Diagnosing WNV infection must be based on laboratory confirmation, as the signs of the disease, including staggering or the inability to rise, can mimic other diseases, including rabies, or other encephalitic diseases, such as western equine encephalitis (WEE) and eastern equine encephalitis (EEE)." WNV has spread to 20 of the United States, following the migratory flight patterns of birds along the eastern seaboard and west as far as Texas. In 2001, 738 horses, donkeys, or other members of the equine family were diagnosed with the disease in the US, and about 20 per cent of the animals had to be euthanized, due to the severity of their illness. "Blue jays, crows, and more than 70 other species of birds can carry the virus, but it is the mosquito that puts the disease cycle in motion," explained Dr. Logan.