Anvil is an insecticide widely employed to combat West Nile fever, a mosquito-borne disease identified in approximately 10,000 residents of the United States from 1999-2006. It is sprayed in Chicago and many other cities. Sumithrin, a synthetic pyrethroid, is the main active ingredient. Anvil is applied aerially via fixed-wing and rotary aircraft or via ground applications (truck/ATV/backpack) using ultra-low volume (ULV) sprayers. According to the Anvil Technical Bulletin published in January 2006, these sprayers create a fine mist of drops that average 17 micrometres in size. A very small amount of active ingredient is used; about 0.6 ounces (17 g) of active ingredient is used to treat 1 acre (0.40 ha) (4.2 kg/km²). The active ingredients in Anvil break down quickly in sunlight and do not bioaccumulate. There are no reentry precautions for Anvil. Anvil has been tested in 43 field trials in the United States against 30 mosquito species.