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-life mouths that are used 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 common to 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, and the a tubaeforme (feline hookworm) infects cats only.
Hookworms are opportunistic parasites, in that unlike many parasites that must be ingested to infect an animal, hookworms can be acquired in that way, but also via larvae penetrating the skin, and through the uterus and milk of affected mothers to their offspring.
The life cycle of the hookworm depends on the way the larvae enter a 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 causes 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 via 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 can 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. In addition, hookworms will often migrate to the newly active mammary glands of a pregnant or lactating dogs, 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 and new larvae are released. Some larvae remain in the host animal to mature and reproduce as well, 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, affecting the clotting ability of the host animals’ blood. As a hookworm attaches itself to the intestine, then moves from that site to attach to another location, the blood in the first 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 loss of blood to the parasites as well as intestinal bleeding can lead to severe cases of blood loss and anemia, serious and potentially fatal conditions.
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 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 be a result of severe hookworm infestation.
Diagnosis of hookworms is typically made by finding the larvae in the feces. Adult hookworms are typically less than ¼ 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 he or she lives in is treated also. Hookworm larvae can live 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 animals bedding. Feces in the yard should be picked up daily, to avoid allowing an animal to be re-infested.
Hookworms are a zoonotic parasite, meaning they can be transmitted from animals to humans. Use of common sense, such as washing hands after playing with their pet and before eating, as well as not walking barefoot in soil where the animal may defecate can help to reduce risk of infection. While dog and cat hookworms do not migrate to the intestinal tract of humans, the larvae can burrow into the human skin, causing itching and pustules on the skin.