Influenza A Viruses Found Preserved in Siberian Lake Ice
5 Dec, 2006 03:35 pm
Influenza A viruses have been known to appear, disappear, and reappear in cycles lasting decades. The influenza virus that caused an epidemic in Europe and North America in 1951 ?disappeared?, but then reappeared in 1977, causing the infamous Russian flu epidemic.
Recently, researchers found the genetic material (RNA, in this case) encoding the H1 protein, in Siberian lake ice . The lake that had the highest populations of migratory birds also had the highest amount of H1 RNA. Of the three lakes sampled, 83 H1 RNA sequences were found in the lake frequented by migratory waterfowl, and only 1 H1 RNA sequence was found in another lake that had few avian visitors. In the third lake, where there were few bird visits, no H1 could be found. Were the migrating birds depositing viruses into the water during the summer months which persisted during the winter when frozen? Was this a source of infection for the incoming migratory birds the following spring? It has long been known that wild birds harbor influenza viruses in their gastrointestinal tract which are then shed in feces and from their upper respiratory tract. It is possible that various subtypes of influenza viruses are preserved from year to year in northern lakes through this avian deposition mechanism. Moreover, this could be exacerbated with global warming and the melting of glacial ice.
The Siberian lakes used for Rogersí study freeze and thaw on an annual basis. However, other lakes further north have longer cycles, or only partially thaw during the summer. Therefore, viruses may be entrapped for years, decades, or longer. A previous study reported recovery of RNA from plant viruses (tomato mosaic virus) from glacial ice 500 to more than 100,000 years old . When the ice around the world melts, it releases an enormous number of microbes, including viruses. During times of global warming, these numbers may increase. However, the infectivity of such microbes has yet to be demonstrated.
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