The man comes from the animal kingdom. It is therefore not surprising that some pathogens can be transmitted from animals to humans. The opposite direction, i.e., infections passed on from humans to animals, is also possible. Such diseases are called zoonoses. The various types of pathogens then cause infectious diseases. Read here about the zoonoses and how you can protect yourself from them!

What is a zoonosis?

What are zoonoses? Zoonoses are diseases that occur in both humans and animals. The World Health Organization defines zoonoses as “diseases and infections that are naturally transmitted between vertebrates and humans.” Over 200 different zoonoses are known worldwide.

In biology and medicine, a distinction is made between different forms of zoonosis, depending on the direction in which and how the pathogens are transmitted. The diseases can also be classified according to how they are transmitted between living beings.

Corona virus

The novel coronavirus Sars-CoV-2 causes the disease Covid-19. Read more about symptoms, course, and treatment!

Classification of zoonoses according to the main direction of infection

In the case of zoonoses, scientists differentiate whether the pathogens are transmitted from animals to humans or from humans to animals. They also talk about the direction of infection. With some pathogens, both directions of disease are possible.

The technical terms for the three directions of infection are:

  • Zooanthroponoses: The pathogens are mainly transferred from the animal kingdom to humans.
  • Anthropozoonoses: Humans transmit pathogens to animals.
  • Amphixenoses: Transmission is mutual. This means that the pathogens can be transmitted from animals to humans and humans to animals.

Classification of zoonoses according to transmission routes

In the case of zoonoses, the path by which the pathogens are transferred from one living being to another can also be very different. There are these transmission options:

  • Direct zoonosis: Transmission by direct contact or a mechanical vector such as wind
  • Latent zoonosis: The pathogen requires an intermediate host. There it matures, leaves the intermediate host, and only then colonizes the definitive host. An example of this is the beef tapeworm. 
  • Metazoonosis: Invertebrates such as mosquitoes, lice, or ticks are intermediate hosts for pathogens. In the case of a bite or sting from an infected intermediate host, the pathogens enter the human body and cause diseases such as TBE.
  • Saprozoonosis: The pathogens, or certain intermediate forms of the pathogen (e.g., larvae), are not found in other animals but the soil or in water. Through contact with these pathogens, it reaches an (intermediate) host.
  • Cyclozoonoses: During their development, the pathogens need different hosts – they must move between various vertebrates. How many hosts are necessary before the pathogen reaches its definitive host varies.

Zoonoses from A to Z

How can I become infected with a zoonosis?

Since different types of pathogens can pass between humans and animals, there are also very different ways of becoming infected. The transmission routes of zoonoses include:

  • Smear infections: In the case of smear infection (also called contact infection), pathogens travel from one organism to the next via a chain of touches. This happens, for example, directly from person to person or, in the case of zoonoses, directly from an animal to a person. Pathogens can also stick to objects.
  • Bite injuries: If an infected animal bites a human, pathogens such as viruses or bacteria can get into the bite wound and infect the human.
  • Contaminated food of animal origin (e.g., meat, milk, eggs): Anyone who eats the flesh of infected animals, for example, can become ill. An example of this transmission route is the beef tapeworm. The meat can contain the parasite’s eggs, which settle in the human intestine.
  • Vectors (e.g., wind, mosquitoes, lice, ticks, fleas): A vector transmits a pathogen to humans. The wind can act as a mechanical vector. In the case of zoonoses, however, it is invertebrates that transport the pathogens into the human organism when they are bitten or stung.
Bite wounds caused by an animal or another human should always be taken seriously. Read here how to provide first aid.

You get insect bites mainly in the summer, which are mostly harmless. Read here when they can nevertheless become dangerous!

Zoonotic Pathogen

Various pathogens can cause zoonoses. This includes:

Zoonotic viruses

virus is a simple, organic structure. It consists of one or more molecules, and a protein shell partially surrounds some viruses. The molecules contain the virus’s genetic material in the form of DNA or RNA. The information for the multiplication of the virus is stored here.

Viruses do not have their metabolism to multiply, and viruses need a host. The virus penetrates the host’s cells and uses the foreign organism’s metabolism to breed there. In this way, the virus then spreads into the host’s cells and destroys them.

The following viruses can spread from animals to humans and vice versa:

Viruses have no metabolism of their own, no generation of energy of their own, and no way of producing proteins. Strictly speaking, they are not living beings.


Viruses are among the most important infectious agents in humans. Read more about the structure of viruses, propagation, and important viral diseases!


