Zoonoses are infectious diseases that are passed from animals to people. There are many of these diseases. And many different animals can carry a wide variety of infections. Some of these diseases can be passed on through a bite or scratch. Others can be passed on by contact with the animal's feces or fur, skin, or feathers. Other diseases are passed on through fleas or ticks on an animal. Hypochondriasis is a mental condition that causes people to think they have a disease when they don’t. Toxicosis is an illness or toxic condition caused by chemicals or drugs. Narcosis is a sleepy or comatose state caused by an overdose of a drug like heroin, morphine, or codeine. Halitosis means bad breath.

Cats can carry more than 60 infectious diseases that can be passed to people. These include cat scratch diseases, toxoplasmosis, toxocariasis, and ringworm. Dogs carry many fewer diseases. Birds can carry diseases such as psittacosis. This can cause pneumonia. It’s extremely rare for pet birds in the U.S. to have a disease that people can catch. Tropical and saltwater fish carry very few diseases that people can catch. But sometimes people can pick up infections from the water the fish are swimming in.

Toxoplasmosis usually doesn’t cause many problems in people who have a healthy immune system. But it can cause serious disease in the developing fetus and in people with a severely weakened immune system. Babies born with toxoplasmosis can develop serious problems. These include mental disability and blindness. Some infected newborns will have brain damage at birth or have serious eye damage. People with advanced AIDS can develop a brain infection from toxoplasmosis.

Despite its name, ringworm is not caused by a worm. It is a fungal infection that causes irritation to the scalp or skin. This makes the skin red or scaly. On the scalp, it can cause a bald patch of scaly skin. On the skin, it often appears as a ring-shaped rash. The type of ringworm passed on from animals makes up only a small percentage of ringworm cases in people. The rest are caused by a fungus that's passed from one child or adult to another through contaminated combs, brushes, hats, hair accessories, pillows, and bath towels. For either type of ringworm, the treatment is a skin cream or oral medicine that kills the fungus.

Dogs are legally required to be vaccinated against rabies, and most dog owners obey the law, so dog-linked rabies is now rare in the U.S. The CDC recommends that cats be vaccinated for rabies. Wild animals almost never get vaccinated. Recently, it has become possible to vaccinate coyotes with food laced with the vaccine. This is being done in Texas to lower the number of coyotes with rabies.

Poultry and turtles often have salmonella. Dogs and cats are much less likely to carry salmonella, although it's possible.

Children get head lice from other children, not from animals. Animals do carry animal lice and mites. Some of these can temporarily infect humans, but head lice infect only people. Effective treatment shampoos and egg removers are available over the counter and should be used exactly as directed.

Hantavirus was first discovered in the desert Southwest, when it caused unexplained deaths from pulmonary failure. The CDC found that mice in the area carried hantavirus. In the U.S., hantavirus is carried by the deer mouse, white-footed mouse, and cotton rat. The virus is found in mice urine, droppings, and saliva, which dries and mixes with dust. The virus can be passed on through the air when a homeowner does "spring cleaning." This disturbs the dust containing the virus. A person can breathe in the dust and virus. The virus can cause a severe type of pneumonia and lung failure.

This condition is caused by intestinal hookworms shed by dogs and cats in their feces. The larvae of these worms burrow into the skin and make a wandering trail just beneath the skin. Most cases of hookworm caused by dogs or cats are found in the Southeastern U.S., along the Gulf Coast. According to the CDC, children who play in contaminated soil are at risk of getting hookworm. Others at risk are electricians, plumbers, and others who must crawl beneath raised buildings where the hookworm larvae may be found.