Final answer:
The West Nile virus spread through the US in the early 2000s, starting in New York. Mosquitoes, particularly Culex mosquitoes, transmit the virus to humans and birds, leading to its rapid spread across the country.
Step-by-step explanation:
The West Nile virus (WNV) spread through the US in the early 2000s. The first cases were identified in New York in 1999, and by 2004, the virus had spread across the entire continental United States. Over 35,000 cases and 1400 deaths were confirmed in the five-year period between 1999 and 2004. Mosquitoes, particularly Culex mosquitoes, transmit WNV to humans and birds, allowing the virus to spread quickly to different areas.