Swine-Flu Expert says Human from Eurasia May be Origin of Recent Outbreak
May 5, 2009 - 1:19 PMA top expert says it's likely that the most recent strain of swine influenza A H1N1 didn't originate in North America, but came from Eurasia.
And it may not even have originated in pigs.
“We don’t know where this particular virus formed, but because people and swine can be infected with similar viruses, the formation of this particular virus could have happened in either species – either humans or pigs,” said Dr. Bruce Jahnke, a professor of veterinary medicine at Iowa State University in Ames, Iowa.
“I have a feeling that it didn’t happen here in North America, but that’s just my opinion,” Jahnke told CNSNews.com on Monday. “I think the (genetic) re-assortment (of the virus) probably is more likely to have happened in Europe or Asia – and probably came over in a person, to be honest. That would seem to make the most logical sense.
“More people than pigs come from Europe and Asia to North America,” Jahnke said.
Jahnke underscored that he is not saying that he knows for sure where the virus originated.
“I don’t have anything to back that up, it’s just from what we know about viruses and pigs and people in different parts of the world,” he said. “That’s one scenario, but it might not be what happened.”
The virus could have occurred in swine somewhere and passed to humans, he admitted.
“But it also could have been somebody working with pigs who was infected with two different kinds of virus. We’ll probably never know.
“I think it’s more likely to have happened in Europe or Asia,” he said.
“There is a lot of back and forth between humans and swine with these viruses,” Jahnke said. “We’ve had more changes recently in viruses that we find in swine that have really occurred with the introduction of genes from human viruses.
“Pigs have probably had more problems with contracting human viruses, than the other way around,” Jahnke said. “In fact, there have been recommendations to make sure people that are working with pigs be vaccinated against human flu so they won’t be spreading viruses to the pigs.”
In 1998, Jahnke was part of a team that identified a new subtype of Swine Influenza Virus (SIV) - the first new subtype detected since the disease was discovered in the U.S. in 1918.
Swine flu in pigs is not considered a major threat, he said.
“Influenza is a very common virus in swine, and we’ve dealt with it for years,” Jahnke said. “The first one that we ever really found in swine happened after the 1918 human pandemic, so it probably moved from people into pigs. We’ve been dealing with it ever since. For the most part in the intervening years, people recognized it, they knew what it was, it passed through pigs and they looked tough for a couple of days and they recovered. There wasn’t even an impetus to produce vaccines until twenty-some years ago. It is not a highly serious disease in pigs.”
The strain involved in the outbreak among humans in Mexico isn’t one found in swine, he said.
“We have no evidence that this virus, as it exists in the form that has be moving through people, has ever existed in the swine populations of this country before,” Jahnke said.
Asia, however, is known as a hotbed for viruses that have the potential to be lethal, Jahnke said.
“That’s why there is so much interest in what’s going on in Asia, because you look at the pandemics that have occurred – it appears that in those areas, there have been opportunities for different viruses to get together and reassort and form a virus that forms a pandemic,” the scientist added.
Dr. Todd Hatchette of Dalhousie University in Halifax, Nova Scotia, one of Canada’s top influenza experts, agreed that we simply don’t know where this strain originated.
“Ultimately we have no idea where this came from,” Hatchette said. “They keep publishing this little boy as patient zero, but I don’t know how they can concretely say that. I’m sure that many labs are looking intently at the genetic components of this virus and doing studies to see exactly where this virus came from or at least to give an indication of where it came from.”
One thing both agree on: it looks like the Mexican outbreak involves mild cases of the flu – not unlike the seasonal varieties.
“What we do know about viruses would suggest that this one probably won’t get out of hand,” Jahnke told CNSNews.com.
“Right now we’re seeing cases of relatively mild influenza,” Hatchette told CNSNews.com, “which is different from the reports that were coming from Mexico, and no one really knows why that is. Part of it may be that the complete epidemiology in Mexico is not well teased-out yet – and there may be many more people infected and the few deaths that they have seen may not be unexpected if you have thousands of people who have the infection.”
He added: “The virus that we’re seeing now seems to be behaving more like our seasonal influenza than the severe pandemic virus that the people were preparing for.”