Hookworms

Introduction:

Hookworms are another common parasite found in dogs and cats in the United States. There are 4 species of hookworms: Ancyclostoma caninum, Ancyclostoma tubaeforme, Ancyclostoma brazieliense, and Uncinaria stenocephala.¹

The geographic distribution of A. caninum and A. tubaeforme are found in mostly tropical and subtropical environments while A. braziliense and U. stenocephala are more limited in their distribution. A. braziliense is found in warm coastal areas and U. stenocephala prefer colder climates such as the northern US, Canada, and Europe. Both young and old dogs and cats can harbor hookworms with infection rates higher in pets kept outdoors.

Life Cycle:

Adult hookworms live in the small intestine and shed non-embryonated eggs in the pet feces and into the environment. While in the environment the eggs will embryonate, hatch, and develop into infective third-stage larvae. This development occurs from 2 to 9 days depending on the temperature and humidity. Pets become infected when they ingest the third stage larvae from a contaminated environment, from the larval stage penetrating the skin, or from ingesting another animal’s tissue contaminated with hookworm larvae. Even cockroaches can be infected and infect another animal when it’s eaten. The hookworm species A. caninum can be transmitted through the mammary tissue from the mother to the pups while they are nursing. In dogs over 3 months of age, the larvae may become dormant in the tissues of the body including the small intestine. This dormancy occurs after the larvae migrate through the lungs and is known as arrested development. The dormant larvae are activated to complete their maturation process after removal of adult worms (such as after a deworming is dosed), or during times of stress such as pregnancy where the larvae accumulate in the mammary glands ready to be secreted to the pups when nursing. The hookworm species A. tubeaeforme is not transmitted through nursing but are acquired through environmental contamination after birth. They mature similarly to roundworms. They are transported to the lungs by the bloodstream, migrate to the trachea, are coughed up, swallowed, and make their way to the intestine where they mature, mate, and produce eggs. When infected larvae are ingested, some may penetrate the oral cavity or the gastrointestinal tract lining and migrate as described while others mature in the small intestine. Larvae that are indirectly ingested through predation travel to the small intestine and mature into adult worms. Immature and mature hookworms attach to the wall of the small intestine by a large mouth cavity, digest the tissue, inject anticoagulants so the blood will not clot, and take a bloodmeal. They can detach and reattach at new sites along the wall. Small bleeding ulcers form where the worms were previously attached. Adult worms may live 4 months to 2 years in the small intestine.  The prepatent period, or the time from infection to detection of the hookworm, is approximately 15 to 18 days. If arrested development occurs, the prepatent period may be prolonged.

Disease State:

Since all hookworms feed on blood from attaching to the intestinal tract wall, infected puppies and kittens may present with pale mucus membranes and anemia, ill thrift, failure to grow, poor hair coat, dehydration, and dark tarry diarrhea known as melena. The hookworm species A. caninum are voracious bloodsuckers and can lead to life-threatening anemia in a puppy. Animals with high worm burdens may die from infection or have chronic anemia or low red blood cell counts if they survive. Animals that are well-nourished and have a strong immune system may show few to no signs of disease. Anemia, anorexia, emaciation, and weakness along with bloody diarrhea or dark tarry stool are clinical signs that can be seen in adult dogs who have high hookworm burden. The hookworm species A. tubaeforme is a voracious bloodsucker in kittens causing anemia, diarrhea and weight loss or even death if a large number of worms present.¹ Respiratory disease may occur in puppies and kittens due to migration of large number of hookworms through the lungs or due to secondary anemia. The hookworm species U. stenocephala and A. braziliense are less pathogenic than the other species.¹ Larval hookworms penetrating the pet’s skin on the feet may cause signs of skin infection such as erythema (redness), pruritus (itching) and papules between the paw pads. The hookworms A. caninum and A. braziliense are typically involved with dermatitis.¹

Diagnostics:

Like roundworms, fecal flotation with centrifugation is recommended if a stool sample is available. It is possible for nursing puppies and kittens infected with A. caninum and A. tubaeforme to die from acute anemia because of a large worm burden before eggs are passed in the feces. Hookworm eggs float easily and mixed infections can occur. A female hookworm produces about 20,000 eggs per day. Commercial ELISA test detects an antigen or special protein produced by all species of immature and adult hookworms present in the small intestine.² Similar to roundworm infections, combined microscopic examination of feces for ova and fecal test for antigen ensure the most accurate and broadest detection possible. Adult hookworms may be visually identified in the stool sample.

Treatment:

Similar to roundworms, there are several products available to treat hookworm infections in both dogs and cats. Severely affected dogs or cats may require additional treatment with supportive care and blood transfusions depending on their condition. Many heartworm preventatives are labeled for the effective elimination and/or control of one or more species of hookworms in dogs and cats. 

Similar to roundworms, preserving the environment is important. Prompt removal of stool, leash walking or keeping in a fenced yard to prevent scavenging tendencies, and administering monthly deworming are all ways in which to control and prevent hookworm infections. Treating the pet and cleaning the environment to prevent infection is crucial because the eggs are very hardy and live for years in the environment. Extreme measures such as paving an area, removal of 3-4 feet of topsoil, controlled burning of the area, or treating with steam have shown to effectively remove or destroy hookworm eggs or larvae.

Public Health:

Hookworms can pose a health risk to humans. The Ancyclostoma spp are documented zoonotic disease agents which means they  can infect animals as well as humans. Hookworms are the most common cause of cutaneous larva migrans in people. Cutaneous larva migrans occurs when the larvae migrates into the skin producing pruritic serpentine-like lesions. Infections tend to be self-limiting. The hookworm species A. braziliense penetrates the skin more extensively than the other species of hookworms. The hookworm A. caninum tends to penetrate the skin deeper causing visceral larva migrans. Visceral larva migrans occurs when the larvae migrates through the intestinal wall, into the bloodstream, and infects other organs within the body. Children and adults who come in contact with contaminated soil are most at risk of cutaneous larval migrans and other hookworm associated symptoms. Wearing shoes, gloves when gardening, covering sandboxes, and/or covering contaminated soil in areas of work with plastic liner are recommendations to prevent infections.

The CAPC website and the website Pets and Parasites by CAPC are reliable resources for additional information regarding hookworms and your dog. 

1. CAPC guidelines: hookworms. Companion Animal Parasite Council.