Education, Epidemiology, Infectious Diseases

What Are Zoonotic Diseases? Explainer With Examples

Author Chandana Balasubramanian , 29-Aug-2023

Zoonotic diseases are infectious diseases that can be transmitted from animals to humans. Also known as zoonoses, they are caused by agents like viruses, bacteria, parasites, and fungi. These types of diseases are quite common, with over 200 types of known zoonoses.


Studying the world of zoonotic diseases is important because they are responsible for 60% of known infectious diseases in humans. Additionally, they contribute significantly to the occurrence of new and existing diseases in humans and animals.


There are many ways in which a zoonotic disease jumps from animals to humans. Preventive measures can help reduce the risk of zoonotic infections and protect human and animal populations.


What are zoonotic diseases? 

Zoonotic diseases, or zoonoses, are infections that can be passed between vertebrate animals and humans.  These infections can be spread by bacteria, viruses, parasites, and fungi. They are significant public health concerns because over 60% of all emerging infectious diseases are zoonotic.

The term ‘zoonoses’ comes from the Greek word ‘zoon’ which means animal.


How do zoonotic diseases spread?

Zoonotic diseases can spread in different ways. Common methods of transmission are:

  • Direct contact: with infected animals by touching, petting, grooming, or caring for infected animals.
  • Indirect contact: with contaminated surfaces or substances like animal feces or surfaces that have been contaminated by an animal’s body fluids.
  • Vector-borne transmission: where an intermediate insect or animal, called a vector, helps transmit the disease from an animal host to a human one.
  • Food-borne transmission: Some zoonotic diseases can be transmitted through food. For example, undercooked meat and unpasteurized dairy products from infected animals can be the source of zoonotic transmission.
  • Water-borne transmission: Contaminated water can contain zoonotic pathogens that can infect humans who swim, drink, or come in contact with the water.


Examples of common zoonotic diseases


Rabies is a deadly zoonotic disease that can be transmitted through animal bites, for example, dogs and bats. After symptoms of rabies appear, the disease is always fatal. When symptoms progress, infected individuals can face anxiety, brain dysfunction, confusion, hallucinations, a fear of water (hydrophobia), and even insomnia. According to the Centers for Disease Control and Prevention (CDC), rabies causes 59,000 deaths worldwide. However, rabies is 100% preventable. When bitten by a rabid animal, postexposure prophylaxis is extremely effective at preventing rabies.

Zoonotic Influenza

Zoonotic influenza is caused by animal influenza viruses that spread to humans from animals. Unlike seasonal influenzas, zoonotic influenzas occur at any time of the year and depend on the level of contact with infected animals.

Avian influenza, commonly known as bird flu, is a type of zoonotic influenza. Some viral strains like Human Influenza A H5N1 and H7N9 have caused widespread outbreaks in humans.

A notable outbreak is the H5N1 outbreak in China in 1997 which led to 18 human infections. According to WHO, since 2003, more than 20 countries reported more than 860 H5N1 human infections.


Salmonellosis is a well-known zoonotic disease caused by the Salmonella bacteria. This infectious disease is spread through contaminated food, often raw poultry, eggs, and unpasteurized dairy products.

Symptoms include abdominal pain, diarrhea, and fever which can last a few days. Severe infections may require hospitalization, but most cases resolve without any treatment.

Safe food handling practices and maintaining proper hygiene after handling animals and animal products can lower the risk of salmonella poisoning.

West Nile Virus

West Nile Fever is a mosquito-borne disease that can be fatal. Anyone can be infected with the West Nile Virus (WNV), but older individuals and people with compromised immune systems may be at a higher risk of getting sick.

It is spread by the Culex pipiens mosquito (the common house mosquito). Birds and horses can act as reservoirs for the virus and can spread the disease.

Humans can also get infected when they handle dead birds or contaminated animal tissue without proper protection. 80% of humans who contract WNV remain asymptomatic, and 20% exhibit symptoms.


Ebola is a severe and fatal zoonotic disease caused by the Ebola virus. The virus uses fruit bats as reservoirs and can be transmitted to humans through direct contact with infected bats or their body fluids.

Ebola outbreaks spread rapidly, and the virus has a high mortality rate of 50-90%. Symptoms include fever, fatigue, muscle pain, and severe internal bleeding.


Brucellosis is a zoonotic infection caused by different types of Brucella bacteria. Humans can get brucellosis through direct contact with infected animals like cattle, goats, and sheep or by eating unpasteurized dairy products.

Symptoms of brucellosis include fever, fatigue, and joint pain. If symptoms progress, brucellosis can lead to long-term health issues and affect multiple organs.

