HARRISBURG, Pa. -

A mosquito infected with West Nile in Berks County is the first confirmed case of the virus in Pennsylvania and the earliest ever to test positive since the state began testing in 2000, officials announced Thursday.

The infected mosquito was found May 3 in Exeter Township, said officials with the departments of Environmental Protection and Health.

"The unseasonably warm weather in March caused the virus cycle to begin early this year," said DEP Secretary Mike Krancer. "Our staff will continue to monitor mosquito populations and conduct spraying to reduce the threat to public health."

In 2004, Pennsylvania began its integrated pest management program, which has improved identification and control of mosquito populations.

Certain mosquito species carry the virus, which may cause humans to contract West Nile fever or West Nile encephalitis, an infection that can result in inflammation of the brain.

Typically, the state’s first West Nile virus-carrying mosquito is found in mid-June. The previous earliest find came on May 17, 2011.

Last year, officials said West Nile virus was detected in 59 counties, resulting in six human cases reported statewide.

"Since there is no human vaccine for West Nile virus, the best way to prevent infection is to take precautions to avoid getting mosquito bites," said Department of Health Secretary Dr. Eli Avila.

Although most people do not become ill when infected with West Nile virus, all are at risk, said health officials, adding that older adults and those with compromised immune systems have the highest risk of becoming ill and developing severe complications.

The best defense against West Nile virus is to prevent mosquitoes from breeding. Mosquitoes lay their eggs in stagnant water around homes, weeds, tall grass, shrubbery and discarded tires.

For more information about West Nile virus and the state’s surveillance and control program, visit westnile.state.pa.us.