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Zoonosis - How it Spreads, Risk Factors, and Prevention

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Zoonosis - How it Spreads, Risk Factors, and Prevention

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Infectious disease that spreads to humans from animals is called zoonosis. Learn about the ways these pathogens spread and the most common zoonotic diseases.

Medically reviewed by

Dr. N. Ashok Viswanath

Published At October 5, 2021
Reviewed AtJanuary 29, 2024

What Is Zoonosis?

Animals are essential to the human race as they provide food, livelihood, and fiber. Pet animals are great companions and are also used in various psychological therapy. Humans come in contact with animals almost every day. It might be a pet at home, or they are raised for milk and meat or while traveling to someplace, or while visiting a zoo. Pets have been shown to improve mood and reduce loneliness in people who have a mental health disorder.

But, animals can also be carriers of harmful germs, which can infect humans and cause serious illnesses. Such diseases that spread from animals to humans are called zoonotic diseases or zoonoses. Harmful germs like viruses, bacteria, or parasites can cause zoonotic diseases. Some of these infectious microorganisms might not produce any symptoms in animals, but they might be highly contagious to humans.

Zoonotic illnesses can result in different types of diseases in humans, which can even be fatal. It is estimated that 6 in every 10 infectious diseases in people are spread through animals, and 3 in every 4 new infectious diseases in humans are spread from animals. In the olden days, zoonotic diseases like bubonic plague, bovine tuberculosis, etc., resulted in millions of deaths worldwide. Similar infectious diseases are still a challenge to treat in various developing countries.

What Are the Ways That Germs Spread Between Animals and Humans?

The common ways that you can get infected by animals are:

1) Direct Contact: The germs can spread from the saliva, urine, blood, feces, mucus, and other body fluids of infected animals. You can get infected when an infected animal bites or scratches you or if you do not wash your hands after petting an infected animal. Veterinarians, farmers, pet shop workers, and other people who come into contact with animals on a daily basis are prone to zoonotic diseases. Such people also become carriers and infect other humans.

2) Indirect Contact: When you do not directly touch the infected animal but touch surfaces or objects that have been infected by them is called indirect contact. Examples of such transmission are cleaning the aquarium tank, pet cages, chicken coops, and their food and water dishes.

3) Vector-Borne: Infections that are transmitted by vectors, such as fleas, ticks, lice, and mosquitoes, are called vector-borne diseases. Mosquito bites or bites from other vectors can spread viruses, bacteria, and protozoa.

4) Foodborne: You can get infected by eating contaminated food like raw or undercooked meat, unpasteurized milk, unwashed fruits and vegetables polluted by feces of an infected animal. Eating such contaminated food items can make both humans and animals sick.

5) Waterborne: When you get infected by consuming water that has been contaminated by an infected animal, it is called waterborne infection.

Apart from these causes, climate change, indiscriminate use of antimicrobial medicines, and the use of pesticides are also said to increase the rate of zoonotic diseases.

Risk Factors:

Anybody can get infected from a zoonotic disease, irrespective of how healthy you are. But, the following people are more at risk than others:

  1. Pregnant ladies.

  2. Infants.

  3. Cancer patients.

  4. Organ transplant patients.

  5. AIDS patients.

  6. People with diabetes.

  7. People with a weak immune system.

  8. Poultry farmers.

  9. Veterinarians.

  10. Pet shop workers.

  11. People who work in the zoo.

Such people should protect themselves, as they are more likely to develop severe complications from such infections.

What Are the Ways That Germs Spread Between Animals and Humans?

The following are some of the common zoonotic diseases:

  • Dengue Fever - is a mosquito-borne viral infection caused by the dengue virus. The symptoms like high fever, joint pains, headaches, and skin rash develop between 3 and 14 days after infection.

  • Leptospirosis - is a bacterial infection caused by the bacteria Leptospira. This infection can be spread from pigs, cattle, pet dogs, cats, rats, and mice. When contaminated water or soil comes in contact with a skin sore or break, you might get infected.

