Many believed the virus would spread slowly across America; others thought it wouldn't survive at all. Few predicted a wildfire-like march across the continent that culminated with cases in California just four years later, in 2003.
Now, scientists at the University of Texas Medical Branch at Galveston may have discovered one reason why: Their earlier understanding of how mosquitoes become infected was very likely flawed.
Birds, which can have high levels of the virus in their blood, serve as its natural hosts. Certain kinds of mosquitoes, such as Culex, bite the birds and become infected. These mosquitoes, in turn, bite and infect humans. What the UTMB scientists have discovered — to their amazement — is that mosquitoes also can pass the virus to each other without an infected bird.
Source: Houston Chronicle