A little clarity. A lot of love.
AI DiagAnimalsMADE FOR THE ONES YOU LOVE
English

Language and region

Understand their results
Menu
DISEASE · DOGS

Hookworms in dogs: anemia, blood work and fecal tests

Hookworms are small worms that attach to the wall of the small intestine and feed on blood. Many adult dogs carry a few without signs, but young puppies can lose enough blood to become seriously ill. The blood count and a stool test show what is going on.

Written by the AI DiagAnimals editorial teamReviewed by the AI DiagAnimals TeamUpdated Our editorial policy

The essentials

The canine hookworm Ancylostoma caninum sucks blood. In puppies, the blood count first shows an anemia with normal-sized red cells, then small, pale red cells (low MCV) as iron runs out. Total protein and albumin can be low. A stool test finds the eggs, but puppies infected through their mother’s milk can be very anemic before any eggs appear. In the US, some hookworms now resist several dewormers, so a follow-up stool test after treatment matters. Dog hookworm larvae can also cause an itchy skin rash in people.

Have your dog’s results in front of you? Get every value explained in plain language. Upload the report

What hookworms are

Dog hookworms are 10–20 mm long and live in the small intestine [1]. The main species are Ancylostoma caninum, found throughout the United States and in warm regions, and Uncinaria stenocephala, the “northern hookworm”, which prefers colder climates: the northern US, Canada and Europe [1, 2].

Dogs get infected by swallowing larvae from soil, by larvae going through the skin, or by eating infected rodents. Puppies catch A. caninum through their mother’s milk [1]. In older dogs, some larvae rest in the tissues and wake up during pregnancy, which is why even well-cared-for mothers can pass hookworms to their puppies. Routine dewormers do not kill these resting larvae [1].

Signs to watch for

  • Pale gums and weakness: A. caninum injects anticoagulants, sucks blood and leaves small bleeding ulcers [1]. One worm can take up to 0.1 mL of blood a day [3].
  • Dark, tarry stools (melena), or diarrhea with blood [1, 2].
  • Poor growth in puppies: failure to gain weight, dull coat and dehydration [1]. Infection is most severe in very young puppies infected through nursing [1].
  • Itchy paws: larvae going through the skin can irritate the skin between the toes [1].
  • Few or no signs in many well-fed adult dogs, which can still spread eggs [1, 3].

What the blood work shows

In uncomplicated hookworm disease, the bone marrow keeps working [3]. A low MCV with a high reticulocyte count fits iron deficiency from chronic external blood loss [4].
TestTypical findingWhat it means
Hematocrit (HCT), hemoglobinLowAnemia from blood loss into the gut [1, 3].
Red cell size (MCV) and color (MCHC)Normal at first, then low (small, pale red cells)First a sudden blood loss, then iron deficiency as iron is lost with the blood [1, 3, 4].
ReticulocytesOften raisedThe bone marrow is responding: hookworms do not block red cell production [3, 4].
Total protein, albuminCan be lowProtein is lost with blood and fluid in the gut. U. stenocephala drinks little blood but can lower blood protein by more than 10% [3].
EosinophilsSometimes raisedSeen in an experimental study of infected dogs [10]. A normal count does not rule out worms.

See anemia in dogs, the CBC for dogs and albumin and globulin. Raised eosinophils are explained in eosinophils in dogs and cats.

Reading the MCV line

Here is an illustrative line from a dog with long-standing hookworm blood loss.

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
MCV Mean corpuscular volume58fL66–77L
  1. Abbreviation MCV: the average size of the red cells.
  2. Result 58 fL in this illustrative line: the red cells are smaller than normal.
  3. Unit fL (femtoliters), the same unit in every country.
  4. Laboratory interval An illustrative adult dog interval; each laboratory sets its own.
  5. Flag L: below the interval. Small, pale red cells with signs of regeneration point to iron deficiency from chronic blood loss [4]. Hookworms are a classic cause in dogs [1, 3].

Stool tests and why puppies can test negative

  • Fecal flotation with centrifugation is the recommended test: hookworm eggs float easily [1]. Ancylostoma and Uncinaria eggs look almost the same [2].
  • Puppies can be sick before eggs appear. A. caninum sucks blood before it lays eggs, so a puppy infected through milk can become severely anemic, or die, before any eggs are passed [1, 3]. Eggs usually appear 2–3 weeks after infection, sometimes 10–12 days after birth in nursing puppies [1].
  • Fecal antigen tests detect young and adult worms, including infections before egg laying and single-sex infections [1, 2]. Fecal PCR detects worm DNA and can find some markers of drug resistance [1].
  • Repeat testing: CAPC advises testing for intestinal parasites at least four times in the first year and at least twice a year in adults [1].

Other stool parasites seen in young dogs: Giardia and coccidia.

