AROOSTOOK COUNTY, Maine — Biologists with the United States Department of Agriculture are in Maine this week, dropping rabies vaccines from planes over rural parts of the state.

The oral rabies vaccine distribution program has been in existence since 2003 -- but this year, biologists are dropping more than 350,000 vaccines in a 2,400 square-kilometer zone.

RELATED: Oral rabies vaccines to be dropped over Maine woods

Raccoons, skunks, foxes, and even coyotes ingest these vaccines, which stops the spread of rabies in its tracks.

The biologists target very rural parts of the state without homes, schools, businesses, or many people. They focus their efforts on places where animals with rabies have been seen, trapped or killed.

"We know that rabies is prevalent in the central and southern parts of the state of Maine -- however, we do have occasional cases that pop up in northern Maine, such as Aroostook County," said USDA Wildlife Services biologist Jesse Morris. "Therefore, we have to stop the spread of rabies moving north before we can start to prevent it or manage it in central and southern parts of the state."

Morris said the biologists go back to the drop sites about a month later to trap some of the animals to get a sense of how many ingested the vaccines and whether they're working.

The bait drops are done with two planes, eight times a day, and are expected to continue through Tuesday afternoon.

RELATED: How to keep your kids, your pets, and yourself safe from rabies