We Americans love our pets, and according to the American Pet Products Association, 68 percent of homes have at least one. Studies show that pets provide companionship that lifts our moods, helps us relax, and even lengthens our lives. Unfortunately, they can also make us sick.
 

Most common illnesses, such as colds and upper respiratory illnesses, are caused by different viruses in humans and animals, so they usually aren't spread back and forth. Still, there are a number of zoonotic diseases — those that spread between humans and animals — that can make you miserable or even be fatal. They include:

ALERT: Never Catch the Flu or Common Cold Again
 

1. Cat-scratch disease. Cat-scratch disease is the most common bacterial disease associated with cats, and is caused by an infected cat biting or scratching a person. Symptoms are swollen lymph nodes, fever, headache, fatigue, sore muscles, and headaches. Although healthy adults should have no lasting effects, they may experience lingering symptoms for months, and the disease can even be fatal for those with compromised immune systems. Approximately 25,000 cases are diagnosed every year in the United States.
 

2. Toxoplasmosis. Cats are mostly commonly infected by toxoplasmosis when they eat raw prey, and the parasite is commonly transferred to people through cat feces while cleaning out a litter box. Often humans don't show symptoms (if they do, they are similar to flu or mononucleosis), but if a pregnant woman is infected, the disease can cause miscarriage or serious problems in children such as mental disability, hearing loss, and eye infections.
 

3. Ringworm. Ringworm is actually a skin infection caused by a fungus, not a worm, and it is usually transmitted by contact with the skin or fur of an infected dog or cat. Ringworm is characterized by a round, itchy, crusted lesion that is often more red on the edges. It can be treated with antifungal medications.
 

4. Lyme disease. If you walk or hike in Lyme-infested woods, you know to check yourself for ticks when you return. However, if your dogs and cats play outdoors, they can bring infected ticks into your home where you can be bitten. Instead of disappearing over a few days, the small bump caused by an infected tick will cause a rash that will expand into a bull's-eye pattern with a clear area in the middle. Lyme disease causes flu-like symptoms. If the disease is caught early and treated with antibiotics, patients usually recover completely.
 

5. Rabies. Rabies is rare in the United States and can be prevented by keeping your pets' vaccinations up to date. Humans usually get it from the bite of an infected animal. If your pet comes in contact with a rabid animal (rabies is usually carried by wild animals such as bats and raccoons) and you think you've been exposed, get medical care immediately: If left untreated, rabies is almost always fatal, but a series of shots post-exposure can protect you from the virus.
 

6. Salmonella. Salmonella is the most common cause of food poisoning in the United States, and it's usually caused by contaminated poultry, eggs, and other foods. If you bring turtles into your home, though, beware — up to 90 percent of turtles carry salmonella. Other pet reptiles and baby chicks can also carry the bacteria. Symptoms of salmonella poisoning include diarrhea, fever, nausea, and abdominal cramps that last several days. Victims usually improve without treatment, but the disease can be more dangerous in people with compromised immune systems. 
 

7. Plague. Yes, plague. Although rare, about 10 human cases of bubonic plague are reported every year from southwestern states, usually caused by people letting their flea-infested pets sleep with them. Symptoms include fever, chills, weakness, and swollen lymph nodes. Treatment includes antibiotics for both the human and pet. Keeping your pets free of fleas should help minimize the risk.
 

Simple steps, such as washing your hands with warm, soapy water after touching pets (and especially after such chores as cleaning a litter box), avoiding cat scratches and bites, and keeping your pets' vaccinations current will go a long way to protecting you from harm.