What are zoonotic diseases - and how dangerous are they?

It’s estimated that 60% of known infectious diseases and up to 75% of new or emerging infectious diseases are zoonotic in origin.

But what exactly is a zoonotic disease - and how dangerous can they be?

A zoonosis is an infectious disease that has transitioned from a vertebrate animal to humans. Zoonotic pathogens can be bacterial, viral or parasitic, and can spread to humans by direct contact with domestic, agricultural or wild animals, or through food and water. They can cause many different types of illness in people ranging from mild to serious, and even death.

Some of the most dangerous zoonotic diseases include COVID-19 and avian flu, salmonellosis and the Ebola virus.

Experts say the destruction of natural habitats caused by urbanization has increased the risk of zoonotic diseases due to greater contact between humans and wild animals.

As global trade and travel expands, zoonoses are posing increasing concerns for the international community - as most prominently borne out by the COVID-19 pandemic.

According to the World Health Organization (WHO), markets selling the meat or by-products of wild animals are especially high-risk due to the large numbers of undocumented pathogens known to exist in some animal populations.

The first outbreak of COVID-19 was initially suspected to have originated in a market in Wuhan, China. However, this has still not been confirmed and the WHO Director General, Dr Tedros Adhanom Ghebreyesus, said that “all hypotheses remain on the table”. By the start of July 2022, there had been more than 550 million confirmed cases of COVID-19 worldwide, and over 6.3 million deaths, according to Johns Hopkins University.

The UN estimates the global population will grow to 9.7 billion by 2050. A growing global population means a rising demand for food. This has led to an increased susceptibility to food-borne zoonoses, according to the Lancet scientific journal.

Pathogens in the livestock production chain have caused repeated outbreaks of disease from meat and dairy products, as well as meat by-products used for food flavouring, oils or stock. Farming practices in some parts of the world - in terms of method of confinement, mixing species, feeding and slaughtering, as well as inadequate disease-control methods - increase the likelihood of zoonotic diseases spreading in livestock and can provide a source of new infections in human populations, says the Lancet. How products are stored, packed, transported and prepared for consumption also affects the chances of outbreaks of disease.

Although consumption of wildlife products for food globally is considerably less than it is for domestic livestock, estimates of annual meat consumption in Central African countries alone total around 1 billion kg. The Lancet says reducing demand isn’t straightforward, as increasing “livestock production in countries without adequate disease-management practices could lead to the emergence of new pathogens due to the introduction of new hosts”.

World Zoonoses Day takes place on 6 July each year to commemorate the work of the French biologist Louis Pasteur, who successfully administered the first vaccine against rabies on that day in 1885.

To help the fight against the threat of zoonotic diseases, a groundbreaking initiative to reduce global health inequality was launched at the World Economic Forum’s Annual Meeting in Davos in May. The Accord for a Healthier World is led by pharmaceutical giant Pfizer who will offer all its patent-protected medicines and vaccines, including the COVID-19 jab, on a not-for-profit basis to 1.2 billion people in 45 lower-income countries.

“Even before the current pandemic, it was estimated that zoonoses are responsible for 2.5 billion cases of human illness and 2.7 million human deaths worldwide each year. Clearly Zoonotic diseases represent critical threats to global health security,” says Shyam Bishen, Head, Shaping the Future of Health and Healthcare at the World Economic Forum.

“Effective mitigation of the impact of endemic and new zoonotic diseases requires multisectoral collaboration. The World Economic Forum has worked with different sectors to establish public-private partnerships to help identify pathogens through proper surveillance and data sharing which will help us prevent, diagnose and treat zoonotic diseases.”