‘Live animals are the largest source of infection’: dangers of the export trade
Transporting more livestock will increase transmission of diseases, including some that could also threaten humans
The growth of the live animal export trade will make the spread of diseases more likely, experts have warned.
Almost 30% more pigs, goats, cows and sheep were shipped, flown and driven across the world in 2017 than a decade earlier, according to the UN’s Food and Agriculture Organization.
The figure is set to rise further, partly because it is still often cheaper to move live animals than use refrigerated transport, despite advances in technology.
Consumer demand for fresh meat is also rising as the global population approaches 8 billion, including many who are increasingly adopting diets rich in meat.
But transporting live animals around the world increases the risk of disease transmission, according to veterinarians and epidemiologists who fear the growing industry may have already caused viruses to spread.
Jeroen Dewulf, a veterinarian at Ghent University in Belgium, said the introduction of the African swine fever virus (ASF) into Belgium had almost certainly been caused by human interference: either through imported contaminated animal products or by illegal movements of wild boar.
“There are several drivers of spreading diseases, but live animals are the largest source of infection,” Dewulf said. “The more you are going to move animals, the more you run the risk that diseases will be spread through these animals. There are other routes, the virus can be transmitted in meat products for example, but it’s much more efficient to transmit via live animals.”
David McIver, a senior scientist and epidemiologist at biotech company Metabiota, said the rise in live animal exports was a growing issue for many other diseases, such as avian influenza virus, mad cow disease and Nipah virus, while he warned that ASF could one day feasibly threaten humans in some form.
“The first case of Nipah virus in 1998 came after an outbreak in Malaysia following the expansion of pig farming in pristine rainforest areas,” he said.
“Bats were eating fruit, they dropped it with their saliva on it, it was eaten by pigs, then it gets into humans and there were 105 deaths. Tons of swine had to be culled to get the outbreak under control. If we’re exporting those animals around the world we’re potentially moving unknown pathogens to new places.”
In another well-known case, British live cattle exports, as well as those of beef products, were banned in the 1990s due to the fear of spreading bovine spongiform encephalopathy, commonly known as mad cow disease.
It is believed that variant Creutzfeldt-Jakob disease, a rare, fatal brain disorder, is likely to be caused by people ingesting meat contaminated with mad cow disease.
The authors of a study in journal BioMed warned in 2015: “Animal trade is an effective way of introducing, maintaining and spreading animal diseases, as observed with the spread of different strains of foot and mouth disease in Africa, the Middle East and Asia and the spread of bovine spongiform encephalopathy (BSE), for example, into Oman and Canada through the importation of infected cattle.”
McIver added: “Even though ASF doesn’t affect humans now, pigs and people are not so different biologically and immunologically, so it is conceivable that a few small changes in the genetics of the virus can allow that to hop into people and then we’ve got ourselves a serious problem.”
Prof Dirk Pfeiffer, from City University in Hong Kong and the Royal Veterinary College in London, said the risk depends on where you are in the world. “It’s very regulated in high-income countries with fairly effective measures in place protecting their livestock populations from spread of infectious diseases,” he said.
“The real issue is in many of the low- to medium-income countries where there are new opportunities for money to be made, and that includes increased meat demand. Movements of live animals in these parts of the world play a role in spreading animal disease.” In China, for example, live animals are regularly moved around the country in order to supply the ‘wet markets’ where butchers serve up freshly slaughtered meat. These places have long been connected with disease risk – and, indeed, the recent outbreak of coronavirus has been traced back to a wet market in Wuhan.
A system managed by the World Organisation for Animal Health monitors disease outbreaks and provides information based on the reporting of affected countries. While it is praised for its role, it has to rely on prompt and honest reporting from states to be fully effective.
“One of the perverse incentives about the surveillance system is that the harder you research the more likely you’ll find something, and then the country will be a victim of finding something,” Dewulf said.
“In Belgium, for example, with the recent ASF outbreak, we were carefully monitoring, we notified all the responsible agencies, and then we faced all the consequences, such as trade restrictions, etc. In consequence, our animal industry has been hit very hard.”
But despite the growing realisation of the need to control exports more robustly, experts warn that it would be impossible to screen all animals.
“In most cases where we look at the transmission of disease, whether in humans or livestock, we tend to see them move quicker and in more diverse ways than our surveillance systems are able to keep up with,” McIver said.
Nor are these systems designed to screen live animals or meat products entering or leaving countries, he said, before warning of diseases which have not yet been identified.
“Due to the sheer volume of animals that move around, the budgets that are allocated towards it are not always sufficient and in many cases we’re only able to look for things we know about. Animals may be coming or going with pathogens that are potentially really dangerous but we just haven’t dealt with them yet.”