Dubai: Earlier this week, medical investigators for the first time have confirmed the Mers coronavirus in a camel, one belonging to a Saudi man also ill with the new virus. The tie has provided a critical clue into the virus’s animal hosts and transmission
The first definitive confirmation of the Mers coronavirus in the camel provides a “missing link” for disease experts, said Henry L. Niman, a microbiologist in Pittsburgh who tracks the Middle East virus and other infectious diseases.
Mers typically causes severe respiratory problems. The virus typically spreads in limited fashion from person to person after appearing in a community, but medical experts have been mystified as to the original source animal.
Owning racing stables or farms with camels and other livestock is popular among Saudi and other Gulf residents with the means to do so. Some, but not all, of the originating human cases in clusters of Mers have been found to have come in contact with camels or other livestock.
But the reality too is that if you walk past the endless rows of vegetables, past the dozens of stalls selling every possible part of animals in any market around the world, scores of people are selling and butchering live animals, breathing the same air and in constant contact with the animals’ blood, urine and faeces.
Of the roughly 400 emerging infectious diseases that have been identified since 1940, more than 60 per cent are zoonotic — 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.”
—With inputs from agencies