Zoonotic diseases not only affect people but also impact wildlife conservation. Learning more about these diseases can protect humans and animals from suffering and loss.


Diagnosing zoonotic diseases

Various diagnostic methods have been developed to detect zoonotic diseases. Here are some commonly used techniques:

Clinical examination and assessment

The first step in diagnosing zoonotic diseases usually involves a physician’s examination, review of medical and travel history, and records of exposure to animals.

Culture-based and microscopy techniques

Culture and microscopic examination involve taking blood, urine, or tissue cultures from infected individuals for analysis under a microscope.

Serological assays

Antigen-based assays and serological tests have optimized sample handling, decreased reporting time, and improved diagnostics. Techniques like IFA, DAT, ELISA, and Western blotting help detect antibodies in serum samples.

Molecular diagnostic tools

Methods like electron microscopy, cell culture, and molecular techniques like microarray and Polymerase Chain Reaction (PCR) or RT-PCR have improved viral detection.

These tests can identify specific pathogens quickly and accurately, making them particularly useful when dealing with novel or emerging zoonoses.

Next-generation sequencing (NGS)

Next-generation sequencing or NGS offers comprehensive insights into viral composition, aiding research and diagnosis of zoonotic diseases. This technology rapidly sequences RNA or DNA, which allows for deeper genomic insights.


Treating zoonotic diseases

Zoonotic diseases can be difficult to manage because there are many differences between them. However, with early detection and appropriate medical intervention, many zoonotic diseases can be effectively managed.

Treatment in humans

Treating infected humans with zoonotic diseases typically involves a combination of antiviral or antibacterial medications depending on the specific disease agent.

For example, Lyme disease is caused by bacteria and is treated with antibiotics such as doxycycline or amoxicillin. On the other hand, rabies is a viral infection that requires post-exposure prophylaxis, including vaccination and administration of immune globulin.

Treatment in animals

The approach for treating zoonoses in animals varies based on species and disease type. However, it often includes quarantine measures alongside targeted therapies like anthelmintics for parasitic infections or antifungals for fungal diseases.

Importance of veterinarian involvement

Veterinary involvement is crucial not only for treating infected animals but also preventing further spread within animal populations.

Regular examinations can assist in discovering potential health issues before they become more serious predicaments.


Preventing zoonotic diseases

Zoonotic diseases are a major public health concern. As a result, controlling their spread is crucial.

Basic precautions

The first line of defense against zoonotic diseases involves practicing good hygiene, using appropriate personal protective equipment when dealing with animals or animal products, and ensuring pets are vaccinated regularly.

Veterinary intervention

To prevent and control zoonotic diseases, adopting veterinary public health policies with international collaboration is crucial. Regular reviews and surveillance are vital in addressing emerging and re-emerging diseases, ensuring global public health protection.

Educational programs

Education programs aimed at raising awareness about zoonosis among both healthcare professionals and the general public can also be effective in disease control. These programs should focus on identifying symptoms early and seeking prompt medical attention.

Surveillance systems

Robust surveillance systems need to be established for early detection and rapid response to outbreaks of zoonotic diseases. Such systems should include regular monitoring of both human populations and animal reservoirs for signs of disease activity.


Reporting zoonotic diseases

Healthcare professionals play a crucial role in safeguarding public health by promptly reporting cases of zoonotic diseases to the appropriate authorities. Here are effective steps that healthcare professionals can take to report zoonotic disease cases:

Be aware and identify diseases accurately

The first step towards effective reporting is being able to identify potential zoonotic diseases accurately. Familiarize yourself with common symptoms and signs of zoonoses. Early detection can greatly improve patient outcomes and prevent further transmission.

Use approved reporting systems

In the United States, healthcare providers are required by law to report certain infectious diseases, including many zoonoses, to local or state health departments.

Maintain patient confidentiality

While it’s essential to share pertinent details about the case with public health officials, you must also ensure patient confidentiality as per HIPAA regulations.

Communicate promptly

If you suspect or confirm a case of a notifiable zoonosis, communicate promptly with your local health department. This allows them time for necessary investigations and interventions.



Zoonotic diseases are infections that can be transmitted from animals to humans, and it’s crucial for healthcare professionals to diagnose, treat, and control their spread.

Proper reporting of cases is essential in preventing outbreaks, and continued education and awareness efforts can help reduce the impact of these illnesses on our communities.


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Chandana Balasubramanian

Chandana Balasubramanian is an experienced healthcare executive who writes on the intersection of healthcare and technology. She is the President of Global Insight Advisory Network, and has a Masters degree in Biomedical Engineering from the University of Wisconsin-Madison, USA.

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