Zoonotic diseases

Zoonotic diseases - Masked lady in city

Animals can sometimes carry harmful germs that can spread to people and cause illness – these are known as zoonotic diseases or zoonoses. Such diseases may be caused by viruses, bacteria, parasites or fungi. They may be mild or serious, and in some cases may cause death. Animals can sometimes appear healthy even when they are carrying a virus, for example, that can make people very ill. 

How many people are affected by zoonotic disease? 

Taken together, the top 13 diseases caught from animals, cause 2.4 billion cases of illness and 2.2 million deaths per year (Grace et al., 2012).

Scientists estimate that more than six out of every 10 known infectious diseases in people can be spread from animals, and three out of every four new or emerging infectious diseases in people come from animals (CDC, 2014). 

Modern intensive farming methods, designed to keep the cost of meat as low as possible, have led to the emergence of many new zoonotic diseases such as BSE, avian influenza (bird flu) and Escherichia coli (E. coli) O157. The conditions in which we keep farmed animals today, packed into filthy, overcrowded sheds, standing on top of each other, in their own faeces, physically stressed and pushed to the limit, provide an ideal breeding ground for emerging viruses and bacteria.   

A further problem is wildlife 'wet' markets, where all manner of live animals are caged in cramped conditions alongside each other in busy markets also packed with people. It is thought the new coronavirus that causes COVID-19, which emerged in China in 2019, may have originated in such a market. 

Ebola, SARS, MERS and AIDS

Other notable zoonotic diseases include Ebola, SARS and MERS all caused by viruses that 'spilled over' from bats to chimpanzees (hunted for bushmeat), civets cats (in wet markets) and camels, respectively. The HIV virus that causes acquired immune deficiency syndrome (AIDS) is thought to have jumped to humans from primates hunted for bushmeat (chimpanzees and sooty mangabey monkeys). If we keep invading and decimating wild landscapes, killing wild animals or capturing them and taking them to markets, we will inevitably shake viruses loose from their natural hosts. 

One way to take control is for large numbers of people to stop eating meat and remove the viruses and superbugs’ breeding ground.

Grace D, Mutua F, Ochungo P, Kruska R, Jones K, Brierley L, Lapar L, Said M, Herrero M, Pham Duc Phuc, Nguyen Bich Thao, Akuku I and Ogutu F. 2012. Mapping of poverty and likely zoonoses hotspots. ILRI, Kenya. 
CDC, 2014. Zoonotic Diseases. https://www.cdc.gov/onehealth/basics/zoonotic-diseases.html