Move Over Swine Flu, Ebola’s Back
Porcine discovery rouses moribund Plum Island
(07/16/2009) A new swine Ebola virus has been discovered at the Plum Island Animal Disease Center. The news comes after a quiet winter there following an announcement that the facility’s operations would move to Kansas, a move thrown into doubt last week when the Senate refused to fund it pending further study.
The discovery of Ebola at Plum Island marked the first time the virus was known to have infected pigs. The samples came from dead animals found in the Philippines, and last summer they were sent to the lab, where they were suspected of containing blue ear disease, not Ebola.
The strain, called Ebola Reston, was discovered in monkeys sent to Reston, Va., in 1989. Before crossing species to swine, it had been confined to only Philippine monkeys.
Although the disease can infect humans, it is not known to produce illness or the same symptoms as the Ebola viruses in Africa that lead people to hemorrhage after their blood loses the ability to clot. It is also not clear whether it causes illness in pigs, even though they too can carry it.
Michael McIntosh of the Department of Agriculture’s Animal and Plant Health Inspection Services, who was working at Plum Island at the time, was one of the researchers who made the discovery.
He said in an e-mail message that the Centers for Disease Control and other organizations were still investigating whether it was the Ebola virus that caused the pigs’ deaths.
The virus had been detected previously in humans exposed to infected monkeys. He noted that in a report published in the journal Science “the World Health Organization, Food and Agriculture Organization of the United Nations, and Philippines Ministry of Health had 141 people that were closely associated with the farms serologically tested and 6 individuals were found by the Centers for Disease Control and Prevention to have developed antibodies to ebolavirus.”
He added that the positive result “is considered indirect evidence of infection and confirms the possible transmission from pigs to humans. In all instances prior and including the recent incidence with Reston ebolavirus in pigs, infected humans showed no clinical signs of illness. These are low numbers of healthy adults, so the fact that Reston ebolavirus is known to cause disease in non-human primates makes it a concern for public health. There is no evidence at this time, however, to suggest that it does cause disease in humans.”
Until the virus had been discovered in these samples, there was no evidence that pigs could carry the disease. Only with new genetic testing that has been recently developed have researchers been able to find viruses other than ones they are specifically looking for in samples. The new tests “permit one to survey a sample for the presence of genetic material from many potential pathogens all at once, as opposed to looking for one predicted pathogen at a time. In this instance, we knew what the virus wasn’t because the U.S.D.A. tested for a specific known disease of pigs and found none in the culture sample, but we did not know what it was.”
The new tests enabled the researchers “to discover something we would normally not expect to see in pigs. These approaches are relatively new, and typically used only on complex or high-priority disease investigations. Over time, perhaps they will become more common and I expect more unexpected discoveries will be made. Such discoveries should help us understand things like disease syndromes that may be caused by more than one pathogen at a time.”
When they were able to reconfirm that the strain was 95-percent identical to the Reston Ebola virus, the researchers contacted the Centers for Disease Control in Atlanta and the samples were sent there directly by hand courier or destroyed.
All Ebola strains are pathogens that require Biosafety Level 4 precautions to study them, and Plum Island has only a Biosafety Level 3 rating. It studies primarily foot-and-mouth disease, a highly contagious pathogen to livestock that rarely infects humans and does not cause illness in them. The higher-rated diseases are those that can be transferred from animals to humans, may be life threatening, and for which no cure is known.
Dr. McIntosh said the Reston Ebola was the only level 4 virus that he knew of that “is not connected to disease in humans and of course was not known to be a potential hazard in diagnostic samples from pigs.”
Because of its higher rating, however, “the C.D.C. was requested to check all staff that handled or worked near any samples from that case,” he said. “Though the Reston ebolavirus is not known to cause disease in humans, because it is known to cause disease in non-human primates and because there is limited information available about it in humans, the W.H.O. and the C.D.C. continue to classify it as a [Biosafety Level 4] agent. Given the potential risk, it was certainly a prudent measure to have the C.D.C. verify our staff was safe from any risk of exposure.”
During hearings in Southold last year, when Plum Island was being considered as the site of a new facility now intended for Kansas, East End residents came up with a number of scary scenarios that a higher-rated facility might bring about. But representatives from the Department of Homeland Security said repeatedly that the new facility was not going to study diseases like Ebola, even with added precautions such as further restricting access and placing labs in a strictly controlled area within an isolated building.
Although Representative Tim Bishop was not available for comment this week, his office said it had been assured by the Department of Homeland Security that it had handled the situation under specific protocols and that everyone involved was deemed free of the disease.
Dr. McIntosh agreed that for samples suspected of “possibly containing a [Biosafety Level 4] agent, the C.D.C. should be immediately contacted and they should certainly not be sent anywhere other than a BSL4 lab.”
“For any diagnostic laboratory, a risk assessment is conducted to avoid potential risks to human health. Indeed, if there was a known or suspected human health risk associated with these samples, they would not have been accepted by the Plum Island Animal Disease Center.”
Although the Plum Island lab is scheduled to close once the new facility is operational, the Senate’s refusal to fund the new Kansas lab in the latest appropriations bill could keep Plum Island open longer or even indefinitely as researchers debate the wisdom of moving the study of highly contagious livestock diseases such as foot-and-mouth onto the mainland, where they could be much more easily transmitted among animals through the air.
Senator Jon Tester of Montana, who introduced the legislation to remove the funding for the new site and halt construction until the risks of moving such studies to the mainland could be more fully assessed, suggested that Plum Island once again be considered as the site of the new Biosafety Level 4 facility. He made his comments during a Senate hearing on the nomination of Tara O’Toole to be the undersecretary for the Department of Homeland Security’s Science and Technology Directorate.
Dr. O’Toole, who is an expert on biosecurity, said she believed that the containment offered by a Biosafety Level 4 facility would be enough to protect the surrounding region, but that she would study the pending Government Accountability Office report on the risks of taking foot-and-mouth to the mainland before coming to any conclusions.