Hookworms are one of the most common intestinal parasites among dogs and cats. They are very thin worms that are only about one-quarter to one-half inch in size. Even with treatment the parasites can cause severe diarrhea and anemia within the animal and if left untreated, the animal could sadly die. While they’re found throughout North America, different types of the species live in different areas, depending on the climate. These parasites can be transmitted to humans, usually without any real consequence. Hookworms in dogs however, can be very serious and can make your pet quite sick.

Types of Hookworms

There are four main types of hookworms:

• Canine hookworm – infects dogs, foxes, and possibly humans through the intestine
• Canine and feline hookworm – infects dogs, cats, foxes, and humans through the skin
• Northern canine hookworm – infects dogs, cats, foxes
• Feline hookworm – infects cats

Canine and feline hookworm can be found primarily in semitropical and tropical climates while Northern canine hookworm, as the name implies, prefer colder areas in the north.

What Causes Hookworms in Dogs?

Hookworms can infect an animal when they enter a host, either through ingestion or by burrowing through the skin. Once living in the host animal, they use their teeth, or hooks, to attach themselves onto the host’s intestine and suck blood and tissue fluids from the host. In addition to being painful and uncomfortable, this can also lead to severe blood loss and malnutrition. These adult parasites will lay eggs which will largely be passed out through the feces. Once the eggs hatch, the larvae will swim through dew and vegetation, looking for a host.

There are three ways that they can end up finding one:

• Through the skin. When hookworms enter a dog’s system through the skin, they simply dig into it until they reach the bloodstream. Once there they’ll travel to the lungs and trachea, where they are then coughed up and swallowed by the dog. Once swallowed the larvae will travel through the digestion tract and into the intestine, which is where they will attach themselves to the wall of the intestine and continue the cycle of laying eggs that produce larvae.
• Through ingestion. There are a number of ways a dog can ingest hookworm larvae, causing them to become infected. Contaminated food or water, moist surfaces, and even eating infected hosts or their feces, are all just some of the ways hookworm larvae can be ingested by your pet. After being ingested most of the larvae will make their way to the intestine where they’ll grow into adults but some will be coughed up and swallowed. Some larvae might stop halfway and encyst in muscles, fat, and other tissues.
• Through the milk, or in utero. If a pregnant female is infected with the parasite, she can pass it on to her unborn litter. Dormant larvae in a pregnant female can also travel to her unborn, even though she never displayed any signs of being sick. Hookworm larvae will also travel to the mammary glands of a lactating female, where they will then be ingested by the nursing puppies. This is one of the most serious cases of hookworms, with infestation in puppies occurring during the first two months of the pup’s life. Puppies can become very sick very quickly and can even tragically die.

Hookworms can also infect humans by burrowing through a person’s skin, typically through the bare feet and travel through it. This can cause lesions to appear, which will sometimes break open when they reach the surface of the skin. Human infection is not serious and the larvae will typically die within two weeks and the infection will clear up. This doesn’t mean that humans won’t suffer any consequence from hookworms however, as they can cause lung disease and aching muscles.

With canine hookworms in particular, humans can suffer from intestinal infections.

Symptoms of Hookworms in Dogs

All hookworms can cause disease but with canine hookworm, that illness can be even more severe. Because hookworms feed off the blood and tissue fluid of the host, dogs can become anemic, malnourished, and dehydrated. All of these can have severe consequences, especially if the hookworms are left untreated for too long.

There are symptoms dog owners can watch for to catch the infection as early as possible. These include:

• Pale gums
• Weakness
• Stools that have a black tarry appearance, or have blood in it
• Vomiting
• Diarrhea
• Stunted growth in young dogs
• Dull and/or dry coat
• Pneumonia, in severe infestations
• Abnormally thin, emaciated

Symptoms will usually appear within 2 to 10 days of exposure, although dogs with chronic hookworms often don’t show any symptoms at all.

Diagnosing Hookworms

The only way a vet can confirm the presence of hookworms is to find the eggs in the feces. The eggs aren’t present in the feces for two or three weeks so it’s common for a sick dog to have a negative stool exam if enough time hasn’t yet passed. For this reason, vets will often recommend that the dog have another stool exam in a week or two. If the dog is very sick and still has a negative stool sample returned, the vet will often make a diagnosis based on observation, looking for clinical signs.

Because puppies can become so sick so rapidly from the infection, vets will often make a diagnosis with no stool exam, or a negative stool exam, to keep the puppy from becoming too sick.

Preventing Hookworms in Dogs

Although hookworms don’t always cause dogs to become extremely sick, prevention is still important to keep your dog as healthy as possible and keep other animals from becoming ill. Here are a few things that can be done:

• Clean yards and kennels daily
• Clean up and dispose of fecal matter immediately
• Keep mice and other rodents under control, as these animals can be transport hosts
• Keep infected animals quarantined from other animals, to decrease the possibility of transmission
• Practice good hygiene to stop transmission to humans, and teach children the importance of proper hand-washing
• Do not allow children to play in areas where animals have defecated
• Do not allow cats or dogs to use sandboxes or the garden to relieve themselves
• If working on the ground for long periods of time, such as when gardening or working in crawl space, place an impervious material between you and the ground.
• Do not walk barefoot on lawns, beaches, or anywhere else animals may have been.

Hookworms in dogs is very common, but it’s an infection that can become very serious, especially in young puppies. It’s important that all dogs are being treated throughout the year, both with medication and through fecal exams, to ensure that your dog is not sick. It’s also important to practice good prevention at all times, to keep your dog from getting sick in the first place.