skip to main content
Orange stars
MSD Manual LogoMSD ManualConsumer Version
Search icon
zoonotic

Zoonotic Diseases Hub

As human populations grow and expand into new areas, our contact with wild and domestic animals is changing, creating the need for a better understanding that the health of people is inextricably linked with the health of animals and our shared environment.

Human & Veterinary Medical Expertise in One Resource

See how zoonotic diseases affect both people and animals. Explore clinical guidance in the Professional Edition or animal-health information in the Veterinary Edition.

Central Information Hub

Explore zoonotic disease information - from common symptoms and prevention strategies to treatment options and what to know about recent outbreaks.

Connecting Human, Animal, and Environmental Health

Navigate to information about specific diseases and toggle easily to learn how both humans and animals are affected.

video

Zoonotic Diseases: When Infections Cross Species

More than half of emerging infectious diseases come from animals. Learn how zoonotic diseases spread and how to protect yourself and those around you.

Trending Topics

Explore Zoonotic Diseases by Type

Meet The Experts

Our content is written by a multidisciplinary panel of experts in human and veterinary medicine. Learn about our editorial process. Meet some of our featured experts:

  • Brenda L. Tesini

    MD

    University of Rochester School of Medicine and Dentistry

    Pediatric Infectious Disease

  • Christina A. Muzny

    MD, MSPH

    Division of Infectious Diseases, University of Alabama at Birmingham

    Internal Medicine, ID

  • Michael Croix

    MD

    University of Rochester Medical Center

    Infectious Diseases, Mycobacterial diseases, Transplant Infectious Diseases

  • Christina A. Muzny

    MD, MSPH

    Division of Infectious Diseases, University of Alabama at Birmingham

    Internal Medicine, ID

  • Michael Croix

    MD

    University of Rochester Medical Center

    Infectious Diseases, Mycobacterial diseases, Transplant Infectious Diseases

  • Edward R. Cachay

    MD, MAS

    Mayo Clinic, Arizona

    Infectious disease, HIV – AIDS, Human Papillomavirus and anal dysplasia/cancer, Hepatitis C and liver comorbidities in people with HIV

  • Michael Croix

    MD

    University of Rochester Medical Center

    Infectious Diseases, Mycobacterial diseases, Transplant Infectious Diseases

  • Edward R. Cachay

    MD, MAS

    Mayo Clinic, Arizona

    Infectious disease, HIV – AIDS, Human Papillomavirus and anal dysplasia/cancer, Hepatitis C and liver comorbidities in people with HIV

  • Robyn S. Klein

    MD, PhD

    University of Western Ontario

Frequently Asked Questions

Explore answers to frequently asked questions about zoonotic diseases, including how infections spread between animals and people, who is at risk, prevention strategies, diagnosis, and the role of One Health in protecting human and animal health.

Zoonotic diseases, or zoonoses, are caused by infectious organisms that spread between animals and people and cause illness. The organisms can be bacteria, viruses, parasites and fungi.

A common transmission scenario occurs when infectious organisms circulate among animals in their natural environment, whether or not they cause illness in those animals. Then humans and animals interact with each other at the human-animal-environment interface, and transmission from animals to people occurs (called spillover).

Transmission of zoonoses can be:

  • foodborne: from food contaminated with feces from an infected animal,
  • waterborne: from water contaminated with feces from an infected animal,
  • vector-borne: such as being bitten by a tick, mosquito or flea,
  • direct contact: coming into contact with body fluids of an infected animal including bites and scratches, or
  • indirect contact: through contact with inanimate objects or environmental contamination, such as pet habitats, barns, aquariums, soil, food and water dishes.

Some examples of zoonotic diseases and their animal hosts are:

Bacteria

  • Anthrax, Bacillus anthracis from cattle and other farm and wild animals
  • Brucellosis, Brucella abortus from cattle, Brucella melitensis from sheep, Brucella suis from pigs
  • Campylobacter enteritis, Campylobacter jejuni from poultry

Viruses

  • Rabies, Rabies virus from bats, raccoons, skunks, and other wildlife
  • Avian influenza, Influenza A virus from poultry and wild birds
  • Ebola, Ebola virus from non-human primates

Parasites

  • Visceral larva migrans, Baylisascaris procyonis from raccoons
  • Cryptosporidiosis, Cryptosporidium parvum from cattle and other farm animals

Fungi

  • Histoplasmosis, Histoplasma capsulatum var. capsulatum from bat and bird droppings and contaminated soil

Vector-borne

  • Rocky mountain spotted fever, Rickettsia rickettsii, from the bite of an infected tick, such as the American dog tick, Rocky Mountain wood tick or Brown dog tick; dogs and wild animals serve as amplifying hosts


People can pass infections to animals as well. This is called reverse zoonosis or spillback. Some examples are (human) tuberculosis in pets and captive wild animals and COVID-19 (SARS-CoV-2 virus) in pets, farmed and zoo animals, and wildlife.

Animals can appear healthy while still spreading infectious organisms that can make people sick. These organisms can cause a wide range of illnesses in both people and animals, from mild infections to serious disease or even death.