ST. PAUL - A University of Minnesota study says farmers who actively tilled fields near turkey barns in the early days of last year's bird flu outbreak may have unwittingly helped spread the virus.

The Center for Animal Health and Food Safety says soil in those fields may have been contaminated with droppings from migrating birds believed to be a source of the highly pathogenic H5N2 virus.

The report says the virus can survive cold soil temperatures, and tilling may have created airborne particles that could carry the virus.

The authors urge caution, saying their findings should be viewed as "hypothesis-generating rather than confirmatory" and tmore research is needed.

They also say rendering trucks used to dispose of dead birds also were a likely factor in the spread.