Influenza viruses may be preserved in glaciers and Arctic ice for thousands of years and released into the environment when the frozen water is thawed, potentially touching off lethal pandemics, researchers said.
Global warming may speed the release of the microbes, increasing the frequency of outbreaks, according to a study in the December issue of the Journal of Virology. The study is based on tests of water and ice from three lakes in Siberia, where large populations of migratory waterfowl breed before traveling to North America, southern Asia, Europe and Africa. The finding may help explain the constant emergence of influenza A-type viruses that cause seasonal epidemics and occasionally set off pandemics capable of killing millions of people. Disease trackers are monitoring flu viruses amid an outbreak of the H5N1 strain, known to have infected 258 people in 10 countries in the past three years, killing 153 of them. “One expectation in relation to this phenomenon would be an increased rate of release of these microbes during times of global, or local, warming events and a decrease during cooler periods,” said the authors, led by Gang Zhang from Ohio's Bowling Green State University. Last year was the warmest in more than a century, according to the National Aeronautics and Space Administration's Goddard Institute for Space Studies in New York. Climatologists there monitoring global annual average surface temperatures found that the four previous hottest years since the 1890s were 1998, 2002, 2003 and 2004. The spread of H5N1 in late 2003 has put the world closer to another pandemic than at any time since 1968, when the last of the previous century's three major outbreaks occurred, according to the World Health Organization. The H5N1 virus killed about 200 chickens at a South Korean farm, the second outbreak in three days, fueling concerns that the disease may be spreading in the country again after three years. The farm, in the southwestern city of Iksan, is about 3 kilometers (1.9 miles) from a property where H5N1 was confirmed November 25, said Kim Yang Il, an agriculture ministry spokesman. In Indonesia, the country with the most H5N1 fatalities, the virus killed a 35-year-old woman in a Jakarta hospital early today. The woman from Banten province was most likely infected by diseased poultry, said Joko Suyono, an official at the health ministry.
Almost all human H5N1 cases have been linked to close contact with sick or dead birds, such as children playing with them or adults butchering them or plucking feathers. A pandemic can start when a novel influenza A-type virus, to which almost no one is naturally immune, emerges and begins spreading. Experts believe that a pandemic in 1918, which may have killed as many as 50 million people, began when an avian flu virus jumped to people from birds. Aquatic birds, such as ducks and geese, are the primary host of all influenza viruses. The virus is shed in feces and frequently deposited in rivers and lakes. Many species of aquatic birds flock to Siberia and other areas near the Arctic Circle for breeding during the Northern Hemisphere's summer before flying south during the fall. As the birds visit lakes along their paths they shed viruses into the water and onto any ice present, and drink water containing viruses discharged by other birds or released from the ice by thawing, the authors said in the study.
In previous studies, the authors, who include researchers from Israel's Bar-Illan University and the Russian Academy of Sciences, documented the preservation of viruses, bacteria, and fungi in glacial ice for as long as 140,000 years. Surveillance of Arctic lakes may help disease trackers predict which flu strains will cause future outbreaks and shape long-term vaccination strategies, the researchers said. Ice, ice-covered lakes and glaciers have “the potential for being major sources of viruses that cause pandemics and epizootics in birds and other animals,” they wrote. Until refreezing takes place, viruses of both present and past strains may be contracted by the waterfowl, allowing old and new viruses to continually recombine, the study said. “Conceivably, such ongoing perpetual mechanisms have been operating cyclically throughout the virus's evolution, enabling recurrent emergence of past genes,” according to the authors. The same pattern of evolution probably occurs in other diseases as well, the authors said, adding that “this awaits thorough examination.” It may explain why some influenza virus strains have appeared, disappeared, and then re-emerged decades later virtually unchanged, they said. A Russian H1N1 influenza virus that caused an epidemic in 1977 was almost identical to the H1N1 strain that caused an epidemic in 1950. Other strains, most notably variants of H2N2 and H3N2 and several H1 varieties, have made similar returns, the researchers said. (Bloomberg)