The Covid-19 pandemic was a wake-up call if we ever needed it about how diseases can cross over from animals to humans.
Although never proven fully, it was widely accepted that the novel coronavirus that caused Covid-19 originated in a wet food market in the Chinese city of Wuhan. Virologists believe Severe Acute Respiratory Syndrome coronavirus 2 (Sars-CoV-2) jumped from various wild animals to humans multiple times, resulting in more than one strain of the novel coronavirus emerging in China around the same time.
Wet food markets are prevalent in sub-Saharan Africa and in a lot of Asian countries, where the transportation of wild animals for sale — often crammed into cages placed on top of each other — creates a perfect breeding ground for viruses to cross through species barriers into humans.
Researchers say that scientists and health officials must improve wildlife trade in China and other countries with wet markets by promoting more comprehensive testing of live animals sold in such markets to avoid them being the starting point of future pandemics.
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The One Health approach — which recognises that all life on the planet is connected in a single ecosystem — is more urgent now than ever, according to Dr Kieran Meade, associate professor ofiImmune-biology at University College Dublin and chairman of the recent European Veterinary Immunology workshop held at UCD.
“Covid-19 has taught us that the risk from zoonotic infections [zoonoses are infectious diseases that cross between animals, birds, insects and humans] is real, impactful and costly on many levels and that we can’t afford to let our guard down,” says Meade.
Controlling infection at source is essential, he says. “It’s incredible to think that over one-fifth of the total global animal production is lost annually to disease. Also, zoonotic diseases caused by bacteria, viruses, fungi and parasites can move between species so prevention of infection at source — often in animal and wildlife populations is key.”
Researchers claim that understanding the immune response in all animal species is the best way forward to develop new breeding techniques, DNA editing and vaccination strategies to prevent disease before they make animals sick.
Prof Alison Van Eenennaam, professor of animal biotechnology and genomics at the University of California (Davis), spoke at the workshop. She is an expert in gene editing, an approach which is now widely used to build disease resistance in animals including cattle, sheep, goats and chickens.
“The technique with gene editing is to make sure that the target binding site for the virus is no longer present,” she explains. Ideally, such an approach will make the animal resistant to the disease but researchers also need to ensure they can’t harbour a “reservoir” of the disease while being resilient themselves.
“We are always concerned that animals aren’t harbouring the virus — especially in the case of zoonotic diseases,” Eenennaam says.
Several countries including Argentina, Australia, Brazil, Colombia and Japan, have adopted a regulatory policy that similarly treats gene-edited animals to those produced using conventional breeding. This approach has resulted in certain food products developed from cattle in Argentina and Brazil and disease-resistant pigs in Colombia.
In Japan, a Kyoto-based start-up has started selling gene-edited red sea bream and tiger puffer fish after regulators found no adverse effects on humans. The European Union is however more cautious about regulating gene-edited food for human consumption.
Eenennaam notes that the Court of Justice of the European Union in 2018 decided that gene-edited organisms would be treated the same as genetically modified organisms (GMOs). “This has stopped anything from getting commercialised in Europe even with pushback from scientists.”
She argues that activating a gene within an animal to turn off a function is not the same as bringing novel DNA into an animal. And, if the EU holds back on such decisions, it will be less competitive than other parts of the world, she predicts.
“Europe hasn’t made a formal decision on plants yet and because animals are sentient beings, there will be welfare considerations for animals too,” she says.
Meanwhile, Delia Grace, professor of food safety systems at the University of Greenwich in the UK, highlighted the risks arising from endemic zoonoses.
She is a UCD graduate and is leading research into zoonoses and food-borne diseases at the International Livestock Research Institute (ILRI) in Nairobi, Kenya. And in that part of the world, she says that while epidemic zoonoses are more dreaded, endemic zoonoses have a more negative impact on poor farmers in low and middle-income countries.
“Bird flu, Ebola, Covid-19 and now monkey pox (Mpox). The list of widely recognised zoonotic diseases continues to lengthen yet hundreds of millions of people in Africa are much more likely to get sick and die from the food they eat than the new and alarming disease that can close down their economies,” says Grace.
According to the World Health Organisation, the health burden of food-borne diseases is comparable to that of the big three infectious diseases (ie malaria, HIV-Aids and tuberculosis). The most impactful zoonoses in low and middle-income countries include brucellosis, tuberculosis, rabies and zoonoses causing food-borne diseases.
Developing livestock vaccines that are cost-effective, stable and scalable is one of the most important strategies to combat animal disease, according to the ILRI.
Grace and other researchers at the ILRI are also keenly aware of the need to develop better food safety in domestic markets in the developing world.
“Unlike earlier projects which focused on either end of the food chain — the farm and household — new projects are addressing food sellers as earlier research found that informal markets were a neglected but natural point to promote food safety,” says Himadri Pal, a researcher with the ILRI.
Meade points to the importance of proactively sampling what variants are in circulation as a way of monitoring future zoonoses. “As we expand our land base to feed the growing global population, there is inevitably more contact between livestock and wildlife leading to issues of diseases crossing between species,” he says.
The Coalition for Epidemic Preparedness Innovations (CEPI) and researchers at the One Health Institute in the University of California campus (Davis) use the so-called Spillover viral ranking app to identify zoonotic viruses which are most likely to lead to a new disease with a pandemic potential.
The open database ranks hundreds of viruses, hosts and environmental risk factors to identify the viruses with the highest risk of zoonotic spillover from wildlife to humans and to highlight those most likely to spread and cause human outbreaks.
The CEPI plan is to help the world construct a library of vaccines that are ready to be adapted against the next “Disease X” within 100 days of its identification.
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