Hookworms in the Dog

Is your puppy anemic? Does he appear to be losing weight, and is the hair coat dull and thinning? Have you noticed that your dog’s bowel movements are dark and tarry? Then your pet may be suffering from a hookworm infection.

Hookworms are small thread-like worms that suck blood from the small intestinal tract of infected pets. The most common types of hookworms infecting dogs include Ancylostoma caninum, Ancylostoma braziliense, and Uncinaria stenocephala.

Puppies and nursing female dogs are at the highest risk for the development of a hookworm infection. As a dog becomes older it is typically more resistant to infection by hookworms. Other factors determining the severity of an infection include the virulence of the hookworm species, the ability of the dog to compensate for the blood loss caused by the hookworms, the animal's hematopoietic capacity (the ability of the infected pet to manufacture blood), the body condition of the individual at the time of infection, and the presence or absence of any other stress on the dog.

Adult worms reside in the small intestinal tract of infected individuals, passing their oval-shaped eggs out in the stool. Infection occurs through the ingestion of the 3rd-stage larvae from a contaminated environment; the penetration of the skin by the infective larvae; consumption of vertebrates with infective larvae in their tissues; or through the milk of an infected mother dog to her puppies (transmammary infection). An infected mother dog may transmit hookworm larvae in her milk for up to the next three lactations following infection.

Latent infections occur when the hookworm larvae arrest their development within the intestinal wall and skeletal muscle tissue of adult dogs serving as a reservoir for later infection. This is believed to be especially common in mammary gland milk transfer of larvae to nursing puppies. In other latent infections the larvae may migrate directly to the intestinal lumen or by way of the lungs to the intestinal tract.

Hookworm infections may appear quite diverse clinically. A hookworm infection can range from inapparent to so severe, in peracute infections, that they result in severe anemia and even death. Peracute infections are more commonly seen in young puppies through transmammary infection. These puppies may appear healthy and sleek at birth, but by the second week of life rapidly become anemic and deteriorate rapidly. The feces will be liquid and dark in appearance due to the presence of digested blood. Eggs may not be apparent in a fecal analyses and therefore diagnosis must be made on the basis of clinical signs alone. The prognosis in these cases may be guarded to poor regardless of the treatment used.

Sudden exposure to large numbers of infective larvae may result in an acute infection. Fecal analysis may show large numbers of hookworm eggs to none at all. The production of eggs may be preceded by clinical signs of infection by up to four days. Clinical signs,
again, include anemia and the presence of a dark-tarry stool or diarrhea.

Chronic infection with hookworms is typically asymptomatic. Most cases are picked up on a routine fecal analysis. Still other chronic infections will show some degree of anemia, emaciation, and in general an unthrifty or malnourished individual.

The prepatent period, or time from infection with third-stage larvae until eggs are visible in the stool, is 16 days.

One adult female hookworm can lay 25,000 to 30,000 eggs per day. Larva develops whenever the weather is favorable, typically in the late spring, summer, and early autumn, particularly when the mild weather is accompanied by adequate levels of rainfall. Favorite areas for larval development include gravel, sand, and unpaved runs where the fecal material mixes with soil.   

Treatment involves an appropriate anthelmintic, and in cases of severe anemia, a blood transfusion may become necessary. Anemia caused by blood loss secondary to hookworms, especially in severely affected puppies, is often termed “hookworm anemia.”

Numerous products are effective against hookworms and include: Nemex® manufactured by Pfizer, Ridworm® marketed by Hartz, Drontal or Drontal Plus® produced by Bayer Animal Health, and Panacur C® marketed by Intervet to name a few products currently available.

Since hookworm eggs are not always detected on fecal analysis, especially in young puppies. Even peracute infections may sometimes not be confirmed upon fecal analysis. The "Companion Animal Parasite Council, or CAPC," advocates strategic deworming of puppies every two weeks from the time the puppies are two weeks of age until they are eight weeks old. Thereafter, the CAPC suggests the implementation of a continuous program for parasite control.

Continuous control of hookworms in dogs is now possible through the use of various pharmaceutical products available as heartworm preventatives or combinations of a heartworm product and an anthelmintic, typically given monthly. One such product, Advantage Multi®, is available from Bayer Animal Health. Advantage Multi® is a combination of imidacloprid and moxidectin used topically for the control of heartworms, hookworms, roundworms, whipworms, ear mites, and fleas. Additional products for continuous control of hookworms include: Heartguard®, which is marketed for the control of hookworms and heartworms and is available from Merial; Interceptor® or Sentinal®, from Novartis Animal Heath, which may be used for the prevention of heartworms, hookworms, whipworms, and roundworms, and in the case of Sentinal®, fleas; Revolution®, a product from Pfizer Animal Health, is available for the prevention of heartworms, hookworms, ear mites, and for dogs, some species of ticks; a product from Virbac called Iverhart Max® is effective against heartworms, hookworms, and roundworms and is the only heartworm product currently effective against tapeworms.

Sodium borate may be used for environmental hookworm larvae control at a rate of 10 lbs. per 100 sq. ft of surface area. The sodium borate should be raked into the area and will destroy the hookworm larvae in gravel or in loamy-surfaced runs. The sodium borate will also destroy any vegetation present.

Paved surfaces, runs, or kennels may be cleaned with a 1% sodium hypochlorite or Clorox solution. This treatment will kill the larvae or leave them susceptible to environmental desiccation (drying out).

Zoonotic infections (those transmittable to humans) may occur through ingestion or by direct penetration of the skin by infective larvae. Skin penetration often occurs by walking barefoot in a contaminated area, and most of these cases are believed to originate at the beach. Soft, damp sand in front of beach buildings just above the high tide mark is an ideal environment for larval development. Hookworm larval development is but one reason dogs are not allowed on the beach in many areas. The skin or cutaneous form of
hookworm infection occurring in humans is commonly termed “creeping eruption,”
because migrating larvae produce a linear, tortuous (crooked), erythematous (red and inflamed), and intensely pruritic (itchy) eruption. The parasite may travel from a fraction of an inch to several inches a day, typically moving more at night.

References:

“Continuous Control of Hookworms in Dogs and Cats.” Clinician’s Brief. July 2008 supplement. July 2008. Pp. 1-8.

Georgi, Jay and Marion Georgi. Parasitology for Veterinarians. 5th Edition. 1990. W.B. Saunders. Pp. 172-177.

Virbac Animal Health. "Iverhart." Virbac. 2009 http://www.virbacvet.com/iverhart/product/iverhart_max/

Companion Animal Parasite Council (CAPC). www.capcvet.org

Center for Disease Control and Prevention (CDC). www.cdc.gov