Chinese soil clue to killer viruses

Areas of China where the soil is deficient in an element called selenium may be responsible for turning mild influenza strains into killer viruses.

Researchers now believe that many strains of human influenza originate in China where people live in close proximity to their pigs and ducks.

These domestic animals have their own flu viruses that freely swap genetic material with the human forms to produce new strains against which existing vaccines are ineffective.

But Dr Melinda Beck, of the University of North Carolina, believes that a dietary deficiency - lack of the essential trace element selenium - among people in some regions of China may drive mutations of the virus in the direction of increased virulence.

Dr Beck is trying to verify her hypothesis by infecting mice raised on a selenium-deficient diet with flu and then later testing the virulence of the virus on mice raised on normal diets. She discovered that it had mutated and caused disease even when resistance might have been expected.

She has already proved that another virus - coxsackie - mutates into virulence in this manner. Some coxsackie infection in humans produces only mild cold-like symptoms. Other strains so damage the heart muscle that a transplant is necessary, Dr Beck told the American Association for the Advancement of Science.

In areas of China where the soil is deficient in selenium, coxsackie is linked to Kesease. This is a damaging inflammation of the heart muscle which, until recently, affected thousands of infants, children, and women of child-bearing age.