Since Canadian officials announced in May that pigs on an Alberta farm housed the new H1N1 virus that causes the swine flu outbreak, scientists have struggled to explain its origins. Researchers had hoped scrutiny swine virus isolates clarify things, but new sequences published on a public database yesterday had many unusual mutations that have raised more disturbing questions.
Many mysteries remain about the origin of the pandemic in humans and Alberta pigs received intense attention, as they were the first pigs found to harbor the virus. From the outset, the Canadian Food Inspection Agency (CFIA) has rejected the possibility that pigs have spread the virus to humans, saying it was "highly probable" that the animals had become infected with carpenter working on the farm who had recently returned from Mexico with a respiratory illness. But the carpenter, Adrian Blaak says science Insider on June 24 that it has tested negative for the virus on several tests, the Alberta health officials have confirmed. However, the CFIA maintained a human probably infected pigs, as this farm is isolated and has no pigs from other sources. (Pigs on a farm in Argentina recently tested positive for the virus, and officials there also suspect that he was human to pig transmission.)
May 14, the CFIA sent GenBank, a base public data, the sequence of one isolate Alberta pork. evolutionary biologist Andrew Rambaut of the University of Edinburgh in the UK co-founded a website wiki on evolution and the origin of the new virus and that he had noticed an unusual number of mutations compared to human sequences . But with only one isolate, Rambaut had difficulty to understand. Then, on July 9, the CFIA published partial sequences of 10 more swine isolates; these, too, have not seen many mutations in the virus found in humans, he said.
Although Rambaut agreed that the most likely man infected pigs, he said he had trouble understanding the evolutionary relationship between pork and human isolates from Alberta. "At first glance, it seems that they are quite genetically diverse, and I fear that this could be interpreted to mean the virus are in some way the ancestral human epidemic," said Rambaut. But he suspects that mutations are a laboratory artifact. Specifically, if the swine isolates are older than humans, they must share the same mutations, he said. But these isolates pigs each have unique mutations apparently scattered willy-nilly. Rambaut released its preliminary analysis of the sequences of pig on its wiki site.
The intuition of Rambaut is that mutations can be introduced when Canadian scientists isolates prepared for sequencing. As a study published in 00 in Proceedings of the National Academy of Sciences found, increasing influenza isolates in eggs prior to sequence the mutations may be introduced. John Pasick CFIA, who helped sequence the swine isolates, said Science Insider that the laboratory has grown isolates in eggs. "It could be these mutations may be adaptations of virus growth in chicken embryos," said Pasick, who grew them in eggs, because he runs a laboratory for avian influenza.
A another explanation Pasick said, is that the swine virus had adapted to humans, and when he returned in the Alberta herd, he transferred to readjust to the pigs. "We find a little unusual mutations "Pasick said, adding that his group is preparing a manuscript dealing with his conclusions. He says they also have the original stamps collected from pigs and" time and resources allow, "increase the virus in a medium containing cells and resequence to see if the mutations were introduced by growing them in eggs.
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