Lower Saucon Township horse is 2012's first reported case of West Nile Virus in Pennsylvania

Officials did not have the exact location or the date of the euthanization, but said it was likely done by a veterinarian after testing on the animal indicated an infection.

DEP spokesman Kevin Sunday said the unseasonably warm weather probably played a factor in the early arrival. "Obviously it's been a very warm winter and mosquitoes like warmth," he said.

Mosquitoes get infected with the West Nile virus by feeding on infected birds. The infected mosquitoes then spread the virus by biting humans and other animals such as horses.

The DEP usually starts full-time monitoring and testing of mosquitoes in April.

According to the National Weather Service, the average temperature this March in the Allentown area was 50.2 degrees. Historically, the average for the month is 39.8 degrees in the area; this February's average temperature of 36.6 degrees was also about 5 degrees warmer than the historical average, the weather service reports.

Other parts of the country also are experiencing a higher risk of West Nile virus because of the unseasonable warm temperatures. On Thursday, Kentucky's agriculture commissioner warned that the weather could make horses more vulnerable to infection. Health officials in West Virginia expressed similar concerns last week.

Sunday, from the DEP, said factors other than temperature could also be at play. Wet weather plays a role in part because mosquitoes lay eggs in standing water, he said.

The department spokesman said he's hopeful the case in Lower Saucon Township will serve as a reminder that people should avoid keeping tires, buckets and other items that collect standing water outdoors. He also said the case is an example of why livestock owners should vaccinate their animals against the West Nile Virus.

According to a statement from the DEP, collection and testing of dead birds begins May 1 and can be reported on www.westnile.state.pa.us or by calling 717-346-8238. In Warren County, call the county mosquito commission at 908-453-3585.