If your dog is doing something that really grosses you out, such as snacking from the cat's litter box, you may be worried about him catching a disease from cat feces. This is a valid fear, as there are several diseases that can be passed in the feces of a sick cat.
Dogs are more prone than cats to many of the worms that infect companion animals. However, one intestinal worm that infects cats and dogs equally is the roundworm. This little critter is responsible for making its host very sick. If a cat has roundworms, she will shed the roundworm eggs when she defecates. The roundworm egg shell is hard and protective, making it hardy enough to survive outside a host for years. If a dog eats the eggs, he could become a host. Another way the eggs may enter the dog's body is through the soil. Outdoor cats use soil to bury their feces. If a dog were to walk through a soiled area, and then lick his paws, he could become infected.
Other worms that can be transmitted through cat feces include hookworms and whipworms. These worms are not seen in cats as often as they are in dogs, but they do infect cats and can also leave larvae in the bowel that can be shed through cat poop. Hookworms can be spread through the skin, so if your dog, like so many dogs, enjoys rolling around in smelly goo, he could pick up the hookworms or eggs and give them access to his body by penetration through the skin. Whipworms, so called because of the way they appear under a microscope, are transmitted through ingestion. A dog who eats infected cat poo, or walks through an infected area and then licks his paws, can become the next whipworm host. Roundworms, hooks and whips are all easily eradicated through deworming medication.
Toxoplasmosis is a global problem and is very common. It comes from eating raw meat from an animal that was infected with it. Only cats have the chemical makeup in their bodies to support the life cycle of this particular protozoan. Dogs can become hosts, but the organism cannot reproduce in their bodies as it can in cats. Cats can shed the eggs in their feces, and if a dog comes in contact with that feces, she can also become infected. The eggs hatch and can make Fido feverish and frail. Fortunately, though toxoplasmosis is very common in both dogs and cats, it doesn't usually cause any harm.
Another pesky protozoan is giardia. This organism causes diarrhea and can make dogs and cats very ill. Giardia is shed as a cyst through the feces. If a dog consumes contaminated fecal matter, he could potentially become infected. Even just a little cursory sniff of the feces can cause trouble. The cysts will then attach to the dog's nose, where they can be licked off and sent to the dog's intestinal system to wreak havoc and live a nice long life. Giardia is usually easy to treat with medication, and is a serious risk only to elderly animals and those with depressed immune systems.
Michelle A. Rivera is the author of many books and articles. She attended the University of Missouri Animal Cruelty School and is certified with the Florida Animal Control Association. She is the executive director of her own nonprofit, Animals 101, Inc. Rivera is an animal-assisted therapist, humane educator, former shelter manager, rescue volunteer coordinator, dog trainer and veterinary technician.