Via Medscape.com (free registration required): An Epidemic of Epidemics. Excerpt from a long, informative post:
During the past 2-3 years, we have witnessed a virtual "epidemic of epidemics" in the United States. These will be reviewed briefly in the following categories: insect-borne infections, fungal infections, imported infections, vaccine-preventable diseases, viral respiratory tract infections, and foodborne infections.
West Nile virus. Infection with West Nile virus was first reported in New York City in 1999, and the virus subsequently made its way across the United States so that it is now endemic in all 48 contiguous states. In 2012, 5674 cases were reported, including 2873 (51%) with neuroinvasive disease.  This was the highest number of cases in the United States since 2003, reflecting large outbreaks in California and the middle of the country (Illinois, Michigan, Texas, Louisiana, Oklahoma, and Mississippi). The sudden surge of cases after continuous annual declines indicates that this virus is unpredictable and is likely to cause regional outbreaks for many years. 
Lyme disease. The annual incidence of Lyme disease in the United States had been reported to be about 30,000 cases, but has suddenly jumped 10-fold.  The increase is largely based on new data from the Centers for Disease Control and Prevention (CDC) using a combination of insurance claims data for a 6-year period, clinical laboratory reports, and self-reports instead of the standard surveillance reports. This would indicate a serious problem with underreporting, and a much bigger problem with Lyme disease than previously believed.
Points of Emphasis
It is humbling that we still have not controlled these 2 relatively new insect-borne diseases in the United States. The recognition of these new epidemics, followed by an endless pursuit to find, diagnose, treat, and prevent them, are the result of acts of medical heroism.
The credit for West Nile virus goes mainly to Dr. Marcelle Layton and colleagues at the New York City Health Department, and for Lyme disease, we are grateful to Dr. Allen Steere for his aggressive pursuit of a microbial cause for an epidemic of what was commonly thought to be juvenile rheumatoid arthritis in Old Lyme, Connecticut.