Hookworms can infect dogs of all ages but are most dangerous in puppies. People can get infected from animal hookworms as well, usually by penetration through the skin of the feet. Fortunately, early detection of “hooks” (from a stool sample) and routine preventative care can help protect your dog and your family.
All hookworms suck blood, but the most common type (A. caninum) are voracious bloodsuckers that can bleed a puppy to death!
Companion Animal Parasite Council (CAPC)
All About Hookworms
Hookworms are small, white, bloodsucking worm parasites that live within a dog’s digestive tract. Three species infect dogs in the U.S., Ancylostoma caninum (by far the most common and most likely to cause illness), Ancylostoma braziliense, and Uncinaria stenocephala. Adults range in size from 1-2 centimeters in length and are very thin (just ½ millimeter in width), so can be difficult to see in dog stool without careful observation.
Hookworms get their name from their hook-like mouthpieces, which they use to latch onto the inside of the intestine. Once attached, they feed on the dog’s blood which can lead to serious blood-loss anemia from their voracious feeding and from small bleeding ulcers on the intestines where the worms previously fed.
Hookworms are common in dogs across the U.S. and especially in tropical and subtropical areas of the world. They are more prevalent in the southern U.S. where it is warmer with higher humidity, and more common in pets kept primarily outdoors. Veterinarians throughout the U.S. regularly screen dog stool samples for hookworms.
Puppies can get hookworms while still in the womb or through nursing from their infected mothers. Adult dogs will accidently ingest hookworms or get infected through the skin of their paws. They then harbor the infection and pass the eggs in their stool, contaminating the outdoor environment with hookworm eggs for weeks to months.
The adult hookworm looks to be straight out of a horror movie. It has a fishing hook appearance to its front end and “teeth” or “cutting plates” in the mouth cavity. Adult hookworms are white in color and quite small (1-2 cm), but may be visible by the naked eye wiggling in a fresh stool sample. Hookworm eggs are only detectable by examining a stool (fecal) sample under a microscope (ClueJay Dog Stool Test Level 1, 2, or 3). If found, it’s a giveaway that adult hookworms have infected the dog and treatment is needed.
Adult dogs that are otherwise healthy and well-nourished may harbor small numbers of hookworms without ever showing signs of infection. These dogs can act as carriers for the worms, spreading their eggs into the environment when passing stool and putting other dogs at risk. If the infection is heavy in adult dogs (larger number of worms) or if puppies are infected, symptoms can be quite severe such as:
- Dark, tarry, or bloody diarrhea (from blood loss into intestines)
- Weight loss or failure to gain weight
- Poor appetite
- Pale gums (from blood loss)
- Dull or dry hair coat
- Skin irritation (feet between pads)
- Coughing or even pneumonia (more likely in puppies)
- Death (puppies)
Significant blood loss—resulting in anemia—is the primary concern for dogs infected with hookworms and can become life-threatening for puppies without treatment.[2,3,4] If your dog is acting sick, please contact a veterinarian right away.
Cats can accidently swallow hookworm larvae by eating soil (licking dirt from feet), grass, or plants contaminated from old stool, or drinking water with hookworm larvae. They can even get hookworms by eating cockroaches with infective larvae. Hookworm larvae can also burrow directly through dog skin (usually skin of the feet or belly) upon contact with contaminated soil.[1,2]
Puppies are especially susceptible to illness from hookworms. If a pregnant mother was previously infected, she can pass the larvae on to her pups even if her stool samples don’t show hookworms. Pregnancy hormones trigger inactive larvae in her tissues to “wake up” and migrate to the puppies through the womb or into the breast milk for ingestion. Thus early deworming in all puppies is crucial to their health.[2,3,4,5,6]
Adult female hookworms release eggs into the intestinal tract of the dog which are then passed in the stool. After a few days, these eggs hatch into larvae that can remain infective in the ground for a few months. Another animal becomes infected when these larvae are either accidently ingested (such as when licking dirt from feet) or penetrate the skin (usually through the belly or between the paw pads).
