Zoonotic Diseases Passed From Animals to Humans

While we often think of contagious diseases as those that can be passed from person to person, a large number have made the leap from animals to humans. Some, like malaria, are directly transmitted from animals, often as the primary route of infection. Others, like HIV, have evolved into a separate disease after being transferred from the animal source.

Mosquito biting a person's skin
Ryan Lebel Photography / Getty Images

These types of infectious diseases, in their entirety, are referred to as zoonotic.

How Zoonotic Diseases Cause Infection

Zoonotic diseases can involve viruses, bacteria, and parasites that are transmitted through blood-borne, water-borne, food-borne, or air-borne infections, as well as through direct contact with animals, animal products, or animal waste. These include:

  • Animal bites that break the skin
  • Insect bites, including mosquitos and fleas
  • Drinking tainted water or dairy products
  • Eating infected meat
  • Inhaling pathogenic droplets or particles
  • Direct skin-to-skin contact
  • Direct or indirect contact with animal feces or urine

Animals can often transmit a disease by which they are not affected. We often see this with bats. On the other hand, there are diseases, like rabies, that affect both humans and animals equally.

In some cases, we can reverse the route of transmission and inadvertently infect certain animals. This has happened with primates, who share physiological similarities to humans but have vastly different immune responses to pathogens.

Types of Zoonotic Diseases

The range of zoonotic diseases is surprisingly diverse. Some are fast-acting, causing serious illness in a short span of time. Others are slowly progressive and may or may not cause symptomatic illness.

The most familiar examples of zoonotic diseases include:

  • ​Anthrax, which can be spread through animal contact or animal products
  • Bird flu, transferred almost exclusively from birds to humans
  • Bubonic plaque, which is spread through fleas
  • Ebola, which is spread through contact with infected persons
  • E. coli bacteria, spread largely through food
  • HIV, which made the leap to human from chimpanzees
  • Leptospirosis, which can be caused by contact with water or soil containing animal urine
  • Lyme disease, which you can get from a tick bite
  • Malaria, which is spread by mosquitoes
  • Rabies, which we associated with infected dogs and wild animals
  • Ringworm, caused by direct contact with stray animals, farm animals, or pets
  • Salmonella, spread largely by eating tainted eggs or dairy products
  • Toxoplasmosis, often passed through contact with cat litter

While these diseases can affect anyone, some of them are more likely to cause serious illness in children under 5, pregnant women, adults over 65, and persons with severely compromised immune systems.

15 Ways to Prevent Exposure

Since the route of infection varies by the type of disease involved, there is no one way to prevent zoonotic infection. There are, however, some guidelines you should follow to reduce risk:

  • Washing your hands with soap and water when in contact with animals
  • Wearing gloves when cleaning the litter box
  • Having a hand sanitizer on hand with a minimum 60 percent alcohol content
  • Using insect repellent to prevent mosquito, tick, or flea bites
  • Using mosquito netting in areas where mosquito-borne diseases are prevalent
  • Avoid going barefoot in soil or grass where farm animals live
  • Avoiding drinking water from or swimming in rivers, streams, or lakes
  • Avoiding drinking water in countries where water-borne diseases are common
  • Cooking meat to appropriate temperatures
  • Cooking meat well done if it is from hunted wild game
  • Following food safety practices: wash all produce thoroughly, use different cutting boards for raw meat and produce, and wash hands and surfaces often
  • Avoid playing with stray animals
  • Avoid getting scratched by pets
  • Getting your pets vaccinated for rabies and other transmittable diseases
  • Getting updated travel and health advisories if planning a trip overseas
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  • Centers for Disease Control and Prevention (CDC). "Zoonotic Diseases." Atlanta, Georgia; updated October 25, 2016.