Jha '13 (Alok Jha, Guardian reporter and science correspondent for ITV News and the author of The Water Book: the Extraordinary Story of Our Most Ordinary Substance"A deadly disease could travel at jet speed around the world. How do we stop it in time?", The Guardian, November 12, https://www.theguardian.com/science/2013/nov/12/deadly-disease-modern-global-epidemic, CL)
Walk past the endless rows of vegetables, past the dozens of stalls selling every possible part of a pigand, at the centre of Cao Lanh city's market, a woman is doing a brisk trade in selling rats for food. Two cages swarm with them on a table next to her. Live frogs are available too, and, on the floor near her stall is a box of sluggish snakes. Chickens and duckscluck and quack nearby. A faint smell of urine thickens air that is already heavy from the previous night's rains. Rats are a staple source of meat in Vietnam, farmed and sold much like any other livestock. The stallholder butchers the animals to order. Reaching into the cage she will grab an animal by its tail, hit its head across a large stone, chop off its feet and head with a large pair of scissors, skin it, cut it into pieces and place everything into a small yellow plastic bag. Inevitably, the animal's blood ends up on her hands. Scores of people are selling and butchering live animals, breathing the same air and in constant contact with the animals' blood, urine and feces. This woman, and many others like her who work in the farms and abattoirs deep in southern Vietnam's Mekong delta, are doing what they have done for generations. And now they are in the front line in a new scientific race to predict the next pandemic. Of the roughly 400 emerging infectious diseases that have been identified since 1940, more than 60% are zoonotic ie they came from animals. Throughout history this has been common. HIV originated in monkeys, ebola in bats, influenza in pigs and birds. The rate at which new pathogens are emerging is on the rise, even taking into account the increase in awareness and surveillance. Which pathogens will cross the species barrier next, and which one is the greatest potential public health concern, is a subject of intense interest. A modern outbreak, caused by a previously unknown virus, could travel at jet-speed around the world, spreading across the continents in just a few days, causing illness, panic and death.
Pathogens have transferred from animals to people for as long as we have had contact. The ancient domestication of livestock led to the emergence of measles, and further intensification of farming in recent decades has caused problems such as the brain-wasting Creutzfeldt-Jakob disease, the human form of BSE. Expanding trade routes in the 14th century spread the rat-borne Black Death across Europe and smallpox to the Americas in the 16th century. Today's tightly connected world has seen the spread of swine flu, Sars, West Nile virus and H5N1 bird flu. The biggest pandemic on record was the 1918 Spanish influenza, which killed 50 million people at a time when the fastest way to travel the globe was by ship. In 2009 swine flu was the most recent pandemic that got public health officials concerned; first detected in April of that year in Mexico, it turned up in London within a week. One of the most worrying recent outbreaks for scientists was the re-emergence of the H5N1 bird flu virus in 2005. Jeremy Farrar, a professor of tropical medicine and global health at Oxford University and, until recently head of the university's clinical research unit in Vietnam, says he remembers the night a young girl came into the children's hospital in Ho Chi Minh City with a serious lung infection. Initially, he thought that it might have been Sars – a coronavirus that had first been identified in China in late 2002 and had spread rapidly to Canada among other places – making its comeback. That was until he heard the girl's story from a colleague. "This is years ago and I remember the story as if it was yesterday," he says. "She had been playing with her duck, arguing with her brother. They had buried it when it died and she had dug it up later to re-bury it somewhere she wanted to bury it." The duck was the crucial part of the evidence in determining that this was a new outbreak and Farrar says that for the next few hours, no one knew how bad it would get. Would the girl's family come in during the night with infections? Would the nurses and doctors be affected? H5N1 did not become the next Sars and was contained, although 98 people were infected and 43 died in 2005. It has not gone away, says Farrar, and is still circulating in poultry and ducks in almost the whole of Asia, remaining a major concern for human cases, given how virulent it is when people get infected.
A successful zoonotic pathogen manages to jump from an animal to a person, invades their cells, replicates and then finds a way to transmit to other people. Working out which pathogens will make the leap – a process called "spillover" – is not easy. A pathogen from a primate, for example, is more likely to spill over to humans than a pathogen from a rat, which is more likely to do so than something from a bird. Frequency of contact is also important; someone working on a live bird farm is more likely to be exposed to a multitude of animal viruses than someone living in a city who only sees a monkey in a zoo. "The truth is, we really don't know how much of this happens," says Derek Smith, a professor of infectious disease informatics at the University of Cambridge. "Much more is noticed today than was noticed 50 years ago and was noticed 50 years before that. There are reasons to think this might be because we disrupt habitats and come into contact with animals we haven't been in contact with before. We have different things that we do socially, perhaps, than we did in the past. But we also look harder." Viruses and other pathogens continually flow between species, often with no effects, sometimes mutating, once in a while causing illness. This mixing is known as "viral chatter" and the more different species come into regular close contact, thehigher the chances of a spillover event occurring. "This is how viruses have always worked, the big change is us," says Mark Woolhouse, a professor of infectious disease epidemiology at the University of Edinburgh. "The big change happened probably several thousands of years ago when we became a crowd species and that gave these viruses new opportunities which they hadn't had before in humans. Ever since then, from time to time a new virus has come along to take advantage of this new, very densely populated, crowded species – humans – that it can now spread between much more easily. That process is still happening; the viruses are still discovering us. We like to think we discover viruses, but it's also the viruses discovering us." Tracking what is moving between which species is the task of Stephen Baker's team, based at the Oxford University clinical research unit in Ho Chi Minh City. Baker is an infectious disease biologist who co-ordinates the Vizions project and I met him at his lab while I was making a Radio 4 documentary about the scientific hunt for the next big pandemic. His sampling teams visit farms, markets and abattoirs across Vietnam to take regular blood from people at high risk of being subject to a spillover event. This high-risk cohort, which will eventually number 1,000 people, will be monitored every six months and, if they ever turn up sick at a hospital, Baker's team will get an alert. The sampling teams also take blood and faecal swabs from pigs, chickens, dogs, cats and rats and anything else living nearby. During a trip to a smallholding near the Cao Lanh food market, Baker explains that it is at places like this, where people are in regular and close contact with animals, that scientists will be able to get their first hints of any spillovers that might become a bigger threat. The farm, which is typical of Vietnam and other parts of south-east Asia, has a range of animals – pigs, ducks and free-range chickens. They are in close exposure to each other and any farmworkers, too. The farms next door are only separated by lines of trees or small fences. As well as the farm animals, Baker's team also do their best to sample wild animals in the vicinity, including civets, rats and bats, that can easily transport pathogens across wide distances.