Hookworm larvae that are swallowed will either migrate out of the digestive tract and into the dog’s tissues or get carried into the intestine where they “hook” (attach) to the inner lining. Hookworm larvae that enter through the skin migrate to (and injure) the lungs to get coughed up and swallowed into the digestive tract. Regardless of how the exposure occurs, hookworms that make it to the intestine will “hook” (attach) to the inner lining where they use potent anticoagulants (blood thinners) to feed on the dog’s blood. When they shift feeding locations, the previous locations may keep bleeding because of the anticoagulants leading to more blood loss from the dog. These feeding hookworms mature, mate, and release eggs which are passed in the stool.
Whether from oral or skin penetration, some hookworm larvae will migrate and encyst themselves in the dog’s tissues and go dormant. These inactive hookworm larvae can periodically become active and lead to a “surprise” intestinal infection in the adult dog or be triggered awake during pregnancy to be passed to the mother’s pups either in the womb or via her milk.
Yes, hookworms can infect humans and other pets, including cats. Infection in people occurs from direct skin contact with larvae (e.g. walking in contaminated soil or sand with bare feet). Upon contact, larvae burrow into the skin, causing inflammation and irritation. In most cases, infections in humans are easily treatable or resolve on their own in a month or two.] It’s best to prevent children from playing in areas contaminated with dog stool.
Stool testing your dog, regular deworming, and picking up dog stool right away are the best ways to avoid spreading hookworm infections to other dogs and people. Also, practice good hygiene by thoroughly washing your hands with soap and water (get those thumbs too!) after touching stool, soil, and other materials that could be contaminated with pet stool.
Cats are also at risk of getting hookworms. They can become infected by both oral ingestion of larvae and through direct skin contact. It’s important to regularly deworm cats and promptly remove stool from the litterbox to avoid spreading the eggs and infective larvae.[2,8] Cats can occasionally get hookworms from infected dogs.
Hookworms are an unwanted pest for dogs but deworming for them is common and routine. Dog owners can choose from a variety of over-the-counter (OTC) and veterinary-prescribed deworming options.
The best way to control hookworms is through regular deworming, before they become a problem and need treatment. Puppies are typically dewormed multiple times (3-4 times) before a year of age while dogs can be dewormed monthly for hookworms using a combination “heartworm” preventative. This is because many heartworm preventatives on the market also deworm for hookworms.[1,3] A veterinary consultation can help you determine the best options for you and your dog.
Since hookworm eggs are not easy to remove from contaminated soil, it’s best to prevent them from getting there in the first place. This is done through regular dog deworming as described. Also cleaning up dog stool (feces) quickly so the eggs can’t become infective larva in decomposing stool and become a source of infection for other animals or reinfection of your dog.
While ClueJay does not dispense or prescribe medications, there are numerous deworming medications available over-the-counter (OTC) and through veterinarians for hookworm prevention and treatment. Hookworm medications are even included in many monthly heartworm preventatives. Pyrantel pamoate, milbemycin oxime, moxidectin, selamectin, ivermectin, emodepside/praziquantel, and fenbendazole are common medications used to reduce or eliminate hookworms from the dog.[3,4]
It’s always best to consult with a veterinarian prior to administering any medication, even an OTC version, to make sure it will be safe and effective for your pet. Always read the medication administration directions carefully and be on the lookout for potential side effects (like vomiting) when any deworming medication is administered.
Veterinarians recommend stool (fecal) testing puppies 2 to 4 times during their first year of life, and 1 to 2 times each year in adult dogs. Veterinarians often call this stool test a “Fecal O&P”, with the O&P meaning “ova (eggs) and parasites”. It includes special preparations of the stool sample and analysis using a microscope to look for certain types of parasites like hookworms. This same test is also used to recheck stool samples after treatment. Typically, a recheck stool test is done 2-4 weeks after deworming a dog that was treated for hookworms to help confirm that the treatment was effective.
