Hookworms are intestinal parasites that are common in dogs, and while most infections are not life-threatening, they can cause fatal blood loss in puppies. There are several hookworm species that affect dogs, the most common of which in North America is Ancylostoma caninum. Hookworm larvae can also affect humans by migrating through the skin.
Hookworms are small, thin worms that are less than an inch long. The appearance of the mouthparts varies by species, but all hookworms have hook-like teeth or plates. These structures 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 bleeding ulcers where they have previously fed.
The severity of symptoms varies but anemia due to blood loss can be debilitating to adults and fatal to puppies.
Hookworm eggs are passed in the feces. After several days and under warm, moist conditions these hatch into larvae. 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 be ingested by a dog that eats the infected animal.
- Puppies can also be infected by larvae present in their mother's milk.
Once the hookworm larvae get into a dog, they may develop into adult worms while living in the intestines. They may also migrate through the tissues to the dog's lungs 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 body tissues and can become mobile again later.
The larvae commonly become active during pregnancy, which is why they're so commonly passed on to puppies. Some kinds of hookworm larvae can go to the mammary glands. Others develop into adults in the mother's intestines, producing eggs, which act as a source of infection for puppies.
Hookworms can produce any of the following symptoms, though they may only appear with heavy infections:
- Failure to gain weight or weight loss
- Loss of appetite
- Anemia (pale gums, weakness), which is life-threatening for puppies
- Bloody or tarry stools
- Coughing, due to the larval migration through the lungs (with very heavy infections)
- Skin irritation, most often on the feet between the toes, due to burrowing larvae
The symptoms vary depending on the species of hookworm involved, as well as the number of worms and the age and health of the infected dog.
The eggs of hookworms can be detected under the microscope in a routine check of a stool sample. It takes a while for infected puppies to shed eggs, so routine deworming of puppies is recommended, even if no signs of hookworms are yet visible.
Treatment is the same, regardless of the hookworm species. There are a number of medications that can be used and your vet can help you pick the right one 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. For instance, the vet may recommend treating at two-week intervals. The number of treatments necessary will depend on the age of the dog and its particular situation.
If you have a pregnant dog, consult your vet for a deworming protocol for both the mother and pups.
Once dewormed, many of the monthly medications designed for heartworm and other parasite control contain medication that will prevent hookworm infections on an ongoing basis.
If your dog is not on one of these preventatives, your vet will recommend regular fecal testing and/or a 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 Hookworms
The larvae of hookworms can infect people as well as dogs. The larvae usually don't develop into adult hookworms in people. However, 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." People become infected when their skin comes in contact with contaminated soil or sand.
Proper treatment and prevention of hookworm infections are important to prevent these human health concerns, as is good hygiene. The same protocols that can prevent hookworms from spreading from dog-to-dog, namely cleaning up waste and the appropriate use of dewormers, can prevent humans from becoming infected too.