EAST PEORIA — Mosquitoes collected at the end of August in East Peoria tested positive for West Nile virus, Tazewell County Health Department officials said Tuesday.

The virus is transmitted by mosquitoes that have bitten infected birds.

Ordinary virus symptoms include fever, nausea, headache and muscle aches, and can last between a few days and a few weeks.

The largest at-risk populations are those older than 50 and people with weakened immune systems.