Hookworm Infection in Dogs

What are hookworms?

Hookworms (Ancylostoma caninum, Ancylostoma braziliense, Uncinaria stenocephala) are intestinal parasites found in cats and dogs. They get their name from the hook-like mouthparts they use to anchor themselves to the lining of the intestinal wall. They are only about 1/4" to 3/4" (1-1.9 cm) long and so small that it is very difficult to see them with the naked eye. 

Despite their small size, hookworms ingest large amounts of blood from the tiny vessels in the intestinal wall. A significant number of hookworms can cause inflammation in the dog’s intestine, and a life-threatening decrease in red blood cells (anemia). Anemia is most common in puppies but can occur in adult dogs.

Hookworms are more common in warm, moist environments. Conditions of overcrowding and poor sanitation contribute to infection.

How do dogs get hookworms?

Dogs may become infected with hookworms via one or all the following routes:

• Oral ingestion of larvae 
• Oral ingestion of an animal with infective larvae in their tissues (e.g., a cockroach)
• Skin penetration
• Through the mother's milk

A dog may become infected when it inadvertently swallows hookworm larvae, often by grooming its feet, sniffing feces, or sniffing contaminated soil. Dogs can also become infected if they eat other larval hosts, such as cockroaches. The larvae may also burrow into the dog’s skin if it walks or lies on contaminated ground.

Most hookworm larvae that a dog swallows move to the intestines, where they mature into adult worms. The larvae that enter through the skin migrate through the body to the lungs. From there, they are coughed up and swallowed, gradually moving to the intestinal tract, where they mature into adults.

In the intestines, female hookworms lay hundreds of microscopic eggs that leave the dog with their feces and contaminate the environment. Larvae hatch from the eggs and can remain infective in the soil for weeks to months.

Some larvae don’t complete the normal life cycle right away. Instead, they migrate into tissues like muscles or the intestinal lining and go dormant (this means they’re still alive, but not active). They can become re-activated if adult worms in the small intestine are removed through deworming or during pregnancy. Larvae in pregnant dogs move into mammary glands, resulting in milk that infects puppies when they nurse — a common way that puppies become infected.

What are the clinical signs of hookworm infection in dogs?

The most significant clinical signs are related to intestinal distress and anemia. The parasites anchor themselves to the intestinal lining so that they can feed on tissue fluids and blood while injecting an anticoagulant substance that prevents the blood from clotting. This can cause continued bleeding after the hookworm has detached from the feeding site. Therefore, the dog can suffer blood loss from the hookworms' feeding, as well as continued bleeding into the bowel from the attachment sites. Pale gums and weakness are common signs of anemia.

"The most significant clinical signs are related to intestinal distress and anemia."

Some dogs experience significant weight loss, bloody diarrhea, and a dull and dry coat. Puppies may fail to grow properly. It is not uncommon for young puppies to die from severe hookworm infections. In a heavily infested environment, dogs may have skin irritation and itching, especially of the paws, caused by larvae burrowing into and along the skin. Dogs may also exhibit coughing, in severe cases.

How is hookworm infection diagnosed?

Hookworm infection is diagnosed using a technique called fecal flotation. The stool is mixed with a solution that causes the parasite eggs to float to the top and adhere to a glass slide placed on the surface. Hookworm infections are easily detected because they produce many eggs daily and the eggs have a unique appearance. It takes two to three weeks for hookworm larvae to mature and begin producing eggs. For this reason, a fecal examination may be less reliable in young puppies than in adult dogs. Adult hookworms are rarely spotted in the stool, because they are small and firmly attached to the intestinal wall.

How is a hookworm infection treated?

There are several effective drugs, called anthelmintics, that will eliminate hookworms. Most are given orally and have few, if any, side effects. However, these drugs only kill adult hookworms, so it is necessary to treat an infected dog again in two to three weeks to kill any new adult worms that were larvae at the time of the first treatment.

With appropriate diagnosis and treatment, the prognosis is good for full recovery from hookworm infection. In rare cases, a blood transfusion may be necessary for dogs with severe anemia. These patients have a poorer prognosis and extensive treatments are usually necessary.

Are hookworms infectious to people?

Adult hookworms do not infect humans internally; however, the larvae can burrow into human skin (usually through bare feet). This causes itching, commonly called “ground itch”, but the worms do not mature into adults and will die within several weeks.

More dangerous is the condition in which hookworm larvae migrate throughout the human body, damaging the eyes and internal organs. This is called visceral larval migrans. To contract this condition, human skin must have contact with moist, larvae-infected soil, so infection is extremely rare if normal hygiene practices are observed.

Can a hookworm infection be prevented?

Prevention of hookworm infection should include the following measures:

• All puppies should be treated with a veterinary-approved anthelmintic product at two to three weeks of age. In addition, prompt deworming should be given if the parasites are detected. Periodic deworming may be appropriate for pets at high risk of infection.
• Ensure prompt disposal of dog feces, especially in yards, playgrounds, and public parks.
• Strict hygiene is important, especially for children. Do not allow children to play in potentially contaminated environments. Frequent handwashing and bathing are essential in preventing human infections.
• Nursing female dogs should be dewormed at the same time as their puppies are. Pregnancy and nursing may reactivate a dormant hookworm infection in the female dog, which will then infect her puppies.
• Most heartworm prevention products contain medication to treat hookworm infections. Some of these products kill the adults, while others will also kill larval stages and prevent infestations. Your veterinarian can advise you on the best product for your dog.