Caution should be exercised in handling infected dogs. Disease is more likely to be severe if the person has a weakened immune system.
Roundworms (Toxicara canis and T. cati)
Most infected people show no symptoms, but fever, a persistent increase in eosinophils, and an enlarged liver (sometimes with lung involvement) may occur. These signs result from a condition known as visceral larva migrans, which occurs when roundworm larvae migrate through different organs. Rarely, a larva may settle in the retina of the eye and impair vision, resulting in a condition known as ocular larva migrans. Because the eggs adhere to many surfaces and become mixed in soil and dust, strict hygiene should be observed by people (especially children) exposed to potentially contaminated animals or areas. The risk of infection is greater if puppies or kittens are in the environment.
Hookworms (Ancylostoma braziliense; less of an issue with A. caninum, A. tubaeforme and Uncinaria stenocephala)
The infective larvae of canine hookworms, particularly those of A. braziliense, may penetrate and wander under the skin of people and cause cutaneous larva migrans.
Tapeworms (cestodes, Echinococcus and some Taenia species)
These tapeworms can be contracted by humans in association with infected dogs. Eggs are passed in dog feces. Disease in people depends on where the intermediate stage goes in the body.
Tapeworms (cestodes, Dipylidium caninum)
This tapeworm of dogs and cats occasionally infects people. Infection occurs when the person accidentally ingests a dog or cat flea containing the parasite. Infection in the intestine is not generally harmful but the eggs or worm segments can be seen in the feces.
Trematodes (flukes, Alaria species)
This fluke of dogs and cats occasionally infects people and may invade various organs.