Zoonoses are infections or diseases that can be transmitted directly or indirectly between animals and humans, for instance by consuming contaminated foodstuffs or through contact with infected animals. The severity of these diseases in humans varies from mild symptoms to life-threatening conditions.
Research indicates that between one third and one half of all human infectious diseases have a zoonotic origin, that is, are transmitted from animals. About 75% of the new diseases that have affected humans over the past 10 years (such as the West Nile Virus) have originated from animals or products of animal origin.
Zoonoses are transmissible between animals and humans in a variety of ways and an infection can also often be transmitted through multiple ways:
Food-borne zoonotic diseases
- Food-borne zoonotic pathogens are transmitted through consumption of contaminated food or drinking water. Infectious agents in foodstuffs include bacteria such as Salmonella and Campylobacter, viruses such as norovirus or hepatitis A virus, and parasites such as Trichinella.
- The infectious agent which causes Bovine Spongiform Encephalopathy (BSE) in cattle can also be transmitted to humans through consumption of contaminated meat causing variant Creuzfeldt-Jakob disease. Unlike other food-borne diseases which are spread by microorganisms, BSE is caused by a prion, which is an abnormal form of a protein (known as PrPc).
Non-food-borne zoonotic diseases
- By vectors, i.e. living organisms that transmit infectious agents from an infected animal to a human or another animal. Vectors are frequently arthropods, such as mosquitoes, ticks, flies, fleas and lice and can transmit diseases such as malaria, West-Nile virus and Lyme disease.
- Through direct contact or close proximity with infected animals. Diseases that are mainly transmissible to other animals or humans in this way include:
- Avian influenza , which is a viral disease occurring in poultry and other birds. Pigs can also be carriers of this virus as well as of other influenza viruses. Avian influenza primarily affects birds, but there have been cases of viruses being transmitted to humans and other animals through close contact with infected birds.
- Q fever is a disease, caused by the Coxiela burnetti bacterium, affecting animals and humans. It has been reported to be present in a wide range of species, including cattle, sheep and goats as well as birds and arthropods. Human infection mainly results from the inhalation of dust contaminated with bacteria from the placenta and birth fluids or faeces from infected animals. Other modes of transmission, such as through contaminated water or the feces of infected arthropods are rare.
- A specific strain of the Meticillin-resistant Staphylococcus aureus (MRSA) bacterium (CC398) which can be transmitted through contact with live animals.
- Salmonella infections can originate from contact with infected reptiles and amphibians such as pet snakes, iguanas and frogs or their environment.
- Verotoxin-producing Escherichia coli (E. coli) can be acquired through contact with infected farm animals.
- These diseases can also be transmitted through the environment, e.g. Verotoxin-producing E. coli in contaminated swimming water.