The U.S. Centers for Disease Control and Prevention is warning that the West Nile virus is spreading faster and farther than usual this season — affecting 38 states, infecting up to 1,118 people, and leading to at least 41 deaths. Over the past week, the number of West Nile virus infections in the country has jumped more than 60 percent, and the CDC says the rates of infection are on track to make this the biggest-ever outbreak of the disease. West Nile cases tend to crop up during the summer months because the virus is usually transmitted from infected birds to people through mosquito bites. Although federal officials are unsure why this August has been so much worse than usual, they speculate that it is yet another negative effect of global climate change. “One observation that has occurred over many decades … has been that hot weather seems to promote West Nile virus outbreaks,” Dr. Lyle Petersen, director of the CDC’s vector-borne infectious diseases division, explained.