Sunday, 2 August 2009
Ebola - Link Swine to Humans
January 24, 2009
Pig-to-Human Ebola Case Suspected in Philippines
By DONALD G. McNEIL Jr.
In the first known case of what may be transmission of the Ebola virus from a pig to a human, a pig handler in the Philippines has tested positive for a strain of the virus, world health officials and the Philippine government announced Friday.
But the strain — Ebola Reston — is not known to be dangerous to humans, and the worker, who was infected at least six months ago, is healthy, officials said.
The development is worrying, because pigs are mixing vessels for other human and animal viruses, like flu, and because it shows that pigs may also be able to transmit the lethal strains of Ebola. Far more humans are in regular contact with pigs than with apes, monkeys or bats, the other known hosts.
But Dr. Juan Lubroth, chief of animal health at the United Nations Food and Agricultural Organization, said that there was “more need to investigate than to worry” and that many unanswered questions remained.
Ebola Reston, normally a monkey virus, was first found in pigs last year in the Philippines. Health authorities closed two farms and took blood samples from 6,000 pigs and 50 workers on the farms and in slaughterhouses. Only four pigs and the one worker tested positive, the Philippine health secretary, Francisco Duque, said at a news conference in Manila.
Dr. Lubroth said the first pigs tested were very sick, but turned out to have more than one infection, including a virulent reproductive and respiratory syndrome. The Reston virus may not have been what sickened them.
“But farmers, of course, would prefer to have pigs without Ebola,” he said. “So we want to do more testing to see what they can do to protect them.”
Broader sampling will determine, among other things, whether the disease is more common in pigs and humans than is known, whether it causes fever and how long its incubation period is.
Ebola Reston was first found in monkeys from the Philippines that died after arriving at a laboratory in Reston, Va., in 1989. Antibodies to it were found in more than 20 workers in several labs, but it is not known to have caused more than a mild flu.
By contrast, the Zaire, Sudan and Bundibugyo strains of Ebola, found in African apes, cause fatal hemorrhagic fever in humans.
It is not known how the pigs were infected, but Dr. Lubroth noted that studies in Africa found Ebola viruses in fruit bats. Similar bats live in the Philippines, and fruit bats are thought to have transmitted the deadly Nipah virus to pigs, possibly through their droppings or dead bodies.
Even if the Ebola Reston virus can be shared between pigs and people, there is little chance it will mutate to become more lethal, said Dr. Pierre Rollin, acting chief of special pathogens for the Centers for Disease Control and Prevention, who also visited the Philippines for the investigation.
“This virus is very stable, not like flu or H.I.V.,” he said. “Previously, when the virus went from primates to humans, it did not change. The identical virus was found in both.”
Also, humans do not carry other members of the filovirus family that could mix with it, the way that influenza strains from birds, pigs and humans can swap parts of genes.
The infection does suggest that pigs could transmit lethal Ebola, which inspired germ-terror movies like “Outbreak.” Fortunately, Dr. Rollin noted, there are no large pig-farming operations in Sudan, a Muslim country, in rural Congo or in most other places where the fatal strains flourish.
“It’s probably a rare event that pigs get infected,” said Dr. Thomas G. Ksiazek, a pathogens specialist at the University of Texas Medical School in Galveston. “It hasn’t led to a past catastrophe. We’d know about a catastrophe.”
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