Zoonotic Diseases Passed From Animals to Humans

While contagious diseases are often thought of 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 human immunodeficiency virus (HIV), have evolved into a separate disease after being transferred from the animal source.

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, waterborne, foodborne, or airborne infections, as well as through direct contact with animals, animal products, or animal waste. Such instances 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 that they, themselves, are not affected by. This is often seen with bats. On the other hand, there are diseases, like rabies, that affect both humans and animals equally.

In some cases, the route of transmission can be reversed, and humans can 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 slow to progress and may or may not cause symptomatic illness.

Some of 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 is 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 cat feces and 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 a zoonotic infection. There are, however, some guidelines you should follow to reduce risk:

• Wash your hands with soap and water when in contact with animals.
• Wear gloves when cleaning a litter box.
• Have hand sanitizer (minimum 60% alcohol content) on hand.
• Use insect repellent to prevent mosquito, tick, or flea bites.
• Use mosquito netting in areas where mosquito-borne diseases are prevalent.
• Avoid going barefoot in soil or grass where farm animals live.
• Avoid drinking water from or swimming in rivers, streams, or lakes.
• Avoid drinking water in countries where waterborne diseases are common.
• Cook meat to appropriate temperatures, cooking to well done if it is hunted wild game.
• Follow 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.
• Get your pets vaccinated for rabies and other transmittable diseases.
• Get updated travel and health advisories if planning a trip overseas.