One of the most common intestinal parasites that can infect dogs and cats, hookworms can cause severe side effects, and even death if left untreated. Hookworms are named for their hook-like mouths, which they use to “bite” into the intestinal wall of affected hosts. Hookworms can affect both dogs and cats and are of particular concern as a zoonotic parasite — a parasite that is contagious to humans.
There are several common varieties of hookworms found in North America. The A. caninum (canine hookworm) can infect dogs, foxes, and humans. The A. braziliense (canine and feline hookworm) affects dogs, cats, foxes, and humans. The U. stenocephala (northern canine hookworm) affects dogs, cats, and foxes, while the A. tubaeforme (feline hookworm) infects cats only.
Hookworms are opportunistic parasites. Unlike many parasites that must be ingested to infect an animal, hookworms can be acquired through ingestion, but also via larvae penetrating the skin, and through the uterus and milk of affected mothers to their offspring.
The Life Cycle of Hookworms
The life cycle of a hookworm depends on how the larvae enter the host.
Hookworm larvae that are absorbed into the skin enter the bloodstream, where they travel to the lungs and trachea. The irritation caused by the worms leads the animal to cough them up into the mouth, and then swallow them back into the intestinal tract. There, the larvae attach themselves to the intestinal wall, where they mature, mate, and produce eggs.
Infected dogs can shed hookworm larvae through shared water sources, soil, and other means of direct contact. A dog that comes into contact with a contaminated substance or item swallows the larvae directly into their intestinal tract, where the parasites attach themselves to the intestinal wall to mature and reproduce.
While most larvae that infect an animal travel to the intestinal tract, a small percentage of the parasites migrate to the muscles, fat, and other tissues in the body, where they encyst and lie dormant. When an animal becomes pregnant, the hookworms are attracted to the uterus and infect the fetuses before they are even born. Additionally, hookworms will often migrate to the newly active mammary glands of a pregnant or lactating dog, and nursing puppies will then ingest the larvae orally to begin the cycle.
Once hookworms enter the intestinal tract of an infected animal, they “bite” into and attach to the intestinal wall, surviving by feeding on the blood supply to the intestines. They lay eggs that disperse among the feces in the intestines, and 2-10 days later, the eggs hatch, releasing new larvae. Some larvae remain in the host animal to mature and reproduce, while others are carried out of the body via the stool and can infect new hosts via contamination.
Hookworms produce an anticoagulant in their saliva, which affects the clotting ability of the host animal’s blood. As a hookworm attaches itself to the intestine and moves from one site to another, the blood at the initial site is unable to clot and continues to bleed.
Because hookworms can infect puppies and kittens before they are even born, animals can become infested with large quantities of parasites at a very young age. This is of special importance, as the continued blood loss due to the parasites, as well as intestinal bleeding, can lead to severe blood loss and anemia — serious and potentially fatal conditions.
Symptoms and Diagnosis of Hookworm Infection
Hookworms in any animal can cause severe symptoms, though puppies and kittens are usually the most seriously affected. Hookworms can rapidly cause anemia by feeding on the blood of their hosts. Pale mucous membranes (gums) can be an indication of anemia, and animals may appear weak or show a poor appetite. The blood loss into the intestines may cause the animal to have black, tarry stools, as well as vomiting and diarrhea. If allowed to continue untreated, growth in young animals can be stunted, and their coat may look dull and dry due to their inability to properly absorb nutrients into their damaged gut. Death, especially in young animals, can result from severe hookworm infestation.
Diagnosis of hookworms is typically made by finding the larvae in the feces. Adult hookworms are usually less than ¼ inch long and are rarely found in feces. Therefore, simply examining a fecal sample visually is not an accurate way to detect a hookworm infection. A fecal flotation examined under the microscope is generally very accurate for detecting hookworms, as the eggs are constantly being expelled in the feces.
Unfortunately, in some very young animals, hookworms may be present before detection is possible in the feces. Many breeders and shelters routinely deworm for hookworms as early as 2 weeks of age to ensure that if the parasite is present, it is eradicated. However, because of their tenacious nature, it is important to have young animals checked for hookworms (as well as other intestinal parasites) again at 8-12 weeks to ensure further treatment is not required.
In young animals showing clinical signs of hookworms, more intensive care must be taken to both eradicate the worms and correct the damage they have caused. Severely anemic puppies and kittens may require a blood transfusion to boost their red blood cell count to normal levels. IV fluids, as well as medications, may be required to correct the effects of and prevent further episodes of vomiting and diarrhea. When the animal is more stable, deworming may then be performed under medical supervision to ensure a reaction does not occur when large numbers of parasites suddenly die off.
Once your dog or cat has been treated for hookworms, it is imperative that the environment they live in is treated as well. Hookworm larvae can live for several weeks in cool, moist soil, but are easily susceptible to freezing cold or very high temperatures. Use a 1% bleach solution on all floors, as well as in the laundry to wash all of the animal’s bedding. Feces in the yard should be picked up daily to avoid re-infestation.
Hookworms are a zoonotic parasite, meaning they can be transmitted from animals to humans. Use common sense, such as washing your hands after playing with your pet and before eating, as well as not walking barefoot in soil where the animal may defecate, to help reduce the risk of infection. While dog and cat hookworms do not migrate to the intestinal tract of humans, the larvae can burrow into human skin, causing itching and pustules.