Bacteria are made up of cells without a nucleus. Their genetic information is located directly inside the cell in the form of DNA. There is a wide variety of bacteria. Some live symbiotic coexistence with humans, for example, on the skin’s surface or in the gut. 

However, other bacteria are harmful to humans. They cause various diseases. Bacteria can also be transmitted from animals to humans – or vice versa.

Zoonoses include the following bacteria and the infections they cause:

  • Bacillus anthracis: These bacteria cause anthrax, also known as anthrax
  • Borrelia: The pathogen is responsible for the disease Lyme disease
  • Brucella: Causes the disease brucellosis
  • Campylobacter: Causes diarrheal diseases
  • Coxiella burnetii: Trigger for the so-called Q fever
  • Escherichia coli: causative agent of various diarrheal diseases, including EHEC
  • Francisella tularensis: Bacteria trigger tularemia (rabbit fever).
  • Mycobacterium tuberculosis complex: Various bacteria that cause tuberculosis
  • Rickettsia: Bacteria transmitted by fleas, lice, ticks, or mites that cause fevers in humans
  • Staphylococci: Cause infections in different parts of the body (e.g., skin, joints, organs)
  • Vibrios: There are so-called non-cholera vibrios and cholera toxin-producing Vibrio cholerae. The bacteria Vibrio cholerae causes the disease cholera.

Bacteria are tiny organisms that live all around you, all of the time. They provide you with meals, make tools, and work to make the planet a great place for you to live. While you might think of them as a nuisance, they serve an essential purpose.

Bacteria are protozoa, some of which can cause diseases in humans. Read more about bacteria and bacterial infections!

Lyme Disease is a bacterial disease caused by a spirochete called Borrelia burgdorferi. This disease affects humans and many mammals. The bite of infected ticks spreads the condition. Symptoms include fever, headache, fatigue, muscle aches, joint pains, and swollen lymph nodes.

Here you can find out everything you need to know about the routes of infection, symptoms and treatment of Lyme disease

In 2015, more than 1,800 cases of enterohemorrhagic E. coli (EHEC) were reported, resulting in 44 deaths in the United States. These E. coli cause bloody diarrhea, stomach cramps, and vomiting. Outbreaks have been associated with consuming raw milk or consuming undercooked ground beef. As of 2018, 1,900 cases of EHEC have been reported, resulting in 114 deaths. With humanity’s number 1 food, meat, coming into more direct contact with our stomachs, we’re taking a more significant risk than ever.

Enterohemorrhagic E. coli (EHEC) usually leads to watery diarrhea. Sometimes, serious complications are possible. Learn everything you need to know about E. coli!


Parasites are organisms that use a host for food or habitat. So the host serves to feed and reproduce the parasites and has no advantages whatsoever from this unwanted coexistence.

There are many different parasites. They can consist of one or more cells. Unicellular parasites are about:

  • Leishmania: carried by mosquitoes and causing leishmaniasis
  • Toxoplasma gondii: parasites found in feces of cats that cause toxoplasmosis in humans
  • Plasmodium: Causes the tropical-subtropical infectious disease malaria. Depending on the type of pathogen, different forms of the disease develop.

Multicellular parasites are also called helminths. However, they are better known colloquially as worms. Helminth parasitic zoonoses include:

Malaria is a tropical disease caused by a parasite called plasmodium, which is passed on through the bites of infected Anopheles mosquitos. Malaria is a potentially fatal disease, especially in children, pregnant women, and people with weakened immune systems. It’s currently affecting over 60 million individuals (about 3% of the global population) in 105 countries. In 2018, there were 216,000 malaria-related deaths, making it the fourth leading cause of death worldwide.

Read everything you need to know about malaria (intermittent fever)!

The dreaded toxoplasmosis infection manifests symptoms of flu-like illnesses, such as fever, headache, chills, blisters, and swollen glands. However, toxoplasmosis can also be asymptomatic or latent, meaning symptoms can’t be detected until later in life. The infection is commonly caused by eating undercooked meat, resulting in miscarriages, stillbirths, and congenital disabilities in pregnant women. The best way to avoid toxoplasmosis is to avoid handling raw meat and wash your hands thoroughly after handling raw meat.

Read everything you need to know about Toxoplasmosis (toxoplasma)!

Parasites cause over 250 million cases of illness worldwide each year, but many people don’t know that parasites can also infect humans. The Centers for Disease Control and Prevention says that parasites, like worms and roundworms, can be found in various body parts, particularly the nose, intestines, and mouth. But parasites can also be spread through contact with infected animals, such as dogs, cats, and rodents.

