Many virus and bacteria are triggered by outdoor air conditions including such entities as West Nile virus (WNV) and Lyme disease. Mosquito-borne diseases involve the transmission of viruses and parasites from animal to animal, animal to person, or person to person, without afflicting the insect vectors with symptoms of disease. WNV, Eastern Equine Encephalitis, western equine encephalitis, St. Louis encephalitis, La Crosse encephalitis, dengue and yellow fever all of which are transmitted by mosquitoes. Arthropod-borne viruses are the most diverse, numerous, and serious diseases transmitted to susceptible vertebrate hosts by mosquitoes and other blood-feeding arthropods. According to Petersen, mosquito bites account for nearly all human infections. Persons infected through transplant of infected organs are at extreme risk of developing neuroinvasive disease; however, conflicting data exist regarding risk among previous organ recipients infected via mosquito bite. Controversy accompanied the decision to use wide-scale aerial pesticide applications to reduce exposure to disease-carrying mosquitoes.