Ebola virus is seen in this file photo. A form of the rare hemorrhagic fever has been discovered in pigs.
Embattled pigs source of Ebola virus, too: study
July 09, 2009
Health Reporter
Pity the poor pigs. Seems they can catch anything but a break.
First they were the source of the H1N1 virus that's now reached pandemic proportions around the globe.
And now a form of Ebola — a contagious hemorrhagic ailment that can make the worst swine flu look like a case of the sniffles — has been found in pigs, a new study in the journal Science says.
The disease, which can cause bleeding from every cavity and organ and an agonizing death, was thought to reside largely within remote monkey populations.
But the confirmation of Ebola in at least two pig herds in the Philippines has placed the disease a disconcerting step closer to humans, researchers says.
"Humans are in close proximity to swine, we're in contact with them all the time," says Michael McIntosh, the senior study author.
"And with the swine in close contact with each other they can spread it amongst themselves and then you can get a large amount of virus. You have to worry about it getting amplified in swine."
Fortunately, McIntosh says, the disease strain found in the Philippine pigs last year was the Reston Ebola virus, to which humans are resistant.
But Reston is still classified as a level four biological safety hazard — the most dangerous ranking — because it so closely resembles all other known Ebola strains, says McIntosh, a top scientist with New York's Plum Island Animal Disease Center.
"And all the other members of this virus family can cause fatal disease in humans, and this virus can cause fatal disease in non-human primates," he says.
What's more, unlike other known strains, which are transmitted through close contact with bodily fluids, Reston Ebola is an airborne virus, making it exponentially more contagious.
More troubling yet, pigs are known to churn out new mutations of many viruses, and this strain of Ebola could behave the same, McIntosh says.
Already there is some evidence of mutation, he says: The Reston viruses collected from infected Philippine pigs showed marked DNA alterations between different samples.
When McIntosh's lab helped identify the swine-based Ebola last year, the World Health Organization and other international groups scrambled to get teams of experts to the offending farms, where both the pigs and their handlers were tested for the virus.
McIntosh says six of the human handlers tested positive for Reston antibodies, but that none had experienced symptoms of the illness.
It's not even clear, McIntosh says, whether the pigs, which were dying in droves, were being killed by Ebola or by another common swine disease that also appeared on viral screens. As well, it's not clear how long the virus has been present in the herds.
And Dr. Bhagirath Singh, head of infectious diseases with the Canadian Institutes of Health Research says the study should not spark panic.
"We don't want to scare anyone, this particular strain does not infect humans, so that's one good thing," says Singh, a University of Western Ontario medical professor.
"The virus did have a contact with humans, but none of the people who were tested had the disease."
Singh says the chance of this particular virus mutating is likely mitigated by the fact that it's been in the pigs for several year.
The Reston virus is named after a sleepy Virginia town where it was first identified in a research animal quarantine centre in 1989.
A group of macaque monkeys were dying in large numbers at the suburban-based facility. And when U.S. military scientists examined samples of the diseased monkey cells, it sent the fear of God through them.
Not only did the "filo virus" they found teaming in the samples closely resemble previous strains of Ebola that had caused two hideous human outbreaks in Africa and Germany, the Reston strain appeared to be airborne.
In the end, U.S. military personnel sealed off the building and flooded it with deadly gases to destroy all life within.
But if pigs in the Philippines can be infected with Ebola, then so can African swine, experts say. And the African strains of the disease have all proven lethal to humans, with outbreaks that saw 70 per cent mortality rates.
As well, many of the African outbreaks could be traced back to the consumption of monkey meat, which means that some forms of the ailment can be transmitted through the food chain.