Mosquitoes, fleas, and lice have always accompanied people – here, and you can find out which parasites exist and what you can do about them.


Next to plants and animals, fungi form the third large group of creatures with a cell nucleus. If a fungus settles on or in the human body, it is a mycosis. Fungi can cause various diseases. They often affect the skin, mucous membranes, and nails.

Some fungal infections can spread from animals to humans. This includes:

  • Cryptococcus: Yeast found in bird droppings, which primarily causes pneumonia
  • Trichophytes: filamentous fungi that infect and damage skin, hair, and nails
  • Microsporum canis: a filamentous fungus that is transmitted to humans from dogs (but also cats); it affects the skin (scalp, face, trunk, and extremities)
There are around 60,000 different types of fungi, approximately 300 of which are considered pathogens.

As drug-resistant fungal infections rise, people are taking more excellent care to follow proper hygiene and hygiene practices. Most people know to wash their hands with soap and water after going to the bathroom, changing diapers, and handling food, but many don’t know that there are also several other ways to prevent infections. These tips can help you to avoid fungal infections.

Antifungal drugs are medications used to treat fungal infections. Read more about antifungal drug types, uses, and side effects!


Prions are proteins that occur naturally in the human body but can also harm health. Prions have only been known to be pathogens for a few years and have not yet been thoroughly researched. Scientists suspect that prions are formed when a typical protein is folded incorrectly.

The altered structure spreads to other proteins in the body. These changes can be isolated or caused by a genetic defect. Zoonotic prion diseases include, for example, Creutzfeld-Jakob disease, a fatal disease of the nervous system.

Creutzfeldt-Jakob syndrome (CJD) also known as subacute spongiform encephalopathy. Creutzfeldt-Jakob syndrome is a degenerative brain disorder that strikes people between 50 and 70. It causes patients to experience symptoms that gradually worsen over the years: personality changes, memory loss, trouble speaking, loss of muscle coordination, seizures, and eventually death. The cause of CJD is still unknown, but it is believed that the degeneration is caused by a misfolded protein, called a prion, that enters the brain.

Creutzfeldt-Jakob disease (CJD) is a disease of the nervous system. Patients suffering from dementia and movement disorders. Read more here.

Apart from zoonoses, there are a variety of infectious diseases. You can find out which ones are involved and how they are treated on the “Infectious diseases” topic page.

Infectious diseases are diseases caused by pathogens such as bacteria, viruses, or fungi. Read here about how infections are transmitted and how you can protect yourself from infection.

Protection against zoonoses

In order to protect oneself effectively against zoonoses, various measures are required.

Hygiene measures

Various hygiene measures protect you from infection with zoonosis. These include:

  • Regular and thorough hand washing or disinfection
  • Household hygiene (especially if animals live in the household)
  • no direct contact with animal feces

Proper hygiene when preparing food also protects against zoonoses:

  • In vacation countries, only drink water from sealed bottles or boiled water
  • Refrain from eating raw meat or eggs
  • Fry the meat well before eating. It kills pathogens

In nature, you can become infected with pathogens of zoonoses. Therefore:

  • Avoid contact with dead animals
  • Do not touch wild animals
  • Do not drink water straight from a lake or river
  • Do not eat mushrooms or fruits close to the ground
  • Check for ticks after spending time in nature
  • When camping, sleep under a mosquito net
  • In (sub)tropical areas: Cover the body with clothing and use insect repellent on exposed skin


Vaccination offers the most effective protection against a specific infection. The body learns the pathogen through the vaccine and forms a functioning defense system. If it encounters the “real” pathogen during an infection, the immune system can fight it and prevent the disease. You can read about the individual vaccinations in specialist texts on the unique zoonoses.

Measles, flu, or hepatitis: which vaccinations are essential? When do I need to refresh them? What vaccinations do children and pregnant women need?

Strong immune system

The immune system ensures that not every contact with a pathogen immediately leads to an illness. There are some tips on how to strengthen your body’s defenses:

  • Wholesome nutrition (balanced with lots of fresh fruit and vegetables and whole grain products)
  • At least two liters of water or unsweetened tea a day
  • Sufficient and regular exercise
  • Regular sleep rhythm
  • No ongoing stress for body and mind

Also, avoid stimulants such as alcohol and nicotine. These can inhibit the performance of the immune system.

Scientific standards:

This text corresponds to the requirements of specialist medical literature, medical guidelines, and current studies and has been checked by medical professionals.