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Do Humans Cause Diseases?

Jenn Smith

Posted on April 08 2020

Hunting, farming and the global move of people to cities has led to massive declines in biodiversity and increased the risk of dangerous viruses like Covid-19 spilling over from animals to humans, a major study has concluded.

In a paper that suggests the underlying cause of the present pandemic is likely to be increased human contact with wildlife, scientists from Australia and the US traced which animals were most likely to share pathogens with humans.

Taking 142 viruses known to have been transmitted from animals to humans over many years, they matched them to the IUCN’s red list of threatened species.

Domesticated animals like cattle, sheep, dogs and goats shared the highest number of viruses with humans, with eight times more animal-borne viruses than wild mammal species.

Wild animals that have adapted well to human-dominated environments also share more viruses with people. Rodents, bats and primates – which often live among people, and close to houses and farms – together were implicated as hosts for nearly 75% of all viruses. Bats alone have been linked to diseases like Sars, Nipah, Marburg and Ebola.

The study, published in the journal Proceedings of the Royal Society B, found that the spillover risk was highest from threatened and endangered wild animals whose populations had declined largely due to hunting, the wildlife trade and loss of habitat.

“Human encroachment into biodiverse areas increases the risk of spillover of novel infectious diseases by enabling new contacts between humans and wildlife … We found that species in the primate and bat orders were significantly more likely to harbour zoonotic viruses compared to all other orders,” it said.

“Spillover of viruses from animals are a direct result of our actions involving wildlife and their habitat,” said lead author Christine Kreuder Johnson, director of the EpiCenter for Disease Dynamics at the One Health Institute, a programme of the UC Davis School of Veterinary Medicine.

“The consequence is they’re sharing their viruses with us. These actions simultaneously threaten species survival and increase the risk of spillover. In an unfortunate convergence of many factors, this brings about the kind of mess we’re in now,” she said.

“We need to be really attentive to how we interact with wildlife and the activities that bring humans and wildlife together. We obviously don’t want pandemics of this scale. We need to find ways to co-exist safely with wildlife, as they have no shortages of viruses to give us,” said Johnson.

Separately, more than 200 of the world’s wildlife groups have written to the World Health Organization (WHO) calling on it to recommend to countries a highly precautionary approach to the multi-billion dollar wildlife trade, and a permanent ban on all live wildlife markets and the use of wildlife in traditional medicine.

The Covid-19 pandemic, says the letter, is believed to have originated at wildlife markets in China, and to have been transmitted to humans as a result of the close proximity between wildlife and people.

The groups, which include the International Fund for Animal Welfare, the Zoological Society of London and Peta, say a ban on wildlife markets globally will help prevent the spread of disease, and address “one of the major drivers of species extinction”.

“This decisive action, well within the WHO’s mandate, would be an impactful first step in adopting a highly precautionary approach to wildlife trade that poses a risk to human health,” says the letter.

The organisations argue that zoonotic diseases are responsible for over 2 billion cases of human illness and over 2 million human deaths each year, including from Ebola, Mers, HIV, bovine tuberculosis, rabies, and leptospirosis.

The letter follows acting UN biodiversity chief Elizabeth Maruma Mrema’s call in the Guardian this week for a global ban on wildlife markets.

Unlike the conservation groups, Mrema, the acting executive secretary of the UN Convention on Biological Diversity, emphasised that millions of people, particularly in Africa, depend on wild animals for food and that alternatives to wet markets are needed.

In a growing sign that global organisations are embarrassed by the emergence of zoonotic diseases in traded animals, Cites, the body which regulates the international trade of animals, refused to be drawn into the growing debate about the origins of Covid-19.

In a terse statement it said: “Matters regarding zoonotic diseases are outside of Cites’s mandate and the Secretariat does not have the competence to make comments on the recent news on the possible links between human consumption of wild animals and Covid-19.”

Story re-posted from The Guardian. By John Vidal.