(NewsNation) — In America’s ecosystem, bats serve as the country’s pest control. The USDA even estimates that they save us billions of dollars a year because of their knack for eating insects.

But some state public health departments are now warning rabid rats may be a real concern.

“The summer and especially August are the most important months for people to get exposed to bats,” said Illinois-based public health veterinarian Dr. Connie Austin during an appearance on “NewsNation Now.” “This year alone, we’ve already had to recommend rabies exposure treatment for 400 people.”

Health officials in states ranging from California to Maine are warning the public to keep doors and windows closed in order to keep bats out.

Rabid bats are the leading cause of rabies deaths in the United States, according to the Centers for Disease Control and Prevention.

“We don’t want people to be afraid, we just want people to know that when you have a bat encounter there are many questions as to whether a person may have been exposed,” said Los Angeles-based public health veterinarian Emily Beeler during an appearance on “NewsNation Now.”