State health officials have raised the threat level for West Nile Virus from low to moderate, after three people were infected.

Summer is almost over, but that does not mean the end of mosquito bites or your potential exposure to West Nile Virus.

“The vast majority of people who get infected, don’t get sick,” said Dr. Ira Helfand of Family Care Medical Center in Springfield. “It’s still an illness you need to take fairly serious.”

The Department of Public Health announced it was raising the state’s threat level for West Nile virus from low to moderate Tuesday.

Last week, health officials announced three human cases were reported in Worcester, Middlesex, and Suffolk counties.

And  in Hampshire County, a horse had to be euthanized after contracting the virus. 

So far, a total of 45 states and the District of Columbia have reported infections in people, birds, or mosquitoes. 

West Nile Virus spreads to humans and animals after they are bitten by a infected mosquito. Mosquitos become infected after having fed on an infected bird. 

There is currently no vaccine for West Nile Virus.

“About 1 in 150 to 200 people who get infected with the virus, develop a more serious meningitis or encephalitis,” said Helfand. “And it’s particular true for people who are elderly. In those cases it can quite a severe illness.”

In severe cases, people often need to be hospitalized

The most effective way to avoid West Nile virus is to prevent mosquito bites. 

Wear long sleeves during peak mosquito biting hours, which are from dusk to dawn, and use insect repellents with DEET.