Zoonosis: Definition, Causes and Treatment

What is a Zoonosis?

A zoonosis (plural: zoonoses) is an infectious disease that can naturally be transmitted between vertebrate animals and humans. The term derives from the Greek words zôon (animal) and nosos (disease). Zoonotic diseases can be caused by bacteria, viruses, parasites, or fungi. According to the World Health Organization (WHO), more than 60% of all known human infectious diseases are of zoonotic origin, making them a major global public health concern.

Causes and Transmission Routes

Zoonoses can be transmitted from animals to humans through various direct and indirect routes:

Direct Transmission

• Contact with infected animals: through bites, scratches, or direct physical contact (e.g., rabies from dog bites)
• Contact with animal excretions: urine, feces, or saliva of infected animals (e.g., leptospirosis)
• Consumption of animal products: raw or undercooked meat, unpasteurized milk, or eggs (e.g., salmonellosis, listeriosis)

Indirect Transmission

• Vectors: transmission via insects or arachnids such as ticks, mosquitoes, or fleas (e.g., Lyme disease, malaria, leishmaniasis)
• Contaminated water or food: drinking water or food sources polluted by animal excretions
• Aerosols: inhalation of dust or dried animal excretions containing pathogens (e.g., Q fever, hantavirus)

Common Zoonotic Diseases

There are numerous well-known zoonoses. Among the most significant and frequently occurring are:

• Salmonellosis: bacterial disease caused by Salmonella species, commonly transmitted through poultry and eggs
• Lyme Disease: bacterial infection transmitted by ticks, caused by Borrelia burgdorferi
• Rabies: caused by the rabies virus, usually transmitted through bites of infected mammals
• Toxoplasmosis: parasitic disease caused by Toxoplasma gondii, often transmitted via cat feces or raw meat
• Avian Influenza (Bird Flu): viral infection primarily transmitted from poultry to humans
• Q Fever: caused by Coxiella burnetii, transmitted from livestock animals
• Hantavirus Infection: transmitted by rodents through aerosols or contact with excretions
• Brucellosis: bacterial diseases caused by Brucella species, often through raw milk or contact with infected animals

Symptoms

Symptoms of a zoonosis vary widely depending on the pathogen and the organ systems affected. Common general symptoms include:

• Fever and chills
• Fatigue and general malaise
• Headache and muscle pain
• Gastrointestinal complaints (diarrhea, nausea, vomiting)
• Skin changes (e.g., migratory erythema in Lyme disease)
• Respiratory symptoms (e.g., in hantavirus infection, Q fever, or avian influenza)

Some zoonoses can take a severe course and become life-threatening, particularly in immunocompromised individuals, the elderly, pregnant women, and young children.

Diagnosis

Diagnosis of a zoonosis typically involves a combination of the following approaches:

• Medical history: questions about animal contact, travel history, occupational exposure, and food consumption
• Laboratory tests: blood count, serology (antibody detection), pathogen culture, PCR testing
• Imaging procedures: if organ involvement is suspected (e.g., ultrasound, X-ray)

If a zoonotic infection is suspected, especially following known contact with animals or animal products, medical advice should be sought promptly.

Treatment

Treatment depends on the specific pathogen involved:

• Bacterial zoonoses: typically treated with antibiotics (e.g., doxycycline for Lyme disease or Q fever)
• Viral zoonoses: often managed symptomatically; antiviral medications are available in some cases (e.g., for influenza)
• Parasitic zoonoses: treated with specific antiparasitic agents (e.g., pyrimethamine for toxoplasmosis)
• Rabies: immediate wound care and post-exposure vaccination following exposure is lifesaving

Prevention and Protective Measures

Health authorities recommend the following measures to prevent zoonotic infections:

• Regular hand washing after contact with animals
• Thoroughly cooking meat and other animal products
• Avoiding raw milk and raw milk products
• Using tick repellents and appropriate clothing in nature
• Vaccination where available (e.g., rabies vaccine for high-risk groups, TBE vaccine)
• Regular veterinary checks for pets and livestock
• Maintaining hygiene standards in animal husbandry and food production

Reporting Obligations

Many zoonotic diseases are subject to mandatory reporting requirements in most countries. In Germany, reporting is governed by the Infection Protection Act (IfSG), and the Robert Koch Institute (RKI) monitors and documents the occurrence of zoonoses nationally. At the European level, the EFSA (European Food Safety Authority) and the ECDC (European Centre for Disease Prevention and Control) jointly coordinate the surveillance of zoonotic diseases.

References

1. World Health Organization (WHO): Zoonoses. Available at: https://www.who.int/news-room/fact-sheets/detail/zoonoses (accessed 2024)
2. Robert Koch Institut (RKI): Zoonoses and ecological health. Available at: https://www.rki.de (accessed 2024)
3. European Food Safety Authority (EFSA) & ECDC: The European Union One Health 2022 Zoonoses Report. EFSA Journal, 2023.