First West Nile virus sample of the season detected in Mass.

State public health officials said they have detected the first positive mosquito sample for West Nile virus of the season, putting Massachusetts slightly ahead of previous trends.

The virus was found in a sample collected from Shrewsbury on June 13, the Department of Public Health announced Tuesday. There have been no human or animal WNV cases so far.

"Mid-June is earlier than we typically first find West Nile virus-infected mosquitoes in Massachusetts," Department of Public Health Commissioner Robbie Goldstein said in a statement. "WNV activity is very difficult to predict in advance, which is why the mosquito surveillance system is so important."

Last season, officials identified the first positive West Nile virus mosquito sample in late June.

Massachusetts logged 19 human West Nile cases last year, with the virus typically caused by bites from infected mosquitos. There were also four human cases of Eastern equine encephalitis, which has not yet been detected this season, officials said.

"Even though this is a little early, it doesn't necessarily mean we will have a bad season," State Epidemiologist Catherine Brown said. "We recommend that everyone start using a mosquito repellent with an EPA-registered ingredient, wear clothing to reduce exposed skin, drain standing water, and repair window screens."

People ages 50+ face a greater risk of severe disease caused by WNV, according to DPH. Symptoms can include fever and flu-like illnesses, though most infected individuals will not experience symptoms.

The first day of summer is Friday, June 20.