The blood is tested for the presence of antibodies to encephalitis viruses. If antibodies are found, it means the chickens have been bitten by virus-carrying mosquitoes. ISU then alerts communities to take extra precautions against mosquitoes. The problems occur when mosquito populations get so high that the mosquitoes move from feeding on birds to humans. We used to capture wild birds to test, but that was too time-consuming.
Chickens work much better.
Some believe the viruses overwinter in cold-blooded animals like frogs or snakes. So far this summer there have been no cases of encephalitis. Eight to 12 cases of La Crosse encephalitis are reported in Iowa each year. Meat inspectors typically rely on visual inspection of carcasses at processing plants. But bacterial contamination of carcasses is invisible to inspectors.