With nearly 4000 cases of West Nile virus reported to the US Centers for Disease Control and Prevention (CDC) as of early October, more than 5 times the number of cases reported in 2011, the 2012 West Nile virus season has been one of the worst since the virus emerged in the United States in 1999.
This surge in cases—which was concentrated in Texas, Mississippi, Michigan, South Dakota, Louisiana, Oklahoma, and California—likely resulted from a confluence of ecological factors, including higher-than-normal temperatures, that may have influenced mosquito and bird abundance, the replication of the virus in its host mosquitoes, and interactions of birds and mosquitoes in hard-hit areas, according to Lyle Petersen, MD, MPH, Director of the CDC's Division of Vector-Borne Diseases. Petersen discussed this year's resurgence of West Nile virus with JAMA.
Kuehn BM. Record Heat May Have Contributed to a Banner Year for West Nile Virus. JAMA. 2012;308(18):1846-1848. doi:10.1001/jama.2012.13495