  • Toxoplasmosis - is a parasitic infection caused by the Toxoplasma gondii parasite. You can get infected by eating contaminated and undercooked food.

  • Bird Flu or Avian Influenza - is a viral infection that is spread mainly from birds. Some strains of this virus can affect birds, humans, and animals, while some strains are restricted to birds. The most common type of bird flu is H5N1.

  • Ebola - otherwise called Ebola virus disease (EVD). It is a viral infection caused by ebolaviruses, which results in a hemorrhagic fever in humans. This disease spreads by handling infected animals such as fruit bats, chimpanzees, and forest antelope.

  • SARS, MERS, and COVID-19 - Different strains of the coronavirus cause all these diseases. SARS (severe acute respiratory syndrome) and COVID-19 (coronavirus disease 2019) are believed to have jumped to humans from infected bats or civet cats, while camels are said to be the carriers of viruses that cause MERS (Middle East respiratory syndrome).

  • Anthrax - is a rare but severe bacterial infection caused by Bacillus anthracis, which is a spore-forming bacterium. This bacteria mainly affects wild game and livestock and can infect humans through direct or indirect contact.

  • Cat Scratch Fever - otherwise called cat scratch disease (CSD). It is a bacterial infection that spreads when Bartonella henselae bacteria is transmitted to humans through a cat scratch or bite.

  • Rabies - It is a potentially fatal viral infection spread through the bite of an infected dog. The virus causes inflammation of the brain.

  • Salmonella Infection (Salmonellosis) - the Salmonella bacteria results in intestinal infection. These bacteria live in the intestines of humans, birds, and animals. Humans get infected after eating undercooked or raw seafood and meat.

  • West Nile Fever - is a mosquito-borne viral infection caused by the West Nile virus (WNV). It can be fatal to some, as this infection can result in the inflammation of the spinal cord or brain.

  • Plague - is a bacterial infection caused by the bacterium, Yersinia pestis. Humans get infected by getting bitten by infected rodents or touching an infected animal.

  • Brucellosis - is a bacterial infection that is spread when people eat contaminated food. Humans can also get infected through the air.

  • Lyme Disease - is also a bacterial infection caused by the Borrelia bacterium. Ticks spread this bacteria.

Campylobacter infection, cryptosporidiosis, fish tank granuloma, giardiasis, hepatitis E, malaria, rat-bite fever, ringworm, trichinellosis, etc., are some other zoonotic diseases.

How to Prevent Zoonotic Infections?

The following are some ways to prevent such infections:

  1. Wash your hands thoroughly, especially after touching your pet or other animals.

  2. Use mosquito and other insect repellents.

  3. Wash meat and seafood properly before consuming them.

  4. Make sure your pets are vaccinated regularly.

  5. Avoid drinking or touching your eyes or mouth while you are close to animals.

  6. Use proper protective wear while handling or treating sick animals.

  7. Regularly clean your pet’s cage.

  8. Do not touch animals or go close to them if they appear sick or infected.

Most types of zoonotic infections can be treated effectively, but some might result in long-term or permanent damage. Get vaccinated and eat healthily! For more information, consult an infectious specialist doctor online now.

Frequently Asked Questions


What Are the Symptoms of Zoonosis In Humans?

The symptoms of zoonoses are:
- Gastrointestinal symptoms:
- Diarrhea.
- Poor appetite.
- Abdominal cramps.
- Nausea and vomiting.
- Flu-like symptoms:
- Fever.
- Headache.
- Body pain.
- Weakness.
- Swelling of the lymph nodes.
Skin lesions like scratches.


Is Ebola a Zoonotic Disease?

Ebola is a deadly and complex zoonotic disease that is highly virulent in humans. It is considered to have originated in fruit bats, which then contaminated the other animals before the virus affected humans. Humans get affected by the Ebola virus when they come in contact with the blood or any bodily fluids of the infected animal.


