Zoonotic Diseases

What Are They, Symptoms, Prevention, and More

Author: Lily Guo, MD

Editor: Alyssa Haag, MD

Editor: Emily Miao, MD, PharmD

Editor: Kelsey LaFayette, DNP, ARNP, FNP-C

Illustrator: Abbey Richard, MSc

Modified: Jan 06, 2025

What are zoonotic diseases?

Zoonotic diseases, or zoonoses, refer to infectious diseases that can be spread from animals to humans or vice versa. The infection can be caused by various pathogens, including bacteria, viruses, fungi, protozoa, and parasites. There are over 200 known types of zoonoses. Those who are immunocompromised, children under 5 years, and adults over 65 are more susceptible to zoonotic diseases.

An infographic detailing zoonotic diseases.

What are examples of zoonotic diseases?

Zoonotic diseases can be classified based on etiology: bacterial, viral, parasitic, fungal, or prion. Examples of bacterial zoonoses include salmonellosis, tuberculosis, Lyme disease, cat scratch disease from Bartonella henselae, psittacosis from Chlamydophila psittaci, and brucellosis. Examples of viral zoonoses include coronavirus-19 (COVID-19), rabies, Ebola, hantaviruses, and avian influenza. Parasitic zoonoses include giardiasis, malaria, and trichinosis. Fungal zoonoses include ring worm and blastomycosis from the fungus Blastomyces dermatitidis. Other examples include prion diseases which are caused by acellular non-viral pathogenic agents, including transmissible spongiform encephalopathies such as mad cow disease.

How are zoonotic diseases transmitted?

Zoonotic diseases can be transmitted through direct contact, indirect contact, through a vector (e.g., mosquito, tick, flies), or through consumption of contaminated food and water. Direct contact includes contact with the saliva, blood, urine, mucus, feces, and other bodily fluids of the infected animal. This can occur if a human touches or pets an infected animal, or from an animal biting or scratching a human.

Indirect contact includes touching objects and surfaces that have been in contact with the infected animal. For example, aquarium tanks, chicken coops, barns, pet water dishes, and plants and soil may all be objects harboring the causative microorganism.

Another example is when an infected animal sneezes or coughs, sending infectious droplets into the air which humans can inhale. Vector-born illnesses can be transmitted through an insect bite. For example, West Nile virus can be transmitted by mosquito bites.

Foodborne and waterborne illnesses occur after eating or drinking contaminated food and water, respectively. Food sources that can transmit zoonotic disease include unpasteurized milk, undercooked or raw meat or eggs, and raw fruits and vegetables contaminated with the feces of an infected animal. Similarly, water that has been contaminated by the feces of an infected animal can transmit zoonoses.

How can zoonotic diseases be prevented?

Zoonotic diseases can be prevented by avoiding consumption of high-risk foods including undercooked or raw meat. Cooking or boiling meat, especially pork and poultry, can help eliminate foodborne zoonotic agents. Individuals should avoid unpasteurized dairy products including milk and cheese. The process of pasteurization involves heating dairy products at a high temperature to destroy harmful pathogens in the food. Those who work closely with animals including farmers and hunters can prevent zoonotic diseases by using rubber gloves, goggles, and other protective clothing to prevent transmission of infected fluids into the eyes or a potential abrasion on the skin. Avoiding animals that are common vectors (i.e., infectious agent carrier) for disease (e.g., bats, ticks) and ensuring that all proper vaccinations are administered on schedule can also reduce the risk of zoonoses. Lastly, not sharing food with pets and washing your hands with soap after leaving areas with animals, such as petting zoos, are further preventative measures.

What are signs and symptoms of zoonotic diseases?

The signs and symptoms of zoonotic diseases may generally include constitutional signs and symptoms such as fever, headache, weakness and fatigue, anorexia, muscle and joint pains, swollen lymph nodes, profuse sweating, chills, weight loss and generalized aching. Specific symptoms may differ and can vary in severity depending on the specific zoonotic disease. For example, rabies is characterized by central nervous system dysfunction including sensitivity to light and sound, hydrophobia (i.e., fear of water) resulting in intermittent contraction of the pharynx, hallucinations, and muscle spasms, and it is almost always fatal once symptoms appear. Cat scratch disease is characterized by blisters or papules at the sites of the bites and scratches and swelling of the lymph nodes. Brucellosis can be characterized by more specific symptoms including arthritis, orchitis (i.e., swelling of the testicle), and endocarditis (i.e., inflammation of heart lining and valves). Infection with Hantavirus is associated with pulmonary symptoms including cough and shortness of breath or with renal symptoms including kidney failure and acute shock.

How are zoonotic diseases diagnosed?

Zoonotic diseases can be diagnosed by a healthcare professional after obtaining a detailed history including recent travel, exposure to animals, diet, and occupational history. They may ask about the symptoms experienced and perform a thorough physical examination. Laboratory testing may be performed to aid in diagnosis, including blood, stool, sputum, or salivary tests to detect pathogens in body fluids. Blood tests may also be performed to look for antibodies against zoonotic pathogens. While imaging is not typically used to make the diagnosis of zoonoses, chest X-ray or CT scan can help confirm a diagnosis in certain cases (e.g., blastomycosis, psittacosis).

How are zoonotic diseases treated?

Treatment for zoonotic illness depends on the infection and not all have specific treatment options. Medical management may include antibiotics (e.g., doxycycline, amoxicillin), anti-parasitics (e.g., ivermectin, albendazole), antifungals
(e.g., itraconazole, griseofulvin), or antivirals (e.g., ribavirin, tecovirimat, brincidofovir) depending on the cause of disease. Generally, supportive management is also used to treat zoonotic diseases including drinking plenty of fluids to prevent dehydration and getting rest.

What are the most important facts to know about zoonotic diseases?

Zoonotic diseases are infections transmitted between animals and humans. There are over 200 known types and they can be caused by bacteria, viruses, fungi, parasites, or prions. Examples include bacterial infections like salmonellosis and Lyme disease; viral infections such as COVID-19 and rabies; parasitic diseases like malaria; and fungal infections such as ringworm. Transmission can occur through indirect or direct contact with animals; through bites from ticks, mosquitos, and fleas; and by consuming contaminated water and food. Preventing zoonotic disease includes avoiding raw and undercooked meat, using protective gear when handling animals, and staying updated on vaccinations. Symptoms vary but often include fever, fatigue, and muscle aches. Diagnosis involves a detailed history, physical exams, and laboratory testing. Treatment depends on the pathogen, and includes supportive care like hydration and rest, and/or antibiotics, anti-parasitics, antifungals, and antivirals.

References

Centers for Disease Control and Prevention. About Zoonotic Diseases. One Health. Published May 16, 2024. https://www.cdc.gov/one-health/about/about-zoonotic-diseases.html

Elsohaby I, Villa L. Zoonotic diseases: Understanding the risks and mitigating the threats. BMC Vet Res. 2023;19(1):186. Published 2023 Oct 3. doi:10.1186/s12917-023-03736-8

Rahman MT, Sobur MA, Islam MS, Ievy S, Hossain MJ, El Zowalaty ME, Rahman AT, Ashour HM. Zoonotic diseases: Etiology, impact, and control. Microorganisms. 2020 Sep 12;8(9):1405. doi: 10.3390/microorganisms8091405. PMID: 32932606; PMCID: PMC7563794.

World Health Organization. Zoonoses. World Health Organization. Published July 29, 2020. https://www.who.int/news-room/fact-sheets/detail/zoonoses