Drug-resistant hookworms in the US

Since 2019, US researchers have confirmed A. caninum that resists several dewormer classes [5, 6]. The problem started in greyhounds: in 219 greyhounds, the average egg count was still 822 eggs per gram despite treatment, and a resistance marker was found in 99% of samples [7]. In a laboratory database of over 25 million results, the median time to a negative test was 71–72 days in greyhounds versus 1–2 days in other breeds [8]. Resistant hookworms are now found in dogs of all breeds, ages and regions of the continental US [9].

This is why a stool test after treatment matters. The Merck Veterinary Manual advises a fecal exam 14 days after treatment. A fecal egg count reduction test compares the egg count on the day of treatment and 14 days later: a drop of less than 75% suggests resistance, more than 95% means the treatment worked [3]. In Europe, ESCCAP reports virtually no proven cases so far [2].

Related articles

Anemia in dogs

Hematocrit, reticulocytes and how severe the anemia is.

Read the article

Other gut problems that lower protein: protein-losing enteropathy. Another cause of bloody diarrhea in puppies: parvo.

En français : ankylostomes du chien.

Questions to ask your veterinarian

  1. How low is the hematocrit, and is the anemia regenerative?
  2. Is the MCV low, which would point to iron deficiency?
  3. Are total protein and albumin low?
  4. Should we add a fecal antigen or PCR test, since a puppy can be negative on flotation?
  5. When should we repeat the stool test to make sure treatment worked?
YOUR PET’S FULL REPORT

Get your dog’s blood count and chemistry explained together.

AI DiagAnimals reads the hematocrit, red cell indices, reticulocytes and protein values together with your laboratory’s intervals, and prepares the questions for your vet. The service opens soon: leave your email to be told first.

Explain my dog’s reportSee a sample report

Frequently asked questions

What are the signs of a dog having hookworms?

Pale gums, weakness, dark tarry stools or diarrhea with blood, weight loss, and poor growth in puppies. Many adult dogs show no signs at all [1, 2].

Can humans get dog hookworms?

Yes. Dog hookworm larvae in soil or sand can enter human skin and cause cutaneous larva migrans: itchy, winding red tracks, usually self-limiting. A. caninum occasionally causes gut inflammation in people [1]. Wearing shoes and picking up feces promptly reduce the risk [1].

What are hookworms?

Small blood-feeding worms, 10–20 mm long, that hook onto the wall of the small intestine [1]. Their mouthparts are bent at an angle, hence the name [2].

How long does it take to get rid of hookworms in dogs?

Most dogs test negative quickly after treatment, but a stool test about 14 days later is advised to check it worked [3]. Resistant infections, common in greyhounds, can take months or longer [1, 8].

Why can a puppy be anemic with a negative stool test?

Because A. caninum sucks blood before it starts laying eggs. A puppy infected through milk can be very anemic before eggs appear; a fecal antigen test can be positive earlier [1, 2].

Sources

  1. Companion Animal Parasite Council (CAPC). Hookworms for dog. Updated 28 February 2025. capcvet.org/guidelines/hookworms
  2. ESCCAP. Guideline 01: Worm control in dogs and cats, 7th edition, June 2025. esccap.org/guidelines/gl1
  3. Peregrine AS. Hookworms in small animals. Merck Veterinary Manual. merckvetmanual.com/digestive-system/gastrointestinal-parasites-of-small-animals/hookworms-in-small-animals
  4. eClinPath, Cornell University College of Veterinary Medicine. RBC indices interpretation. eclinpath.com/hematology/tests/rbc-indices-interpretation
  5. Jimenez Castro PD et al. Multiple drug resistance in the canine hookworm Ancylostoma caninum: an emerging threat? Parasit Vectors. 2019;12(1):576. doi.org/10.1186/s13071-019-3828-6
  6. Kitchen S et al. Isolation and characterization of a naturally occurring multidrug-resistant strain of the canine hookworm, Ancylostoma caninum. Int J Parasitol. 2019;49(5):397-406. doi.org/10.1016/j.ijpara.2018.12.004
  7. Jimenez Castro PD et al. Multiple drug resistance in hookworms infecting greyhound dogs in the USA. Int J Parasitol Drugs Drug Resist. 2021;17:107-117. doi.org/10.1016/j.ijpddr.2021.08.005
  8. Burton KW et al. Retrospective analysis of canine fecal flotation and coproantigen immunoassay hookworm positive results in Greyhounds and other dog breeds. Vet Parasitol Reg Stud Reports. 2024;51:101026. doi.org/10.1016/j.vprsr.2024.101026
  9. Kaplan RM et al. American Association of Veterinary Parasitologists Hookworm Task Force review on best practices for diagnosis and treatment of multidrug-resistant hookworms. J Am Vet Med Assoc. 2026;264(9):1214-1222. doi.org/10.2460/javma.26.02.0094
  10. Dracz RM et al. Parasitological and hematological aspects of co-infection with Angiostrongylus vasorum and Ancylostoma caninum in dogs. Vet Parasitol. 2014;200(1-2):111-116. doi.org/10.1016/j.vetpar.2013.12.003

Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.

Cookie Policy