The number of Illinois counties reporting West Nile virus (WNV) activity grew to 82 with the Aug. 19 confirmation that a horse from Massac County has tested positive for the mosquito-transmitted virus.

In addition to the Massac County horse, nine other horses–in Clay (1), Montgomery (1), Madison (4), Union (2) and Wabash (1) counties-–were reported positive Monday for West Nile virus after tests by the Illinois Department of Agriculture Laboratory in Galesburg. A total of nine humans, including one death; 390 birds; 196 mosquito batches; and 23 horses in 82 of the state’s 102 counties have tested positive this year for WNV since surveillance for the virus began May 1