Toxocariasis (commonly known as visceral larva migrans or VLM) is an infection caused by ascaridic roundworms found in the intestines of dogs (Toxocara canis) and cats (T. cati). Symptoms in humans may be produced by the presence of the larval worms mi-grating in parts of the body. These infections can cause ocular larva migrans when larva enter the eye. This may cause inflammation and scaring on the retina. Each year more than 700 people infected with toxocariasis experience permanent, partial loss of vision.

Repeated or heavy Toxocara infections, although rare, can cause VLM with swelling of organs or the central nervous system. Symptoms of VLM, due to movement of the worms through the body, include fever, coughing, asthma, or pneumonia. In most cases, these infections are not serious, and many adults infected by a small number of larvae may not notice any symptoms. Organs commonly affected are the eye, brain, liver, and lung, where infections can cause permanent visual, neurologic, or other tissue damage. The most severe cases are more likely to occur in young children, who often play in or eat dirt (pica) contaminated by dog or cat stool.

Dogs can also become infected with Baylisascaris procyonis, the common raccoon ascarid, which can cause serious disease in other animals and humans.

Almost 14% of the U.S. population is infected with Toxocara passed from animals to humans. Recent study of a representative sample of the population show this infection to be more widespread and common than previously understood.

A recent national survey of animal shelters revealed that almost 36% of dogs nationwide, and 52% of dogs from southeastern states harbored helminths capable of causing human disease. The Toxocara infection is common in dogs and cats, and puppies and kittens can get the infection from the mother before birth or from her milk. The immature larvae mature rapidly in the intestines, and produce large numbers of eggs in the feces that contaminate the environment. Eggs soon develop into infective larvae, and humans can become infected after ingesting infective Toxocara eggs in soil or other contaminated surfaces.

Hookworms (Ancylostoma spp.) are common intestinal parasites of dogs and cats. While hookworms are most commonly diagnosed in puppies and kittens, infections can occur in dogs and cats of all ages. 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. Patent intestinal infections can occur as early as 2 weeks (dogs) – 3 weeks (cats) of age, leading to environmental contamination with infective larvae.

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.

The growing popularity of dogs and cats in the U.S., together with high rates of hookworm infections, has resulted in widespread contamination of the soil with infective eggs and larvae. Epidemiologic studies have implicated the presence of dogs, particularly puppies, in a household, and pica (dirt eating) as the principal risk factors for human disease. Children’s play habits and their attraction to pets put them at higher risk for infection than adults.

Humans can become infected with hookworms through ingestion of infective larvae or through direct penetration of the skin. When infective larvae penetrate the skin, they undergo a prolonged migration that causes a condition known as cutaneous larva migrans. These larval migrations are characterized by the appearance of progressive, intensely pruritic, linear eruptive lesions, which are usually more extensive with A. braziliense infections. A. caninum larvae may also penetrate into deeper tissues and induce symptoms of visceral larva migrans, or migrate to the intestine and induce an eosinophilic enteritis.