Dogs should also be tested when symptoms of possible hookworm infection are present such as dark, tarry, or bloody diarrhea, weight loss or failure to gain weight, poor appetite, pale gums, weakness, dull or dry hair coat, skin irritation (feet between pads), or coughing. Please contact a veterinarian right away if your dog is acting sick.
Some veterinarians still do the Fecal O&P at their practice with trained veterinary technicians. Most however, “refer” or ship their patient’s stool samples to an external animal reference laboratory for preparation (including centrifugation), analysis, and reporting, where the laboratory technicians and testing processes are more specialized. Routine stool testing can identify the presence hookworms but doesn’t typically distinguish between species of hookworms (A. caninum; A. braziliense; U. stenocephala).
With the simple and convenient ClueJay testing solution from home (ClueJay Dog Stool Test Level 1, 2, or 3), you can directly access this same professional reference lab testing for hookworms that veterinary professionals use every day. ClueJay uses reference quality stool preparation techniques and centrifugation, along with a highly trained laboratory team to maximize the likelihood of finding hookworms and their eggs if present in the sample. All three levels of ClueJay dog stool tests search for hookworms.
Finding hookworms or hookworm eggs in your dog’s stool sample likely means your dog is infected with hookworms and should be treated with a deworming medication. A test result is not the same as a veterinarian’s diagnosis. It’s always best to consult with a veterinarian about your dog’s test results to determine the safest and most effective treatment and prevention plan, and when to do follow-up stool tests.
ClueJay dog stool tests report hookworm positive results using a quantitative estimation scale of 1 (1 egg or parasite was seen), 1+ (2 to 4 eggs or parasites were seen), 2+ (5 to 10 eggs or parasites were seen), 3+ (11 to 50 eggs or parasites were seen), or 4+ (>50 eggs or parasites were seen) per (approximately) one gram of stool. This is based on both a naked-eye visual and then a microscopic exam of the stool after special preparation and centrifugation techniques. This scale provides some perspective on the potential burden of worm infection (more eggs likely means more worms in the intestines).
Most veterinarians will recommend rechecking a dog’s stool sample 2-4 weeks after treatment for hookworms. If you have another dog or cat in the household, they should be tested as well since hookworms in one pet may lead to hookworms in another.
If your dog had a stool O&P (fecal ova and parasite) test and hookworms were not seen, that is great news. It may mean that you are doing a good job preventing hookworm infections by regularly deworming your dog or maybe, you and your dog were just lucky! Either way no one wants their dog shedding hookworm eggs into the home or community environment, putting other dogs at risk of infection, your dog at risk of re-infection, or you or your human family at risk of infection. Most veterinarians recommend retesting your adult dog for hookworms every 6 to 12 months.
Keep in mind that it is possible for dogs to have hookworm infections without their eggs being found in the stool test (called a “false negative” result); especially if the infection is mild (very small number of worms) or is recent (hookworms are still too young to shed eggs). Some hookworm larvae will migrate and encyst themselves in the dog’s tissues and go dormant (will not produce eggs during this time). These inactive hookworm larvae can periodically become active and lead to a “surprise” intestinal infection in the adult dog or be triggered awake during pregnancy to be passed to the mother’s pups either in the womb or via her milk. Lastly, depending on their lifestyle, dogs can remain at risk of hookworm exposure so a negative test result today doesn’t mean it couldn’t be positive later. This explains why regularly testing for hookworms (1-2 times per year in adult dogs; 3-4 times for puppies) is most often combined with regular deworming treatments throughout the dog’s life.
- Pets and Parasites, Dog Owners – Hookworms
- American Kennel Club, Understanding Hookworms in Dogs
- Companion Animal Parasite Council, Hookworms
- PetMD, Hookworms in Dogs
- Veterinary Partner, Hookworms in Dogs and Cats
- VCA Hospitals, Hookworm Infection in Dogs
- Encyclopedia Britannica, Hookworm
- Centers for Disease Control and Prevention, Parasites – Zoonotic Hookworm
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