New findings about West Nile confound researchers

For more than five years, scientists have believed mosquitoes spread West Nile virus with the help of a highly infected middleman - birds.

Now, a study suggests mosquitoes may be able to spread the virus directly to one another when they feed together.

This discovery still may not resolve the mystery of how the virus has swept across North America so quickly since 1999. But the unexpected finding illustrates how, after more than five years of intense research, West Nile continues to confound scientists and stump health officials as they try to protect the public from the disease's advance.