There is a parasite lurking in our area that the public should be aware of, and that all dog owners can help to control. That parasite is called hookworm. Hookworm is found throughout the world, however, in Minnesota, we see two different species: Ancylostoma caninum and Uncinaria stenocephala which are both carried by dogs.
Hookworm disease is a terrible disease for both dogs and humans. It is zoonotic, meaning that it can be spread from dogs to humans (although indirectly as will be explained later).
Early in the disease, dogs may have no symptoms, but they can be spreading hookworm eggs in the stool and contaminating the environment. Later in the disease, patients will develop diarrhea and weight loss. Hookworms are voracious blood suckers. They attach to the intestinal lining and release an anti-coagulant to stimulating bleeding. Hookworm disease can cause anemia, and puppies that are exposed to hookworm as neonates can become so anemic that they die. Humans that are exposed to dog hookworm typically develop a skin rash. The migrating larvae leave red, itchy tracks under the surface of the skin.
Hookworms are spread through a variety of sources. Puppies can get hookworm from their mother’s milk and animals like cockroaches can also transmit the disease. The primary way hookworm is transmitted, however, is through the stool. Dogs with adult hookworms in their GI tract will pass hookworm eggs in the stool. One hookworm can produce 600-6,000 eggs per day. Usually patients have many adult worms in their body when they are infected so they are passing tens of thousands of eggs through the stool every day. These eggs take 2-9 days to become infective larvae. An animal or human that comes into contact with the eggs won’t develop a hookworm infection. But, if that stool stays in the environment for more than several days, the eggs will hatch into infective larvae. Often times, the stool has mixed with soil by this time, and you can’t tell that the area is contaminated.
It’s these infective larvae that enter the body causing disease. In dogs, the larvae will grow into adult worms in the GI tract within 2 weeks of exposure. Very quickly the infected dog can start contaminating the environment and spread the infection to others. In humans, the most common route of entry into the body is through the skin. Contaminated soil needs to only be in contact with skin for 5-10 minutes for the larvae to penetrate the skin.
In Hennepin County, the Companion Animal Parasite Council (CAPC) reports a hookworm incident rate of 2%. At our clinic in Southwest Minneapolis, we are seeing an incident rate closer to 3%. Three in every 100 fecal samples examined are positive for hookworm.
It takes a community effort to help control the spread of hookworm. You can do your part to control this disease by following these tips:
Pick up your dog's stool and throw it away as soon as it is produced. Fresh stool is not immediately infective. It takes 2-9 days for the eggs to hatch into infective larvae. These larvae live for several months in the environment.
Keep your dog on a monthly parasite preventative, even in the winter. The monthly heartworm preventative you give your dog likely covers hookworm, but it would be prudent to double check with your vet. At our clinic, we recommend Heartgard brand heartworm preventative as it is effective against the two types of hookworm seen in Minnesota. The hookworm species Uncinaria is considered a “cold weather hookworm” meaning that the eggs and larvae can survive freezing temperatures. Because of that, it is important to continue giving the pills year round.
Keep your dog on a leash to control him eating soil which might be contaminated with hookworm larvae.
For humans, wear gloves when gardening, and shoes when walking outside. It doesn’t take long for microscopic hookworm larvae to penetrate the skin and cause disease.
Wash all fresh fruits and vegetables. Hookworm can also enter people through accidental ingestion of contaminated soil.
Have your veterinarian screen your dog's stool on a regular basis for parasite eggs, even if he is not showing diarrhea or illness. Early in the disease, dogs are usually asymptomatic and during that time (sometimes months), they can be spreading disease and contaminating their environment. The Companion Animal Parasite Council recommends that all adult dogs have a routine fecal exam for parasites twice a year.
If your dog develops a hookworm infection, it is important to know that hookworm can sometimes be difficult to manage. Dogs that have an infection have often contaminated their environment. The hookworm larvae can live for months in the soil, so the patient can easily get reinfected. Also, Some hookworm larvae will move out of the intestinal tract and turn into cysts in the muscle. These cysts are resistant to any type of deworming medication. The cysts stay dormant until they get the signal to hatch. The signal for these cysts to hatch is when the GI tract is finally clear of adult hookworms. What this means, is that we can kill all of the adult worms in a dog’s GI tract and think that we have cleared an infection. For patients with hookworm cysts, however, this “empty gut” is the signal to hatch and repopulate the gut. This phenomenon is known as “larval leak” and is very difficult to control.
All veterinarians take an oath upon graduation of veterinary school to not only serve animals, but to help protect public health. Hookworms are a serious public health concern, and we need everyone’s help to try to reduce the incidence of hookworm disease in our area.
For more information on hookworm disease, the Companion Animal Parasite Council and the Center for Disease Control websites are good resources.