Worms in Humans That Come From Dogs
Dogs can contract a number of intestinal parasites that are colloquially referred to as worms. Some of these parasites are known to be zoonotic, which means they also can infect humans. See a doctor if you suspect that you or another member of your family has acquired an intestinal parasite from a dog.
Roundworms are among the most common zoonotic parasites that affect dogs, who may carry these relatively large worms in their small intestines. Most canine roundworm infections are caused by the species Toxocara canis, which dogs usually acquire from their mothers, as fetuses or during nursing. Puppies are therefore most at risk for roundworm infections. However adult dogs -- and humans -- can become infected if they eat soil or feces that contain roundworm eggs. Young children prone to putting their unwashed hands in their mouth are particularly susceptible. A roundworm infection, called toxocariasis, may show no symptoms in humans. In some cases, however, the larvae may invade organs or become lodged in one of the eyes, where they can impair vision and damage the retina. One type of roundworm that affects dogs, known as a threadworm, can cause abdominal pain and diarrhea in people, particularly in individuals whose immune systems are compromised.
Dogs can become infected with several types of zoonotic hookworms, which latch on to the walls of the small intestine via a mouth cavity and feed on blood. One species, Ancylostoma caninum, is typical of subtropical and tropical climates and is particularly worrisome because it can cause fatal bleeding, especially in puppies. Dogs contract Ancylostoma caninum by eating larvae that another dog has shed, consuming insects that carry the parasite or while nursing from an infected female. Hookworm larvae also can penetrate a dog's skin, which is the most common way that people become infected. While it is possible for hookworms to travel to a person's intestines, hookworm infections in humans typically manifest as a cutaneous larva migrans, an itchy skin condition characterized by raised lesions.
Dogs can contract zoonotic tapeworms, which also attach themselves to the intestines. Tapeworms are less dangerous than hookworms, however, because they do not extract as much blood. Symptoms may be mild enough for the infection to go undetected, except for the segments that may be visible in the dog’s feces. The most common tapeworm that parasitizes dogs is Dipylidium caninum, which both animals and humans contract by ingesting infected fleas. Dipylidium caninum infections are therefore rare in humans. Also rare, but possible, in dogs and humans are infections by Echinococcus tapeworms, which canines acquire by eating contaminated raw meat. In humans, who can become infected if they ingest eggs that a dog has passed in his feces, Echinococcus tapeworms can cause life-threatening cysts in major organs, including the brain.
Preventing Intestinal Parasite Infections
Having your dog dewormed -- treated with medicines to kill intestinal parasites -- by a veterinarian is one way to protect him and yourself from such infections. Puppies should be dewormed several times during their first three months of life, with the first dose administered in the first three weeks. To further minimize the risk of worms, dispose of your dog's fecal material quickly, especially if he is known to be suffering from intestinal parasites. Always be diligent about washing your hands. Children especially should be encouraged to wash their hands after interacting with dogs and visiting public areas frequented by companion animals. Wearing shoes outdoors, especially in parks, beaches and other areas where dogs and cats roam, goes a long way towards preventing hookworm infections.
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