What are hookworms?
Hookworms are parasites named for the hook-like mouth parts they use to attach to the intestinal wall. They are only about 1/8-inch long and so small in diameter that they are almost invisible to the naked eye. Despite their small size, they suck large amounts of blood from tiny vessels in the intestinal wall.
A large number of hookworms can cause anemia. This problem is most common in puppies, but it will occasionally occur in adult dogs.
How did my dog get hookworms?
Dogs may become infected with hookworms via different routes: through the mouth, through the skin, or through the mother's milk with nursing puppies.
A dog may become infected when he/she swallows hookworm larvae, or immature worms. The larvae may also penetrate the skin and migrate to the intestine to mature and complete the life cycle. If a pregnant dog has hookworms, the pregnancy may reactivate larvae. These larvae will enter the female's circulation and pass to the puppies through the mother's milk. This is considered to be an important route of infection for young dogs.
What kinds of problems do hookworms cause for my dog?
The most significant problems appear related to intestinal distress and anemia.
Blood loss results from the parasites sucking blood from intestinal capillaries. The presence of pale gums, diarrhea or weakness might suggest the need to specifically determine the dog's red blood cell count.
Some dogs experience significant weight loss, bloody diarrhea or failure to grow properly with hookworm infection.
Skin irritation and itching may also indicate a heavily infested environment. The larvae burrow into the skin and cause the dog a great deal of itching and discomfort.
How is hookworm infection diagnosed?
Hookworms are diagnosed with a microscopic examination of a small stool sample. Since there are so many eggs produced on a daily basis, they are rather easily detected. There are also sensitive PCR tests that detect the hookworm DNA. 
One adult female hookworm is reported to produce thousands of eggs a day, and therefore can lead to heavy environmental contamination in soil or dirt.
How are the hookworms treated?
There are several effective drugs that will kill hookworms. These can be given topically or orally and have few, if any, side effects. However, it is important to note that these drugs only kill the adult hookworms. Therefore, it is necessary to treat again in about two to four weeks to kill any newly-formed adult worms that were larvae at the time of the first treatment. Regular preventatives used monthly can help protect against hookworm infections.
Hospitalization or a blood transfusion may be necessary for dogs that experience anemia.
Are canine hookworms infectious to people?
Adult hookworms do not infect humans; however, the larvae can burrow into human skin. This causes itching commonly known as ground itch, but the worms do not mature into adults. Direct contact of human skin to moist, hookworm-infested soil is required. Fortunately, this does not occur very often if proper hygiene practices are observed. Humans do have separate species that can infect them though with true intestinal infections.
In rare instances, the hookworms will penetrate into deeper tissues and partially mature in the human intestine. A few reports of hookworm enterocolitis (small and large intestinal inflammation) have occurred.
What can be done to control hookworm infection in dogs and to prevent human infection?
  • All pups should be treated at two to three weeks of age.
  • Prompt deworming should be given when parasites are detected; periodic deworming may be appropriate for pets at high risk for reinfection.
  • Prompt disposal of dog feces should occur, especially in yards, playgrounds and public parks.
  • Strict hygiene is important, especially for children. Do not allow children to play in potentially contaminated environments like sandboxes or soil/gardens.
  • Nursing females should be treated concurrently with their pups to avoid reactivating infection.
  • Most heartworm prevention products contain a drug that will stave off hookworm infections and can kill the adult and some larval stages depending on the product.
See Feline Hookworm Infection