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Ascarids and Hookworms

Ascarids (Toxocara canis, T. cati) and hookworms (Ancylostoma spp.) are common intestinal parasites of dogs and cats (referred to here as pets). Not only can ascarids and hookworms cause disease in their respective hosts, they are also well-known causes of larva migrans syndromes in humans, especially children. While ascarids and hookworms are most commonly diagnosed in puppies and kittens, infections can occur in dogs and cats of all ages. Dogs can also become infected with Baylisascaris procyonis, the common raccoon ascarid, which can cause serious disease in other animals and humans.

Ascarids

Because of the occurrence of both transplacental and transmammary transmission of T. canis, puppies are usually born with or acquire ascarid infections early in life. Kittens do not become infected before they are born, but like puppies, can acquire ascarids (T. cati) through the queen's milk. The tissue-migrating and early intestinal stages of these worms may cause severe, sometimes life-threatening, disease in the first few weeks of life. Intestinal infections can develop within the first 2.5 - 3 weeks of life. Left untreated, this can lead to widespread contamination of the environment with infective eggs.

Hookworms

Both puppies and kittens acquire hookworm infections (A. caninum, A. braziliense, and A. tubaeforme) through ingestion of or skin penetration by infective larvae, or from infective larvae passed in their dam's milk (A. caninum). Hookworms suck large amounts of blood from their hosts and while infected animals may look healthy in the first week of life, they can develop a rapidly severe, often fatal, anemia.

The prevalence of these infections varies with climatic conditions; however, they are present in all parts of the United States and must be viewed as a potential public health hazard. Because puppies, kittens, and pregnant and nursing animals are at highest risk for these infections, and therefore responsible for most of the environmental contamination and human disease, anthelmintic treatments are most effective when they are initiated early and targeted at these populations.

Because puppies, kittens, and pregnant and nursing animals are at highest risk for these infections, and therefore responsible for most of the environmental contamination and human disease, anthelmintic treatments are most effective when they are initiated early and targeted at these populations.

While it has long been recognized that transplacental and transmammary infection of ascarids and hookworms could be prevented through prophylactic treatment of pregnant dogs, no drugs are currently approved for this use. However, the effectiveness of this approach with different drugs approved for parasite control in dogs has been well documented. Daily treatment of pregnant dogs with fenbendazole from the 40th day of gestation through the 14th day of lactation has been shown to inhibit T. canis larvae in tissues, thereby preventing or greatly reducing the incidence of infection in puppies.

Alternatively, studies have shown that treatment with ivermectin on day 0, 30, 60 of gestation and 10 days post whelping, reduced the adult T. canis worm burden in pups by 100% and prevented the shedding of eggs.20 In yet another study, treatment with selamectin at 10 and 40 days both before and after parturition was effective in reducing T. canis fecal egg counts in both pups and their dams, and adult worms in the pups. If the mother did not receive prophylactic treatment, puppies and kittens must be treated early and repeatedly in order to prevent patent infections.

Drugs for the Treatment of Ascarid and Hookworm Infections