Zoonotic Diseases and How They Are Spread

Protecting Yourself and Your Pets

Pet dog laying on the ground staring up


A zoonosis is a disease that animals have that can be naturally transmitted to humans. These diseases may be spread by viruses, bacteria, parasites, or fungi. The form and severity of the disease may be different in humans than it is in animals. It may be mild or even produce no symptoms in an animal but produce serious disease in humans, and the opposite is also true for some zoonotic diseases.

How Zoonotic Diseases Are Spread

The infectious agents that cause zoonotic diseases are spread in many different ways. Here are the most common categories:

  • Direct contact: You may acquire the germ through physical contact, being bitten or scratched, or coming into contact with urine, feces, or other body fluids from an animal that is infected.
  • Indirect contact: The germs may be spread from the animal into the environment, contaminating surfaces, water, or soil. You acquire the germs by contacting what the animal contaminated.
  • Vector-borne: Vectors include mosquitoes, fleas, and ticks who deliver the germ when they bite you.
  • Foodborne: You are exposed to the germ through eating animal products that are contaminated or foods that are contaminated with an infected animal's feces.

Examples Of Zoonotic Diseases

Zoonotic diseases have a long history. Ancient Greece and the Bible mention the plague. The number of potential zoonotic diseases today is impressive. You are likely to hear about rabies, ringworm, and Lyme disease, but many other diseases pose a threat to humans. These are examples of zoonotic diseases and the animals that can transmit them to humans:

  • Plague: Plague is caused by the Yersinia pestis bacteria and can be spread by rodents, cats, rabbits, squirrels, and related animals. The bacteria is transmitted by fleas, aerosols, and handling infected animals.
  • Cat Scratch Disease: This disease is caused by a bacterium, Bartonella henselae. When scratched by a domestic or feral cat, or possibly when bitten by an infected flea, you can get this illness.
  • HantavirusHantavirus is spread through the urine and droppings of infected rodents and can produce a fatal hantavirus pulmonary syndrome.
  • Tick Paralysis (various animals affected): The spread of this disease requires the tick to be attached to the human and the tick to release venom. This disease is classified under a broader definition of zoonotic diseases.

Who Is at Risk For Zoonotic Disease?

Any human in contact with an infected animal or disease vector is at risk. A vector is a disease carrier such as an insect or rodent that spreads the disease from an infected animal to an uninfected human. Disease incidence varies greatly with the region. You are at more or less risk for specific zoonotic diseases depending on your location.

Some humans are more at risk than others:

  • Infants and small children are at risk due to immature immune systems and poor hygiene, such as placing their hands in their mouths.
  • Pregnant women are at risk because their immune systems are more susceptible and there are additional hazards to the fetus.
  • Elderly people are at risk because their immune systems may be impaired.
  • Immunocompromised people, such as those undergoing cancer therapy and HIV/AIDS patients are at increased risk.
  • Veterinarians and other animal healthcare workers have more exposure to animals and therefore are at a higher risk.

Diagnosing Zoonotic Diseases

When a veterinarian sees or suspects a zoonotic disease, it is the responsibility of the veterinarian to alert the owner of the potential for disease spread to humans. Veterinarians cannot offer a diagnosis or treatment for humans but must urge the owner to contact their human physician for consultation.

Finding More Information on Zoonotic Diseases

Your pet's veterinarian is a good first source for information. Find out about the disease and most importantly, how to care for your animal and prevent spread to humans. Most veterinarians have professional brochures and handouts on the common zoonotic diseases for your area.

Your state, county, or city health department is another good resource for information. The Center for Disease Control has a state-by-state data map for state-specific information.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.