Feeding a fever

Poor nutrition may contribute to the development of deadlier human viruses,
suggests influenza research on mice

height The human influenza virus mutates into a more virulent form after infecting mice deficient in the mineral selenium. This suggests that poor nutrition in people may contribute to the development of deadlier viruses, says a US team. "Our findings are potentially disturbing because they suggest nutritional deficiencies can promote epidemics in a way not appreciated before," says researcher Melinda Beck of the University of North Carolina, Chapel Hill. Selenium is an antioxidant and is important for normal immune system functioning. Exactly how a deficiency in the mineral promotes mutations in the flu virus that make it more virulent is not clear, says Beck. But she suspects that other RNA viruses - such as HIV and Ebola - could also mutate into more virulent forms in people with selenium deficiency. Ron Eccles of the Common Cold Centre at Cardiff University says that while the research is "of great interest, the mice were totally deficient in selenium. And the authors themselves admit that selenium deficiency is rare in humans."

Spanish flu

However, people living in parts of China, New Zealand and Europe have historically had diets low in selenium. The "Spanish flu" epidemic of 1918 originated in China, and new, more virulent strains of flu have recently surfaced in China and Hong Kong. "It is interesting that a lot of the new flu strains do come out of China - and it's fun to speculate that selenium deficiency in local animals and humans might have played some kind of part," Beck says. "But I have no evidence that this is the case." Beck's team studied 40 mice. Half were given diets containing no selenium. The mice were then infected with Influenza A Bangkok, a mild strain of human influenza virus.
The researchers sequenced viral genome samples from three mice from both of the groups. In each of the three samples from the selenium-deficient mice they found 29 mutations in the gene for a protein that surrounds the viral RNA. They did not find any mutations in the viral RNA from mice fed a normal diet. The selenium-deficient mice also developed much more severe flu symptoms. "The normal mice had little pockets of inflammation in their lungs. But in the selenium deficient mice, there was a major increase in pathology. Their lungs were totally full of inflammatory cells," Beck says.

Remarkable mutations

Beck's team had previously shown that the cocksackie B3 virus develops into a more virulent form in selenium-deficient mice. And researchers have known for years that malnourished people are more susceptible to infectious diseases. But the team did not know whether other RNA viruses would behave in the same way in animals deficient in selenium. Finding identical viral mutations in the three deficient mice is "remarkable" Beck says. More research is needed to find an explanation, she says. One possibility is that the low level of antioxidant selenium in the body allows oxygen free radicals to damage the virus directly. More work is also needed to establish at what level of selenium deficiency the increase in viral mutations kicks in. This will help establish the possible role of human antioxidant deficiency in viral mutation. It could be that other antioxidants, such as vitamin C, are equally important as selenium, say both Beck and Eccles.

More at: FASEB journal (vol 15, issue 8)
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