes anemia, making the gums and tongue shift from pink to a pale, whitish color.

Small intestinal diarrhea and bloody stools: Damage to the intestinal lining can result in soft stools or feces mixed with blood.

Weight loss: Even with a good appetite, your pet may lose weight as the parasites deprive them of essential nutrients.

Lethargy and loss of appetite: Anemia can cause your pet to refuse walks, tire more quickly than usual, and eat less.

Coarse, dull coat: Nutrient depletion can lead to a rough, unhealthy-looking hair coat.

Pica: Your pet may show a decreased appetite or, conversely, develop pica—an urge to eat non-food items like dirt or other unusual substances.

These signs require an immediate emergency visit

If your dog’s gums are very pale or grayish, they’re breathing rapidly, collapsing, or unable to stand, or if they repeatedly pass black stools, they may have hemorrhagic anemia and require a blood transfusion. Puppies aged 2 to 6 months are especially vulnerable, as their anemia can progress rapidly and become life-threatening within 24 hours. In such cases, seek emergency veterinary care immediately, even at night.

How is diagnosis performed?

The cornerstone of diagnosis is a fecal examination, specifically using the flotation method to identify hookworm eggs under a microscope. However, since eggs may not be visible in the early stages of infection, we often recommend repeat testing at intervals of a few days even if the initial result is negative. We also perform a complete blood count (CBC) to assess the degree of anemia and check for bleeding. In severe cases, we additionally monitor protein levels (albumin) and serum iron. For puppies, if clinical signs are pronounced, we may initiate presumptive treatment even if the fecal test comes back negative.

Treatment — Deworming medication and anemia supportive care

The cornerstone of treatment is deworming medication.

Fenbendazole: Administered orally at 50 mg/kg for three consecutive days; it is relatively safe even for puppies.

Pyrantel: Given as a single dose of 5–10 mg/kg, followed by a repeat dose 7–10 days later. It is approved for all worm species and can be used in nursing mothers.

Milbemycin: This ingredient is also included in heartworm preventatives.

If anemia is severe, we will also administer fluids, iron supplements, and blood transfusions (whole blood or packed red blood cells). Because a single deworming treatment may leave behind dormant larvae, a follow-up dose 7–10 days later is essential. Your veterinarian will determine the exact dosage and schedule based on your puppy’s weight.

A veterinarian administering deworming medication to a puppy

Comparison of main deworming ingredients

Item	Fenbendazole	Pyrantel	Milbemycin
Dosing method	Oral for 3 consecutive days	Once + repeat dose 7–10 days later	Oral once a month
Young puppies	From 2 weeks of age	From 2 weeks of age	From 6 weeks of age
Nursing mother dogs	Allowed	Allowed	Consult veterinarian
Heartworm prevention	False	False	True
Roundworm/whipworm coverage	True	True	True

The exact dose and dosing schedule are determined by the veterinarian according to the puppy's body weight, age, and health status

Daily management to prevent reinfection

Even after treatment, if eggs remain in the environment, reinfection can occur.

Wipe paws after walks: Clean the paws and around the anus to remove eggs and larvae.

Dispose of feces immediately: Clean up feces from the yard or walking paths on the same day.

Monthly broad-spectrum preventatives: Milbemycin and moxidectin-based products prevent both heartworm and hookworm infections.

Deworm all dogs in multi-dog households: If one dog is infected, treat all dogs simultaneously.

Manage pregnant and nursing dogs: Consult your veterinarian to deworm at a safe time.

Zoonotic parasites that can be transmitted to humans

Hookworms can be transmitted to humans. Walking barefoot on contaminated soil allows larvae to penetrate the skin, potentially causing cutaneous larva migrans, characterized by itching and red, serpiginous tracks. Households with young children or pregnant women should ensure rigorous deworming for their dogs and regularly maintain yard soil and sandboxes. Always wash your hands thoroughly after handling feces.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently asked questions

Is giving dewormer just once enough?

Not exactly. Dewormers are most effective against adult worms and have limited efficacy against larvae that are dormant within tissues. Repeated dosing at regular intervals is necessary to eliminate newly developing larvae. For example, with pyrantel, the standard protocol is to administer a second dose 7 to 10 days after the initial treatment.

When should I start deworming my puppy?

The standard deworming schedule begins at two weeks of age, with treatments administered every two weeks for a total of four doses (at weeks 2, 4, 6, and 8). It’s also important to deworm the mother dog to prevent transmission through nursing.

Can I rest assured if the fecal test comes back negative?

Not necessarily. In the early stages of infection, eggs may not yet be present in the stool, which can result in a negative test. If symptoms are suspected, a follow-up test after a few days to a week is recommended, or in the case of young puppies, empirical treatment may be initiated first.

Does a heartworm preventive also cover intestinal worms?

It depends on the active ingredient. Macrocyclic lactones (such as milbemycin, moxidectin, and selamectin) have deworming effects, but their efficacy varies by species. Please check the product label or follow your veterinarian’s instructions.

How long does it take for anemia to recover after treatment?

The prognosis for roundworm infection is generally good to excellent, with gradual recovery following parasite removal and anemia management. The speed of recovery depends on the severity of the anemia, as well as the puppy’s age and overall health. During recovery, a diet rich in protein and iron, along with adequate rest, can be beneficial. It’s also a good idea to consult your veterinarian and monitor progress through blood tests.