Health officials throughout Arizona have been monitoring mosquito-borne virus activity for decades. Similar mosquito-borne viruses (St Louis and western equine encephalitis viruses) are found every year in Arizona. Mosquito-borne virus activity is usually most prevalent from May through October when mosquitoes are most abundant. Arizona has expanded its longstanding mosquito-borne virus surveillance network to detect, monitor and control mosquito-borne diseases such as St Louis encephalitis (SLE) and West Nile virus (WNV). The focus of the surveillance program is to detect virus activity in mosquitoes, sentinel chicken flocks, dead birds, sick horses, as well as humans. 

Every month from March through October over 300 samples of mosquitoes are collected by health officials throughout Arizona and tested at the Arizona State Health Laboratory. Also, dead birds are tested for WNV at the University of Arizona’s Veterinary Diagnostic Laboratory. There are also between 15-20 flocks of sentinel chickens statewide that are tested twice a month to determine whether they were bitten by virus infected mosquitoes. Additionally, reporting of mosquito-borne disease in humans and horses by physicians and veterinarians, is critical for detecting and responding to WNV statewide. Surveillance data allows health officials to identify communities at higher risk for WNV transmission, and appropriate measures can be taken to reduce risk.