Testicular self-exam, as described in the text Faithful felines and devoted dogs provide innumerable benefits to their owners, but sometimes they can spread infections to humans. There are several steps you can take to reduce the likelihood of contracting an infection from your pet.

With more than 110 million pets in US homes, transmission of an infectious disease from pet to owner can occur. But common sense and proper veterinary care can keep these occurrences relatively low.

"It's not one of the public health situations that are threatening the nation, by any means," says Peter Schantz, VMD, a veterinarian and epidemiologist with the Centers for Disease Control and Prevention (CDC) Division of Parasitic Disease. "However, the diseases are completely avoidable, usually by steps that are also protective of the pet."

Many infectious diseases tend to be specific to certain species. However, bacteria or parasites that live harmlessly or cause limited disease in one species may cause more serious illness in another.

When People Have Suppressed Immune Systems

The chance of Fluffy or Fido passing a nasty bug on to a human family member increases if the person's immune system does not function optimally, such as with human immunodeficiency virus (HIV) infections. Richard B. Ford, DVM, MS, a professor at the College of Veterinary Medicine at North Carolina State University, believes the benefits of animal companionship far outweigh the hazards and feels that the health impact of isolation may far exceed the risk of catching something from a pet.

Some doctors have suggested that people with suppressed immune systems give up household pets to prevent opportunistic infections, but few patients heed the recommendation. The 1999 US Public Health Service (USPHS) and Infectious Diseases Society of America (IDSA) Guidelines for the Prevention of Opportunistic Infections in Persons Infected with Human Immunodeficiency Virus advise people infected with HIV not to give away their pets. Rather, they suggest the following tips:

  • Avoid contact with animal feces and reptiles, such as snakes, lizards, iguanas and turtles.
  • Wash hands after handling pets.
  • Adopt a dog or cat older than six months, but don't adopt a stray.

What Can Pets Pass Along?

About 250 infections can be classified as "zoonotic," or shared by animals and humans, but contact with dogs and cats can cause only about 30 types of infection.

Bites present the most problems for people, according to infectious disease specialist, James S. Tan, MD, chairman of the Department of Medicine for Summa Health System in Akron, Ohio. The risk of infection increases if the wound is not properly or fully cleansed, or if more than 24 hours pass before the person receives medical care.

  • Cat Scratch Disease (CSD) . CSD is caused by the bacteria Bartonella henselae , which healthy cats can carry. CSD results after a cat scratches the skin or if the cat licks an open sore or the eye. About a week later, the point of contact develops raised bumps. In about two weeks, the person's regional lymph nodes swell. About a third of patients develop a fever, and fewer develop fatigue, loss of appetite, or vomiting. A headache, sore throat, or serious neurological complications can occur.
  • Toxoplasmosis . Another infection that can result from contact with cats, toxoplasmosis poses the most danger to unborn children of women who do not have immunity or antibodies to the agent. Cats harboring Toxoplasma gondii , the causative parasite, may not show any symptoms but will shed spores in their feces. The spores become infectious within a day or two.
    "Toxoplasmosis can cause congenital abnormalities or, later in the pregnancy, mental retardation," says Dr. Tan. To play it safe, pregnant women and people with suppressed immune systems should let someone else empty the litter box, daily. If they must care for the box, they should wear gloves and wash their hands after removing the gloves.
  • Gastroenteritis . Gastroenteritis, or inflammation of the intestine, can trigger diarrhea, fever, headache, and abdominal pain. Bacterial infections of the intestine, from bacteria such as Campylobacter and Salmonella occur most often after people ingest contaminated food or beverages, but can also be passed from pets to humans, mostly from puppies or dogs with diarrhea.
  • Giardiasis . This protozoan intestinal disease is spread through ingestion of water or food that has been contaminated by feces containing the causative organism.
    "Children playing with puppies can get this one," Dr. Schantz says. " Giardia is the most common intestinal parasite of pets and humans in the United States, however you won't find any agreement on the frequency that it's transmitted from pets to people or vice versa."
  • Ringworm . This itchy, fungal skin infection can occur after contact with an infected pet, as can scabies and mites.
  • Roundworms and hookworms . These intestinal pet parasites can make the move to people through contact with contaminated dirt.
    "Roundworms need a couple of weeks to develop in the soil before they are infectious," says Dr. Schantz. "The infections occur when children share environments with pets, dogs, and cats."
    While hookworms enter the feet and cause intense itching, ingested roundworm eggs can make their way to the liver or brain, resulting in tumor-like masses or death.
  • Rabies . A bite from an infected animal can cause rabies. Routine vaccination of your pets eliminates this risk.
  • Vector-borne diseases . Other diseases can be passed to people through a vector or carrier. For example, mosquitoes can spread dog heartworm to other dogs or to people.


Preventing the spread of disease from pets to people involves common sense, good hygiene, a bit of training, and proper veterinary care. Steps that can decrease the risk of disease transmission from pets include the following:

  • Provide pets with routine veterinary care, testing, and vaccination.
  • Discuss pet-related health risks with your veterinarian. Vets are often more well versed on the topic than family physicians.
  • Take your pet to the vet whenever it is ill, even for bouts of diarrhea or skin rashes.
  • Teach pets not to scratch you or others, even in play.
  • Instruct children how to play with pets to decrease the chance of bites.
  • Wash skin scratches or bites with soap and water, and seek medical attention if the pet punctures the skin.
  • Keep animals' nails clipped.
  • Train animals' not to drink out of the toilet.
  • Feed animals pet food or cooked meat.
  • Do not let pets eat feces or hunt for prey.
  • Avoid letting animals lick your mouth or open sores.
  • Pick up feces as soon as pets defecate, and do not use the stool as fertilizer.
  • Do not let children play in public areas where animals may have defecated.
  • Empty the litter box daily and wear gloves.
  • Wash your hands after picking up droppings or cleaning the litter box.

"If they take good care of their pets," Dr. Tan concludes, "pet owners should be all right."