Hookworms are small, thin worms that are less than an inch long. The appearance of the mouthparts vary by species, but all hookworms have structures (hook-like teeth or plates) to help them attach to the intestinal wall.
Unlike roundworms, which just float around and steal nutrients from the dog's meals, hookworms attach to the intestinal wall and feed on blood and/or tissues. They can detach and move to other spots, leaving little ulcers where they have fed previously.
The severity of symptoms varies between the hookworm species and most infections are not life-threatening, but one species of hookworm, Ancylostoma caninum can cause fatal blood loss in puppies.
The Hookworm Life Cycle
Hookworm eggs are passed in the feces, and under warm, moist conditions hatch into larvae after several days. These larvae have several ways they can infect dogs:
- They can be ingested directly, as when dogs lick the ground or groom themselves when larvae are present on their fur.
- They can migrate through the skin, usually through the belly or paws.
- They can be ingested by another animal such as a rodent, and then ingested by a dog that eats that infected animal.
- Puppies can also be infected by larvae present in the mom's milk.
Once the hookworm larvae get into a dog, they may develop into adults in the intestines or migrate through the tissues to the lungs, from where they are coughed up and swallowed, and then finally develop into adults in the intestines. In older dogs, migrating hookworm larvae commonly enter a dormant state within in body tissues and can become mobile again later.
The larvae commonly become mobilized during pregnancy, where they can either go to the mammary glands (for some kinds of hookworms) or develop into adults in the mom's intestines, producing eggs which act as a source of infection of puppies -- explaining why hookworm infections are so common for them.
Signs and Symptoms of Hookworms
Hookworms can produce any of the following symptoms -- though symptoms may only appear with heavy infections:
- Failure to gain weight or weight loss
- Loss of appetite
- Anemia (pale gums, weakness) sometimes seen and can be a cause of death in puppies
- Bloody or tarry stools may be present
- Sometimes coughing can occur due to the larval migration through the lungs (with very heavy infections)
- Skin irritation, most often on the feet between the toes, due to migrating larvae
The severity of the disease depends on the species of hookworm involved, as well as the number of worms and the age and health of the infected dog.
Diagnosis of Hookworms
The eggs of hookworms can be detected under the microscope in a routine check of a stool sample (the test process is called fecal flotation). It takes a while for infected puppies to shed eggs, so routine deworming of puppies is recommended.
Treatment is the same, regardless of the species. There are a number of medications that can be used to treat hookworms, and your vet can help you pick the one right for your dog. Medications will only affect hookworms in the intestines, not migrating larvae. Treatment should be repeated to deal with larvae as they mature (e.g. at 2-week intervals). The number of treatments necessary will depend on the age of the dog and the situation and will be recommended by your vet.
If you have a pregnant dog, consult your vet for a deworming protocol for both the mom and pups. Once dewormed, many of the monthly medications designed for parasite control contain medication that will prevent hookworm infections on an ongoing basis—options that can be discussed with your vet.
If your dog is not on one of these preventatives, your vet will recommend a regular deworming protocol to keep hookworms at bay. Keeping pet wastes picked up, and preventing pets from eating rodents can also help prevent infection with worms.
People and Dog Hookworms
The larvae of hookworms can infect people as well as dogs, which happens when eggs are ingested. The larvae usually don't develop into adult hookworms in people, but the larvae migrating through the skin can cause irritation and inflammation, though most cases are not serious.
Migration of hookworm larvae through human skin is called "cutaneous larva migrans." Recently, there have been a few cases reported where one kind of hookworm took up residence in the intestines of humans, as well.
Proper treatment and prevention of hookworm infections are important to prevent these human health concerns, as is good hygiene. Keeping pet waste picked up, especially in areas where children or other people contact the ground (e.g. sandboxes) is also helpful in preventing human cases.
Please note: this article has been provided for informational purposes only. If your pet is showing any signs of illness, please consult a veterinarian as quickly as possible.