for the past four years , and Petersen says he does n't expect this year to be any different . It should reach its peak between mid-July and mid-September . Health Minute : More on West Nile virus risk '' `` People tend to discount this as a significant problem , '' Petersen said , `` but more than 1.5 million people have been infected so far in the United States , and about 300,000 have had West Nile fever . '' West Nile virus emerged in the U.S. nine years ago . The virus is spread by the bite of an infected mosquito . Mosquitoes contract the illness by feeding on infected birds . The CDC reported that in rare cases , West Nile virus has spread through blood transfusions , organ transplants and breastfeeding . The disease is not spread through casual contact . The symptoms range from mild to severe and typically develop between three and 14 days after a person is bitten . Explainer : West Nile 101 '' Debbie Koma , a 50-year old hairdresser from Atlanta , Georgia , developed West Nile virus two years ago . She described it as `` unlike anything
ATLANTA , Georgia -LRB- CNN -RRB- -- All Lyle Petersen wanted to do was get his mail . Lyle Petersen , a CDC expert who was infected with West Nile virus , says , `` it will ruin your summer . '' In the time it took him to walk down his driveway in Fort Collins , Colorado , chat briefly with a neighbor and return to his house , Petersen got infected with a potentially serious mosquito-borne illness called West Nile virus . Within hours of being bitten , he said , he began to feel symptoms he recognized . And how was he sure so quickly ? Petersen , as director of the division of vector borne diseases at the Centers for Disease Control and Prevention , is one of the foremost experts in the world on the condition . A blood test confirmed his suspicion . `` From my own experience , I can tell you it 's not a very mild illness , '' Petersen cautioned . `` It will ruin your summer . '' Experts are expecting another epidemic of the disease this summer . The incidence of West Nile virus has remained the same