What are the Types of Zoonotic Diseases?

There are different types of zoonotic diseases shared between animals and humans. Some of the most common types are:
- Zoonotic influenza.
- Salmonellosis.
- Ebola.
- West Nile virus.
- Plague.
- Rabies.
- Brucellosis.
- Lyme disease.
- Anthrax.
- Cat Scratch Fever.
- Cryptosporidiosis.


Who Is Most At Risk For Zoonotic Disease?

People who are at high risk of developing the zoonotic disease are:
- Children who are under the age of 5.
- People with AIDS.
- Elderly people.
- Organ transplant recipients.
- People on cancer treatment or any other treatment which weakens the immune system.
- Pregnant women.


Which Virus Is a Classic Example of a Zoonotic Virus?

Some of the classic examples of zoonotic viruses are:
- Rabies.
- Hantaviruses.
- West Nile virus.
- Yellow fever virus.
- Chikungunya virus.
- Arenaviruses.
- Crimean-congo hemorrhagic fever virus.


Which Fungal Disease Is Zoonotic?

Some of the fungal zoonotic diseases are:
- Histoplasmosis.
- Sporotrichosis.
- Dermatophytosis.
- Basidiobolomycosis.


How Do You Get Zoonotic Disease And How Is It Transmitted to Others?

Humans get infected when they come in close contact with the blood or bodily fluids of the infected animal or person. A zoonotic disease is transmitted in the following ways:
- Through air.
- By eating the contaminated meat or the produce of the infected animal.
- By touching the surface or the area that an infected person or animal had touched.
- Through insect bites.


What Are Parasitic Zoonotic Diseases?

A zoonotic disease is a kind of disease that is transmitted between animals and humans. It can be caused by a virus, fungi, or parasite. When a zoonotic disease is caused by a parasite, then it is called parasitic zoonotic disease. Some of the examples of parasitic zoonotic diseases are:
- Cryptosporidiosis.
- Trichinellosis.


What Are Reverse Zoonoses?

Reverse zoonoses mean the transmission of diseases from humans to animals. Generally, zoonotic diseases are spread from animals to humans. For example, swine and bird flu. Whereas in cases of reverse zoonoses, the diseases pass from humans to animals.


When Are Zoonotic Diseases Likely To Spread?

Zoonotic diseases are spread by eating or drinking raw (unpasteurized) milk, undercooked meat or any animal produce, or any fruits or vegetables that are contaminated with the feces of the infected animal or by eating raw fruits or vegetables bitten by the infected animal.


What Are the Emerging Zoonotic Diseases?

While the endemic zoonoses have still not been eliminated, the region is seeing outbreaks of emerging zoonotic diseases. The agents that are responsible for the emerging zoonotic diseases are:
- Borrelia burgdorferi.
- Campylobacter jejuni.
- E.coli.
- Helicobacter pylori.
- Listeria monocytogenes.
- California serogroup viruses.


Why Do Zoonoses Happen?

Animals can sometimes carry harmful or infectious pathogens and can spread them to people and cause an illness. These illnesses are called zoonotic diseases or zoonoses. Zoonotic diseases can be caused by viruses, bacteria, parasites, or fungi. Animals can even appear healthy but still can carry pathogens that can make people sick.


Is Coronavirus a Zoonosis?

Certain studies say that Coronaviruses are zoonotic, but there are not many sufficient investigations to prove the same. There are several known Coronaviruses that have been circulating among animals that have not yet infected humans.


Is There a Cure For Zoonosis?

Mostly, the signs and symptoms of zoonotic diseases resolve without any medical treatment. The disease-causing agents like cutaneous larva migrans do not survive more than 5 to 6 weeks in the human host. But in certain cases, treatment may help control the symptoms and to prevent further secondary infections.
Dr. N. Ashok Viswanath
Dr. N. Ashok Viswanath

Infectious Diseases


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